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RE2PY(1)							      RE2PY(1)

NAME
       re2py - generate	fast lexical analyzers for Python

SYNOPSIS
       re2py [ OPTIONS ] [ WARNINGS ] INPUT

       Input can be either a file or - for stdin.

INTRODUCTION
       re2py  works  as	a preprocessor.	It reads the input file	(which is usu-
       ally a program in Python, 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 re2py. It translates	them to	code in	Python
       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:

	  # re2py $INPUT -o $OUTPUT

	  def lex(yyinput):
	      yycursor = 0
	  %{
	      re2c:yyfill:enable = 0;
	      re2c:indent:top =	1;

	      [1-9][0-9]* { return True	}
	      *		  { return False }
	  %}

	  assert lex(b"1234\0")

       In the output re2py replaced the	block in the middle with the generated
       code:

	  # Generated by re2py
	  # re2py $INPUT -o $OUTPUT

	  def lex(yyinput):
	      yycursor = 0

	      yystate =	0
	      while True:
		  match	yystate:
		      case 0:
			  yych = yyinput[yycursor]
			  yycursor += 1
			  if yych <= 0x30:
			      yystate =	1
			      continue
			  if yych <= 0x39:
			      yystate =	2
			      continue
			  yystate = 1
			  continue
		      case 1:
			  return False
		      case 2:
			  yych = yyinput[yycursor]
			  if yych <= 0x2F:
			      yystate =	3
			      continue
			  if yych <= 0x39:
			      yycursor += 1
			      yystate =	2
			      continue
			  yystate = 3
			  continue
		      case 3:
			  return True
		      case _:
			  raise	"internal lexer	error"

	  assert lex(b"1234\0")

BASICS
       A re2py program consists	of a sequence of blocks	intermixed  with  code
       in  the	target	language.  A block may contain definitions, configura-
       tions, 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 re2py 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 re2py behavior and cus-
	      tomize the generated code. For a	full  list  of	configurations
	      supported	 by re2py see the configurations section. Depending on
	      a	particular configuration, the value can	be a keyword,  a  non-
	      negative integer number or a one-line string which should	be en-
	      closed in	double or single quotes	unless it consists of alphanu-
	      meric  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.  re2py 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 re2py 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, re2py 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, con-
	      figurations and rules of its own,	which are added	 to  those  of
	      the  referenced  rules  block.  Prior  to	 re2py 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 re2py. 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	 re2py
	      (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	 re2py
	      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 re2py:

       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
	      re2py 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	re2py 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, re2py automatically	generates a conversion
	      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
       re2py 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 re2py:

       !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 re2py:

       !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. re2py does not	(and cannot) check the
       definitions, so if anything is missing or defined incorrectly, the gen-
       erated program may have compile-time or run-time	errors.	  This	manual
       provides	examples of API	definitions in the most	common cases.

       re2py has three API flavors that	define the core	set of primitives used
       by a program:

       Simple API
	      This  is	the default API	for the	Python backend.	It consists of
	      the following primitives:	YYINPUT	(which should be defined as  a
	      sequence	of  code units,	e.g. a string) and YYCURSOR, YYMARKER,
	      YYCTXMARKER, YYLIMIT (which should be defined as indices in  YY-
	      INPUT).

       Record API
	      Record API is useful in cases when lexer state must be stored in
	      a	 class.	  It is	enabled	with --api record option or re2c:api =
	      record configuration. This API consists of a  variable  yyrecord
	      (the  name  can be overridden with re2c:yyrecord)	that should be
	      defined as a class with attributes 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). re2py gen-
	      erates 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  re2py blocks connected with goto or func-
	      tion 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. re2py as-
	      sumes that the character range is	0 -- 0xFF and  character  size
	      is 1 byte.

