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RE2OCAML(1)							   RE2OCAML(1)

NAME
       re2ocaml	- generate fast	lexical	analyzers for OCaml

SYNOPSIS
       re2ocaml	[ OPTIONS ] [ WARNINGS ] INPUT

       Input can be either a file or - for stdin.

INTRODUCTION
       re2ocaml	 works	as  a  preprocessor. It	reads the input	file (which is
       usually a program in OCaml, but can be anything)	and looks  for	blocks
       of code enclosed	in special-form	start/end markers. The text outside of
       these  blocks  is copied	verbatim into the output file. The contents of
       the blocks are processed	by re2ocaml. It	translates  them  to  code  in
       OCaml and outputs the generated code in place of	the block.

       Here  is	 an  example  of a small program that checks if	a given	string
       contains	a decimal number:

	  (* re2ocaml $INPUT -o	$OUTPUT	-i *)

	  open String

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	  }

	  %{
	      re2c:YYFN	= ["lex;bool", "yyrecord;state"];
	      re2c:yyfill:enable = 0;

	      [1-9][0-9]* { true }
	      *		  { false }
	  %}

	  let main () =
	      let st = {yyinput	= "1234"; yycursor = 0}
	      in if not	(lex st) then raise (Failure "error")

	  let _	= main ()

       In the output re2ocaml replaced the block in the	middle with the	gener-
       ated code:

	  (* Generated by re2ocaml *)
	  (* re2ocaml $INPUT -o	$OUTPUT	-i *)

	  open String

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	  }

	  let rec yy0 (yyrecord	: state) : bool	=
	      let yych = unsafe_get yyrecord.yyinput yyrecord.yycursor in
	      yyrecord.yycursor	<- yyrecord.yycursor + 1;
	      match yych with
		  | '1'..'9' ->	(yy2 [@tailcall]) yyrecord
		  | _ -> (yy1 [@tailcall]) yyrecord

	  and yy1 (yyrecord : state) : bool =
	      false

	  and yy2 (yyrecord : state) : bool =
	      let yych = unsafe_get yyrecord.yyinput yyrecord.yycursor in
	      match yych with
		  | '0'..'9' ->
		      yyrecord.yycursor	<- yyrecord.yycursor + 1;
		      (yy2 [@tailcall])	yyrecord
		  | _ -> (yy3 [@tailcall]) yyrecord

	  and yy3 (yyrecord : state) : bool =
	      true

	  and lex (yyrecord : state) : bool =
	      (yy0 [@tailcall])	yyrecord

	  let main () =
	      let st = {yyinput	= "1234"; yycursor = 0}
	      in if not	(lex st) then raise (Failure "error")

	  let _	= main ()

BASICS
       A re2ocaml program consists of a	sequence  of  blocks  intermixed  with
       code  in	the target language. A block may contain definitions, configu-
       rations,	rules, actions and directives in any order:

       name = regular-expression ;
	      A	definition binds name to regular-expression. Names may contain
	      alphanumeric characters and underscore. The regular  expressions
	      section gives an overview	of re2ocaml syntax for regular expres-
	      sions.  Once  defined, the name can be used in other regular ex-
	      pressions	and in rules.  Recursion in named definitions  is  not
	      allowed,	and  each  name	should be defined before it is used. A
	      block inherits named definitions from the	global scope. Redefin-
	      ing a name that exists in	the current scope is an	error.

       configuration = value ;
	      A	configuration allows one to change re2ocaml behavior and  cus-
	      tomize  the  generated  code.  For a full	list of	configurations
	      supported	by re2ocaml see	the configurations section.  Depending
	      on  a  particular	 configuration,	 the value can be a keyword, a
	      nonnegative integer number or a one-line string which should  be
	      enclosed	in  double  or single quotes unless it consists	of al-
	      phanumeric characters. A block inherits configurations from  the
	      global  scope  and may redefine them or add new ones. Configura-
	      tions defined inside of a	block affect the whole block, even  if
	      they appear at the end of	it.

       regular-expression code
	      A	 rule binds regular-expression to its semantic action (a block
	      of code in curly braces, or a block of code that starts with  :=
	      and ends on a newline followed by	any non-whitespace character).
	      If  the  regular-expression matches, the associated code is exe-
	      cuted.  If multiple rules	match, the longest match takes	prece-
	      dence. If	multiple rules match the same string, the earliest one
	      takes  precedence. There are two special rules: the default rule
	      *	and the	end of input rule $.  Default rule  should  always  be
	      defined,	it  has	the lowest priority regardless of its place in
	      the block, and it	matches	any code unit (not necessarily a valid
	      character, see the encoding support section). The	end  of	 input
	      rule  should be defined if the corresponding method for handling
	      the end of input is used.	 With start conditions rules have more
	      complex syntax.

       !action code
	      An action	binds a	user-defined block of  code  to	 a  particular
	      place  in	the generated finite state machine (in the same	way as
	      semantic actions bind code to the	final states). See the actions
	      section for a full list of predefined actions.

       !directive ;
	      A	directive is one of the	special	 predefined  statements.  Each
	      directive	 has  a	unique purpose.	See the	directives section for
	      details.

   Blocks
       Block start and end markers are either /*!re2c and */,  or  %{  and  %}
       (both  styles are supported). Starting from version 2.2 blocks may have
       optional	names that allow them to be referenced in other	blocks.	 There
       are different kinds of blocks:

       /*!re2c[:<name>]	... */ or %{[:<name>] ... %}
	      A	global block contains definitions, configurations,  rules  and
	      directives.   re2ocaml  compiles	regular	expressions associated
	      with each	rule into a deterministic finite automaton, encodes it
	      in the form of conditional jumps in the target language and  re-
	      places  the  block with the generated code. Names	and configura-
	      tions defined in a global	block are added	to  the	 global	 scope
	      and  become  visible  to	subsequent blocks. At the start	of the
	      program  the  global  scope  is  initialized  with  command-line
	      options.

       /*!local:re2c[:<name>] ... */ or	%{local[:<name>] ... %}
	      A	local block is like a global block, but	the names and configu-
	      rations  in  it  have  local  scope  (they  do  not affect other
	      blocks).

       /*!rules:re2c[:<name>] ... */ or	%{rules[:<name>] ... %}
	      A	rules block is like a local block, but it  does	 not  generate
	      any  code	 by  itself,  nor  does	 it add	any definitions	to the
	      global scope -- it is meant to be	reused in other	 blocks.  This
	      is  a  way  of sharing code (more	details	in the reusable	blocks
	      section).	Prior to re2ocaml version 2.2 rules blocks required -r
	      --reusable option.

       /*!use:re2c[:<name>] ...	*/ or %{use[:<name>] ... %}
	      A	use block that references a previously defined rules block. If
	      the name is specified, re2ocaml looks for	a  rules  blocks  with
	      this name. Otherwise the most recent rules block is used (either
	      a	 named	or  an	unnamed	one). A	use block can add definitions,
	      configurations and rules of its own, which are added to those of
	      the referenced rules block. Prior	to re2ocaml  version  2.2  use
	      blocks required -r --reusable option.

       /*!max:re2c[:<name1>[:<name2>...]] ... */ or
       %{max[:<name1>[:<name2>...]] ...	%}
	      A	block that generates YYMAXFILL definition. An optional list of
	      block  names specifies which blocks should be included when com-
	      puting YYMAXFILL value (if the list is empty, all	blocks are in-
	      cluded).	By default the generated code  is  a  macro-definition
	      for  C (#define YYMAXFILL	<n>), or a global variable for Go (var
	      YYMAXFILL	int = <n>). It can be customized with an optional con-
	      figuration format	that specifies a template string where @@{max}
	      (or @@ for short)	is replaced with the numeric value  of	YYMAX-
	      FILL.

       /*!maxnmatch:re2c[:<name1>[:<name2>...]]	... */ or %{maxn-
       match[:<name1>[:<name2>...]] ...	%}
	      A	 block	that  generates	YYMAXNMATCH definition (it requires -P
	      --posix-captures option).	An optional list of block names	speci-
	      fies which blocks	should be included when	computing  YYMAXNMATCH
	      value  (if  the list is empty, all blocks	are included).	By de-
	      fault the	generated code is a macro-definition  for  C  (#define
	      YYMAXNMATCH  <n>),  or a global variable for Go (var YYMAXNMATCH
	      int = <n>). It can be customized with an optional	 configuration
	      format that specifies a template string where @@{max} (or	@@ for
	      short) is	replaced with the numeric value	of YYMAXNMATCH.

       /*!stags:re2c[:<name1>[:<name2>...]] ...	*/,
       /*!mtags:re2c[:<name1>[:<name2>...]] ...	*/ or
       %{stags[:<name1>[:<name2>...]] ... %}, %{mtags[:<name1>[:<name2>...]]
       ... %{
	      Blocks  that  specify  a template	piece of code that is expanded
	      for each s-tag/m-tag variable generated by re2ocaml. An optional
	      list of block names specifies which blocks  should  be  included
	      when  computing  the set of tag variables	(if the	list is	empty,
	      all blocks are included).	 There	are  two  optional  configura-
	      tions:  format  and separator.  Configuration format specifies a
	      template string where @@{tag} (or	@@ for short) is replaced with
	      the name of each tag variable.  Configuration  separator	speci-
	      fies  a  piece  of code used to join the generated format	pieces
	      for different tag	variables.

       /*!svars:re2c[:<name1>[:<name2>...]] ...	*/,
       /*!mvars:re2c[:<name1>[:<name2>...]] ...	*/ or
       %{svars[:<name1>[:<name2>...]] ... %}, %{mvars[:<name1>[:<name2>...]]
       ... %{
	      Blocks that specify a template piece of code  that  is  expanded
	      for  each	s-tag/m-tag that is either explicitly mentioned	by the
	      rules (with --tags option) or implicitly generated  by  re2ocaml
	      (with  --captvars	or --posix-captvars options). An optional list
	      of block names specifies which blocks should  be	included  when
	      computing	 the set of tags (if the list is empty,	all blocks are
	      included).  There	are two	optional  configurations:  format  and
	      separator.   Configuration  format  specifies  a template	string
	      where @@{tag} (or	@@ for short) is replaced  with	 the  name  of
	      each  tag.   Configuration  separator  specifies a piece of code
	      used to join the generated format	pieces for different tags.

       /*!getstate:re2c[:<name1>[:<name2>...]] ... */ or %{get-
       state[:<name1>[:<name2>...]] ...	%}
	      A	block that generates conditional dispatch on the  lexer	 state
	      (it requires --storable-state option). An	optional list of block
	      names  specifies	which  blocks  should be included in the state
	      dispatch.	The default transition goes to the start label of  the
	      first  block  on	the list. If the list is empty,	all blocks are
	      included,	and the	default	transition goes	to the first block  in
	      the  file	that has a start label.	 This block type is incompati-
	      ble with the --loop-switch option, as  it	 requires  cross-block
	      transitions that are unsupported without goto or function	calls.

       /*!conditions:re2c[:<name1>[:<name2>...]] ... */, /*!types:re2c... */
       or %{conditions[:<name1>[:<name2>...]] ... %}, %{types... %}
	      A	block that generates condition enumeration (it requires	--con-
	      ditions option). An optional list	of block names specifies which
	      blocks  should  be included when computing the set of conditions
	      (if the list is empty, all blocks	are included).	By default the
	      generated	code is	an enumeration	YYCONDTYPE.  It	 can  be  cus-
	      tomized with optional configurations format and separator.  Con-
	      figuration format	specifies a template string where @@{cond} (or
	      @@  for  short) is replaced with the name	of each	condition, and
	      @@{num} is replaced with a  numeric  index  of  that  condition.
	      Configuration  separator	specifies a piece of code used to join
	      the generated format pieces for different	conditions.

       /*!include:re2c <file> */ or %{include <file> %}
	      This block allows	one to include <file>, which must  be  a  dou-
	      ble-quoted  file	path.  The  contents of	the file are literally
	      substituted in place of the block, in the	same way  as  #include
	      works  in	C/C++. This block can be used together with the	--dep-
	      file option to generate build system  dependencies  on  the  in-
	      cluded files.

       /*!header:re2c:on*/ or %{header:on %}
	      This  block  marks the start of header file. Everything after it
	      and up  to  the  following  header:off  block  is	 processed  by
	      re2ocaml	and  written  to  the  header  file  specified with -t
	      --type-header option.

       /*!header:re2c:off*/ or %{header:off %}
	      This block marks the end of header file started with header:on*/
	      block.

       /*!ignore:re2c ... */ or	%{ignore ... %}
	      A	block which contents are ignored and removed from  the	output
	      file.

   Configurations
       Here is a full list of configurations supported by re2ocaml:

       re2c:api, re2c:input
	      Same as the --api	option.

       re2c:api:sigil
	      Specify  the  marker  ("sigil") that is used for argument	place-
	      holders in the API primitives. The default is @@.	A  placeholder
	      starts with sigil	followed by the	argument name in curly braces.
	      For  example,  if	sigil is set to	$, then	placeholders will have
	      the form ${name}.	Single-argument	APIs may use  shorthand	 nota-
	      tion  without  the name in braces. This option can be overridden
	      by options for individual	API primitives,	e.g.   re2c:YYFILL@len
	      for YYFILL.

       re2c:api:style
	      Specify  API  style.  Possible values are	functions (the default
	      for C) and free-form (the	default	for Go and  Rust).   In	 func-
	      tions  style  API	primitives are generated with an argument list
	      in parentheses following the name	of the	primitive.  The	 argu-
	      ments  are  provided  only for autogenerated parameters (such as
	      the number of characters passed to YYFILL), but not for the gen-
	      eral lexer context, so the primitives behave more	like macros in
	      C/C++ or closures	in Go and Rust.	 In free-form style API	primi-
	      tives do not have	a  fixed  form:	 they  should  be  defined  as
	      strings  containing  free-form  pieces of	code with interpolated
	      variables	of the form @@{var} or @@ (they	 correspond  to	 argu-
	      ments  in	function-like style).  This configuration may be over-
	      ridden for individual API	primitives, see	for  example  re2c:YY-
	      FILL:naked configuration for YYFILL.

       re2c:bit-vectors, re2c:flags:bit-vectors, re2c:flags:b
	      Same  as	the  --bit-vectors  option,  but  can be configured on
	      per-block	basis.

       re2c:captures, re2c:leftmost-captures
	      Same as the --leftmost-captures option, but can be configured on
	      per-block	basis.

       re2c:captvars, re2c:leftmost-captvars
	      Same as the --leftmost-captvars option, but can be configured on
	      per-block	basis.

       re2c:case-insensitive, re2c:flags:case-insensitive
	      Same as the --case-insensitive option, but can be	configured  on
	      per-block	basis.

       re2c:case-inverted, re2c:flags:case-inverted
	      Same  as	the  --case-inverted  option, but can be configured on
	      per-block	basis.

       re2c:case-ranges, re2c:flags:case-ranges
	      Same as the --case-ranges	 option,  but  can  be	configured  on
	      per-block	basis.

       re2c:computed-gotos, re2c:flags:computed-gotos, re2c:flags:g
	      Same  as	the  --computed-gotos option, but can be configured on
	      per-block	basis.

       re2c:computed-gotos:threshold, re2c:cgoto:threshold
	      If computed goto is used,	this configuration specifies the  com-
	      plexity  threshold  that	triggers the generation	of jump	tables
	      instead of nested	if statements and bitmaps. The	default	 value
	      is 9.

       re2c:cond:abort
	      If set to	a positive integer value, the default case in the gen-
	      erated condition dispatch	aborts program execution.

       re2c:cond:goto
	      Specifies	 a  piece  of code used	for the	autogenerated shortcut
	      rules :=>	in conditions. The default is goto @@;.	 The @@	place-
	      holder is	substituted with condition  name  (see	configurations
	      re2c:api:sigil and re2c:cond:goto@cond).

       re2c:cond:goto@cond
	      Specifies	  the	sigil	used   for  argument  substitution  in
	      re2c:cond:goto definition. The default value is  @@.   Overrides
	      the more generic re2c:api:sigil configuration.

       re2c:cond:divider
	      Defines  the divider for condition blocks.  The default value is
	      /*  ***********************************  */.   Placeholders  are
	      substituted   with   condition   name  (see  re2c:api;sigil  and
	      re2c:cond:divider@cond).

       re2c:cond:divider@cond
	      Specifies	 the  sigil  used   for	  argument   substitution   in
	      re2c:cond:divider	 definition. The default is @@.	 Overrides the
	      more generic re2c:api:sigil configuration.

       re2c:cond:prefix, re2c:condprefix
	      Specifies	the prefix used	for condition labels.  The default  is
	      yyc_.

       re2c:cond:enumprefix, re2c:condenumprefix
	      Specifies	 the  prefix  used for condition identifiers.  The de-
	      fault is yyc.

       re2c:debug-output, re2c:flags:debug-output, re2c:flags:d
	      Same as the --debug-output option,  but  can  be	configured  on
	      per-block	basis.

       re2c:empty-class, re2c:flags:empty-class
	      Same  as	the  --empty-class  option,  but  can be configured on
	      per-block	basis.

       re2c:encoding:ebcdic, re2c:flags:ecb, re2c:flags:e
	      Same as the --ebcdic option, but can be configured on  per-block
	      basis.

       re2c:encoding:ucs2, re2c:flags:wide-chars, re2c:flags:w
	      Same  as	the  --ucs2 option, but	can be configured on per-block
	      basis.

       re2c:encoding:utf8, re2c:flags:utf-8, re2c:flags:8
	      Same as the --utf8 option, but can be  configured	 on  per-block
	      basis.

       re2c:encoding:utf16, re2c:flags:utf-16, re2c:flags:x
	      Same  as	the --utf16 option, but	can be configured on per-block
	      basis.

       re2c:encoding:utf32, re2c:flags:unicode,	re2c:flags:u
	      Same as the --utf32 option, but can be configured	 on  per-block
	      basis.

       re2c:encoding-policy, re2c:flags:encoding-policy
	      Same  as	the --encoding-policy option, but can be configured on
	      per-block	basis.

       re2c:eof
	      Specifies	the sentinel symbol used with the end-of-input rule $.
	      The default value	is -1 ($ rule is  not  used).  Other  possible
	      values  include  all  valid code units. Only decimal numbers are
	      recognized.

       re2c:fn:sep
	      Specifies	separator used in YYFN	elements  (defaults  to	 semi-
	      colon).

       re2c:header, re2c:flags:type-header, re2c:flags:t
	      Specifies	 the name of the generated header file relative	to the
	      directory	of the output file. Same as the	--header option	except
	      that the file path is relative.

       re2c:indent:string
	      Specifies	the string used	for indentation. The default is	a sin-
	      gle tab character	"\t". Indent string should contain  whitespace
	      characters only.	To disable indentation entirely, set this con-
	      figuration to an empty string.

       re2c:indent:top
	      Specifies	 the minimum amount of indentation to use. The default
	      value is zero. The value should be a non-negative	 integer  num-
	      ber.

       re2c:invert-captures
	      Same  as	the --invert-captures option, but can be configured on
	      per-block	basis.

       re2c:label:prefix, re2c:labelprefix
	      Specifies	the prefix used	for DFA	state labels. The  default  is
	      yy.

       re2c:label:start, re2c:startlabel
	      Controls	the  generation	 of  a	block start label. The default
	      value is zero, which means that the  start  label	 is  generated
	      only  if	it  is used. An	integer	value greater than zero	forces
	      the generation of	start label even if it is unused by the	lexer.
	      A	string value also forces start label generation	and  sets  the
	      label  name  to the specified string. This configuration applies
	      only to the current block	(it is reset to	default	for  the  next
	      block).

