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+@q  Copyright (c) 1990 The Regents of the University of California. @>
+@q  All rights reserved. @>
+
+@q  This code is derived from software contributed to Berkeley by @>
+@q  Vern Paxson. @>
+
+@q  The United States Government has rights in this work pursuant @>
+@q  to contract no. DE-AC03-76SF00098 between the United States @>
+@q  Department of Energy and the University of California. @>
+
+@q  This file is part of SPLinT. @>
+
+@q  Redistribution and use in source and binary forms, with or without @>
+@q  modification, are permitted provided that the following conditions @>
+@q  are met: @>
+
+@q  1. Redistributions of source code must retain the above copyright @>
+@q     notice, this list of conditions and the following disclaimer. @>
+@q  2. Redistributions in binary form must reproduce the above copyright @>
+@q     notice, this list of conditions and the following disclaimer in the @>
+@q     documentation and/or other materials provided with the distribution. @>
+
+@q  Neither the name of the University nor the names of its contributors @>
+@q  may be used to endorse or promote products derived from this software @>
+@q  without specific prior written permission. @>
+
+@q  THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR @>
+@q  IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED @>
+@q  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR @>
+@q  PURPOSE. @>
+
+@**The \ifbootstrapmode flex \else\flex\ \fi parser stack.
+\ifbootstrapmode % this is a bootstrap run to generate the tables
+    \input limbo.sty
+    \def\optimization{5}
+    \input yy.sty
+    \modebootstrap
+\else % otherwise set up the pretty printing of tokens
+    \let\hostparsernamespace\flexnamespace
+\fi
+The scanner generator, \flex, uses \bison\ to produce a parser for its
+input language. Its lexer is output by \flex\ itself so both are
+reused to generate the parser and the scanner for pretty printing
+\flex\ input.
+
+This task is made somewhat complicated by the dependence of the \flex\
+input scanner on the correctly placed whitespace\footnote{For example,
+each regular expression definition in section~1 must start at the
+beginning of the line.}, as well as the reliance of the said scanner
+on rather involved state switching. Therefore, making subparsers for
+different fragments of \flex\ input involves not only choosing an
+appropriate subset of grammar rules to correctly process the
+grammatic constructs but also setting up the correct lexer states.
+
+The first subparser is designed to process a complete \flex\
+file. This parser is not currently part of any parser stack and is
+only used for testing. This is the only parser that does not rely on
+any custom adjustments to the lexer state to operate correctly.
+@(fip.yy@>=
+@G
+%{@> @<Preamble for the \flex\ parser@> @=%}
+ @> @<Options for \flex\ parser@> @= 
+%union {@> @=}
+%{@> @<Postamble for \flex\ parser@> @=%} 
+ @> @<Token definitions for \flex\ input parser@>@= 
+%%
+ @> @<Productions for \flex\ parser@> @= 
+%%
+@g
+
+@ The selection of options for \bison\ parsers suitable for \splint\
+have been discussed
+\ifbootstrapmode\else\locallink{bison.options}earlier \endlink\fi so we
+list them here without further comments.
+@<Options for \flex\ parser@>=
+@G
+%token-table
+%debug
+%start goal
+@g
+
+@ A parser for section~1 (definitions and declarations). This parser requires a custom
+lexer, as discussed above, to properly set up the state. Short of
+this, the lexer may produce the wrong kind of tokens or even generate
+an error.
+@(ddp.yy@>=
+@G
+%{@> @<Preamble for the \flex\ parser@> @=%}
+ @> @<Options for \flex\ parser@> @= 
+%union {@> @=}
+%{@> @<Postamble for \flex\ parser@> @=%} 
+ @> @<Token definitions for \flex\ input parser@>@= 
+%%
+ @> @<Exclusive productions for \flex\ section~1 parser@> @= 
+ @> @<Productions for \flex\ section~1 parser@> @= 
+%%
+
+@ A parser for section~2 (rules and actions). This subparser must also
+use a custom set up for its lexer as discussed above.
+@(rap.yy@>=
+@G
+%{@> @<Preamble for the \flex\ parser@> @=%}
+ @> @<Options for \flex\ parser@> @= 
+%union {@> @=}
+%{@> @<Postamble for \flex\ parser@> @=%} 
+ @> @<Token definitions for \flex\ input parser@>@= 
+%%
+ @> @<Special \flex\ section~2 parser productions@> @= 
+ @> @<Productions for \flex\ section~2 parser@> @= 
+%%
+@g
+
+@ A parser for just the regular expression syntax. A custom
+lexer initialization must precede the use of this parser, as well.