       --empty-class <match-empty | match-none | error>
	      Define  the  way	re2py  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 re2py treats Unicode surrogates.  With fail re2py
	      aborts with an error when	a surrogate is encountered.  With sub-
	      stitute re2py silently replaces surrogates with the  error  code
	      point  0xFFFD. With ignore (the default) re2py treats surrogates
	      as normal	code points. The Unicode standard says that standalone
	      surrogates are invalid, but real-world  libraries	 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. re2py looks for FILE in the directory
	      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 re2py parses regular  expressions.   With	 ascii
	      (the default) re2py handles input	as ASCII-encoded: any sequence
	      of  code	units  is  a sequence of standalone 1-byte characters.
	      With utf8	re2py handles input  as	 UTF8-encoded  and  recognizes
	      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.	re2py  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.  re2py  as-
	      sumes  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.	re2py  assumes
	      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.	re2py  assumes
	      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  re2py.  The
	      moore option is the Moore	algorithm (it is the default). The ta-
	      ble  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 re2py 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,
	      re2py  silently ignores such escapes, but	this may as well indi-
	      cate 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 re2py binary.	Users may pro-
       vide  a	custom syntax file that	overrides a few	configurations for one
       of supported languages, or they may choose to redefine  all  configura-
       tions  (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  re2py  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 re2py 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, re2py repeats  expressions  the
	  right	 hand  side of the column a few	times, each time replacing oc-
	  currences of the list	variable with a	value specific to this repeti-
	  tion.	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  re2py reads syntax	file, it checks	that each code
	  template uses	only the variables and conditionals that  are  allowed
	  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 re2py 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	(re2py version that was	used to	gener-
		 ate 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  re2py  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 re2py should use "unsafe" blocks in order to generate
		 faster	 code  (--unsafe, re2c:unsafe =	1). This is only rele-
		 vant for languages that have "unsafe" feature.

	  .version
		 True if the generated fingerprint should contain  re2py  ver-
		 sion.

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. re2py	supports a few
       different methods for handling the end of input.	Which one to  use  de-
       pends on	the complexity of regular expressions, the need	for buffering,
       performance  considerations  and	other factors. Here is a list of meth-
       ods:

        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.

	  # re2py $INPUT -o $OUTPUT

	  # expect a null-terminated string
	  def lex(yyinput):
	      yycursor = 0
	      count = 0

	      while True: %{
		  re2c:yyfill:enable = 0;
		  re2c:indent:top = 2;

		  *	 { return -1 }
		  [\x00] { return count	}
		  [ ]+	 { break }
		  [a-z]+ {
		      count += 1
		      break
		  }
	      %}

	  assert lex(b"\0") == 0
	  assert lex(b"one two three\0") == 3
	  assert lex(b"f0ur\0")	== -1

   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.

	  # re2py $INPUT -o $OUTPUT

	  # expect a null-terminated string
	  def lex(yyinput):
	      yycursor = 0
	      yylimit =	len(yyinput) - 1 # terminating null not	included
	      count = 0

	      while True: %{
		  re2c:yyfill:enable = 0;
		  re2c:eof = 0;
		  re2c:indent:top = 2;

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

		  *    { return	-1 }
		  $    { return	count }
		  [ ]+ { break }
		  str  {
		      count += 1
		      break
		  }
	      %}

	  def test(str,	count):
	      #	termunating null not included in `lim`
	      assert count == lex(str)

	  test(b"\0", 0);
	  test(b"'qu\0tes' 'are' 'fine:	\\'' \0", 3);
	  test(b"'unterminated\\'\0", -1)

   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.

	  # re2py $INPUT -o $OUTPUT

	  %{max	%}

	  def lex(yyinput):
	      yycursor = 0
	      yylimit =	len(yyinput)
	      count = 0

	      while True: %{
		  re2c:YYFILL =	"return	-1";
		  re2c:indent:top = 2;

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

		  [\x00] {
		      #	check that it is the sentinel, not some	unexpected null
		      return count if yycursor == yylimit - YYMAXFILL +	1 else -1
		  }
		  str {
		      count += 1
		      break
		  }
		  [ ]+ { break }
		  *    { return	-1 }
	      %}

	  def test(str,	count):
	      padded_str = str + (b"\0"	* YYMAXFILL)
	      assert lex(padded_str) ==	count

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

   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.

	  # re2py $INPUT -o $OUTPUT

	  # expect a string without terminating	null
	  def lex(str):
	      cur = 0
	      lim = len(str)
	      count = 0

	      while True: %{
		  re2c:api = generic;
		  re2c:YYPEEK =	"str[cur] if cur < lim else 0";
		  re2c:YYSKIP =	"cur +=	1";
		  re2c:yyfill:enable = 0;
		  re2c:indent:top = 2;

		  *	 { return -1 }
		  [\x00] { return count	}
		  [ ]+	 { break }
		  [a-z]+ {
		      count += 1
		      break
		  }
	      %}

	  assert lex(b"") == 0
	  assert lex(b"one two three") == 3
	  assert lex(b"f0ur") == -1

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 re2py 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.