       re2c:label:yyFillLabel
	      Specifies	 the prefix of YYFILL labels used with re2c:eof	and in
	      storable state mode.

       re2c:label:yyloop
	      Specifies	the name of the	label marking the start	of  the	 lexer
	      loop with	--loop-switch option. The default is yyloop.

       re2c:label:yyNext
	      Specifies	the name of the	optional label that follows YYGETSTATE
	      switch  in  storable state mode (enabled with re2c:state:nextla-
	      bel). The	default	is yyNext.

       re2c:lookahead, re2c:flags:lookahead
	      Deprecated (see the deprecated --no-lookahead option).

       re2c:monadic
	      If set to	non-zero, the generated	lexer will use	monadic	 nota-
	      tion (this configuration is specific to Haskell).

       re2c:nested-ifs,	re2c:flags:nested-ifs, re2c:flags:s
	      Same  as	the  --nested-ifs  option,  but	 can  be configured on
	      per-block	basis.

       re2c:posix-captures, re2c:flags:posix-captures, re2c:flags:P
	      Same as the --posix-captures option, but can  be	configured  on
	      per-block	basis.

       re2c:posix-captvars
	      Same  as	the  --posix-captvars option, but can be configured on
	      per-block	basis.

       re2c:tags, re2c:flags:tags, re2c:flags:T
	      Same as the --tags option, but can be  configured	 on  per-block
	      basis.

       re2c:tags:expression
	      Specifies	 the  expression  used	for tag	variables.  By default
	      re2ocaml generates expressions of	the form yyt<N>. This might be
	      inconvenient, for	example	if tag variables are defined as	fields
	      in a struct. All occurrences of @@{tag} or @@ are	replaced  with
	      the actual tag name. For example,	re2c:tags:expression = "s.@@";
	      results  in  expressions	of  the	form s.yyt<N> in the generated
	      code.  See also re2c:api:sigil configuration.

       re2c:tags:negative
	      Specifies	the constant expression	that is	used for negative  tag
	      value (typically this would be -1	if tags	are integer offsets in
	      the input	string,	or null	pointer	if they	are pointers).

       re2c:tags:prefix
	      Specifies	the prefix for tag variable names. The default is yyt.

       re2c:sentinel
	      Specifies	 the  sentinel symbol used for the end-of-input	checks
	      (when bounds checks are disabled with  re2c:yyfill:enable	 =  0;
	      and  re2c:eof  is	 not  set). This configuration does not	affect
	      code generation: its purpose is to verify	that the  sentinel  is
	      not  allowed  in the middle of a rule, and ensure	that the lexer
	      won't read past the end of buffer. The default value is -1`  (in
	      that  case  re2ocaml assumes that	the sentinel is	zero, which is
	      the most common case). Only decimal numbers are recognized.

       re2c:state:abort
	      If set to	a positive integer value, the default case in the gen-
	      erated state dispatch aborts program execution, and an  explicit
	      -1 case contains transition to the start of the block.

       re2c:state:nextlabel
	      Controls if the YYGETSTATE switch	is followed by an yyNext label
	      (the default value is zero, which	corresponds to no label).  Al-
	      ternatively  one can use re2c:label:start	to generate a specific
	      start label, or an  explicit  getstate  block  to	 generate  the
	      YYGETSTATE switch	separately from	the lexer block.

       re2c:unsafe, re2c:flags:unsafe
	      Same  as	the  --no-unsafe  option,  but	can  be	 configured on
	      per-block	basis.	If set to zero,	it suppresses  the  generation
	      of unsafe	wrappers around	YYPEEK.	The default is non-zero	(wrap-
	      pers are generated).  This configuration is specific to Rust.

       re2c:YYBACKUP, re2c:define:YYBACKUP
	      Defines generic API primitive YYBACKUP.

       re2c:YYBACKUPCTX, re2c:define:YYBACKUPCTX
	      Defines generic API primitive YYBACKUPCTX.

       re2c:YYCONDTYPE,	re2c:define:YYCONDTYPE
	      Defines API primitive YYCONDTYPE.

       re2c:YYCTYPE, re2c:define:YYCTYPE
	      Defines API primitive YYCTYPE.

       re2c:YYCTXMARKER, re2c:define:YYCTXMARKER
	      Defines API primitive YYCTXMARKER.

       re2c:YYCURSOR, re2c:define:YYCURSOR
	      Defines API primitive YYCURSOR.

       re2c:YYDEBUG, re2c:define:YYDEBUG
	      Defines API primitive YYDEBUG.

       re2c:YYFILL, re2c:define:YYFILL
	      Defines API primitive YYFILL.

       re2c:YYFILL@len,	re2c:define:YYFILL@len
	      Specifies	the sigil used for argument substitution in YYFILL de-
	      finition.	  Defaults   to	  @@.	 Overrides  the	 more  generic
	      re2c:api:sigil configuration.

       re2c:YYFILL:naked, re2c:define:YYFILL:naked
	      Overrides	the more generic re2c:api:style	configuration for  YY-
	      FILL.  Zero value	corresponds to free-form API style.

       re2c:YYFN
	      Defines API primitive YYFN.

       re2c:YYINPUT
	      Defines API primitive YYINPUT.

       re2c:YYGETCOND, re2c:define:YYGETCONDITION
	      Defines API primitive YYGETCOND.

       re2c:YYGETCOND:naked, re2c:define:YYGETCONDITION:naked
	      Overrides	 the  more  generic  re2c:api:style  configuration for
	      YYGETCOND. Zero value corresponds	to free-form API style.

       re2c:YYGETSTATE,	re2c:define:YYGETSTATE
	      Defines API primitive YYGETSTATE.

       re2c:YYGETSTATE:naked, re2c:define:YYGETSTATE:naked
	      Overrides	the  more  generic  re2c:api:style  configuration  for
	      YYGETSTATE. Zero value corresponds to free-form API style.

       re2c:YYGETACCEPT, re2c:define:YYGETACCEPT
	      Defines API primitive YYGETACCEPT.

       re2c:YYLESSTHAN,	re2c:define:YYLESSTHAN
	      Defines generic API primitive YYLESSTHAN.

       re2c:YYLIMIT, re2c:define:YYLIMIT
	      Defines API primitive YYLIMIT.

       re2c:YYMARKER, re2c:define:YYMARKER
	      Defines API primitive YYMARKER.

       re2c:YYMTAGN, re2c:define:YYMTAGN
	      Defines generic API primitive YYMTAGN.

       re2c:YYMTAGP, re2c:define:YYMTAGP
	      Defines generic API primitive YYMTAGP.

       re2c:YYPEEK, re2c:define:YYPEEK
	      Defines generic API primitive YYPEEK.

       re2c:YYRESTORE, re2c:define:YYRESTORE
	      Defines generic API primitive YYRESTORE.

       re2c:YYRESTORECTX, re2c:define:YYRESTORECTX
	      Defines generic API primitive YYRESTORECTX.

       re2c:YYRESTORETAG, re2c:define:YYRESTORETAG
	      Defines generic API primitive YYRESTORETAG.

       re2c:YYSETCOND, re2c:define:YYSETCONDITION
	      Defines API primitive YYSETCOND.

       re2c:YYSETCOND@cond, re2c:define:YYSETCONDITION@cond
	      Specifies	 the sigil used	for argument substitution in YYSETCOND
	      definition. The default value is @@.  Overrides the more generic
	      re2c:api:sigil configuration.

       re2c:YYSETCOND:naked, re2c:define:YYSETCONDITION:naked
	      Overrides	the more generic re2c:api:style	configuration for  YY-
	      SETCOND. Zero value corresponds to free-form API style.

       re2c:YYSETSTATE,	re2c:define:YYSETSTATE
	      Defines API primitive YYSETSTATE.

       re2c:YYSETSTATE@state, re2c:define:YYSETSTATE@state
	      Specifies	the sigil used for argument substitution in YYSETSTATE
	      definition. The default value is @@.  Overrides the more generic
	      re2c:api:sigil configuration.

       re2c:YYSETSTATE:naked, re2c:define:YYSETSTATE:naked
	      Overrides	 the more generic re2c:api:style configuration for YY-
	      SETSTATE.	Zero value corresponds to free-form API	style.

       re2c:YYSETACCEPT, re2c:define:YYSETACCEPT
	      Defines API primitive YYSETACCEPT.

       re2c:YYSKIP, re2c:define:YYSKIP
	      Defines generic API primitive YYSKIP.

       re2c:YYSHIFT, re2c:define:YYSHIFT
	      Defines generic API primitive YYSHIFT.

       re2c:YYCOPYMTAG,	re2c:define:YYCOPYMTAG
	      Defines generic API primitive YYCOPYMTAG.

       re2c:YYCOPYSTAG,	re2c:define:YYCOPYSTAG
	      Defines generic API primitive YYCOPYSTAG.

       re2c:YYSHIFTMTAG, re2c:define:YYSHIFTMTAG
	      Defines generic API primitive YYSHIFTMTAG.

       re2c:YYSHIFTSTAG, re2c:define:YYSHIFTSTAG
	      Defines generic API primitive YYSHIFTSTAG.

       re2c:YYSTAGN, re2c:define:YYSTAGN
	      Defines generic API primitive YYSTAGN.

       re2c:YYSTAGP, re2c:define:YYSTAGP
	      Defines generic API primitive YYSTAGP.

       re2c:yyaccept, re2c:variable:yyaccept
	      Defines API primitive yyaccept.

       re2c:yybm, re2c:variable:yybm
	      Defines API primitive yybm.

       re2c:yybm:hex, re2c:variable:yybm:hex
	      If set to	nonzero, bitmaps for the --bit-vectors option are gen-
	      erated in	hexadecimal format. The	default	is zero	 (bitmaps  are
	      in decimal format).

       re2c:yych, re2c:variable:yych
	      Defines API primitive yych.

       re2c:yych:emit, re2c:variable:yych:emit
	      If  set  to zero,	yych definition	is not generated.  The default
	      is non-zero.

       re2c:yych:conversion, re2c:variable:yych:conversion
	      If set to	non-zero, re2ocaml automatically generates  a  conver-
	      sion  to YYCTYPE every time yych is read.	The default is to zero
	      (no conversion).

       re2c:yych:literals, re2c:variable:yych:literals
	      Specifies	the form of literals that  yych	 is  matched  against.
	      Possible	values are: char (character literals in	single quotes,
	      non-printable ones use escape sequences that  start  with	 back-
	      slash), hex (hexadecimal integers) and char_or_hex (a mixture of
	      both,  character literals	for printable characters and hexadeci-
	      mal integers for others).

       re2c:yyctable, re2c:variable:yyctable
	      Defines API primitive yyctable.

       re2c:yynmatch, re2c:variable:yynmatch
	      Defines API primitive yynmatch.

       re2c:yypmatch, re2c:variable:yypmatch
	      Defines API primitive yypmatch.

       re2c:yytarget, re2c:variable:yytarget
	      Defines API primitive yytarget.

       re2c:yystable, re2c:variable:yystable
	      Deprecated.

       re2c:yystate, re2c:variable:yystate
	      Defines API primitive yystate.

       re2c:yyfill, re2c:variable:yyfill
	      Defines API primitive yyfill.

       re2c:yyfill:check
	      If set to	zero, suppresses the generation	 of  pre-YYFILL	 check
	      for the number of	input characters (the YYLESSTHAN definition in
	      generic  API and the YYLIMIT-based comparison in C pointer API).
	      The default is non-zero (generate	the check).

       re2c:yyfill:enable
	      If set to	zero, suppresses the generation	 of  YYFILL  (together
	      with  the	 check). This should be	used when the whole input fits
	      into one piece of	memory (there is no need  for  buffering)  and
	      the  end-of-input	 checks	do not rely on the YYFILL checks (e.g.
	      if a sentinel character is used).	 Use warnings (-W option)  and
	      re2c:sentinel  configuration  to verify that the generated lexer
	      cannot read past the end of input.  The default is non-zero (YY-
	      FILL is enabled).

       re2c:yyfill:parameter
	      If set to	zero, suppresses the generation	of parameter passed to
	      YYFILL.  The parameter is	the minimum number of characters  that
	      must be supplied.	 Defaults to non-zero (the parameter is	gener-
	      ated).   This  configuration  can	 be  overridden	 with re2c:YY-
	      FILL:naked or re2c:api:style.

   Regular expressions
       re2ocaml	uses the following syntax for regular expressions:

       "foo"  Case-sensitive string literal.

       'foo'  Case-insensitive string literal.

       [a-xyz],	[^a-xyz]
	      Character	class (possibly	negated).

       .      Any character except newline.

       R \ S  Difference of character classes R	and S.

       R*     Zero or more occurrences of R.

       R+     One or more occurrences of R.

       R?     Optional R.

       R{n}   Repetition of R exactly n	times.

       R{n,}  Repetition of R at least n times.

       R{n,m} Repetition of R from n to	m times.

       (R)    Just R; parentheses are used to override precedence. If submatch
	      extraction is enabled, (R) is a  capturing  or  a	 non-capturing
	      group depending on --invert-captures option.

       (!R)   If  submatch extraction is enabled, (!R) is a non-capturing or a
	      capturing	group depending	on --invert-captures option.

       R S    Concatenation: R followed	by S.

       R | S  Alternative: R or	S.

       R / S  Lookahead: R followed by S, but S	is not consumed.

       name   Regular expression defined as name (or literal string "name"  in
	      Flex compatibility mode).

       {name} Regular expression defined as name in Flex compatibility mode.

       @stag  An  s-tag:  saves	the last input position	at which @stag matches
	      in a variable named stag.

       #mtag  An m-tag:	saves all input	positions at which #mtag matches in  a
	      variable named mtag.

       Character  classes and string literals may contain the following	escape
       sequences: \a, \b, \f, \n, \r, \t, \v, \\, octal	escapes	\ooo and hexa-
       decimal escapes \xhh, \uhhhh and	\Uhhhhhhhh.

   Actions
       Here is a list of predefined actions supported by re2ocaml:

       !entry code
	      Entry action binds a user-defined	block of  code	to  the	 start
	      state  of	 the current finite state machine. If start conditions
	      are used,	the entry action can be	set individually for each con-
	      dition. This action may be used to perform initialization,  e.g.
	      to save start location of	a lexeme.

       !pre_rule code
	      Pre-rule	action prepends	a user-defined block of	code to	seman-
	      tic actions of all rules in the current block (or	condition,  if
	      start  conditions	 are  used). This action may be	used to	factor
	      out the common part of all semantic actions (e.g.	saving the end
	      location of a lexeme).

       !post_rule code
	      Post-rule	action appends a user-defined block of code to	seman-
	      tic  actions of all rules	in the current block (or condition, if
	      start conditions are used). This action may be used to emit trap
	      statements that guard against unintended control flow.

   Directives
       Here is a full list of directives supported by re2ocaml:

       !use:name ;
	      An in-block use directive	that merges a previously defined rules
	      block with the specified name into the current block. Named def-
	      initions,	configurations and rules of the	referenced  block  are
	      added  to	 the current ones. Conflicts between overlapping rules
	      and configurations are resolved in the usual way:	the first rule
	      takes priority, and the latest configuration overrides the  pre-
	      ceding ones. One exception is the	special	rules *, $ and <!> for
	      which  a block-local definition always takes priority. A use di-
	      rective can be placed anywhere inside of a block,	 and  multiple
	      use directives are allowed.

       !include	file ;
	      This  directive  is  the	same as	include	block: it inserts file
	      contents verbatim	in place of the	directive.

   Program interface
       The generated code interfaces with the outer program with the  help  of
       primitives,  collectively  referred  to	as  the	API.  Which primitives
       should be defined for a particular program depends on multiple factors,
       including the complexity	of regular expressions,	input  representation,
       buffering and the use of	various	features. All the necessary primitives
       should  be  defined by the user in the form of macros, functions, vari-
       ables or	any other suitable form	that makes the generated code  syntac-
       tically	and semantically correct. re2ocaml does	not (and cannot) check
       the definitions,	so if anything is missing or defined incorrectly,  the
       generated  program may have compile-time	or run-time errors.  This man-
       ual provides examples of	API definitions	in the most common cases.

       re2ocaml	has two	API flavors that define	the  core  set	of  primitives
       used by a program:

       Record API
	      Record  API  is the default API for the OCaml backend.  This API
	      consists of a variable yyrecord (the name	can be overridden with
	      re2c:yyrecord) that should be defined as a  record  with	fields
	      _yyinput,	 _yycursor,  _yymarker,	 _yyctxmarker, _yylimit.  Only
	      the fields used by the generated code need to  be	 defined,  and
	      their names can be configured.

       Generic API
	      This  is the most	flexible API. It is enabled with --api generic
	      option or	re2c:api = generic configuration.  It contains	primi-
	      tives  for generic operations: YYPEEK, YYSKIP, YYBACKUP, YYBACK-
	      UPCTX, YYSTAGP,  YYSTAGN,	 YYMTAGP,  YYMTAGN,  YYRESTORE,	 YYRE-
	      STORECTX,	 YYRESTORETAG,	YYSHIFT, YYSHIFTSTAG, YYSHIFTMTAG, YY-
	      LESSTHAN.

       Here is a full list of API primitives that may be used by the generated
       code in order to	interface with the outer program.

       YYCTYPE
	      The type of the  input  characters  (code	 units).   For	ASCII,
	      EBCDIC and UTF-8 encodings it should be 1-byte unsigned integer.
	      For  UTF-16  or  UCS-2 it	should be 2-byte unsigned integer. For
	      UTF-32 it	should be 4-byte unsigned integer.

       YYCURSOR
	      An l-value that stores the current input position	(a pointer  or
	      an  integer  offset in YYINPUT). Initially YYCURSOR should point
	      to the first input character, and	later it is  advanced  by  the
	      generated	 code.	When  a	rule matches, YYCURSOR position	is the
	      one after	the last matched character.

       YYLIMIT
	      An r-value that stores the end of	input position (a  pointer  or
	      an integer offset	in YYINPUT). Initially YYLIMIT should point to
	      the position after the last available input character. It	is not
	      changed  by  the	generated code.	The lexer compares YYCURSOR to
	      YYLIMIT in order to determine if there are enough	input  charac-
	      ters left.

       YYMARKER
	      An  l-value  that	stores the position of the latest matched rule
	      (a pointer or an integer offset in YYINPUT). It is used  to  re-
	      store  the  YYCURSOR  position if	the longer match fails and the
	      lexer needs to rollback.	Initialization is not needed.

       YYCTXMARKER
	      An l-value that stores the position of the trailing  context  (a
	      pointer  or  an integer offset in	YYINPUT). No initialization is
	      needed. YYCTXMARKER is needed only if the	lookahead  operator  /
	      is used.

       YYFILL A	 generic  API  primitive with one variable len.	 YYFILL	should
	      provide at least len more	input characters or fail.  If re2c:eof
	      is used, then len	is always 1 and	 YYFILL	should	always	return
	      to  the  calling	function; zero return value indicates success.
	      If re2c:eof is not used, then YYFILL return value	is ignored and
	      it should	not return on failure. The maximum value of len	is YY-
	      MAXFILL.