+@(rep.yy@>=
+@G
+%{@> @<Preamble for the \flex\ parser@> @=%}
+ @> @<Options for \flex\ parser@> @= 
+%union {@> @=}
+%{@> @<Postamble for \flex\ parser@> @=%} 
+ @> @<Token definitions for \flex\ input parser@>@= 
+%%
+ @> @<Special productions for regular expressions@> @= 
+ @> @<Rules for \flex\ regular expressions@> @= 
+%%
+
+@*1 Token and state declarations for the \eatone{flex}\flex\ input scanner.
+Needless to say, the original grammar used by \flex\ was not designed
+with pretty printing in mind (and why would it be?). Instead, efficiency
+was the goal which resulted in a number of lexical constructs being
+processed `on the fly', as the lexer encounters them. Such syntax
+fragments never reach the parser, and would not have a chance to be
+displayed by our routines, unless some grammar extensions and
+alterations were introduced.
+
+To make the pretty printing possible, a number of new tokens have been
+introduced below that are later used in a few altered or entirely new
+grammar productions.
+@<Token definitions for \flex\ input parser@>=
+@G
+%token CHAR NUMBER SECTEND SCDECL XSCDECL NAME PREVCCL EOF_OP
+%token OPTION_OP OPT_OUTFILE OPT_PREFIX OPT_YYCLASS OPT_HEADER OPT_EXTRA_TYPE
+%token OPT_TABLES
+
+%token CCE_ALNUM CCE_ALPHA CCE_BLANK CCE_CNTRL CCE_DIGIT CCE_GRAPH
+%token CCE_LOWER CCE_PRINT CCE_PUNCT CCE_SPACE CCE_UPPER CCE_XDIGIT
+
+%token CCE_NEG_ALNUM CCE_NEG_ALPHA CCE_NEG_BLANK CCE_NEG_CNTRL CCE_NEG_DIGIT CCE_NEG_GRAPH
+%token CCE_NEG_LOWER CCE_NEG_PRINT CCE_NEG_PUNCT CCE_NEG_SPACE CCE_NEG_UPPER CCE_NEG_XDIGIT
+
+%left CCL_OP_DIFF CCL_OP_UNION
+
+@ We introduce an additional option type to capture all the non-parametric options used
+by the \flex\ lexer. The original lexer processes these options at the
+point of recognition, while the typesetting parser needs to be aware of them.
+@<Token definitions for \flex\ input parser@>=
+@G
+%token TOP_OP POINTER_OP ARRAY_OP DEF_OP RE_DEF OPT_OTHER OPT_DEPRECATED
+
+@ {\em \POSIX\ and \.{AT\&T} \lex\ place the
+precedence of the repeat operator, \.{\{\}}, below that of concatenation.
+Thus, \.{ab\{3\}} is\/ \.{ababab}.  Most other \POSIX\ utilities use an {\rm Extended
+Regular Expression (ERE)} precedence that has the repeat operator
+higher than concatenation. This causes \.{ab\{3\}} to yield\/ \.{abbb}.
+
+In order to support the \POSIX\ and \.{AT\&T} precedence and the \flex\
+precedence we define two token sets for the begin and end tokens of
+the repeat operator, \prodstyle{BEGIN_REPEAT_POSIX} and\/ \prodstyle{END_REPEAT_POSIX}.  The lexical scanner chooses
+which tokens to return based on whether {\let\it\itbold\prodstyle{posix\_compat} or \prodstyle{lex\_compat}
+are specified. Specifying either \prodstyle{posix\_compat} or \prodstyle{lex\_compat}} will
+cause \flex\ to parse scanner files as per the \.{AT\&T} and \POSIX-mandated behavior.}
+@<Token definitions for \flex\ input parser@>=
+@G
+%token BEGIN_REPEAT_POSIX END_REPEAT_POSIX BEGIN_REPEAT_FLEX END_REPEAT_FLEX
+
+@*1 The grammar for \eatone{flex}\flex\ input.
+The original grammar has been carefully split into sections to
+facilitate the assembly of various subparsers in the \flex's
+stack. Neither the \flex\ parser nor its scanner are part of the
+bootstrap procedure which simplifies both the input file organization,
+as well as the macro design. Some amount of preprocessing is still
+necessary, however, to extract the state names from the lexer file
+(see \ifbootstrapmode\else\locallink{state.grabbing}above \endlink\fi for the
+explanation). We can nevertheless get away with an empty \Cee\ preamble.