	  # re2py $INPUT -o $OUTPUT

	  from enum import Enum
	  import os

	  BUFSIZE = 4096

	  class	State:
	      def __init__(self, fname):
		  self.file = open(fname, "rb")
		  self.yyinput = bytearray(BUFSIZE)
		  self.yylimit = BUFSIZE - 1 # exclude terminating null
		  self.yycursor	= self.yylimit
		  self.yymarker	= self.yylimit
		  self.token = self.yylimit
		  self.eof = False

	      def __del__(self):
		  self.file.close()

	  class	Status(Enum):
	      OK = 0
	      EOF = 1
	      LONG_LEXEME = 2

	  def fill(st):
	      if st.eof:
		  return Status.EOF

	      #	Error: lexeme too long.	In real	life could reallocate a	larger buffer.
	      if st.token < 1:
		  return Status.LONG_LEXEME

	      #	Shift buffer contents (discard everything up to	the current token).
	      st.yyinput = st.yyinput[st.token:st.yylimit]
	      st.yycursor -= st.token;
	      st.yymarker -= st.token;
	      st.yylimit -= st.token;
	      st.token = 0;

	      #	Fill free space	at the end of buffer with new data from	file.
	      bytes = st.file.read(BUFSIZE - st.yylimit	- 1) # -1 for sentinel
	      if not bytes:
		  st.eof = True	# end of file
	      else:
		  st.yylimit +=	len(bytes);
		  st.yyinput +=	bytes

	      st.yyinput += b'\0' # append sentinel

	      return Status.OK

	  def lex(yyrecord, count):
	      while True:
		  yyrecord.token = yyrecord.yycursor
	      %{
		  re2c:api = record;
		  re2c:define:YYFILL = "fill(yyrecord) == Status.OK";
		  re2c:eof = 0;
		  re2c:indent:top = 2;

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

		  *    { return	-1 }
		  $    { return	count }
		  [ ]+ { break }
		  str  {
		      count += 1
		      break
		  }
	      %}

	  def main():
	      fname = "input"

	      #	Prepare	input file.
	      f	= open(fname, "w")
	      for i in range(BUFSIZE):
		  f.write("'qu\0tes' 'are' 'fine: \\'' ")
	      f.close()

	      #	Run lexer on the prepared file.
	      st = State(fname)
	      assert lex(st, 0)	== 3 * BUFSIZE

	      #	Cleanup.
	      os.remove(fname)

	  if __name__ == '__main__':
	      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.

	  # re2py $INPUT -o $OUTPUT

	  from enum import Enum
	  import os

	  BUFSIZE = 4096
	  %{max	%}

	  class	State:
	      def __init__(self, fname):
		  self.file = open(fname, "rb")
		  self.yyinput = bytearray(BUFSIZE)
		  self.yylimit = BUFSIZE - YYMAXFILL
		  self.yycursor	= self.yylimit
		  self.yymarker	= self.yylimit
		  self.token = self.yylimit
		  self.eof = False

	      def __del__(self):
		  self.file.close()

	  class	Status(Enum):
	      OK = 0
	      EOF = 1
	      LONG_LEXEME = 2

	  def fill(st, need):
	      if st.eof:
		  return Status.EOF

	      #	Error: lexeme too long.	In real	life could reallocate a	larger buffer.
	      if st.token < need:
		  return Status.LONG_LEXEME

	      #	Shift buffer contents (discard everything up to	the current token).
	      st.yyinput = st.yyinput[st.token:st.yylimit]
	      st.yycursor -= st.token;
	      st.yymarker -= st.token;
	      st.yylimit -= st.token;
	      st.token = 0;

	      #	Fill free space	at the end of buffer with new data from	file.
	      bytes = st.file.read(BUFSIZE - st.yylimit	- 1) # -1 for sentinel
	      if not bytes:
		  st.eof = True	# end of file
		  st.yylimit +=	YYMAXFILL
		  st.yyinput +=	b"\0" *	YYMAXFILL
	      else:
		  st.yylimit +=	len(bytes);
		  st.yyinput +=	bytes

	      return Status.OK

	  def lex(yyrecord):
	      count = 0
	      while True:
		  yyrecord.token = yyrecord.yycursor
	      %{
		  re2c:api = record;
		  re2c:YYFILL =	"if fill(yyrecord, @@) != Status.OK: return -1";
		  re2c:indent:top = 2;