       YYFN   A	primitive that defines function	prototype in --recursive-func-
	      tions code model.	Its value should be an array of	 one  or  more
	      strings, where each string contains two or three components sep-
	      arated  by  the  string  specified  in re2c:fn:sep configuration
	      (typically a semicolon). The first array element	defines	 func-
	      tion  name  and return type (empty for a void function).	Subse-
	      quent elements define function arguments:	first, the  expression
	      for  the	argument  used in function body	(usually just a	name);
	      second, argument type; third, an optional	formal	parameter  (it
	      defaults	to the first component - usually both the argument and
	      the parameter are	the same identifier).

       YYINPUT
	      An r-value that stores  the  current  input  character  sequence
	      (string, buffer, etc.).

       YYMAXFILL
	      An  integral constant equal to the maximum value of the argument
	      to YYFILL.  It can be generated with a max block.

       YYLESSTHAN
	      A	generic	API primitive with one variable	len.  It should	be de-
	      fined as an r-value of boolean type that equals true if and only
	      if there are less	than len input characters left.

       YYPEEK A	generic	API primitive with no variables.  It should be defined
	      as an r-value of type YYCTYPE that is equal to the character  at
	      the current input	position.

       YYSKIP A	 generic  API  primitive that should advance the current input
	      position by one code unit.

       YYBACKUP
	      A	generic	API primitive that should save the current input posi-
	      tion (to be restored with	YYRESTORE later).

       YYRESTORE
	      A	generic	API primitive that should restore  the	current	 input
	      position to the value saved by YYBACKUP.

       YYBACKUPCTX
	      A	generic	API primitive that should save the current input posi-
	      tion  as	the  position  of the trailing context (to be restored
	      with YYRESTORECTX	later).

       YYRESTORECTX
	      A	generic	API primitive that should restore the trailing context
	      position saved with YYBACKUPCTX.

       YYRESTORETAG
	      A	generic	API primitive with one variable	tag  that  should  re-
	      store the	trailing context position to the value of tag.

       YYSTAGP
	      A	 generic API primitive with one	variable tag, where tag	can be
	      a	pointer	or an offset in	YYINPUT	(see submatch extraction  sec-
	      tion  for	 details). YYSTAGP should set tag to the current input
	      position.

       YYSTAGN
	      A	generic	API primitive with one variable	tag, where tag can  be
	      a	 pointer or an offset in YYINPUT (see submatch extraction sec-
	      tion for details). YYSTAGN should	to set tag  to	a  value  that
	      represents non-existent input position.

       YYMTAGP
	      A	 generic  API primitive	with one variable tag.	YYMTAGP	should
	      append the current position to the submatch history of tag  (see
	      the submatch extraction section for details.)

       YYMTAGN
	      A	 generic  API primitive	with one variable tag.	YYMTAGN	should
	      append a value that represents non-existent input	position posi-
	      tion to the submatch history of tag (see the submatch extraction
	      section for details.)

       YYSHIFT
	      A	generic	API primitive with  one	 variable  shift  that	should
	      shift  the current input position	by shift characters (the shift
	      value may	be negative).

       YYCOPYSTAG
	      A	generic	API primitive with two variables,  lhs	and  rhs  that
	      should   copy   right-hand-side	s-tag	variable  rhs  to  the
	      left-hand-side s-tag variable lhs. For most languages this prim-
	      itive has	a default definition that assigns lhs to rhs.

       YYCOPYMTAG
	      A	generic	API primitive with two variables,  lhs	and  rhs  that
	      should   copy   right-hand-side	m-tag	variable  rhs  to  the
	      left-hand-side m-tag variable lhs. For most languages this prim-
	      itive has	a default definition that assigns lhs to rhs.

       YYSHIFTSTAG
	      A	generic	 API primitive with two	variables, tag and shift  that
	      should  shift  tag  by  shift code units (the shift value	may be
	      negative).

       YYSHIFTMTAG
	      A	generic	API primitive with two variables, tag and  shift  that
	      should  shift  the  latest  value	in the history of tag by shift
	      code units (the shift value may be negative).

       YYMAXNMATCH
	      An integral constant equal to the	maximal	number of  POSIX  cap-
	      turing groups in a rule. It is generated with a maxnmatch	block.

       YYCONDTYPE
	      The type of the condition	enum.  It can be generated either with
	      conditions block or --header option.

       YYGETACCEPT
	      A	 primitive  with one variable var that stores numeric selector
	      of the accepted rule. For	most languages this  primitive	has  a
	      default definition that reads from var.

       YYSETACCEPT
	      A	 primitive with	two variables: var (an l-value that stores nu-
	      meric selector of	the accepted rule), and	val (the value of  se-
	      lector). For most	languages this primitive has a default defini-
	      tion that	assigns	var to val.

       YYGETCOND
	      An  r-value of type YYCONDTYPE that is equal to the current con-
	      dition identifier.

       YYSETCOND
	      A	primitive with one variable cond that should set  the  current
	      condition	identifier to cond.

       YYGETSTATE
	      An  r-value  of  integer type that is equal to the current lexer
	      state. It	should be initialized to -1.

       YYSETSTATE
	      A	primitive with one variable state that should set the  current
	      lexer state to state.

       YYDEBUG
	      This primitive is	generated only with -d,	--debug-output option.
	      Its purpose is to	add logging to the generated code (typical YY-
	      DEBUG  definition	 is a print statement).	YYDEBUG	statements are
	      generated	in every state and have	two variables: state (either a
	      DFA state	index or -1) and symbol	(the current input symbol).

       yyaccept
	      An l-value of unsigned integral type that	stores the  number  of
	      the  latest matched rule.	User definition	is necessary only with
	      --storable-state option.

       yybm   A	table containing compressed bitmaps for	up  to	8  transitions
	      (used  with  the	--bitmaps option). The table contains 256 ele-
	      ments and	is indexed by 1-byte code units.  Each	8-bit  element
	      combines	boolean	 values	 for  up to 8 transitions. k-Th	bit of
	      n-th element is true iff n-th code unit is in the	range of  k-th
	      transition.  The	idea  of  this	bitmap	is  to replace many if
	      branches or switch cases with one	check of a single bit  in  the
	      table.

       yych   An l-value of type YYCTYPE that stores the current input charac-
	      ter.  User definition is necessary only with -f --storable-state
	      option.

       yyctable
	      Jump table generated for the initial condition dispatch (enabled
	      with  the	 combination  of --conditions and --computed-gotos op-
	      tions).

       yyfill An l-value that stores the result	of YYFILL call	(this  may  be
	      necessary	 for  pure  functional	languages,  where  YYFILL is a
	      monadic function with complex return value).

       yynmatch
	      An l-value of unsigned integral type that	stores the  number  of
	      POSIX  capturing	groups in the matched rule.  Used only with -P
	      --posix-captures option.

       yypmatch
	      An array of l-values that	are used to hold the tag values	corre-
	      sponding to the capturing	parentheses in the matching rule.  Ar-
	      ray  length must be at least yynmatch * 2	(usually YYMAXNMATCH *
	      2	is a good choice).  Used only with -P --posix-captures option.

       yystable
	      Deprecated.

       yystate
	      An l-value used with the --loop-switch option to store the  cur-
	      rent DFA state.

       yytarget
	      Jump  table that contains	jump targets (label addresses) for all
	      transitions from a state.	This table is  local  to  each	state.
	      Generation  of  yytarget tables is enabled with --computed-gotos
	      option.

   Options
       Some of the  options  have  corresponding  configurations,  others  are
       global  and cannot be changed after re2c	starts reading the input file.
       Debug options generally require building	re2c in	 debug	configuration.
       Internal	 options are useful for	experimenting with the algorithms used
       in re2c.

       -? --help -h
	      Show help	message.

       --api <simple | record |	generic>
	      Specify the API used by the generated  code  to  interface  with
	      used-defined  code.  Option simple shold be used in simple cases
	      when there's no need for	buffer	refilling  and	storing	 lexer
	      state. Option record should be used when lexer state needs to be
	      stored in	a record (struct, class, etc.).	 Option	generic	should
	      be  used in complex cases	when the other two APIs	are not	flexi-
	      ble enough.

       --bit-vectors -b
	      Optimize conditional jumps using bit masks.  This	option implies
	      --nested-ifs.

       --captures, --leftmost-captures
	      Enable  submatch	extraction  with  leftmost  greedy   capturing
	      groups. The result is collected into an array yybmatch of	capac-
	      ity 2 * YYMAXNMATCH, and yynmatch	is set to the number of	groups
	      for the matching rule.

       --captvars, --leftmost-captvars
	      Enable   submatch	 extraction  with  leftmost  greedy  capturing
	      groups. The result is collected into variables yytl<k>,  yytr<k>
	      for k-th capturing group.

       --case-insensitive
	      Treat  single-quoted  and	double-quoted strings as case-insensi-
	      tive.

       --case-inverted
	      Invert the meaning of single-quoted and  double-quoted  strings:
	      treat  single-quoted strings as case-sensitive and double-quoted
	      strings as case-insensitive.

       --case-ranges
	      Collapse consecutive cases in a switch statements	into  a	 range
	      of the form low ... high.	This syntax is a C/C++ language	exten-
	      sion that	is supported by	compilers like GCC, Clang and Tcc. The
	      main advantage over using	single cases is	smaller	generated code
	      and faster generation time, although for some compilers like Tcc
	      it  also	results	 in  smaller binary size.  This	option is sup-
	      ported only for C.

       --computed-gotos	-g
	      Optimize conditional jumps using	non-standard  "computed	 goto"
	      extension	 (which	 must  be supported by the compiler). re2ocaml
	      generates	jump tables only in complex cases with a lot of	condi-
	      tional branches. Complexity threshold  can  be  configured  with
	      cgoto:threshold  configuration.  This  option implies --bit-vec-
	      tors. It is supported only for C.

       --conditions --start-conditions -c
	      Enable support of	Flex-like "conditions":	multiple  interrelated
	      lexers  within  one  block.  This	 is an alternative to manually
	      specifying different re2ocaml  blocks  connected	with  goto  or
	      function calls.

       --depfile FILE
	      Write  dependency	 information to	FILE in	the form of a Makefile
	      rule <output-file> : <input-file>	[include-file ...].  This  al-
	      lows  one	to track build dependencies in the presence of include
	      blocks/directives, so that updating include files	 triggers  re-
	      generation  of  the  output  file.   This	 option	depends	on the
	      --output option.

       --ebcdic	--ecb -e
	      Generate a lexer that reads input	in EBCDIC  encoding.  re2ocaml
	      assumes that the character range is 0 -- 0xFF and	character size
	      is 1 byte.

       --empty-class <match-empty | match-none | error>
	      Define  the  way	re2ocaml  treats empty character classes. With
	      match-empty (the default)	empty class matches empty input	(which
	      is illogical, but	backwards-compatible). With  match-none	 empty
	      class  always  fails  to match.  With error empty	class raises a
	      compilation error.

       --encoding-policy <fail | substitute | ignore>
	      Define the way re2ocaml treats Unicode  surrogates.   With  fail
	      re2ocaml	aborts	with an	error when a surrogate is encountered.
	      With substitute re2ocaml silently	replaces surrogates  with  the
	      error  code  point  0xFFFD.  With	 ignore	(the default) re2ocaml
	      treats surrogates	as normal code points.	The  Unicode  standard
	      says  that standalone surrogates are invalid, but	real-world li-
	      braries and programs behave in different ways.

       --flex-syntax -F
	      Partial support for Flex syntax: in this mode named  definitions
	      don't  need  the	equal  sign and	the terminating	semicolon, and
	      when used	they must be surrounded	with curly braces. Names with-
	      out curly	braces are treated as double-quoted strings.

       --goto-label
	      Use "goto/label" code model: encode DFA in form of labeled  code
	      blocks  connected	 with  goto transitions	across blocks. This is
	      only supported for languages that	have a goto statement.

       --header	--type-header -t HEADER
	      Generate a HEADER	file. The contents of the file can  be	speci-
	      fied  using  special  blocks header:on and header:off. If	condi-
	      tions are	used, the generated header will	have a condition  enum
	      automatically appended to	it (unless there is an explicit	condi-
	      tions block).

       -I PATH
	      Add  PATH	to the list of locations which are used	when searching
	      for include files. This option is	useful in combination with in-
	      clude block or directive.	re2ocaml looks for FILE	in the	direc-
	      tory  of	the parent file	and in the include locations specified
	      with -I option.

       --input <default	| custom>
	      Deprecated alias for --api. Option default corresponds to	simple
	      (it is indeed the	default	for most backends, but not  for	 all).
	      Option custom corresponds	to generic.

       --input-encoding	<ascii | utf8>
	      Specify the way re2ocaml parses regular expressions.  With ascii
	      (the  default)  re2ocaml handles input as	ASCII-encoded: any se-
	      quence of	code units is a	sequence of standalone 1-byte  charac-
	      ters.  With utf8 re2ocaml	handles	input as UTF8-encoded and rec-
	      ognizes multibyte	characters.

       --invert-captures
	      Invert the meaning of capturing and non-capturing	groups.	By de-
	      fault (...) is capturing and (! ...) is non-capturing. With this
	      option (!	...) is	capturing and (...) is non-capturing.

       --lang <none | c	| d | go | haskell | java | js | ocaml | python	| rust
       | v | zig>
	      Specify  the  target language. Supported languages are C,	D, Go,
	      Haskell, Java, JS, OCaml,	Python,	Rust, V, Zig  (more  languages
	      can be added via user-defined syntax files, see the --syntax op-
	      tion).  Option none disables default suntax configs, so that the
	      target language is undefined.

       --location-format <gnu |	msvc>
	      Specify location format in messages.   With  gnu	locations  are
	      printed as 'filename:line:column:	...'.  With msvc locations are
	      printed as 'filename(line,column)	...'.  The default is gnu.

       --loop-switch
	      Use  "loop/switch" code model: encode DFA	in form	of a loop over
	      a	switch statement, where	individual states  are	switch	cases.
	      State  is	 stored	 in  a	variable  yystate. Transitions between
	      states update yystate to the case	label of the destination state
	      and continue execution to	the head of the	loop.

       --nested-ifs -s
	      Use nested if statements instead of switch statements in	condi-
	      tional  jumps.  This usually results in more efficient code with
	      non-optimizing compilers.

       --no-debug-info -i
	      Do not output line directives. This may be useful	when the  gen-
	      erated code is stored in a version control system	(to avoid huge
	      autogenerated diffs on small changes).

       --no-generation-date
	      Suppress date output in the generated file.

       --no-version
	      Suppress version output in the generated file.

       --no-unsafe
	      Do  not generate unsafe wrapper over YYPEEK (this	option is spe-
	      cific to Rust). For  performance	reasons	 YYPEEK	 should	 avoid
	      bounds-checking,	as  the	 lexer	already	 performs end-of-input
	      checks in	a more efficient way.  The user	may choose to  provide
	      a	safe YYPEEK definition,	or a definition	that is	unsafe only in
	      release  builds,	in  which case the --no-unsafe option helps to
	      avoid warnings about redundant unsafe blocks.

       --output	-o OUTPUT
	      Specify the OUTPUT file.

       --posix-captures, -P
	      Enable submatch extraction with  POSIX-style  capturing  groups.
	      The  result  is collected	into an	array yybmatch of capacity 2 *
	      YYMAXNMATCH, and yynmatch	is set to the number of	groups for the
	      matching rule.

       --posix-captvars
	      Enable submatch extraction with  POSIX-style  capturing  groups.
	      The result is collected into variables yytl<k>, yytr<k> for k-th
	      capturing	group.

       --recursive-functions
	      Use  code	 model based on	co-recursive functions,	where each DFA
	      state is a separate function that	may call other state-functions
	      or itself.

       --reusable -r
	      Deprecated since version 2.2 (reusable blocks are	allowed	by de-
	      fault now).

       --skeleton -S
	      Ignore user-defined interface code and generate a	self-contained
	      "skeleton" program.  Additionally,  generate  input  files  with
	      strings  derived	from  the regular grammar and compressed match
	      results that are used to verify "skeleton" behavior on  all  in-
	      puts.  This  option  is useful for finding bugs in optimizations
	      and code generation. This	option is supported only for C.

       --storable-state	-f
	      Generate a lexer which can store its inner state.	 This is  use-
	      ful  in  push-model lexers which are stopped by an outer program
	      when there is not	enough input, and then resumed when more input
	      becomes available. In this mode users should additionally	define
	      YYGETSTATE and YYSETSTATE	primitives, and	variables yych,	 yyac-
	      cept and state should be part of the stored lexer	state.

       --syntax	FILE
	      Load  configurations  from  the specified	FILE and apply them on
	      top of the default syntax	file. Note that	FILE can define	only a
	      few configurations (if it's used to  amend  the  default	syntax
	      file),  or  it  can  define a whole new language backend (in the
	      latter case it is	recommended to use --lang none option).

       --tags -T
	      Enable submatch extraction with tags.

       --ucs2 --wide-chars -w
	      Generate a lexer that reads UCS2-encoded input. re2ocaml assumes
	      that the character range is 0 -- 0xFFFF and character size is  2
	      bytes.  This option implies --nested-ifs.

       --utf8 --utf-8 -8
	      Generate	a  lexer  that reads input in UTF-8 encoding. re2ocaml
	      assumes that the character range is 0 -- 0x10FFFF	and  character
	      size is 1	byte.

       --utf16 --utf-16	-x
	      Generate	a  lexer  that reads UTF16-encoded input. re2ocaml as-
	      sumes that the character range is	0 --  0x10FFFF	and  character
	      size is 2	bytes.	This option implies --nested-ifs.

       --utf32 --unicode -u
	      Generate	a  lexer  that reads UTF32-encoded input. re2ocaml as-
	      sumes that the character range is	0 --  0x10FFFF	and  character
	      size is 4	bytes.	This option implies --nested-ifs.

       --verbose
	      Output a short message in	case of	success.

       --vernum	-V
	      Show version information in MMmmpp format	(major,	minor, patch).

       --version -v
	      Show version information.

       --single-pass -1
	      Deprecated. Does nothing (single pass is the default now).

       --debug-output -d
	      Emit  YYDEBUG  invocations in the	generated code.	This is	useful
	      to trace lexer execution.

       --dump-adfa
	      Debug option: output DFA after tunneling (in .dot	format).

       --dump-cfg
	      Debug option: output control flow	graph  of  tag	variables  (in
	      .dot format).

       --dump-closure-stats
	      Debug  option: output statistics on the number of	states in clo-
	      sure.

       --dump-dfa-det
	      Debug option: output DFA immediately after  determinization  (in
	      .dot format).

       --dump-dfa-min
	      Debug option: output DFA after minimization (in .dot format).

       --dump-dfa-tagopt
	      Debug  option:  output DFA after tag optimizations (in .dot for-
	      mat).

       --dump-dfa-tree
	      Debug option: output DFA under construction with	states	repre-
	      sented as	tag history trees (in .dot format).

       --dump-dfa-raw
	      Debug  option:  output  DFA  under  construction	with  expanded
	      state-sets (in .dot format).

       --dump-interf
	      Debug option: output interference	 table	produced  by  liveness
	      analysis of tag variables.

       --dump-nfa
	      Debug option: output NFA (in .dot	format).

       --emit-dot -D
	      Instead  of  normal  output generate lexer graph in .dot format.
	      The output can be	 converted  to	an  image  with	 the  help  of
	      Graphviz (e.g. something like dot	-Tpng -odfa.png	dfa.dot).

       --dfa-minimization <moore | table>
	      Internal	option:	 DFA  minimization algorithm used by re2ocaml.
	      The moore	option is the Moore algorithm (it is the default). The
	      table option is the "table filling" algorithm.  Both  algorithms
	      should produce the same DFA up to	states relabeling; table fill-
	      ing  is simpler and much slower and serves as a reference	imple-
	      mentation.