+@<Preamble for the \flex\ parser@>=
+
+@ @<Productions for \flex\ parser@>=
+@G
+@t}\vb{\inline\flatten}{@>
+goal:
+   initlex sect1 sect1end
+     sect2 initforrule           {@> @<Assemble a \flex\ input file@> @=}
+ ;
+
+sect1end:
+   SECTEND                       {@> @<Copy the value@> @=}
+ ;
+
+initlex:
+                                 {@> @=}
+ ;
+@g
+
+@ @<Assemble a \flex\ input file@>=
+  @[TeX_( "/yy0{/the/yy(2)/the/yy(4)}" );@]@;
+
+@ @<Productions for \flex\ parser@>=
+@<Productions for \flex\ section~1 parser@>@;
+@<Productions for \flex\ section~2 parser@>@;
+
+@ @<Exclusive productions for \flex\ section~1 parser@>=
+@G
+@t}\vb{\inline\flatten}{@>
+goal:
+   sect1                         {@> @<Assemble a \flex\ section~1 file@> @=}
+ ;
+
+@ @<Assemble a \flex\ section~1 file@>=
+  @[TeX_( "/table/expandafter{/the/yy(1)}" );@]@;
+
+@ @<Productions for \flex\ section~1 parser@>=
+@G
+sect1:
+   sect1 startconddecl namelist1 {@> @<Add start condition declarations@> @=}
+ | sect1 options                 {@> @<Add options to section~1@> @=}
+ |                               {@> @<Create an empty section~1@> @=}
+ | error                         {@> @<Report an error in section~1 and quit@> @=}
+ ;
+ 
+startconddecl:
+   SCDECL                        {@> @<Prepare a state declaration@> @=}
+ | XSCDECL                       {@> @<Prepare an exclusive state declaration@> @=}
+ ;
+ 
+namelist1:
+   namelist1 NAME                {@> @<Add a name to a list@> @=}
+ | NAME                          {@> @<Start a \prodstylens{namelist1}{\flexnamespace} with a name@> @=}
+ | error                         {@> @<Report an error in \prodstylens{namelist1}{\flexnamespace} and quit@> @=}
+ ;
+@g
+
+@ @<Add start condition declarations@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flscondecl/the/yy(2){/the/yy(3)}}" );@]@;
+
+@ @<Add options to section~1@>=
+  @[TeX_( "/yy0{/the/yy(1)/the/yy(2)}" );@]@;
+
+@ @<Create an empty section~1@>=
+  @[TeX_( "/yy0{}" );@]@;
+
+@ @<Report an error in section~1 and quit@>=
+  @[TeX_( "/yyerror" );@]@;
+
+@ @<Prepare a state declaration@>=
+  @[TeX_( "/yy0{{s}/the/yy(1)}" );@]@;
+
+@ @<Prepare an exclusive state declaration@>=
+  @[TeX_( "/yy0{{x}/the/yy(1)}" );@]@;
+
+@ @<Add a name to a list@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flnamesep{}{}/nx/flname/the/yy(2)}" );@]@;
+
+@ @<Start a \prodstylens{namelist1}{\flexnamespace} with a name@>=
+  @[TeX_( "/yy0{/nx/flname/the/yy(1)}" );@]@;
+
+@ @<Report an error in \prodstylens{namelist1}{\flexnamespace} and quit@>=
+  @[TeX_( "/yyerror" );@]@;
+
+@ @<Productions for \flex\ section~1 parser@>=
+@G
+options:
+   OPTION_OP optionlist          {@> @<Start an options list@> @=}
+ | POINTER_OP                    {@> @<Add a pointer option@> @=}
+ | ARRAY_OP                      {@> @<Add an array option@> @=}
+ | TOP_OP '\n'                   {@> @<Add a \prodstylens{\%top}{\flexnamespace} directive@> @=}
+ | DEF_OP RE_DEF                 {@> @<Add a regular expression definition@> @=}
+ | OPT_DEPRECATED                {@> @<Output a deprecated option@> @=}
+ ;
+@t}\vb{\inline\flatten}{@>
+optionlist:
+   optionlist option             {@> @<Add an option to a list@> @=}