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

		  [\x00] {
		      #	Check that it is the sentinel, not some	unexpected null.
		      return count if yyrecord.token ==	yyrecord.yylimit - YYMAXFILL else -1
		  }
		  str {
		      count += 1
		      break
		  }
		  [ ]+ { break }
		  *    { return	-1 }
	      %}

	  def main():
	      fname = "input"

	      #	Prepare	input file.
	      f	= open(fname, "w")
	      for i in range(BUFSIZE):
		  f.write("'qu\0tes' 'are' 'fine: \\'' ")
	      f.close()

	      #	Run lexer on the prepared file.
	      st = State(fname)
	      assert lex(st) ==	3 * BUFSIZE

	      #	Cleanup.
	      os.remove(fname)

	  if __name__ == '__main__':
	      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	 re2py
       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	re2py, or else wrap each block in  a  function
       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.

	  # re2py $INPUT -o $OUTPUT

	  class	State:
	      def __init__(self, str):
		  self.yyinput = str
		  self.yycursor	= 0
		  self.yymarker	= 0

	  # Common re2c	definitions shared between all functions.
	  %{
	      re2c:api = record;
	      re2c:yyrecord = st;
	      re2c:yyfill:enable = 0;
	      re2c:indent:top =	2;
	  %}

	  def parse_u32(str):
	      st = State(str)
	  %{local
	      re2c:indent:top =	1;

	      '0b' / [01]	 { return parse_bin(st)	}
	      "0"		 { return parse_oct(st)	}
	      "" / [1-9]	 { return parse_dec(st)	}
	      '0x' / [0-9a-fA-F] { return parse_hex(st)	}
	      *			 { return None }
	  %}

	  def parse_bin(st):
	      n	= 0
	      while True: %{
		  [01] {
		      n	= n * 2	+ (st.yyinput[st.yycursor - 1] - 48)
		      break
		  }
		  * { return n }
	      %}

	  def parse_oct(st):
	      n	= 0
	      while True: %{
		  [0-7]	{
		      n	= n * 8	+ (st.yyinput[st.yycursor - 1] - 48)
		      break
		  }
		  * { return n }
	      %}

	  def parse_dec(st):
	      n	= 0
	      while True: %{
		  [0-9]	{
		      n	= n * 10 + (st.yyinput[st.yycursor - 1]	- 48)
		      break
		  }
		  * { return n }
	      %}

	  def parse_hex(st):
	      n	= 0
	      while True: %{
		  [0-9]	{
		      n	= n * 16 + (st.yyinput[st.yycursor - 1]	- 48)
		      break
		  }
		  [a-f]	{
		      n	= n * 16 + (st.yyinput[st.yycursor - 1]	- 87)
		      break
		  }
		  [A-F]	{
		      n	= n * 16 + (st.yyinput[st.yycursor - 1]	- 55)
		      break
		  }
		  * { return n }
	      %}

	  assert parse_u32(b"\0") == None
	  assert parse_u32(b"1234567890\0") == 1234567890
	  assert parse_u32(b"0b1101\0")	== 13
	  assert parse_u32(b"0x7Fe\0") == 2046
	  assert parse_u32(b"0644\0") == 420
	  assert parse_u32(b"9999999999\0") == 9999999999

   Start conditions
       Start conditions	are enabled with --start-conditions option. They  pro-
       vide  a	way  to	 encode	multiple interrelated automata within the same
       re2py block.

       Each condition corresponds to a single automaton	and has	a unique  name
       specified  by  the  user	and a unique internal number defined by	re2py.
       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  re2py	generates for conditions depends on whether re2py uses
       goto/label approach or loop/switch approach to encode the automata.

       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	 re2py
       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  ac-
       tions  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) re2py reuses the yys-
       tate variable to	store condition	numbers. Each condition	gets a numeric
       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,	YYGET-
       COND/YYSETCOND are redundant if both storable states and	conditions 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.