       --eager-skip
	      Internal option: make the	generated lexer	advance	the input  po-
	      sition  eagerly  --  immediately after reading the input symbol.
	      This changes the default behavior	when the input position	is ad-
	      vanced lazily -- after transition	to the next state.

       --no-lookahead
	      Internal option, deprecated.  It used to	enable	TDFA(0)	 algo-
	      rithm. Unlike TDFA(1), TDFA(0) algorithm does not	use one-symbol
	      lookahead.  It applies register operations to the	incoming tran-
	      sitions rather than the outgoing ones.  Benchmarks  showed  that
	      TDFA(0) algorithm	is less	efficient than TDFA(1).

       --no-optimize-tags
	      Internal	option:	suppress optimization of tag variables (useful
	      for debugging).

       --posix-closure <gor1 | gtop>
	      Internal option: specify shortest-path algorithm	used  for  the
	      construction of epsilon-closure with POSIX disambiguation	seman-
	      tics:  gor1  (the	default) stands	for Goldberg-Radzik algorithm,
	      and gtop stands for "global topological order" algorithm.

       --posix-prectable <complex | naive>
	      Internal option: specify the algorithm  used  to	compute	 POSIX
	      precedence  table. The complex algorithm computes	precedence ta-
	      ble in one traversal of tag history tree and has quadratic  com-
	      plexity  in  the	number	of TNFA	states;	it is the default. The
	      naive algorithm has worst-case cubic complexity in the number of
	      TNFA states, but it is much simpler  than	 complex  and  may  be
	      slightly faster in non-pathological cases.

       --stadfa
	      Internal	option,	 deprecated.   It  used	to enable staDFA algo-
	      rithm, which differs from	TDFA in	that register  operations  are
	      placed  in  states rather	than on	transitions. Benchmarks	showed
	      that staDFA algorithm is less efficient than TDFA.

       --fixed-tags <none | toplevel | all>
	      Internal option:	specify	 whether  the  fixed-tag  optimization
	      should  be  applied  to  all tags	(all), none of them (none), or
	      only those in toplevel concatenation (toplevel). The default  is
	      all.   "Fixed"  tags  are	 those that are	located	within a fixed
	      distance to some other tag (called "base"). In such  cases  only
	      the base tag needs to be tracked,	and the	value of the fixed tag
	      can  be computed as the value of the base	tag plus a static off-
	      set. For tags that are under alternative	or  repetition	it  is
	      also necessary to	check if the base tag has a no-match value (in
	      that case	fixed tag should also be set to	no-match, disregarding
	      the  offset).  For  tags in top-level concatenation the check is
	      not needed, because they always match.

   Warnings
       Warnings	can be invividually enabled, disabled and turned into  an  er-
       ror.

       -W     Turn on all warnings.

       -Werror
	      Turn  warnings  into errors. Note	that this option alone doesn't
	      turn on any warnings; it only affects those warnings  that  have
	      been turned on so	far or will be turned on later.

       -W<warning>
	      Turn on warning.

       -Wno-<warning>
	      Turn off warning.

       -Werror-<warning>
	      Turn  on warning and treat it as an error	(this implies -W<warn-
	      ing>).

       -Wno-error-<warning>
	      Don't treat this particular warning as an	 error.	 This  doesn't
	      turn off the warning itself.

       -Wcondition-order
	      Warn  if	the generated program makes implicit assumptions about
	      condition	numbering. One should use either  --header  option  or
	      conditions  block	 to  generate  a mapping of condition names to
	      numbers and then use the autogenerated condition names.

       -Wempty-character-class
	      Warn if a	regular	expression contains an empty character	class.
	      Trying  to  match	 an  empty  character class makes no sense: it
	      should always fail.  However, for	backwards  compatibility  rea-
	      sons re2ocaml permits empty character classes and	treats them as
	      empty  strings.  Use  the	--empty-class option to	change the de-
	      fault behavior.

       -Wmatch-empty-string
	      Warn if a	rule is	nullable (matches an empty  string).   If  the
	      lexer  runs  in a	loop and the empty match is unintentional, the
	      lexer may	unexpectedly hang in an	infinite loop.

       -Wswapped-range
	      Warn if the lower	bound of a range is  greater  than  its	 upper
	      bound.  The  default  behavior  is  to  silently	swap the range
	      bounds.

       -Wundefined-control-flow
	      Warn if some input strings cause undefined control flow  in  the
	      lexer  (the  faulty  patterns are	reported). This	is a dangerous
	      and common mistake. It can be easily fixed by adding the default
	      rule * which has the lowest priority, matches any	code unit, and
	      always consumes a	single code unit.

       -Wunreachable-rules
	      Warn about rules that are	shadowed by other rules	and will never
	      match.

       -Wuseless-escape
	      Warn if a	symbol is escaped when it shouldn't be.	  By  default,
	      re2ocaml silently	ignores	such escapes, but this may as well in-
	      dicate a typo or an error	in the escape sequence.

       -Wnondeterministic-tags
	      Warn  if	a  tag	has  n-th degree of nondeterminism, where n is
	      greater than 1.

       -Wsentinel-in-midrule
	      Warn if the sentinel symbol occurs in the	middle of a  rule  ---
	      this  may	 cause reads past the end of buffer, crashes or	memory
	      corruption in the	generated lexer. This warning is only applica-
	      ble if the sentinel method of checking for the end of  input  is
	      used.   It  is set to an error if	re2c:sentinel configuration is
	      used.

       -Wundefined-syntax-config
	      Warn if the syntax file specified	with --syntax option is	 miss-
	      ing  definitions	of some	configurations.	This helps to maintain
	      user-defined syntax files: if a new release adds configurations,
	      old syntax file will raise a warning, and	the user will be noti-
	      fied. If some configurations are unused and do not need a	defin-
	      ition, they should be explicitly set to <undefined>.

   Syntax files
       Support for different languages in re2c is based	on the idea of	syntax
       files.	A  syntax  file	is a configuration file	that defines syntax of
       the target language -- not the whole language, but a small part	of  it
       that  is	used by	the generated code. Syntax files make re2c very	flexi-
       ble, but	they should not	be used	as a replacement for re2c:  configura-
       tions: their purpose is to define syntax	of the target language,	not to
       customize  one  particular  lexer. All supported	languages have default
       syntax files that are part of the distribution (see include/syntax sub-
       directory); they	are also embedded in the re2ocaml binary.   Users  may
       provide	a  custom  syntax file that overrides a	few configurations for
       one of supported	languages, or they may choose to redefine all configu-
       rations (in that	case --lang none option	should be used).  Syntax files
       contain configurations of four different	kinds: feature lists, language
       configurations, inplace configurations and code templates.

       Feature lists
	  A few	list configurations define various  features  supported	 by  a
	  given	 backend,  so that re2ocaml may	give a clear error if the user
	  tries	to enable an unsupported feature:

	  supported_apis
		 A list	of  supported  APIs  with  possible  elements  simple,
		 record, generic.

	  supported_api_styles
		 A  list  of supported API styles with possible	elements func-
		 tions,	free-form.

	  supported_code_models
		 A list	 of  supported	code  models  with  possible  elements
		 goto-label, loop-switch, recursive-functions.

	  supported_targets
		 A  list  of  supported	codegen	targets	with possible elements
		 code, dot, skeleton.

	  supported_features
		 A  list  of  supported	 features   with   possible   elements
		 nested-ifs,  bitmaps,	computed-gotos,	 case-ranges, monadic,
		 unsafe, tags, captures, captvars.

       Language	configurations
	  A few	boolean	configurations describe	features of  the  target  lan-
	  guage	that affect re2ocaml parser and	code generator:

	  semicolons
		 Non-zero if the language uses semicolons after	statements.

	  backtick_quoted_strings
		 Non-zero if the language has backtick-quoted strings.

	  single_quoted_strings
		 Non-zero if the language has single-quoted strings.

	  indentation_sensitive
		 Non-zero if the language is indentation sensitive.

	  wrap_blocks_in_braces
		 Non-zero  if  compound	 statements  must  be wrapped in curly
		 braces.

       Inplace configurations
	  Syntax files define initial values of	all re2c:  configurations,  as
	  they	may differ for different languages. See	configurations section
	  for a	full list of all inplace configurations	and their meaning.

       Code templates
	  Code templates define	syntax of the target language. They are	 writ-
	  ten  in  a simple domain-specific language with the following	formal
	  grammar:

	      code-template ::
		    name '=' code-exprs	';'
		  | CODE_TEMPLATE ';'
		  | '<undefined>' ';'

	      code-exprs ::
		    <EMPTY>
		  | code-exprs code-expr

	      code-expr	::
		    STRING
		  | VARIABLE
		  | optional
		  | list

	      optional ::
		    '('	CONDITIONAL '?'	code-exprs ')'
		  | '('	CONDITIONAL '?'	code-exprs ':' code-exprs ')'

	      list ::
		    '['	VARIABLE ':' code-exprs	']'
		  | '['	VARIABLE '{' NUMBER '}'	':' code-exprs ']'
		  | '['	VARIABLE '{' NUMBER ','	NUMBER '}' ':' code-exprs ']'

	  A code template is a sequence	of  string  literals,  variables,  op-
	  tional  elements and lists, or a reference to	another	code template,
	  or a special value <undefined>. Variables are	placeholders that  are
	  substituted  during  code  generation	phase. List variables are spe-
	  cial:	when expanding list templates,	re2ocaml  repeats  expressions
	  the  right  hand side	of the column a	few times, each	time replacing
	  occurrences of the list variable with	a value	specific to this repe-
	  tition. Lists	have optional bounds (negative values are counted from
	  the end, e.g.	-1 means the last element).  Conditional  names	 start
	  with	a  dot.	  Both	conditionals and variables may be either local
	  (specific to the given code template)	or global (allowed in all code
	  templates). When re2ocaml reads syntax file,	it  checks  that  each
	  code	template uses only the variables and conditionals that are al-
	  lowed	in it.

	  For example, the following code template defines  if-then-else  con-
	  struct for a C-like language:

	      code:if_then_else	=
		  [branch{0}: topindent	"if " cond " {"	nl
		      indent [stmt: stmt] dedent]
		  [branch{1:-1}: topindent "} else" (.cond ? " if " cond) " {" nl
		      indent [stmt: stmt] dedent]
		  topindent "}"	nl;

	  Here	branch	is  a  list  variable:	branch{0} expands to the first
	  branch (which	is special, as there is	no  else  part),  branch{1:-1}
	  expands  to  all  remaining  branches	 (if any). stmt	is also	a list
	  variable: [stmt: stmt] is a nested list that expands to  a  list  of
	  statements in	the body of the	current	branch.	topindent, indent, de-
	  dent	and  nl	are global variables, and .cond	is a local conditional
	  (their meaning is described below). This code	template could produce
	  the following	code:

	      if x {
		  // do	something
	      }	else if	y {
		  // do	something else
	      }	else {
		  // don't do anything
	      }

	  Here's a list	of all code templates supported	by re2ocaml with their
	  local	variables and conditionals. Note that a	particular  definition
	  may, but does	not have to use	local variables	and conditionals.  Any
	  unused code templates	should be set to <undefined>.

	  code:var_local
		 Declaration  or  definition  of  a  local variable. Supported
		 variables: type (the type of the variable), name  (its	 name)
		 and  init  (initial value, if any). Conditionals: .init (true
		 if there is an	initializer).

	  code:var_global
		 Same as code:var_local, except	that it's used in top-level.

	  code:const_local
		 Definition of a local	constant.  Supported  variables:  type
		 (the type of the constant), name (its name) and init (initial
		 value).

	  code:const_global
		 Same as code:const_local, except that it's used in top-level.

	  code:array_local
		 Definition  of	 a  local  array (table). Supported variables:
		 type (the type	of array elements), name  (array  name),  size
		 (its size), row (a list variable that does not	itself produce
		 any  code, but	expands	list expression	as many	times as there
		 are rows in the table)	and elem (a list variable that expands
		 to all	table elements in the current row -- it's meant	to  be
		 nested	in the row list).

	  code:array_global
		 Same as code:array_local, except that it's used in top-level.

	  code:array_elem
		 Reference  to an element of an	array (table). Supported vari-
		 ables:	array (the name	of the array) and index	(index of  the
		 element).

	  code:enum
		 Definition  of	an enumeration (it may be defined using	a spe-
		 cial language construct for enumerations, or simply as	a  few
		 standalone   constants).    Supported	 variables   are  type
		 (user-defined enumeration type	or  type  of  the  constants),
		 elem  (list variable that expands to the name of each member)
		 and init (initializer for each	member).  Conditionals:	 .init
		 (true if there	is an initializer).

	  code:enum_elem
		 Enumeration  element  (a member of a user-defined enumeration
		 type or a name	of a constant, depending on how	 code:enum  is
		 defined).  Supported variables	are name (the name of the ele-
		 ment) and type	(its type).

	  code:assign
		 Assignment  statement.	Supported variables are	lhs (left hand
		 side) and rhs (right hand side).

	  code:type_int
		 Signed	integer	type.

	  code:type_uint
		 Unsigned integer type.

	  code:type_yybm
		 Type of elements in the yybm table.

	  code:type_yytarget
		 Type of elements in the yytarget table.

	  code:cmp_eq
		 Operator "equals".

	  code:cmp_ne
		 Operator "not equals".

	  code:cmp_lt
		 Operator "less	than".

	  code:cmp_gt
		 Operator "greater than"

	  code:cmp_le
		 Operator "less	or equal"

	  code:cmp_ge
		 Operator "greater or equal"

	  code:if_then_else
		 If-then-else statement	with one or more  branches.  Supported
		 variables:  branch (a list variable that does not itself pro-
		 duce any code,	but expands list expression as many  times  as
		 there	are  branches),	cond (condition	of the current branch)
		 and stmt (a list variable that	expands	to all	statements  in
		 the current branch). Conditionals: .cond (true	if the current
		 branch	has a condition), .many	(true if there's more than one
		 branch).

	  code:if_then_else_oneline
		 A  specialization  of code:if_then_else for the case when all
		 branches have one-line	statements. If	this  is  <undefined>,
		 code:if_then_else is used instead.

	  code:switch
		 A  switch  statement  with one	or more	cases. Supported vari-
		 ables:	expr (the switched-on expression)  and	case  (a  list
		 variable  that	 expands  to  all cases-groups with their code
		 blocks).

	  code:switch_cases
		 A group of switch cases that maps to  a  single  code	block.
		 Supported variables are case (a list variable that expands to
		 all  cases  in	this group) and	stmt (a	list variable that ex-
		 pands to all statements in the	code block.

	  code:switch_cases_oneline
		 A specialization of code:switch_cases for the case  when  the
		 code  block  consists of a single one-line statement. If this
		 is <undefined>, code:switch_cases is used instead.

	  code:switch_case_range
		 A single switch case that covers a range of values  (possibly
		 consisting  of	 a  single  value). Supported variable:	val (a
		 list variable that expands to all values in the range).  Sup-
		 ported	 conditionals:	.many  (true  if there's more than one
		 value in the range) and .char_literals	(true  if  this	 is  a
		 switch	 on  character literals	-- some	languages provide spe-
		 cial syntax for this case).

	  code:switch_case_default
		 Default switch	case.

	  code:loop
		 A loop	that runs forever (unless interrupted  from  the  loop
		 body).	 Supported variables: label (loop label), stmt (a list
		 variable that expands to all statements in the	loop body).

	  code:continue
		 Continue  statement.  Supported  variables: label (label from
		 which to continue execution).

	  code:goto
		 Goto statement. Supported variables: label (label of the jump
		 target).

	  code:fndecl
		 Function declaration.	Supported  variables:  name  (function
		 name),	type (return type), arg	(a list	variable that does not
		 itself	 produce  code,	 but  expands  list expression as many
		 times as there	are function arguments), argname (name of  the
		 current  argument),  argtype  (type of	the current argument).
		 Conditional: .type (true if this is a non-void	function).

	  code:fndef
		 Like code:fndecl, but used for	function  definitions,	so  it
		 has  one  additional  list  variable stmt that	expands	to all
		 statements in the function body.

	  code:fncall
		 Function call statement. Supported variables: name  (function
		 name),	 retval	 (l-value where	the return value is stored, if
		 any) and arg (a list variable that expands  to	 all  function
		 arguments).   Conditionals:  .args  (true if the function has
		 arguments) and	.retval	(true if  return  value	 needs	to  be
		 saved).

	  code:tailcall
		 Tail  call  statement.	 Supported  variables:	name (function
		 name),	and arg	(a list	variable that expands to all  function
		 arguments).   Conditionals:  .args  (true if the function has
		 arguments) and	.retval	(true if this is a non-void function).

	  code:recursive_functions
		 Program body with --recursive-functions code model. Supported
		 variables: fn (a list variable	that does not  itself  produce
		 any  code, but	expands	list expression	as many	times as there
		 are functions), fndecl	(declaration of	the current  function)
		 and fndef (definition of the current function).

	  code:fingerprint
		 The fingerprint at the	top of the generated output file. Sup-
		 ported	variables: ver (re2ocaml version that was used to gen-
		 erate this) and date (generation date).

	  code:line_info
		 The format of line directives (if this	is set to <undefined>,
		 no directives are generated). Supported variables: line (line
		 number) and file (filename).

	  code:abort
		 A statement that aborts program execution.

	  code:yydebug
		 YYDEBUG  statement,  possibly specialized for different APIs.
		 Supported variables: YYDEBUG, yyrecord, yych (map to the cor-
		 responding re2c: configurations), state (DFA state number).

	  code:yypeek
		 YYPEEK	statement, possibly specialized	 for  different	 APIs.
		 Supported  variables:	YYPEEK,	 YYCTYPE,  YYINPUT,  YYCURSOR,
		 yyrecord, yych	(map to	 the  corresponding  re2c:  configura-
		 tions).  Conditionals:	.cast (true if re2c:yych:conversion is
		 set to	non-zero).

	  code:yyskip
		 YYSKIP	statement, possibly specialized	 for  different	 APIs.
		 Supported  variables:	YYSKIP,	YYCURSOR, yyrecord (map	to the
		 corresponding re2c: configurations).

	  code:yybackup
		 YYBACKUP statement, possibly specialized for different	 APIs.
		 Supported  variables:	YYBACKUP, YYCURSOR, YYMARKER, yyrecord
		 (map to the corresponding re2c: configurations).

	  code:yybackupctx
		 YYBACKUPCTX statement,	 possibly  specialized	for  different
		 APIs.	 Supported  variables:	YYBACKUPCTX,  YYCURSOR,	YYCTX-
		 MARKER, yyrecord (map to the corresponding  re2c:  configura-
		 tions).

	  code:yyskip_yypeek
		 Combined  code:yyskip	and code:yypeek	statement (defaults to
		 code:yyskip followed by code:yypeek).

	  code:yypeek_yyskip
		 Combined code:yypeek and code:yyskip statement	 (defaults  to
		 code:yypeek followed by code:yyskip).

	  code:yyskip_yybackup
		 Combined code:yyskip and code:yybackup	statement (defaults to
		 code:yyskip followed by code:yybackup).

	  code:yybackup_yyskip
		 Combined code:yybackup	and code:yyskip	statement (defaults to
		 code:yybackup followed	by code:yyskip).

	  code:yybackup_yypeek
		 Combined code:yybackup	and code:yypeek	statement (defaults to
		 code:yybackup followed	by code:yypeek).

	  code:yyskip_yybackup_yypeek
		 Combined code:yyskip, code:yybackup and code:yypeek statement
		 (defaults  to``code:yyskip``  followed	 by code:yybackup fol-
		 lowed by code:yypeek).

	  code:yybackup_yypeek_yyskip
		 Combined code:yybackup, code:yypeek and code:yyskip statement
		 (defaults to``code:yybackup`` followed	 by  code:yypeek  fol-
		 lowed by code:yyskip).

	  code:yyrestore
		 YYRESTORE statement, possibly specialized for different APIs.
		 Supported  variables: YYRESTORE, YYCURSOR, YYMARKER, yyrecord
		 (map to the corresponding re2c: configurations).

	  code:yyrestorectx
		 YYRESTORECTX statement, possibly  specialized	for  different
		 APIs.	 Supported  variables:	YYRESTORECTX, YYCURSOR,	YYCTX-
		 MARKER, yyrecord (map to the corresponding  re2c:  configura-
		 tions).

	  code:yyrestoretag
		 YYRESTORETAG  statement,  possibly  specialized for different
		 APIs.	Supported variables: YYRESTORETAG, YYCURSOR,  yyrecord
		 (map  to  the	corresponding  re2c: configurations), tag (the
		 name of tag variable used to restore position).

	  code:yyshift
		 YYSHIFT statement, possibly specialized for  different	 APIs.
		 Supported  variables: YYSHIFT,	YYCURSOR, yyrecord (map	to the
		 corresponding re2c: configurations), offset  (the  number  of
		 code units to shift the current position).

	  code:yyshiftstag
		 YYSHIFTSTAG  statement,  possibly  specialized	 for different
		 APIs.	Supported variables: YYSHIFTSTAG,  yyrecord,  negative
		 (map  to  the	corresponding  re2c: configurations), tag (tag
		 variable which	needs to be shifted), offset  (the  number  of
		 code  units to	shift).	Conditionals: .nested (true if this is
		 a nested  tag	--  in	this  case  its	 value	may  equal  to
		 re2c:tags:negative, which should not be shifted).

	  code:yyshiftmtag
		 YYSHIFTMTAG  statement,  possibly  specialized	 for different
		 APIs.	Supported variables: YYSHIFTMTAG (maps to  the	corre-
		 sponding  re2c: configuration), tag (tag variable which needs
		 to be shifted), offset	(the number of code units to shift).

	  code:yystagp
		 YYSTAGP statement, possibly specialized for  different	 APIs.
		 Supported  variables: YYSTAGP,	YYCURSOR, yyrecord (map	to the
		 corresponding re2c: configurations), tag (tag	variable  that
		 should	be updated).

	  code:yymtagp
		 YYMTAGP  statement,  possibly specialized for different APIs.
		 Supported variables: YYMTAGP (maps to the corresponding re2c:
		 configuration), tag (tag variable that	should be updated).

	  code:yystagn
		 YYSTAGN statement, possibly specialized for  different	 APIs.
		 Supported  variables: YYSTAGN,	negative, yyrecord (map	to the
		 corresponding re2c: configurations), tag (tag	variable  that
		 should	be updated).

	  code:yymtagn
		 YYMTAGN  statement,  possibly specialized for different APIs.
		 Supported variables: YYMTAGN (maps to the corresponding re2c:
		 configuration), tag (tag variable that	should be updated).

	  code:yycopystag
		 YYCOPYSTAG  statement,	 possibly  specialized	for  different
		 APIs.	 Supported variables: YYCOPYSTAG, yyrecord (map	to the
		 corresponding re2c: configurations), lhs, rhs (left and right
		 hand side tag variables of the	copy operation).

	  code:yycopymtag
		 YYCOPYMTAG  statement,	 possibly  specialized	for  different
		 APIs.	 Supported variables: YYCOPYMTAG, yyrecord (map	to the
		 corresponding re2c: configurations), lhs, rhs (left and right
		 hand side tag variables of the	copy operation).

	  code:yygetaccept
		 YYGETACCEPT statement,	 possibly  specialized	for  different
		 APIs.	Supported variables: YYGETACCEPT, yyrecord (map	to the
		 corresponding	re2c: configurations), var (maps to re2c:yyac-
		 cept configuration).

	  code:yysetaccept
		 YYSETACCEPT statement,	 possibly  specialized	for  different
		 APIs.	Supported variables: YYSETACCEPT, yyrecord (map	to the
		 corresponding	re2c: configurations), var (maps to re2c:yyac-
		 cept configuration) and val (numeric value  of	 the  accepted
		 rule).

	  code:yygetcond
		 YYGETCOND statement, possibly specialized for different APIs.
		 Supported  variables:	YYGETCOND, yyrecord (map to the	corre-
		 sponding re2c:	configurations), var (maps to re2c:yycond con-
		 figuration).

	  code:yysetcond
		 YYSETCOND statement, possibly specialized for different APIs.
		 Supported variables: YYSETCOND, yyrecord (map to  the	corre-
		 sponding re2c:	configurations), var (maps to re2c:yycond con-
		 figuration) and val (numeric condition	identifier).

	  code:yygetstate
		 YYGETSTATE  statement,	 possibly  specialized	for  different
		 APIs.	Supported variables: YYGETSTATE, yyrecord (map to  the
		 corresponding	re2c:  configurations),	var (maps to re2c:yys-
		 tate configuration).

	  code:yysetstate
		 YYSETSTATE  statement,	 possibly  specialized	for  different
		 APIs.	 Supported variables: YYSETSTATE, yyrecord (map	to the
		 corresponding re2c: configurations), var (maps	 to  re2c:yys-
		 tate configuration) and val (state number).

	  code:yylessthan
		 YYLESSTHAN  statement,	 possibly  specialized	for  different
		 APIs.	Supported variables:  YYLESSTHAN,  YYCURSOR,  YYLIMIT,
		 yyrecord  (map	 to  the  corresponding	re2c: configurations),
		 need (the number of code  units  to  check  against).	Condi-
		 tional: .many (true if	the need is more than one).

	  code:yybm_filter
		 Condition that	is used	to filter out yych values that are not
		 covered by the	yybm table (used with --bitmaps	option).  Sup-
		 ported	variable: yych (maps to	re2c:yych configuration).

	  code:yybm_match
		 The  format of	yybm table check (generated with --bitmaps op-
		 tion).	Supported variables: yybm, yych	 (map  to  the	corre-
		 sponding  re2c:  configurations),  offset (offset in the yybm
		 table that needs to be	added to yych) and mask	(bit mask that
		 should	be applied to the table	entry to retrieve the  boolean
		 value that needs to be	checked)

	  Here's  a  list  of  all global variables that are allowed in	syntax
	  files:

	  nl	 A newline.

	  indent A variable that does not produce any code, but	has a side-ef-
		 fect of increasing indentation	level.

	  dedent A variable that does not produce any code, but	has a side-ef-
		 fect of decreasing indentation	level.

	  topindent
		 Indentation string for	 the  current  statement.  Indentation
		 level is tracked and automatically updated by the code	gener-
		 ator.

	  Here's  a list of all	global conditionals that are allowed in	syntax
	  files:

	  .api.simple
		 True if simple	API is used (--api simple or re2c:api  =  sim-
		 ple).

	  .api.generic
		 True  if  generic  API	 is  used (--api generic or re2c:api =
		 generic).

	  .api.record
		 True if record	API  is	 used  (--api  record  or  re2c:api  =
		 record).

	  .api_style.functions
		 True  if  function-like  API  style is	used (re2c:api-style =
		 functions).

	  .api_style.freeform
		 True  if  free-form  API  style  is  used  (re2c:api-style  =
		 free-form).

	  .case_ranges
		 True  if  case	 ranges	 feature  is enabled (--case-ranges or
		 re2c:case-ranges = 1).

	  .code_model.goto_label
		 True if  code model based on goto/label is  used  (--goto-la-
		 bel).

	  .code_model.loop_switch
		 True	if   code   model   based   on	 loop/switch  is  used
		 (--loop-switch).

	  .code_model.recursive_functions
		 True if code model  based  on	recursive  functions  is  used
		 (--recursive-function).

	  .date	 True  if  the generated fingerprint should contain generation
		 date.

	  .loop_label
		 True if re2ocaml generated loops must have a label  (re2c:la-
		 bel:yyloop is set to a	nonempty string).

	  .monadic
		 True  if the generated	code should be monadic (re2c:monadic =
		 1).  This is only relevant for	pure functional	languages.

	  .start_conditions
		 True if start conditions are enabled (--start-conditions).

	  .storable_state
		 True if storable state	is enabled (--storable-state).

	  .unsafe
		 True if re2ocaml should use "unsafe" blocks in	order to  gen-
		 erate	faster	code (--unsafe,	re2c:unsafe = 1). This is only
		 relevant for languages	that have "unsafe" feature.

	  .version
		 True if the generated	fingerprint  should  contain  re2ocaml
		 version.

HANDLING THE END OF INPUT
       One  of the main	problems for the lexer is to know when to stop.	 There
       are a few terminating conditions:

        the lexer may match some rule (including default rule *) and come  to
	 a final state

        the lexer may fail to match any rule and come to a default state

        the lexer may reach the end of	input

       The  first  two	conditions  terminate the lexer	in a "natural" way: it
       comes to	a state	with no	outgoing transitions, and the  matching	 auto-
       matically  stops.  The  third condition,	end of input, is different: it
       may happen in any state,	and the	lexer should be	 able  to  handle  it.
       Checking	 for the end of	input interrupts the normal lexer workflow and
       adds conditional	branches to the	generated  program,  therefore	it  is
       necessary  to  minimize	the number of such checks. re2ocaml supports a
       few different methods for handling the end of input. Which one  to  use
       depends	on the complexity of regular expressions, the need for buffer-
       ing, performance	considerations and other factors. Here is  a  list  of
       methods:

        Sentinel.   This  method  eliminates  the  need  for the end of input
	 checks	altogether. It is simple and efficient,	 but  limited  to  the
	 case  when there is a natural "sentinel" character that can never oc-
	 cur in	valid input. This character may	still occur in invalid	input,
	 but  it should	not be allowed by the regular expressions, except per-
	 haps as the last character of a rule. The sentinel is appended	at the
	 end of	input and serves as a stop signal: when	the lexer  reads  this
	 character,  it	 is either a syntax error or the end of	input. In both
	 cases the lexer should	stop. This method is used if  YYFILL  is  dis-
	 abled with re2c:yyfill:enable = 0; and	re2c:eof has the default value
	 -1.

        Sentinel  with	 bounds	checks.	 This method is	generic: it allows one
	 to handle any input without restrictions on the regular  expressions.
	 The idea is to	reduce the number of end of input checks by performing
	 them  only  on	 certain characters. Similar to	the "sentinel" method,
	 one of	the characters is chosen as a "sentinel" and appended  at  the
	 end  of input.	However, there is no restriction on where the sentinel
	 may occur (in fact, any character can	be  chosen  for	 a  sentinel).
	 When  the  lexer  reads  this	character,  it additionally performs a
	 bounds	check.	If the current position	is within  bounds,  the	 lexer
	 resumes  matching  and	 handles  the sentinel as a regular character.
	 Otherwise it invokes YYFILL (unless it	is disabled). If more input is
	 supplied, the lexer will rematch the last character and  continue  as
	 if  the  sentinel  wasn't there. Otherwise it must be the real	end of
	 input,	and the	lexer stops. This method is  used  when	 re2c:eof  has
	 non-negative value (it	should be set to the numeric value of the sen-
	 tinel). YYFILL	is optional.

        Bounds	 checks	 with  padding.	 This method is	generic, and it	may be
	 faster	than the "sentinel with	bounds checks" method, but it is  also
	 more  complex.	The idea is to partition DFA states into strongly con-
	 nected	components (SCCs) and generate a  single  check	 per  SCC  for
	 enough	 characters to cover the longest non-looping path in this SCC.
	 This reduces the number of checks, but	there is a problem with	 short
	 lexemes  at the end of	input, as the check requires enough characters
	 to cover the longest lexeme. This can be fixed	by padding  the	 input
	 with a	few fake characters that do not	form a valid lexeme suffix (so
	 that  the  lexer  cannot match	them). The length of padding should be
	 YYMAXFILL, generated with a max block.	If there is not	enough	input,
	 the  lexer  invokes  YYFILL which should supply at least the required
	 number	of characters or not return.  This method is used if YYFILL is
	 enabled and re2c:eof is -1 (this is the default configuration).

        Custom	checks.	 Generic API allows one	to override  basic  operations
	 like  reading	a  character,  which  makes it possible	to include the
	 end-of-input checks as	part of	them.  This  approach  is  error-prone
	 and  should  be  used	with  caution.	To use a custom	method,	enable
	 generic API with --api	custom or re2c:api = custom; and  disable  de-
	 fault bounds checks with re2c:yyfill:enable = 0; or re2c:yyfill:check
	 = 0;.

       The following subsections contain an example of each method.

   Sentinel
       This  example uses a sentinel character to handle the end of input. The
       program counts space-separated words in a null-terminated  string.  The
       sentinel	is null: it is the last	character of each input	string,	and it
       is  not	allowed	in the middle of a lexeme by any of the	rules (in par-
       ticular,	it is not included in character	ranges where  it  is  easy  to
       overlook).  If  a null occurs in	the middle of a	string,	it is a	syntax
       error and the lexer will	match default rule *, but it won't  read  past
       the  end	 of  input  or	crash  (use  -Wsentinel-in-midrule warning and
       re2c:sentinel configuration to  verify  this).  Configuration  re2c:yy-
       fill:enable  = 0; suppresses the	generation of bounds checks and	YYFILL
       invocations.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  open String

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	  }

	  (* expect a null-terminated string *)
	  %{
	      re2c:YYFN	= ["lex;int", "yyrecord;state",	"count;int"];
	      re2c:yyfill:enable = 0;

	      *	     { -1 }
	      [\x00] { count }
	      [a-z]+ { lex yyrecord (count + 1)	}
	      [	]+   { lex yyrecord count }
	  %}

	  let test(yyinput, count) =
	      let st = {yyinput	= yyinput; yycursor = 0}
	      in if not	(lex st	0 = count) then	raise (Failure "error")

	  let main () =
	      test("", 0);
	      test("one	two three", 3);
	      test("f0ur", -1)

	  let _	= main ()

   Sentinel with bounds	checks
       This example uses sentinel with bounds checks to	handle the end of  in-
       put  (this  method  was	added  in  version  1.2).  The	program	counts
       space-separated single-quoted strings. The sentinel character is	 null,
       which is	specified with re2c:eof	= 0; configuration. As in the sentinel
       method,	null is	the last character of each input string, but it	is al-
       lowed in	the middle of a	rule (for example, 'aaa\0aa'\0 is valid	input,
       but 'aaa\0 is a syntax error).  Bounds checks  are  generated  in  each
       state  that  matches  an	 input	character,  but	they are scoped	to the
       branch that handles null. Bounds	checks are of the form YYLIMIT <=  YY-
       CURSOR  or  YYLESSTHAN(1)  with	generic	API. If	the check condition is
       true, lexer has reached the end of input	and  should  stop  (YYFILL  is
       disabled	 with  re2c:yyfill:enable  =  0;  as  the  input fits into one
       buffer, see the YYFILL with sentinel section for	an example  that  uses
       YYFILL).	 Reaching  the	end of input opens three possibilities:	if the
       lexer is	in the initial state it	will match the	end-of-input  rule  $,
       otherwise  it  may fallback to a	previously matched rule	(including de-
       fault   rule   *)   or	 go    to    a	  default    state,    causing
       -Wundefined-control-flow.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  open String

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      yylimit: int;
	  }

	  (* expect a null-terminated string *)
	  %{
	      re2c:YYFN	= ["lex;int", "yyrecord;state",	"count;int"];
	      re2c:yyfill:enable = 0;
	      re2c:eof = 0;

	      str = [']	([^'\\]	| [\\][^])* ['];

	      *	   { -1	}
	      $	   { count }
	      str  { lex yyrecord (count + 1) }
	      [	]+ { lex yyrecord count	}
	  %}

	  let test(str,	count) =
	      let st = {
		  yyinput = str;
		  yycursor = 0;
		  yymarker = 0;
		  yylimit = length str - 1; (* terminating null	not included *)
	      }
	      in if not	(lex st	0 = count) then	raise (Failure "error")

	  let main () =
	      test("", 0);
	      test("'qu\x00tes'	'are' 'fine: \\'' ", 3);
	      test("'unterminated\\'", -1)

	  let _	= main ()

   Bounds checks with padding
       This example uses bounds	checks with padding to handle the end of input
       (this method is enabled by default). The	program	counts space-separated
       single-quoted  strings. There is	a padding of YYMAXFILL null characters
       appended	at the end of input, where YYMAXFILL  value  is	 autogenerated
       with  a	max block. It is not necessary to use null for padding --- any
       characters can be used as long as they do not form a valid lexeme  suf-
       fix  (in	this example padding should not	contain	single quotes, as they
       may be mistaken for a suffix of a single-quoted	string).  There	 is  a
       "stop"  rule that matches the first padding character (null) and	termi-
       nates the lexer (note that it checks if null is	at  the	 beginning  of
       padding,	 otherwise  it is a syntax error). Bounds checks are generated
       only in some states that	are determined by the strongly connected  com-
       ponents	of  the	 underlying automaton. Checks have the form (YYLIMIT -
       YYCURSOR) < n or	YYLESSTHAN(n) with generic API,	where n	is the minimum
       number of characters that are needed for	the lexer to proceed (it  also
       means  that  the	next bounds check will occur in	at most	n characters).
       If the check condition is true, the lexer has reached the end of	 input
       and  will  invoke  YYFILL(n) that should	either supply at least n input
       characters or not return. In this example YYFILL	always fails and  ter-
       minates	the  lexer with	an error (which	is fine	because	the input fits
       into one	buffer). See the YYFILL	with padding section  for  an  example
       that refills the	input buffer with YYFILL.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  open String

	  exception Fill

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      yylimit: int;
	  }

	  %{max	%}
	  %{
	      re2c:YYFN	= ["lex;int", "yyrecord;state",	"count;int"];
	      re2c:YYFILL = "raise Fill;";

	      str = [']	([^'\\]	| [\\][^])* ['];

	      [\x00] {
		  (* check that	it is the sentinel, not	some unexpected	null *)
		  if yyrecord.yycursor = length	yyrecord.yyinput - yymaxfill + 1 then count else -1
	      }
	      str  { lex yyrecord (count + 1) }
	      [	]+ { lex yyrecord count	}
	      *	   { -1	}
	  %}

	  let test(str,	count) =
	      let buf =	cat str	(make yymaxfill	'\x00')	in
	      let st = {yyinput	= buf; yycursor	= 0; yylimit = length buf} in
	      let result = try lex st 0	with Fill -> -1	in
	      if not (result = count) then raise (Failure "error")

	  let main () =
	      test("", 0);
	      test("'unterminated\\'", -1);
	      test("'qu\x00tes'	'are' 'fine: \\'' ", 3);
	      test("'unexpected	\x00 null", -1)

	  let _	= main ()

   Custom checks
       This  example  uses  a  custom  end-of-input  handling  method based on
       generic API.  The program counts	space-separated	single-quoted strings.
       It is the same as the sentinel example, except that the	input  is  not
       null-terminated.	To cover up for	the absence of a sentinel character at
       the  end	of input, YYPEEK is redefined to perform a bounds check	before
       it reads	the next input character.  This	is inefficient because	checks
       are  done  very often. If the check condition fails, YYPEEK returns the
       real character, otherwise it returns a fake sentinel character.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  type state = {
	      str: string;
	      mutable cur: int;
	      lim: int;
	  }