	  # re2py $INPUT -o $OUTPUT -c

	  %{conditions %}

	  def parse_u32(yyinput):
	      yycursor = 0
	      yycond = YYC_INIT
	      num = 0

	      while True: %{
		  re2c:yyfill:enable = 0;
		  re2c:indent:top = 2;

		  <INIT> '0b' /	[01]	    :=>	BIN
		  <INIT> "0"		    :=>	OCT
		  <INIT> "" / [1-9]	    :=>	DEC
		  <INIT> '0x' /	[0-9a-fA-F] :=>	HEX
		  <INIT> * { return None }

		  <BIN>	[01] {
		      num = num	* 2 + (yyinput[yycursor	- 1] - 48)
		      break
		  }
		  <OCT>	[0-7] {
		      num = num	* 8 + (yyinput[yycursor	- 1] - 48)
		      break
		  }
		  <DEC>	[0-9] {
		      num = num	* 10 + (yyinput[yycursor - 1] -	48)
		      break
		  }
		  <HEX>	[0-9] {
		      num = num	* 16 + (yyinput[yycursor - 1] -	48)
		      break
		  }
		  <HEX>	[a-f] {
		      num = num	* 16 + (yyinput[yycursor - 1] -	87)
		      break
		  }
		  <HEX>	[A-F] {
		      num = num	* 16 + (yyinput[yycursor - 1] -	55)
		      break
		  }

		  <BIN,	OCT, DEC, HEX> * { return num }
	      %}

	  assert parse_u32(b"\0") == None
	  assert parse_u32(b"1234567890\0") == 1234567890
	  assert parse_u32(b"0b1101\0")	== 13
	  assert parse_u32(b"0x7Fe\0") == 2046
	  assert parse_u32(b"0644\0") == 420
	  assert parse_u32(b"9999999999\0") == 9999999999

   Storable state
       With --storable-state option re2py generates a lexer that can store its
       current	state,	return	to the caller, and later resume	operations ex-
       actly where it left off.	The default mode of operation in  re2py	 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.

	  # re2py $INPUT -o $OUTPUT -f

	  from enum import Enum
	  import os

	  # Use	a small	buffer to cover	the case when a	lexeme doesn't fit.
	  # In real world use a	larger buffer.
	  BUFSIZE = 10
	  DEBUG	= False

	  class	State:
	      def __init__(self, file):
		  self.file = file
		  self.yyinput = bytearray(BUFSIZE)
		  self.yylimit = BUFSIZE - 1 # exclude terminating null
		  self.yycursor	= self.yylimit
		  self.yymarker	= self.yylimit
		  self.token = self.yylimit
		  self.yystate = -1

	  class	Status(Enum):
	      END = 0
	      READY = 1
	      WAITING =	2
	      BIG_PACKET = 3
	      BAD_PACKET = 4

	  def fill(st):
	      #	Error: lexeme too long.	In real	life could reallocate a	larger buffer.
	      if st.token < 1:
		  return Status.BIG_PACKET

	      #	Shift buffer contents (discard everything up to	the current token).
	      st.yyinput = st.yyinput[st.token:st.yylimit]
	      st.yycursor -= st.token;
	      st.yymarker -= st.token;
	      st.yylimit -= st.token;
	      st.token = 0;

	      #	Fill free space	at the end of buffer with new data from	file.
	      bytes = st.file.read(BUFSIZE - st.yylimit	- 1) # -1 for sentinel
	      if bytes:
		  st.yylimit +=	len(bytes);
		  st.yyinput +=	bytes

	      st.yyinput += b'\0' # append sentinel

	      return Status.READY

	  def lex(yyrecord, recv):
	      while True:
		  yyrecord.token = yyrecord.yycursor
	      %{
		  re2c:api = record;
		  re2c:YYFILL =	"return	Status.WAITING,	recv";
		  re2c:eof = 0;
		  re2c:indent:top = 2;

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

		  *	 { return Status.BAD_PACKET, recv }
		  $	 { return Status.END, recv }
		  packet {
		      recv += 1
		      break
		  }
	      %}

	  def test(packets, expect):
	      #	Create a pipe (open the	same file for reading and writing).
	      fname = "pipe"
	      fw = open(fname, "wb")
	      fr = open(fname, "rb")

	      #	Initialize lexer state
	      st = State(fr)

	      #	Main loop. The buffer contains incomplete data which appears packet by
	      #	packet.	When the lexer needs more input	it saves its internal state and
	      #	returns	to the caller which should provide more	input and resume lexing.
	      send = 0
	      recv = 0
	      while True:
		  status, recv = lex(st, recv)

		  if status == Status.END:
		      if DEBUG:	print("done: got {} packets".format(recv))
		      break

		  elif status == Status.WAITING:
		      if DEBUG:	print("waiting...");

		      if send <	len(packets):
			  if DEBUG: print("sent	packet {}: {}".format(send, packets[send]))
			  fw.write(packets[send])
			  fw.flush()
			  send += 1

		      status = fill(st)
		      if DEBUG:	print("queue: '{}', status: {}".format(st.yyinput, status))
		      if status	== Status.BIG_PACKET:
			  if DEBUG: print("error: packet too big")
			  break

		      assert status == Status.READY

		  else:
		      assert status == Status.BAD_PACKET
		      if DEBUG:	print("error: ill-formed packet")
		      break