	  (* expect a string without terminating null *)
	  %{
	      re2c:api = generic;
	      re2c:YYFN	= ["lex;int", "st;state", "count;int"];
	      re2c:YYPEEK = "if	st.cur < st.lim	then st.str.[st.cur] else '\\x00'";
	      re2c:YYSKIP = "st.cur <- st.cur +	1;";
	      re2c:yyfill:enable = 0;

	      *	     { -1 }
	      [\x00] { count }
	      [a-z]+ { lex st (count + 1) }
	      [	]+   { lex st count }
	  %}

	  let test(str,	count) =
	      let st = {str = str; cur = 0; lim	= String.length	str}
	      in if not	(lex st	0 = count) then	raise (Failure "error")

	  let main () =
	      test("", 0);
	      test("one	two three", 3);
	      test("f0ur", -1)

	  let _	= main ()

BUFFER REFILLING
       The need	for buffering arises when the input cannot be mapped in	memory
       all at once: either it is too large, or it comes	in a streaming fashion
       (like reading from a socket). The usual technique in such cases	is  to
       allocate	 a  fixed-sized	memory buffer and process input	in chunks that
       fit into	the buffer. When the current chunk is processed, it  is	 moved
       out  and	new data is moved in. In practice it is	somewhat more complex,
       because lexer state consists not	of a single input position, but	a  set
       of interrelated positions:

        cursor:  the  next  input character to	be read	(YYCURSOR in C pointer
	 API or	YYSKIP/YYPEEK in generic API)

        limit:	the position after the last available input character (YYLIMIT
	 in C pointer API, implicitly handled by YYLESSTHAN in generic API)

        marker: the position of the most recent match,	if  any	 (YYMARKER  in
	 default API or	YYBACKUP/YYRESTORE in generic API)

        token:	 the start of the current lexeme (implicit in re2ocaml API, as
	 it is not needed for the normal lexer operation and  can  be  defined
	 and updated by	the user)

        context  marker: the position of the trailing context (YYCTXMARKER in
	 C pointer API or YYBACKUPCTX/YYRESTORECTX in generic API)

        tag variables:	submatch  positions  (defined  with  stags  and	 mtags
	 blocks	and generic API	primitives YYSTAGP/YYSTAGN/YYMTAGP/YYMTAGN)

       Not all these are used in every case, but if used, they must be updated
       by  YYFILL.  All	 active	positions are contained	in the segment between
       token and cursor, therefore everything between buffer start  and	 token
       can  be	discarded,  the	 segment  from token and up to limit should be
       moved to	the beginning of buffer, and the free  space  at  the  end  of
       buffer  should be filled	with new data.	In order to avoid frequent YY-
       FILL calls it is	best to	fill in	as many	input characters  as  possible
       (even  though  fewer characters might suffice to	resume the lexer). The
       details of YYFILL implementation	are slightly  different	 depending  on
       which  EOF  handling  method  is	used: the case of EOF rule is somewhat
       simpler than the	case of	bounds-checking	with padding. Also  note  that
       if  -f  --storable-state	 option	is used, YYFILL	has slightly different
       semantics (described in the section about storable state).

   YYFILL with sentinel
       If EOF rule is used, YYFILL is a	function-like primitive	 that  accepts
       no  arguments and returns a value which is checked against zero.	YYFILL
       invocation is triggered by condition YYLIMIT <= YYCURSOR	in  C  pointer
       API and YYLESSTHAN() in generic API. A non-zero return value means that
       YYFILL  has  failed.  A successful YYFILL call must supply at least one
       character and adjust input positions accordingly. Limit must always  be
       set  to	one after the last input position in buffer, and the character
       at the limit position must be the sentinel symbol specified by re2c:eof
       configuration. The pictures below show the relative locations of	 input
       positions  in  buffer  before and after YYFILL call (sentinel symbol is
       marked with #, and the second picture shows the case when there is  not
       enough input to fill the	whole buffer).

			 <-- shift -->
		       >-A------------B---------C-------------D#-----------E->
		       buffer	    token    marker	    limit,
							    cursor
	  >-A------------B---------C-------------D------------E#->
		       buffer,	marker	      cursor	    limit
		       token

			 <-- shift -->
		       >-A------------B---------C-------------D#--E (EOF)
		       buffer	    token    marker	    limit,
							    cursor
	  >-A------------B---------C-------------D---E#........
		       buffer,	marker	     cursor limit
		       token

       Here  is	 an  example  of  a program that reads input file input.txt in
       chunks of 4096 bytes and	uses EOF rule.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  open Bytes

	  let bufsize =	4096

	  type state = {
	      file: in_channel;
	      yyinput: bytes;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      mutable yylimit: int;
	      mutable token: int;
	      mutable eof: bool;
	  }

	  type status =	Ok | Eof | LongLexeme

	  let fill(st: state) :	status =
	      if st.eof	then Eof else

	      (* Error:	lexeme too long. In real life could reallocate a larger	buffer.	*)
	      if st.token < 1 then LongLexeme else (

	      (* Shift buffer contents (discard	everything up to the current token). *)
	      blit st.yyinput st.token st.yyinput 0 (st.yylimit	- st.token);
	      st.yycursor <- st.yycursor - st.token;
	      st.yymarker <- st.yymarker - st.token;
	      st.yylimit <- st.yylimit - st.token;
	      st.token <- 0;

	      (* Fill free space at the	end of buffer with new data from file. *)
	      let n = input st.file st.yyinput st.yylimit (bufsize - st.yylimit	- 1) in	(* -1 for sentinel *)
	      st.yylimit <- st.yylimit + n;
	      if n = 0 then
		  st.eof <- true; (* end of file *)
		  set st.yyinput st.yylimit '\x00'; (* append sentinel *)

	      Ok)

	  %{
	      re2c:YYFN	= ["lex;int", "yyrecord;state",	"count;int"];
	      re2c:YYFILL = "fill yyrecord = Ok";
	      re2c:eof = 0;

	      str = [']	([^'\\]	| [\\][^])* ['];

	      *	   { -1	}
	      $	   { count }
	      str  { lex_loop yyrecord (count +	1) }
	      [	]+ { lex_loop yyrecord count }
	  %}

	  and lex_loop st count	=
	      st.token <- st.yycursor;
	      lex st count

	  let main () =
	      let fname	= "input" in

	      (* Prepare input file. *)
	      Out_channel.with_open_bin	fname
		  (fun oc -> for i = 1 to bufsize do
		      output_string oc "'qu\x00tes' 'are' 'fine: \\'' "
		  done);

	      (* Run lexer on the prepared file. *)
	      In_channel.with_open_bin fname
		  (fun ic ->
		      let yylimit = bufsize - 1	in
		      let st = {
			  file = ic;
			  yyinput = create bufsize;
			  yycursor = yylimit;
			  yymarker = yylimit;
			  yylimit = yylimit;
			  token	= yylimit;
			  eof =	false;
		      }	in if not (lex_loop st 0 = 3 * bufsize)	then
			  raise	(Failure "error"));

	      (* Cleanup. *)
	      Sys.remove fname

	  let _	= main ()

   YYFILL with padding
       In the default case (when EOF rule is  not  used)  YYFILL  is  a	 func-
       tion-like  primitive that accepts a single argument and does not	return
       any value.  YYFILL invocation is	triggered by condition (YYLIMIT	-  YY-
       CURSOR)	< n in C pointer API and YYLESSTHAN(n) in generic API. The ar-
       gument passed to	YYFILL is the minimal number of	characters  that  must
       be  supplied. If	it fails to do so, YYFILL must not return to the lexer
       (for that reason	it is best implemented as a macro  that	 returns  from
       the calling function on failure).  In case of a successful YYFILL invo-
       cation  the limit position must be set either to	one after the last in-
       put position in buffer, or to the end of	YYMAXFILL padding (in case YY-
       FILL has	successfully read at least n characters,  but  not  enough  to
       fill the	entire buffer).	The pictures below show	the relative locations
       of input	positions in buffer before and after YYFILL invocation (YYMAX-
       FILL padding on the second picture is marked with # symbols).

			 <-- shift -->		       <-- need	-->
		       >-A------------B---------C-----D-------E---F--------G->
		       buffer	    token    marker cursor  limit

	  >-A------------B---------C-----D-------E---F--------G->
		       buffer,	marker cursor		    limit
		       token

			 <-- shift -->		       <-- need	-->
		       >-A------------B---------C-----D-------E-F	 (EOF)
		       buffer	    token    marker cursor  limit

	  >-A------------B---------C-----D-------E-F###############
		       buffer,	marker cursor			limit
		       token			    <- YYMAXFILL ->

       Here  is	 an  example  of  a program that reads input file input.txt in
       chunks of 4096 bytes and	uses bounds-checking with padding.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  open Bytes

	  %{max	%}
	  let bufsize =	4096

	  exception Fill

	  type state = {
	      file: in_channel;
	      yyinput: bytes;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      mutable yylimit: int;
	      mutable token: int;
	      mutable eof: bool;
	  }

	  type status =	Ok | Eof | LongLexeme

	  let fill (st:	state) (need: int) : status =
	      if st.eof	then Eof else

	      (* Error:	lexeme too long. In real life could reallocate a larger	buffer.	*)
	      if st.token < need then LongLexeme else (

	      (* Shift buffer contents (discard	everything up to the current token). *)
	      blit st.yyinput st.token st.yyinput 0 (st.yylimit	- st.token);
	      st.yycursor <- st.yycursor - st.token;
	      st.yymarker <- st.yymarker - st.token;
	      st.yylimit <- st.yylimit - st.token;
	      st.token <- 0;

	      (* Fill free space at the	end of buffer with new data from file. *)
	      let n = input st.file st.yyinput st.yylimit (bufsize - st.yylimit	- 1) in	(* -1 for sentinel *)
	      st.yylimit <- st.yylimit + n;

	      (* If read zero characters, this is end of input => add zero padding
		 so that the lexer can access characters at the	end of buffer. *)
	      if n = 0 then
		  st.eof <- true; (* end of file *)
		  for i	= 0 to (yymaxfill - 1) do
		      set st.yyinput (st.yylimit + i) '\x00';
		      st.yylimit <- st.yylimit + yymaxfill
		  done;

	      Ok)

	  %{
	      re2c:YYFN	= ["lex;int", "yyrecord;state",	"count;int"];
	      re2c:YYFILL = "if	not (fill yyrecord @@ =	Ok) then raise Fill;";

	      str = [']	([^'\\]	| [\\][^])* ['];

	      [\x00] {
		  (* check that	it is the sentinel, not	some unexpected	null *)
		  if yyrecord.token = yyrecord.yylimit - yymaxfill then	count else -1
	      }
	      str  { lex_loop yyrecord (count +	1) }
	      [	]+ { lex_loop yyrecord count }
	      *	   { -1	}
	  %}

	  and lex_loop st count	=
	      st.token <- st.yycursor;
	      try lex st count with Fill -> -1

	  let main () =
	      let fname	= "input" in

	      (* Prepare input file. *)
	      Out_channel.with_open_bin	fname
		  (fun oc -> for i = 1 to bufsize do
		      output_string oc "'qu\x00tes' 'are' 'fine: \\'' "
		  done);

	      (* Run lexer on the prepared file. *)
	      In_channel.with_open_bin fname
		  (fun ic ->
		      let yylimit = bufsize - yymaxfill	in
		      let st = {
			  file = ic;
			  yyinput = create bufsize;
			  yycursor = yylimit;
			  yymarker = yylimit;
			  yylimit = yylimit;
			  token	= yylimit;
			  eof =	false;
		      }	in if not (lex_loop st 0 = 3 * bufsize)	then
			  raise	(Failure "error"));

	      (* Cleanup. *)
	      Sys.remove fname

	  let _	= main ()

FEATURES
   Multiple blocks
       Sometimes it is necessary to have multiple interrelated lexers (for ex-
       ample, if there is a high-level state machine that transitions  between
       lexer modes). This can be implemented using multiple connected re2ocaml
       blocks. Another option is to use	start conditions.

       The  implementation of connections between blocks depends on the	target
       language.  In languages that have goto statement	(such as C/C++ and Go)
       one can have all	blocks in one function,	each of	them prefixed  with  a
       label.  Transition from one block to another is a simple	goto.  In lan-
       guages that do not have goto (such as Rust) it is necessary  to	use  a
       loop  with  a  switch  on  a  state  variable,  similar	to the yystate
       loop/switch generated by	re2ocaml, or else wrap each block in  a	 func-
       tion and	use function calls.

       The  example below uses multiple	blocks to parse	binary,	octal, decimal
       and hexadecimal numbers.	Each base has its own block. The initial block
       determines base and dispatches to other blocks.	Common	configurations
       are  defined  in	a separate block at the	beginning of the program; they
       are inherited by	the other blocks.

	  (* re2ocaml $INPUT -o	$OUTPUT	-i *)

	  open Int64
	  open Option
	  open String

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	  }

	  let add (num:	int option) (dgt: int) (base: int) : int option	=
	      match num	with
		  | None -> None
		  | Some n ->
		      let n' = add (mul	(of_int	n) (of_int base)) (of_int dgt)
		      in if n' > (of_int32 Int32.max_int) then None else Some (to_int n')

	  %{
	      re2c:yyrecord = "st";
	      re2c:yyfill:enable = 0;
	  %}

	  %{local
	      re2c:YYFN	= ["parse_bin;int option", "st;state", "num;int	option"];
	      [01] { parse_bin st (add num (Char.code st.yyinput.[st.yycursor -	1] - 48) 2) }
	      *	   { num }
	  %}

	  %{local
	      re2c:YYFN	= ["parse_oct;int option", "st;state", "num;int	option"];
	      [0-7] { parse_oct	st (add	num (Char.code st.yyinput.[st.yycursor - 1] - 48) 8) }
	      *	    { num }
	  %}

	  %{local
	      re2c:YYFN	= ["parse_dec;int option", "st;state", "num;int	option"];
	      [0-9] { parse_dec	st (add	num (Char.code st.yyinput.[st.yycursor - 1] - 48) 10) }
	      *	    { num }
	  %}

	  %{local
	      re2c:YYFN	= ["parse_hex;int option", "st;state", "num;int	option"];
	      [0-9] { parse_hex	st (add	num (Char.code st.yyinput.[st.yycursor - 1] - 48) 16) }
	      [a-f] { parse_hex	st (add	num (Char.code st.yyinput.[st.yycursor - 1] - 87) 16) }
	      [A-F] { parse_hex	st (add	num (Char.code st.yyinput.[st.yycursor - 1] - 55) 16) }
	      *	    { num }
	  %}

	  %{local
	      re2c:YYFN	= ["parse;int option", "st;state"];
	      '0b' / [01]	 { parse_bin st	(Some 0) }
	      "0"		 { parse_oct st	(Some 0) }
	      "" / [1-9]	 { parse_dec st	(Some 0) }
	      '0x' / [0-9a-fA-F] { parse_hex st	(Some 0) }
	      *			 { None	}
	  %}

	  let test (yyinput: string) (result: int option) =
	      let st = {yyinput	= yyinput; yycursor = 0; yymarker = 0} in
	      if not (parse st = result) then raise (Failure "error")

	  let main () =
	      test "\x00" None;
	      test "1234567890\x00" (Some 1234567890);
	      test "0b1101\x00"	(Some 13);
	      test "0x7Fe\x00" (Some 2046);
	      test "0644\x00" (Some 420);
	      test "9999999999\x00" None

	  let _	= main ()

   Start conditions
       Start conditions	are enabled with --start-conditions option. They  pro-
       vide  a	way  to	 encode	multiple interrelated automata within the same
       re2ocaml	block.

       Each condition corresponds to a single automaton	and has	a unique  name
       specified by the	user and a unique internal number defined by re2ocaml.
       The  numbers  are used to switch	between	conditions: the	generated code
       uses YYGETCOND and YYSETCOND primitives to get the current condition or
       set it to the given number. Use conditions block,  --header  option  or
       re2c:header  configuration  to  generate	numeric	condition identifiers.
       Configuration re2c:cond:enumprefix specifies the	 generated  identifier
       prefix.

       In condition mode every rule must be prefixed with a list of comma-sep-
       arated  condition  names	in angle brackets, or a	wildcard <*> to	denote
       all conditions. The rule	syntax is extended as follows:

	  < condition-list > regular-expression	code
		 A rule	that is	 merged	 to  every  condition  on  the	condi-
		 tion-list.   It  matches  regular-expression and executes the
		 associated code.

	  < condition-list > regular-expression	=> condition code
		 A rule	that is	 merged	 to  every  condition  on  the	condi-
		 tion-list.   It  matches regular-expression, sets the current
		 condition to condition	and executes the associated code.

	  < condition-list > regular-expression	:=> condition
		 A rule	that is	 merged	 to  every  condition  on  the	condi-
		 tion-list.   It  matches  regular-expression  and immediately
		 transitions to	condition (there is no semantic	action).

	  < condition-list > !action code
		 A rule	that binds code	to the	place  defined	by  action  in
		 every	condition  on the condition-list (see the actions sec-
		 tion for various types	of actions).

	  <! condition-list > code
		 A rule	that prepends code to semantic actions	of  all	 rules
		 for  every  condition	on  the	condition-list.	This syntax is
		 deprecated and	the !pre_rule action should  be	 used  instead
		 (it does exactly the same).

	  < > code
		 A  rule  that	creates	 a special entry condition with	number
		 zero and name "0" that	executes code before jumping to	 other
		 conditions.  This syntax is deprecated, and the !entry	action
		 should	 be used instead (it provides a	more fine-grained con-
		 trol, as the code can be specified on a per-condition	basis,
		 and  one  can	jump directly to condition start without going
		 through condition dispatch).

	  < > => condition code
		 Same as the previous rule, except that	it sets	the next  con-
		 dition.

	  < > :=> condition
		 Same  as  the previous	rule, except that it has no associated
		 code and immediately jumps to condition.

       The code	re2ocaml generates for conditions depends on whether  re2ocaml
       uses  goto/label	 approach  or  loop/switch  approach to	encode the au-
       tomata.

       In languages that have goto statement (such as C/C++ and	Go) conditions
       are naturally implemented as blocks of code prefixed with labels	of the
       form yyc_<cond>,	where cond is a	condition name (label  prefix  can  be
       changed	with re2c:cond:prefix).	Transitions between conditions are im-
       plemented using	goto  and  condition  labels.  Before  all  conditions
       re2ocaml	 generates  an	initial	switch on YYGETSTATE that jumps	to the
       start state of the current condition.  The shortcut  rules  :=>	bypass
       the  initial  switch  and  jump	directly  to  the  specified condition
       (re2c:cond:goto can be used to change the default behavior). The	 rules
       with  semantic actions do not automatically jump	to the next condition;
       this should be done by the user-defined action code.

       In languages that do not	have goto (such	as Rust) re2ocaml  reuses  the
       yystate	variable to store condition numbers. Each condition gets a nu-
       meric identifier	equal to the number of its start state,	and  a	switch
       between	conditions is no different than	a switch between DFA states of
       a single	condition. There is no need for	a separate  initial  condition
       switch.	(Since the same	approach is used to implement storable states,
       YYGETCOND/YYSETCOND  are	 redundant  if both storable states and	condi-
       tions are used).

       The program below uses start conditions to parse	binary,	octal, decimal
       and hexadecimal numbers.	There is a single block	where  each  base  has
       its  own	 condition,  and  the initial condition	is connected to	all of
       them. User-defined variable cond	stores the current  condition  number;
       it is initialized to the	number of the initial condition	generated with
       conditions block.

	  (* re2ocaml $INPUT -o	$OUTPUT	-ci *)

	  open Int64
	  open Option
	  open String

	  %{conditions %}

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      mutable yycond: yycondtype;
	  }

	  let add (num:	int option) (dgt: int) (base: int) : int option	=
	      match num	with
		  | None -> None
		  | Some n ->
		      let n' = add (mul	(of_int	n) (of_int base)) (of_int dgt)
		      in if n' > (of_int32 Int32.max_int) then None else Some (to_int n')

	  %{
	      re2c:YYFN	= ["parse;int option", "st;state", "num;int option"];
	      re2c:yyrecord = "st";
	      re2c:yyfill:enable = 0;

	      <init> '0b' / [01]	:=> bin
	      <init> "0"		:=> oct
	      <init> ""	/ [1-9]		:=> dec
	      <init> '0x' / [0-9a-fA-F]	:=> hex
	      <init> * { None }

	      <bin> [01]  { yyfnbin st (add num	(Char.code st.yyinput.[st.yycursor - 1]	- 48) 2) }
	      <oct> [0-7] { yyfnoct st (add num	(Char.code st.yyinput.[st.yycursor - 1]	- 48) 8) }
	      <dec> [0-9] { yyfndec st (add num	(Char.code st.yyinput.[st.yycursor - 1]	- 48) 10) }
	      <hex> [0-9] { yyfnhex st (add num	(Char.code st.yyinput.[st.yycursor - 1]	- 48) 16) }
	      <hex> [a-f] { yyfnhex st (add num	(Char.code st.yyinput.[st.yycursor - 1]	- 87) 16) }
	      <hex> [A-F] { yyfnhex st (add num	(Char.code st.yyinput.[st.yycursor - 1]	- 55) 16) }

	      <bin, oct, dec, hex> * { num }
	  %}

	  let test (yyinput: string) (result: int option) =
	      let st = {yyinput	= yyinput; yycursor = 0; yymarker = 0; yycond =	YYC_init} in
	      if not (parse st (Some 0)	= result) then raise (Failure "error")

	  let main () =
	      test "\x00" None;
	      test "1234567890\x00" (Some 1234567890);
	      test "0b1101\x00"	(Some 13);
	      test "0x7Fe\x00" (Some 2046);
	      test "0644\x00" (Some 420);
	      test "9999999999\x00" None

	  let _	= main ()

   Storable state
       With  --storable-state option re2ocaml generates	a lexer	that can store
       its current state, return to the	caller,	and  later  resume  operations
       exactly where it	left off. The default mode of operation	in re2ocaml is
       a "pull"	model, in which	the lexer "pulls" more input whenever it needs
       it.  This may be	unacceptable in	cases when the input becomes available
       piece by	piece (for example, if the lexer is invoked by the parser,  or
       if the lexer program communicates via a socket protocol with some other
       program	that  must wait	for a reply from the lexer before it transmits
       the next	message). Storable state feature is intended exactly for  such
       cases:  it  allows  one to generate lexers that work in a "push"	model.
       When the	lexer needs more input,	it stores its state and	returns	to the
       caller. Later, when more	input becomes available,  the  caller  resumes
       the  lexer  exactly where it stopped. There are a few changes necessary
       compared	to the "pull" model:

        Define	YYSETSTATE() and YYGETSTATE(state) primitives.

        Define	yych, yyaccept (if used) and state variables as	a part of per-
	 sistent lexer state. The state	variable should	be initialized to -1.

        YYFILL	should return to the outer program instead of trying to	supply
	 more input. Return code should	indicate that lexer needs more input.

        The outer program should recognize situations when lexer  needs  more
	 input and respond appropriately.

        Optionally  use getstate block	to generate YYGETSTATE switch detached
	 from the main lexer. This only	works for  languages  that  have  goto
	 (not in --loop-switch mode).

        Use re2c:eof and the sentinel with bounds checks method to handle the
	 end of	input. Padding-based method may	not work because it is unclear
	 when to append	padding: the current end of input may not be the ulti-
	 mate end of input, and	appending padding too early may	cut off	a par-
	 tially	 read  greedy  lexeme.	Furthermore, due to high-level program
	 logic getting more input may depend on	processing the lexeme  at  the
	 end  of buffer	(which already is blocked due to the end-of-input con-
	 dition).

       Here is an example of a "push" model lexer that simulates reading pack-
       ets from	a socket. The lexer loops until	it encounters the end of input
       and returns to the calling function. The	calling	function provides more
       input by	"sending" the next packet and  resumes	lexing.	 This  process
       stops when all the packets have been sent, or when there	is an error.

	  (* re2ocaml $INPUT -o	$OUTPUT	-fi *)

	  open Bytes

	  (* Use a small buffer	to cover the case when a lexeme	doesn't	fit.
	     In	real world use a larger	buffer.	*)
	  let bufsize =	10

	  let debug = false
	  let log format = (if debug then Printf.eprintf else Printf.ifprintf stderr) format

	  type state = {
	      file: in_channel;
	      yyinput: bytes;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      mutable yylimit: int;
	      mutable token: int;
	      mutable yystate: int;
	      mutable recv: int;
	  }

	  type status =	End | Ready | Waiting |	BadPacket | BigPacket

	  let fill(st: state) :	status =
	      (* Error:	lexeme too long. In real life could reallocate a larger	buffer.	*)
	      if st.token < 1 then BigPacket else (

	      (* Shift buffer contents (discard	everything up to the current token). *)
	      blit st.yyinput st.token st.yyinput 0 (st.yylimit	- st.token);
	      st.yycursor <- st.yycursor - st.token;
	      st.yymarker <- st.yymarker - st.token;
	      st.yylimit <- st.yylimit - st.token;
	      st.token <- 0;

	      (* Fill free space at the	end of buffer with new data from file. *)
	      let n = In_channel.input st.file st.yyinput st.yylimit (bufsize -	st.yylimit - 1)	in
	      st.yylimit <- st.yylimit + n;
	      set st.yyinput st.yylimit	'\x00';	(* append sentinel *)

	      Ready)

	  %{
	      re2c:YYFN	= ["lex;status", "yyrecord;state"];
	      re2c:YYFILL = "Waiting";
	      re2c:eof = 0;

	      packet = [a-z]+[;];

	      *	     { BadPacket }
	      $	     { End }
	      packet { yyrecord.recv <-	yyrecord.recv +	1; lex_loop yyrecord }
	  %}

	  and lex_loop st =
	      st.token <- st.yycursor;
	      lex st

	  let test (packets: string list) (sts:	status)	=
	      let fname	= "pipe" in

	      let oc = Out_channel.open_bin fname in
	      let ic = In_channel.open_bin fname in

	      let yylimit = bufsize - 1	in
	      let st = {
		  file = ic;
		  (* Sentinel (at `yylimit` offset) is set to null, which triggers YYFILL. *)
		  yyinput = create bufsize;
		  yycursor = yylimit;
		  yymarker = yylimit;
		  yylimit = yylimit;
		  token	= yylimit;
		  yystate = -1;
		  recv = 0;
	      }	in

	      let rec loop packets = match lex_loop st with
		  | End	->
		      log "done: got %d	packets\n" st.recv;
		      End
		  | Waiting ->
		      log "waiting...\n";
		      let packets' = match packets with
			  | [] -> []
			  | p :: ps ->
			      log "sent	packet '%s'\n" p;
			      Out_channel.output_string	oc p;
			      Out_channel.flush	oc; (* without `flush` write happens too late *)
			      ps
		      in (match	fill st	with
			  | BigPacket ->
			      log "error: packet too big\n";
			      BigPacket
			  | Ready -> loop packets'
			  | _ -> raise (Failure	"unexpected status after fill"))
		  | BadPacket ->
		      log "error: ill-formed packet\n";
		      BadPacket
		  | _ -> raise (Failure	"unexpected status")

	      in if not	(loop packets =	sts) then
		  raise	(Failure "error");

	      In_channel.close ic;
	      Out_channel.close	oc;
	      Sys.remove fname

	  let main () =
	      test [] End;
	      test ["zero;"; "one;"; "two;"; "three;"; "four;"]	End;
	      test ["zer0;"] BadPacket;
	      test ["goooooooooogle;"] BigPacket

	  let _	= main ()

   Reusable blocks
       Reusable	  blocks   of	the  form  /*!rules:re2c[:<name>]  ...	*/  or
       %{rules[:<name>]	... %} can be reused any number	of times and  combined
       with  other  re2ocaml blocks. The <name>	is optional. A rules block can
       be used in a use	block or directive. The	code for a rules block is gen-
       erated at every point of	use.

       Use  blocks  are	 defined   with	  /*!use:re2c[:<name>]	 ...   */   or
       %{use[:<name>]  ...  %}.	The <name> is optional:	if it's	not specified,
       the associated rules block is the most recent one (whether named	or un-
       named).	A use block can	 add  named  definitions,  configurations  and
       rules of	its own.  An important use case	for use	blocks is a lexer that
       supports	 multiple input	encodings: the same rules block	is reused mul-
       tiple times with	encoding-specific configurations (see the example  be-
       low).

       In-block	 use  directive	 !use:<name>;  can  be	used  from inside of a
       re2ocaml	block. It merges the referenced	block <name> into the  current
       one.  If	 some  of the merged rules and configurations overlap with the
       previously defined ones,	conflicts are resolved in the usual  way:  the
       earliest	 rule  takes priority, and latest configuration	overrides pre-
       ceding ones. One	exception are the special rules	*, $ and (in condition
       mode) <!>, for which a block-local definition overrides	any  inherited
       ones. Use directive allows one to combine different re2ocaml blocks to-
       gether in one block (see	the example below).

       Named  blocks and in-block use directive	were added in re2ocaml version
       2.2.  Since that	version	reusable blocks	are  allowed  by  default  (no
       special	option	is  needed). Before version 2.2	reuse mode was enabled
       with -r --reusable option. Before version 1.2 reusable blocks could not
       be mixed	with normal blocks.

   Example of a	!use directive
	  (* re2ocaml $INPUT -o	$OUTPUT	*)
	  (* This example shows	how to combine reusable	re2c blocks: two blocks
	     ('colors' and 'fish') are merged into one.	The 'salmon' rule occurs
	     in	both blocks; the 'fish'	block takes priority because it	is used
	     earlier. Default rule * occurs in all three blocks; the local (not
	     inherited)	definition takes priority. *)

	  open String

	  type answer =	Color |	Fish | Dunno

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	  }

	  %{rules:colors
	      *				   { raise (Failure "ah"); }
	      "red" | "salmon" | "magenta" { Color }
	  %}

	  %{rules:fish
	      *				   { raise (Failure "oh"); }
	      "haddock"	| "salmon" | "eel" { Fish }
	  %}

	  %{
	      re2c:YYFN	= ["lex;answer", "yyrecord;state"];
	      re2c:yyfill:enable = 0;

	      !use:fish;
	      !use:colors;
	      *	{ Dunno	} // overrides inherited '*' rules
	  %}

	  let test(str,	ans) =
	      let st = {yyinput	= str; yycursor	= 0; yymarker =	0}
	      in if not	(lex st	= ans) then raise (Failure "error")

	  let main () =
	      test("salmon", Fish);
	      test("what?", Dunno)

	  let _	= main ()

   Example of a	/*!use:re2c ...	*/ block
	  (* re2ocaml $INPUT -o	$OUTPUT	--input-encoding utf8 *)
	  (* This example supports multiple input encodings: UTF-8 and UTF-32.
	     Both lexers are generated from the	same rules block, and the use
	     blocks add	only encoding-specific configurations. *)

	  open Array

	  type 'a state	= {
	      yyinput: 'a array;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	  }

	  %{rules
	      re2c:yyfill:enable = 0;

	      "x y" { Some yyrecord.yycursor }
	      *	      {	None }
	  %}

	  %{use
	      re2c:YYFN	= ["lex8;int option", "yyrecord;char state"];
	      re2c:encoding:utf8 = 1;
	  %}

	  %{use
	      re2c:YYFN	= ["lex32;int option", "yyrecord;int state"];
	      re2c:encoding:utf32 = 1;
	  %}

	  let main() =
	      let st8 =	{
		  yyinput = [|'\xe2'; '\x08'; '\x80'; '\x78'; '\x20'; '\xe2'; '\x88'; '\x83'; '\x79'|];
		  yycursor = 0;
		  yymarker = 0;
	      }	in if not (lex8	st8 = Some (Array.length st8.yyinput)) then raise (Failure "error");

	      let st32 = {
		  yycursor = 0;
		  yymarker = 0;
		  yyinput = [|0x2200; 0x78; 0x20; 0x2203; 0x79|];
	      }	in if not (lex32 st32 =	Some (Array.length st32.yyinput)) then raise (Failure "error");

   Submatch extraction
       re2ocaml	has two	options	for submatch extraction.

       Tags   The first	option is to use standalone tags of the	form @stag  or
	      #mtag,  where  stag  and	mtag are arbitrary used-defined	names.
	      Tags are enabled with -T --tags option or	re2c:tags = 1 configu-
	      ration. Semantically tags	are position markers: they can be  in-
	      serted  anywhere	in  a regular expression, and they bind	to the
	      corresponding position (or  multiple  positions)	in  the	 input
	      string.	S-tags	bind to	the last matching position, and	m-tags
	      bind to a	list of	positions (they	 may  be  used	in  repetition
	      subexpressions,  where a single position in a regular expression
	      corresponds to multiple positions	in the input string). All tags
	      should be	defined	by the user, either manually or	with the  help
	      of  svars	 and  mvars blocks. If there is	more than one way tags
	      can be matched against the input,	ambiguity  is  resolved	 using
	      leftmost greedy disambiguation strategy.

       Captures
	      The  second  option is to	use capturing groups. They are enabled
	      with --captures option or	re2c:captures =	1 configuration. There
	      are two flavours for different disambiguation policies,  --left-
	      most-captures  (the default) is for leftmost greedy policy, and,
	      --posix-captures is for POSIX longest-match policy. In this mode
	      all  parenthesized  subexpressions  are	considered   capturing
	      groups,  and a bang can be used to mark non-capturing groups: (!
	      ... ). With --invert-captures option or re2c:invert-captures = 1
	      configuration the	meaning	of bang	is inverted.   The  number  of
	      groups  for  the	matching rule is stored	in a variable yynmatch
	      (the whole regular expression is group number  zero),  and  sub-
	      match  results  are  stored in yypmatch array. Both yynmatch and
	      yypmatch should be defined by the	user, and yypmatch  size  must
	      be  at  least [yynmatch *	2]. Use	maxnmatch block	to  define YY-
	      MAXNMATCH, a constant that equals	to the maximum value  of  yyn-
	      match among all rules.

       Captvars
	      Another  way to use capturing groups is the --captvars option or
	      re2c:captvars = 1	configuration. The only	difference with	--cap-
	      tures is in the way the generated	code stores submatch  results:
	      instead  of  yynmatch  and yypmatch re2ocaml generates variables
	      yytl<k> and yytr<k> for k-th capturing group  (the  user	should
	      declare  these  using  an	 svars block). Captures	with variables
	      support  two  disambiguation  policies:  --leftmost-captvars  or
	      re2c:leftmost-captvars  =	 1 for leftmost	greedy policy (the de-
	      fault one) and --posix-captvars or re2c:posix-captvars for POSIX
	      longest-match policy.

       Under the hood all these	options	translate into tags and	Tagged	Deter-
       ministic	 Finite	 Automata with Lookahead.  The core idea of TDFA is to
       minimize	the overhead on	 submatch  extraction.	 In  the  extreme,  if
       there're	 no  tags or captures in a regular expression, TDFA is just an
       ordinary	DFA. If	the number of tags is moderate,	the overhead is	barely
       noticeable. The generated TDFA uses a number of tag variables which  do
       not  map	 directly to tags: a single variable may be used for different
       tags, and a tag may require multiple variables to hold all its possible
       values. Eventually ambiguity is resolved, and only one  final  variable
       per  tag	survives. Tag variables	should be defined using	stags or mtags
       blocks. If lexer	state is stored, tag variables should be part  of  it.
       They also need to be updated  by	YYFILL.

       S-tags support the following operations:

        save input position to	an s-tag: t = YYCURSOR with C pointer API or a
	 user-defined operation	YYSTAGP(t) with	generic	API

        save  default	value  to  an  s-tag: t	= NULL with C pointer API or a
	 user-defined operation	YYSTAGN(t) with	generic	API

        copy one s-tag	to another: t1 = t2

       M-tags support the following operations:

        append	input position to an  m-tag:  a	 user-defined  operation  YYM-
	 TAGP(t) with both default and generic API

        append	default	value to an m-tag: a user-defined operation YYMTAGN(t)
	 with both default and generic API

        copy one m-tag	to another: t1 = t2

       S-tags  can  be	implemented  as	 scalar	 values	(pointers or offsets).
       M-tags need a more complex representation, as they need to store	a  se-
       quence  of tag values. The most naive and inefficient representation of
       an m-tag	is a list (array, vector) of tag values; a more	efficient rep-
       resentation is to store all m-tags in a prefix-tree represented as  ar-
       ray  of nodes (v, p), where v is	tag value and p	is a pointer to	parent
       node.