	      #	Check results.
	      assert status == expect
	      if status	== Status.END:
		  assert recv == send

	      #	Cleanup: remove	input file.
	      fr.close()
	      fw.close()
	      os.remove(fname)

	  def main():
	      test([], Status.END)
	      test([b"zero;", b"one;", b"two;",	b"three;", b"four;"], Status.END)
	      test([b"zer0;"], Status.BAD_PACKET)
	      test([b"goooooooooogle;"], Status.BIG_PACKET)

	  if __name__ == '__main__':
	      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 re2py	blocks.	The <name> is optional.	A rules	block  can  be
       used  in	a use block or directive. The code for a rules block is	gener-
       ated 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 re2py
       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 preceding 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 re2py blocks together in  one
       block (see the example below).

       Named  blocks  and  in-block  use directive were	added in re2py 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
	  # re2py $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.

	  from enum import Enum

	  class	Ans(Enum):
	      COLOR = 1
	      FISH = 2
	      DUNNO = 3

	  %{rules:colors
	      *				   { raise "ah"	}
	      "red" | "salmon" | "magenta" { return Ans.COLOR }
	  %}

	  %{rules:fish
	      *				   { raise "oh"	}
	      "haddock"	| "salmon" | "eel" { return Ans.FISH }
	  %}

	  def lex(yyinput):
	      yycursor = 0
	  %{
	      re2c:yyfill:enable = 0;
	      re2c:indent:top =	1;

	      !use:fish;
	      !use:colors;
	      *	{ return Ans.DUNNO } //	overrides inherited '*'	rules
	  %}

	  assert lex(b"salmon")	== Ans.FISH
	  assert lex(b"what?") == Ans.DUNNO

   Example of a	/*!use:re2c ...	*/ block
	  # re2py $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.
	  %{rules
	      re2c:yyfill:enable = 0;
	      re2c:indent:top =	1;

	      "x y" { return yycursor }
	      *	      {	return None }
	  %}

	  def lex_utf8(yyinput):
	      yycursor = 0
	      %{use
		  re2c:encoding:utf8 = 1;
	      %}

	  def lex_utf32(yyinput):
	      yycursor = 0
	      %{use
		  re2c:encoding:utf32 =	1;
	      %}

	  s8 = [0xe2, 0x88, 0x80, 0x78,	0x20, 0xe2, 0x88, 0x83,	0x79]
	  assert lex_utf8(s8) == len(s8)

	  s32 =	[0x2200, 0x78, 0x20, 0x2203, 0x79]
	  assert lex_utf32(s32)	== len(s32)

   Submatch extraction
       re2py 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  re2py  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.

	  # re2py $INPUT -o $OUTPUT

	  from collections import namedtuple

	  SemVer = namedtuple('SemVer',	'major minor patch')

	  NONE = -1

	  def parse(yyinput):
	      yycursor = 0
	  %{
	      re2c:yyfill:enable = 0;
	      re2c:tags	= 1;
	      re2c:indent:top =	1;

	      num = [0-9]+;

	      @t1 num @t2 "." @t3 num @t4 ("." @t5 num)? [\x00]	{
		  major	= int(yyinput[t1:t2])
		  minor	= int(yyinput[t3:t4])
		  patch	= int(yyinput[t5:yycursor - 1])	if t5 != NONE else 0
		  return SemVer(major, minor, patch)
	      }
	      *	{ return None }
	  %}

	  assert parse(b"23.34\0") == SemVer(23, 34, 0)
	  assert parse(b"1.2.99999\0") == SemVer(1, 2, 99999)
	  assert parse(b"1.a\0") == None

       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.

	  # re2py $INPUT -o $OUTPUT

	  from collections import namedtuple
	  from enum import Enum
	  import os

	  BUFSIZE = 4096

	  SemVer = namedtuple('SemVer',	'major minor patch')

	  class	State:
	      def __init__(self, fname):
		  self.file = open(fname, "rb")
		  self.yyinput = bytearray(BUFSIZE)
		  self.yylimit = BUFSIZE - 1 # exclude terminating null
		  self.yycursor	= self.yylimit
		  self.yymarker	= self.yylimit
		  self.token = self.yylimit
		  self.eof = False
		  %{stags format = "\n	      self.@@ =	-1"; %}

	      def __del__(self):
		  self.file.close()

	  class	Status(Enum):
	      OK = 0
	      EOF = 1
	      LONG_LEXEME = 2

	  def fill(st):
	      if st.eof:
		  return Status.EOF

	      #	Error: lexeme too long.	In real	life could reallocate a	larger buffer.
	      if st.token < 1:
		  return Status.LONG_LEXEME

	      #	Shift buffer contents (discard everything up to	the current token).
	      st.yyinput = st.yyinput[st.token:st.yylimit]
	      st.yycursor -= st.token;
	      st.yymarker -= st.token;
	      st.yylimit -= st.token;
	      %{stags format = "\n    if st.@@ != -1: st.@@ -= st.token"; %}
	      st.token = 0;

	      #	Fill free space	at the end of buffer with new data from	file.
	      bytes = st.file.read(BUFSIZE - st.yylimit	- 1) # -1 for sentinel
	      if not bytes:
		  st.eof = True	# end of file
	      else:
		  st.yylimit +=	len(bytes);
		  st.yyinput +=	bytes

	      st.yyinput += b'\0' # append sentinel

	      return Status.OK

	  def lex(st, count):
	      vers = []
	      while True:
		  st.token = st.yycursor
	      %{
		  re2c:api = record;
		  re2c:yyrecord	= st;
		  re2c:YYFILL =	"fill(st) == Status.OK";
		  re2c:eof = 0;
		  re2c:indent:top = 2;
		  re2c:tags = 1;

		  num =	[0-9]+;

		  num @t1 "." @t2 num @t3 ("." @t4 num)? [\n] {
		      major = int(st.yyinput[st.token:t1])
		      minor = int(st.yyinput[t2:t3])
		      patch = int(st.yyinput[t4:st.yycursor - 1]) if t4	!= -1 else 0
		      vers.append(SemVer(major,	minor, patch))
		      break
		  }
		  $ { return vers }
		  * { return None }
	      %}

	  def main():
	      fname = "input"
	      verstr = b"1.22.333\n"
	      expect = [SemVer(1, 22, 333)] * BUFSIZE

	      #	Prepare	input file.
	      f	= open(fname, "wb")
	      for i in range(BUFSIZE):
		  f.write(verstr)
	      f.close()

	      #	Run lexer on the prepared file.
	      st = State(fname)
	      assert lex(st, 0)	== expect

	      #	Cleanup.
	      os.remove(fname)

	  if __name__ == '__main__':
	      main()

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

	  # re2py $INPUT -o $OUTPUT

	  from collections import namedtuple

	  SemVer = namedtuple('SemVer',	'major minor patch')

	  NONE = -1

	  def parse(yyinput):
	      yycursor = 0
	  %{
	      re2c:yyfill:enable = 0;
	      re2c:captvars = 1;
	      re2c:indent:top =	1;

	      num = [0-9]+;

	      (num) "."	(num) ("." num)? [\x00]	{
		  major	= int(yyinput[yytl1:yytr1])
		  minor	= int(yyinput[yytl2:yytr2])
		  patch	= 0 if yytl3 ==	NONE else int(yyinput[yytl3 + 1:yytr3])
		  return SemVer(major, minor, patch)
	      }
	      *	{ return None }
	  %}

	  assert parse(b"23.34\0") == SemVer(23, 34, 0)
	  assert parse(b"1.2.99999\0") == SemVer(1, 2, 99999)
	  assert parse(b"1.a\0") == None

       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.

	  # re2py $INPUT -o $OUTPUT

	  NONE = -1

	  def parse(yyinput):
	      yycursor = 0
	      %{mtags format = '\n    @@ = []';	%} # autogenerated tag variables

	  %{
	      re2c:YYMTAGP = "@@.append(yycursor)";
	      re2c:YYMTAGN = ""; // do nothing
	      re2c:yyfill:enable = 0;
	      re2c:tags	= 1;
	      re2c:indent:top =	1;

	      num = [0-9]+;