       Here is a simple	example	of using s-tags	 to  parse  semantic  versions
       consisting of three numeric components: major, minor, patch (the	latter
       is optional).  See below	for a more complex example that	uses YYFILL.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  open String

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      (* Final tag variables available in semantic action. *)
	      %{svars format = "\n\tmutable @@{tag}: int;"; %}
	      (* Intermediate tag variables used by the	lexer (must be autogenerated). *)
	      %{stags format = "\n\tmutable @@{tag}: int;"; %}
	  }

	  type semver =	{
	      major: int;
	      minor: int;
	      patch: int;
	  }

	  let s2n (str:	string)	(i1: int) (i2: int) : int =
	      let rec f	s i j n	=
		  if i >= j then n else	f s (i + 1) j (n * 10 +	Char.code s.[i]	- 48)
	      in f str i1 i2 0

	  %{local
	      re2c:YYFN	= ["parse;semver option", "st;state"];
	      re2c:yyrecord = "st";
	      re2c:tags	= 1;
	      re2c:yyfill:enable = 0;

	      num = [0-9]+;

	      @t1 num @t2 "." @t3 num @t4 ("." @t5 num)? [\x00]	{
		  Some {
		      major = s2n st.yyinput st.t1 st.t2;
		      minor = s2n st.yyinput st.t3 st.t4;
		      patch = if st.t5 = -1 then 0 else	s2n st.yyinput st.t5 (st.yycursor - 1)
		  }
	      }
	      *	{ None }
	  %}

	  let test (str: string) (result: semver option) =
	      let st = {
		  yyinput = str;
		  yycursor = 0;
		  yymarker = 0;
		  %{svars format = "\n\t\t@@{tag} = -1;"; %}
		  %{stags format = "\n\t\t@@{tag} = -1;"; %}
	      }
	      in if not	(parse st = result) then raise (Failure	"error")

	  let main () =
	      test "23.34" (Some {major	= 23; minor = 34; patch	= 0});
	      test "1.2.99999" (Some {major = 1; minor = 2; patch = 99999});
	      test "1.a" None

	  let _	= main ()

       Here  is	 a more	complex	example	of using s-tags	with YYFILL to parse a
       file with newline-separated semantic versions. Tag variables  are  part
       of  the	lexer  state, and they are adjusted in YYFILL like other input
       positions.  Note	that it	is necessary for s-tags	because	 their	values
       are invalidated after shifting buffer contents. It may not be necessary
       in  a  custom implementation where tag variables	store offsets relative
       to the start of the input string	rather than the	buffer,	which  may  be
       the case	with m-tags.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  open Bytes

	  let bufsize =	4096

	  type state = {
	      file: in_channel;
	      yyinput: bytes;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      mutable yylimit: int;
	      mutable token: int;
	      mutable eof: bool;
	      (* Final tag variables available in semantic action. *)
	      %{svars format = "\n\tmutable @@{tag}: int;"; %}
	      (* Intermediate tag variables used by the	lexer (must be autogenerated). *)
	      %{stags format = "\n\tmutable @@{tag}: int;"; %}
	  }

	  type status =	Ok | Eof | LongLexeme

	  type semver =	{
	      major: int;
	      minor: int;
	      patch: int;
	  }

	  let s2n (str:	bytes) (i1: int) (i2: int) : int =
	      let rec f	s i j n	=
		  if i >= j then n else	f s (i + 1) j (n * 10 +	Char.code (get s i) - 48)
	      in f str i1 i2 0

	  let fill(st: state) :	status =
	      if st.eof	then Eof else

	      (* Error:	lexeme too long. In real life could reallocate a larger	buffer.	*)
	      if st.token < 1 then LongLexeme else (

	      (* Shift buffer contents (discard	everything up to the current token). *)
	      blit st.yyinput st.token st.yyinput 0 (st.yylimit	- st.token);
	      st.yycursor <- st.yycursor - st.token;
	      st.yymarker <- st.yymarker - st.token;
	      st.yylimit <- st.yylimit - st.token;
	      %{stags format = "\n\tst.@@ <- if	st.@@ =	-1 then	-1 else	st.@@ -	st.token;"; %}
	      st.token <- 0;

	      (* Fill free space at the	end of buffer with new data from file. *)
	      let n = input st.file st.yyinput st.yylimit (bufsize - st.yylimit	- 1) in	(* -1 for sentinel *)
	      st.yylimit <- st.yylimit + n;
	      if n = 0 then
		  st.eof <- true; (* end of file *)
		  set st.yyinput st.yylimit '\x00'; (* append sentinel *)

	      Ok)

	  %{
	      re2c:YYFN	= ["lex;(semver	list) option", "st;state", "vers;semver	list"];
	      re2c:YYFILL = "fill st = Ok";
	      re2c:yyrecord = "st";
	      re2c:tags	= 1;
	      re2c:eof = 0;

	      num = [0-9]+;

	      @t1 num @t2 "." @t3 num @t4 ("." @t5 num)? [\n] {
		  let ver = {
		      major = s2n st.yyinput st.t1 st.t2;
		      minor = s2n st.yyinput st.t3 st.t4;
		      patch = if st.t5 = -1 then 0 else	s2n st.yyinput st.t5 (st.yycursor - 1)
		  } in lex_loop	st (ver	:: vers)
	      }
	      $	{ Some (List.rev vers) }
	      *	{ None }
	  %}

	  and lex_loop st vers =
	      st.token <- st.yycursor;
	      lex st vers

	  let main () =
	      let fname	= "input" in

	      (* Prepare input file. *)
	      Out_channel.with_open_bin	fname
		  (fun oc -> for i = 1 to bufsize do
		      output_string oc "1.22.333\n"
		  done);

	      (* Construct the expected	result to compare against. *)
	      let expect = Some	(List.init bufsize
		      (fun _ ->	{major = 1; minor = 22;	patch =	333;}))	in

	      (* Run lexer on the prepared file. *)
	      In_channel.with_open_bin fname
		  (fun ic ->
		      let yylimit = bufsize - 1	in
		      let st = {
			  file = ic;
			  yyinput = create bufsize;
			  yycursor = yylimit;
			  yymarker = yylimit;
			  yylimit = yylimit;
			  token	= yylimit;
			  eof =	false;
			  %{svars format = "\n\t\t@@{tag} = -1;"; %}
			  %{stags format = "\n\t\t@@{tag} = -1;"; %}
		      }	in if (lex_loop	st [] <> expect) then
			  raise	(Failure "error"));

	      (* Cleanup. *)
	      Sys.remove fname

	  let _	= main ()

       Here  is	 an  example  of using capturing groups	to parse semantic ver-
       sions.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  open String

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      (* Final tag variables available in semantic action. *)
	      %{svars format = "\n\tmutable @@{tag}: int;"; %}
	      (* Intermediate tag variables used by the	lexer (must be autogenerated). *)
	      %{stags format = "\n\tmutable @@{tag}: int;"; %}
	  }

	  type semver =	{
	      major: int;
	      minor: int;
	      patch: int;
	  }

	  let s2n (str:	string)	(i1: int) (i2: int) : int =
	      let rec f	s i j n	=
		  if i >= j then n else	f s (i + 1) j (n * 10 +	Char.code s.[i]	- 48)
	      in f str i1 i2 0

	  %{local
	      re2c:YYFN	= ["parse;semver option", "st;state"];
	      re2c:yyrecord = "st";
	      re2c:captvars = 1;
	      re2c:yyfill:enable = 0;

	      num = [0-9]+;

	      (num) "."	(num) ("." num)? [\x00]	{
		  Some {
		      major = s2n st.yyinput st.yytl1 st.yytr1;
		      minor = s2n st.yyinput st.yytl2 st.yytr2;
		      patch = if st.yytl3 = -1 then 0 else s2n st.yyinput (st.yytl3 + 1) st.yytr3
		  }
	      }
	      *	{ None }
	  %}

	  let test (str: string) (result: semver option) =
	      let st = {
		  yyinput = str;
		  yycursor = 0;
		  yymarker = 0;
		  %{svars format = "\n\t\t@@{tag} = -1;"; %}
		  %{stags format = "\n\t\t@@{tag} = -1;"; %}
	      }
	      in if not	(parse st = result) then raise (Failure	"error")

	  let main () =
	      test "23.34" (Some {major	= 23; minor = 34; patch	= 0});
	      test "1.2.99999" (Some {major = 1; minor = 2; patch = 99999});
	      test "1.a" None

	  let _	= main ()

       Here is an example of using m-tags to parse a version with  a  variable
       number of components. Tag variables are stored in a trie.

	  (* re2ocaml $INPUT -o	$OUTPUT	*)

	  open String

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      (* Final tag variables available in semantic action. *)
	      %{svars format = "\n\tmutable @@{tag}: int;"; %}
	      %{mvars format = "\n\tmutable @@{tag}: int list;"; %}
	      (* Intermediate tag variables used by the	lexer (must be autogenerated). *)
	      %{stags format = "\n\tmutable @@{tag}: int;"; %}
	      %{mtags format = "\n\tmutable @@{tag}: int list;"; %}
	  }

	  let s2n (str:	string)	(i1: int) (i2: int) : int =
	      let rec f	s i j n	=
		  if i >= j then n else	f s (i + 1) j (n * 10 +	Char.code s.[i]	- 48)
	      in f str i1 i2 0

	  %{local
	      re2c:YYFN	= ["parse;(int list) option", "st;state"];
	      re2c:YYMTAGP = "@@ <- st.yycursor	:: @@;";
	      re2c:YYMTAGN = ""; // alternatively could	add `-1` to the	list
	      re2c:yyrecord = "st";
	      re2c:tags	= 1;
	      re2c:yyfill:enable = 0;

	      num = [0-9]+;

	      @t1 num @t2 ("." #t3 num #t4)* [\x00] {
		  let x	= s2n st.yyinput st.t1 st.t2 in
		  let xs = List.rev (List.map2 (fun x y	-> s2n st.yyinput x y) st.t3 st.t4) in
		  Some (x :: xs)
	      }
	      *	{ None }
	  %}

	  let test (str: string) (result: (int list) option) =
	      let st = {
		  yyinput = str;
		  yycursor = 0;
		  yymarker = 0;
		  %{svars format = "\n\t\t@@{tag} = -1;"; %}
		  %{mvars format = "\n\t\t@@{tag} = [];"; %}
		  %{stags format = "\n\t\t@@{tag} = -1;"; %}
		  %{mtags format = "\n\t\t@@{tag} = [];"; %}
	      }
	      in if not	(parse st = result) then raise (Failure	"error")

	  let main () =
	      test "1" (Some [1]);
	      test "1.2.3.4.5.6.7" (Some [1; 2;	3; 4; 5; 6; 7;]);
	      test "1.2." None

	  let _	= main ()

   Encoding support
       It  is  necessary  to understand	the difference between code points and
       code units. A code point	is a numeric identifier	of a  symbol.  A  code
       unit is the smallest unit of storage in the encoded text. A single code
       point may be represented	with one or more code units. In	a fixed-length
       encoding	 all  code points are represented with the same	number of code
       units. In a variable-length encoding code  points  may  be  represented
       with  a	different  number of code units.  Note that the	"any" rule [^]
       matches any code	point, but not necessarily any code unit (the only way
       to match	any code unit regardless of the	encoding is the	 default  rule
       *).  The	generated lexer	works with a stream of code units: yych	stores
       a code unit, and	YYCTYPE	is the code unit type. Regular expressions, on
       the  other  hand,  are specified	in terms of code points. When re2ocaml
       compiles	regular	expressions to automata	it translates code  points  to
       code  units. This is generally not a simple mapping: in variable-length
       encodings a single code point range may get  translated	to  a  complex
       code unit graph.	 The following encodings are supported:

        ASCII	(enabled  by default). It is a fixed-length encoding with code
	 space [0-255] and 1-byte code points and code units.

        EBCDIC	(enabled with  --ebcdic	 or  re2c:encoding:ebcdic).  It	 is  a
	 fixed-length  encoding	with code space	[0-255]	and 1-byte code	points
	 and code units.

        UCS2  (enabled	 with  --ucs2  or   re2c:encoding:ucs2).   It	is   a
	 fixed-length  encoding	 with  code  space  [0-0xFFFF] and 2-byte code
	 points	and code units.

        UTF8 (enabled with --utf8  or	re2c:encoding:utf8).  It  is  a	 vari-
	 able-length  Unicode  encoding. Code unit size	is 1 byte. Code	points
	 are represented with 1	-- 4 code units.

        UTF16 (enabled	with --utf16 or	re2c:encoding:utf16). It  is  a	 vari-
	 able-length  Unicode encoding.	Code unit size is 2 bytes. Code	points
	 are represented with 1	-- 2 code units.

        UTF32	(enabled  with	--utf32	 or  re2c:encoding:utf32).  It	is   a
	 fixed-length Unicode encoding with code space [0-0x10FFFF] and	4-byte
	 code points and code units.

       Include	file  include/unicode_categories.re  provides re2ocaml defini-
       tions for the standard Unicode categories.

       Option --input-encoding specifies source	file encoding,	which  can  be
       used  to	 enable	 Unicode  literals in regular expressions. For example
       --input-encoding	utf8 tells re2ocaml that the source file  is  in  UTF8
       (it  differs  from --utf8 which sets input text encoding). Option --en-
       coding-policy specifies the way	re2ocaml  handles  Unicode  surrogates
       (code points in range [0xD800-0xDFFF]).

       Below is	an example of a	lexer for UTF8 encoded Unicode identifiers.

	  (* re2ocaml $INPUT -o	$OUTPUT	--utf8 -i *)

	  open String

	  %{include "unicode_categories.re" %}

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      mutable yyaccept:	int;
	  }

	  %{
	      re2c:YYFN	= ["lex;bool", "yyrecord;state"];
	      re2c:yyfill:enable = 0;

	      // Simplified "Unicode Identifier	and Pattern Syntax"
	      // (see https://unicode.org/reports/tr31)
	      id_start	  = L |	Nl | [$_];
	      id_continue = id_start | Mn | Mc | Nd | Pc | [\u200D\u05F3];
	      identifier  = id_start id_continue*;

	      identifier { true	}
	      *		 { false }
	  %}

	  let main () =
	      let st = {
		  yyinput = "_";
		  yycursor = 0;
		  yymarker = 0;
		  yyaccept = 0;
	      }
	      in if not	(lex st) then raise (Failure "error")

	  let _	= main ()

   Include files
       re2ocaml	 allows	 one  to include other files using a block of the form
       /*!include:re2c FILE */ or %{include FILE %}, or	an in-block  directive
       !include	 FILE  ;,  where  FILE	is  a path to the file to be included.
       re2ocaml	looks for include files	in the directory of the	including file
       and in include locations, which can be specified	with  the  -I  option.
       Include	blocks/directives  in  re2ocaml	 work in the same way as C/C++
       #include: FILE contents	are  copy-pasted  verbatim  in	place  of  the
       block/directive.	 Include files may have	further	includes of their own.
       Use --depfile option to track build dependencies	of the output file  on
       include	files.	 re2ocaml  provides some predefined include files that
       can be found in the include/ subdirectory of the	project.  These	 files
       contain	definitions that may be	useful to other	projects (such as Uni-
       code categories)	 and  form  something  like  a	standard  library  for
       re2ocaml. Below is an example of	using include files.

   Include file	1 (definitions.ml)
	  type number =	Int | Float | NaN

	  %{
	      number = [1-9][0-9]*;
	  %}

   Include file	2 (extra_rules.re.inc)
	  // floating-point numbers
	  frac	= [0-9]* "." [0-9]+ | [0-9]+ ".";
	  exp	= 'e' [+-]? [0-9]+;
	  float	= frac exp? | [0-9]+ exp;

	  float	{ Float	}

   Input file
	  (* re2ocaml $INPUT -o	$OUTPUT	-i *)

	  open String

	  %{include "definitions.ml" %}

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable yymarker:	int;
	      mutable yyaccept:	int;
	  }

	  %{
	      re2c:YYFN	= ["lex;number", "yyrecord;state"];
	      re2c:yyfill:enable = 0;

	      *	     { NaN }
	      number { Int }
	      !include "extra_rules.re.inc";
	  %}

	  let test(str,	num) =
	      let st = {yyinput	= str; yycursor	= 0; yymarker =	0; yyaccept = 0}
	      in if not	(lex st	= num) then raise (Failure "error")

	  let main () =
	      test("123", Int);
	      test("123.4567", Float)

	  let _	= main ()

   Header files
       re2ocaml	allows one to generate header file from	the input .re file us-
       ing --header option or re2c:header configuration	and block pairs	of the
       form /*!header:re2c:on*/	and /*!header:re2c:off*/, or %{header:on%} and
       %{header:off%}. The first block marks the beginning of header file, and
       the  second  block marks	the end	of it. Everything between these	blocks
       is processed by re2ocaml, and the generated code	is written to the file
       specified with --header option or re2c:header configuration (or	stdout
       if neither option nor configuration is used). Autogenerated header file
       may  be	needed	in cases when re2ocaml is used to generate definitions
       that must be visible from other translation units.

       Here is an example of generating	a header file that contains definition
       of the lexer state with tag variables (the number variables depends  on
       the regular grammar and is unknown to the programmer).

   Input file
	  (* re2ocaml $INPUT -o	$OUTPUT	--header lexer/state.ml	-i *)

	  open State
	  open String

	  %{header:on %}
	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable tag: int;
	      %{stags format = "mutable	@@: int;"; %}
	  }
	  %{header:off %}

	  %{
	      re2c:YYFN	= ["lex;int", "yyrecord;State.state"];
	      re2c:tags	= 1;
	      re2c:yyfill:enable = 0;
	      re2c:header = "lexer/state.ml";

	      [a]* @tag	[b]* { yyrecord.tag }
	  %}

	  let main () =
	      let st = {
		  yyinput = "ab";
		  yycursor = 0;
		  tag =	0;
		  %{stags format = "\n\t@@ = 0;"; %}
	      }
	      in if not	(lex st	= 1) then raise	(Failure "error")

	  let _	= main ()

   Header file
	  (* Generated by re2c *)

	  type state = {
	      yyinput: string;
	      mutable yycursor:	int;
	      mutable tag: int;

	  mutable yyt1:	int;
	  }

   Skeleton programs
       With  the -S, --skeleton	option,	re2ocaml ignores all non-re2ocaml code
       and generates a self-contained C	program	that can be  further  compiled
       and  executed.	The program consists of	lexer code and input data. For
       each constructed	DFA (block or condition) re2ocaml generates  a	stand-
       alone lexer and two files: an .input file with strings derived from the
       DFA and a .keys file with expected match	results. The program runs each
       lexer  on  the  corresponding .input file and compares results with the
       expectations.  Skeleton programs	are very useful	for a number  of  rea-
       sons:

        They  can  check  correctness	of various re2ocaml optimizations (the
	 data is generated early in the	process, before	 any  DFA  transforma-
	 tions have taken place).

        Generating  a	set of input data with good coverage may be useful for
	 both testing and benchmarking.

        Generating self-contained executable programs allows one to get mini-
	 mized test cases (the original	code may be large or have a lot	of de-
	 pendencies).

       The difficulty with generating input data is that for all but the  most
       trivial	cases  the number of possible input strings is too large (even
       if the string length is limited). re2ocaml solves  this	difficulty  by
       generating  sufficiently	 many  strings to cover	almost all DFA transi-
       tions. It uses the following algorithm. First, it constructs a skeleton
       of the DFA. For encodings with 1-byte code unit size  (such  as	ASCII,
       UTF-8  and  EBCDIC) skeleton is just an exact copy of the original DFA.
       For encodings with multibyte code units skeleton	is a copy of DFA  with
       certain	transitions  omitted:  namely, re2ocaml	takes at most 256 code
       units for each disjoint continuous range	 that  corresponds  to	a  DFA
       transition.  The	chosen values are evenly distributed and include range
       bounds.	Instead	 of trying to cover all	possible paths in the skeleton
       (which is infeasible) re2ocaml generates	 sufficiently  many  paths  to
       cover all skeleton transitions, and thus	trigger	the corresponding con-
       ditional	 jumps	in the lexer.  The algorithm implementation is limited
       by ~1Gb of transitions and consumes constant amount of memory (re2ocaml
       writes data to file as soon as it is generated).

   Visualization and debug
       With the	-D, --emit-dot option, re2ocaml	does not  generate  code.  In-
       stead,  it dumps	the generated DFA in DOT format.  One can convert this
       dump to an image	of the DFA using Graphviz or  another  library.	  Note
       that this option	shows the final	DFA after it has gone through a	number
       of optimizations	and transformations. Earlier stages can	be dumped with
       various debug options, such as --dump-nfa, --dump-dfa-raw etc. (see the
       full list of options).

SEE ALSO
       You  can	 find  more  information  about	 re2c at the official website:
       http://re2c.org.	  Similar  programs  are   flex(1),   lex(1),	quex(-
       http://quex.sourceforge.net).

AUTHORS
       re2ocaml	   was	  originally	written	   by	 Peter	 Bumbulis   (-
       peter@csg.uwaterloo.ca) in 1993.	 Marcus	Boerger	and Dan	 Nuffer	 spent
       several	years  to  turn	the original idea into a production ready code
       generator. Since	then it	has been maintained and	developed by  multiple
       volunteers,   most   notably,  Brian  Young  (bayoung@acm.org),	Marcus
       Boerger,	Dan Nuffer (nuffer@users.sourceforge.net), Ulya	Trofimovich (-
       skvadrik@gmail.com), Serghei Iakovlev, Sergei Trofimovich, Petr Skocik,
       ligfx raekye and	PolarGoose.

								   RE2OCAML(1)

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