	      @t1 num @t2 ("." #t3 num #t4)* [\x00] {
		  vers = [int(yyinput[t1:t2])]
		  for i	in range(len(t3)):
		      vers.append(int(yyinput[t3[i]:t4[i]]))
		  return vers
	      }
	      *	{ return None }
	  %}

	  assert parse(b"1\0") == [1]
	  assert parse(b"1.2.3.4.5.6.7\0") == [1, 2, 3,	4, 5, 6, 7]
	  assert parse(b"1.2.\0") == None

   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 re2py com-
       piles regular expressions to automata it	translates code	points to code
       units. This is generally	not a simple mapping: in  variable-length  en-
       codings	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  re2py  definitions
       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 re2py that	the source file	is in UTF8 (it
       differs from --utf8 which sets input text  encoding).  Option  --encod-
       ing-policy  specifies  the  way	re2py handles Unicode surrogates (code
       points in range [0xD800-0xDFFF]).

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

	  # re2py $INPUT -o $OUTPUT --utf8

	  %{include "unicode_categories.re" %}

	  def lex(yyinput):
	      yycursor = 0
	  %{
	      re2c:yyfill:enable = 0;
	      re2c:indent:top =	1;

	      // 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 { return True }
	      *		 { return False	}
	  %}

	  assert lex(bytes("_\0", "utf-8"))

   Include files
       re2py 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.
       re2py  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 re2py work in the	same way as C/C++ #in-
       clude: FILE contents are	copy-pasted verbatim in	place of the block/di-
       rective.	Include	files may have further	includes  of  their  own.  Use
       --depfile  option to track build	dependencies of	the output file	on in-
       clude files.  re2py 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 Unicode cate-
       gories) and form	something like a standard library for re2py. Below  is
       an example of using include files.

   Include file	1 (definitions.py)
	  from enum import Enum

	  class	Num(Enum):
	      INT = 1
	      FLOAT = 2
	      NAN = 3

	  %{
	      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	{ return Num.FLOAT }

   Input file
	  # re2py $INPUT -o $OUTPUT

	  %{include "definitions.py" %}

	  def lex(yyinput):
	      yycursor = 0
	  %{
	      re2c:yyfill:enable = 0;
	      re2c:indent:top =	1;

	      *	     { return Num.NAN }
	      number { return Num.INT }
	      !include "extra_rules.re.inc";
	  %}

	  assert lex(b"123\0") == Num.INT
	  assert lex(b"123.4567\0") == Num.FLOAT

   Header files
       re2py  allows one to generate header file from the input	.re file using
       --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 re2py, 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 re2py 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
	  # re2py $INPUT -o $OUTPUT --header lexer/state.py

	  from lexer.state import State

	  %{header:on %}
	  class	State:
	      def __init__(self, str):
		  self.yyinput = str
		  self.yycursor	= 0
		  %{stags format = "\n	      self.@@ =	0"; %}
	  %{header:off %}

	  def lex(yyrecord):
	  %{
	      re2c:api = record;
	      re2c:tags	= 1;
	      re2c:yyfill:enable = 0;
	      re2c:indent:top =	1;
	      re2c:header = "lexer/state.py";

	      [a]* @t [b]* { return t }
	  %}

	  assert lex(State(b"ab\0")) ==	1

   Header file
	  # Generated by re2c

	  class	State:
	      def __init__(self, str):
		  self.yyinput = str
		  self.yycursor	= 0

		  self.yyt1 = 0

   Skeleton programs
       With  the  -S,  --skeleton option, re2py	ignores	all non-re2py 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) re2py generates a standalone 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  expecta-
       tions.  Skeleton	programs are very useful for a number of reasons:

        They  can  check correctness of various re2py optimizations (the data
	 is generated early in the process,  before  any  DFA  transformations
	 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). re2py solves this difficulty by  gen-
       erating	sufficiently many strings to cover almost all DFA transitions.
       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	encod-
       ings  with  multibyte code units	skeleton is a copy of DFA with certain
       transitions omitted: namely, re2py 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.  In-
       stead  of  trying to cover all possible paths in	the skeleton (which is
       infeasible) re2py generates sufficiently	many paths to cover all	skele-
       ton transitions,	and thus trigger the corresponding  conditional	 jumps
       in the lexer.  The algorithm implementation is limited by ~1Gb of tran-
       sitions	and  consumes  constant	amount of memory (re2py	writes data to
       file as soon as it is generated).

   Visualization and debug
       With the	-D, --emit-dot option, re2py does not generate code.  Instead,
       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	 opti-
       mizations  and transformations. Earlier stages can be dumped with vari-
       ous 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
       re2py 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.

								      RE2PY(1)

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