+ |                               {@> @<Make an empty option list@> @=}
+ ;
+@t}\vb{\resetf}{@>
+option:
+   OPT_OUTFILE '=' NAME          {@> @<Record the name of the output file@> @=}
+ | OPT_EXTRA_TYPE '=' NAME       {@> @<Declare an extra type@> @=}
+ | OPT_PREFIX '=' NAME           {@> @<Declare a prefix@> @=}
+ | OPT_YYCLASS '=' NAME          {@> @<Declare a class@> @=}
+ | OPT_HEADER '=' NAME           {@> @<Declare the name of a header@> @=}
+ | OPT_TABLES '=' NAME           {@> @<Declare the name for the tables@> @=}
+ | OPT_OTHER                     {@> @<Output a non-parametric option@> @=}
+ ;
+@g
+
+@ @<Start an options list@>=
+  @[TeX_( "/yy0{/nx/floptions{/the/yy(2)}}" );@]@;
+
+@ @<Add a pointer option@>=
+  @[TeX_( "/yy0{/nx/flptropt/the/yy(1)}" );@]@;
+  
+@ @<Add an array option@>=
+  @[TeX_( "/yy0{/nx/flarrayopt/the/yy(1)}" );@]@;
+
+@ @<Add a \prodstylens{\%top}{\flexnamespace} directive@>=
+  @[TeX_( "/yy0{/nx/fltopopt/the/yy(1)/the/yy(2)}" );@]@;
+
+@ @<Add a regular expression definition@>=
+  @[TeX_( "/yy0{/nx/flredef/the/yy(1)/the/yy(2)}" );@]@;
+  
+@ @<Add an option to a list@>=
+  @[TeX_( "/yy0{/the/yy(1)/the/yy(2)}" );@]@;
+
+@ @<Make an empty option list@>=
+  @[TeX_( "/yy0{}" );@]@;
+
+@ @<Record the name of the output file@>=
+  @[TeX_( "/yy0{/nx/flopt{file}/the/yy(3)}" );@]@;
+
+@ @<Declare an extra type@>=
+  @[TeX_( "/yy0{/nx/flopt{xtype}/the/yy(3)}" );@]@;
+  
+@ @<Declare a prefix@>=
+  @[TeX_( "/yy0{/nx/flopt{prefix}/the/yy(3)}" );@]@;
+  
+@ @<Declare a class@>=
+  @[TeX_( "/yy0{/nx/flopt{yyclass}/the/yy(3)}" );@]@;
+  
+@ @<Declare the name of a header@>=
+  @[TeX_( "/yy0{/nx/flopt{header}/the/yy(3)}" );@]@;
+  
+@ @<Declare the name for the tables@>=
+  @[TeX_( "/yy0{/nx/flopt{tables}/the/yy(3)}" );@]@;
+
+@ @<Output a non-parametric option@>=
+  @[TeX_( "/yy0{/nx/flopt{other}/the/yy(1)}" );@]@;
+
+@ @<Output a deprecated option@>=
+  @[TeX_( "/yy0{/nx/flopt{deprecated}/the/yy(1)}" );@]@;
+
+@ @<Special \flex\ section~2 parser productions@>=
+@G
+goal:
+   sect2                                     {@> @<Output section~2@> @=} 
+ ;
+@g
+
+@ @<Output section~2@>=
+  @[TeX_( "/table/yy(1)" );@]@;
+
+@ This portion of the grammar was changed to make it possible to read the
+action code.
+@<Productions for \flex\ section~2 parser@>=
+@G
+sect2:
+   sect2 scon initforrule flexrule '\n' '\n' {@> @<Add a rule to section~2@> @=}
+ | sect2 scon '{' sect2 '}'                  {@> @<Add a group of rules to section~2@> @=}
+ |                                           {@> @<Start an empty section~2@> @=}
+ | sect2 '\n'                                {@> @<Add a bare action@> @=}
+ ;
+@t}\vb{\inline\flatten}{@>
+initforrule:
+                                            {@> @[TeX_( "/flin@@ruletrue/yylexnext" );@] @=}
+ ;
+@g
+
+@ @<Add a rule to section~2@>=
+    @[TeX_( "/ifflcontinued@@action" );@]@;
+    @[TeX_( "    /toksb{/flactionc}" );@]@;
+    @[TeX_( "/else" );@]@;
+    @[TeX_( "    /toksb{/flaction}" );@]@;
+    @[TeX_( "/fi" );@]@;
+    @[TeX_( "/toksa/expandafter{/astformat@@flaction}" );@]@; /* capture the formatting action */
+    @[TeX_( "/yypushx{/the/yy(1)/the/toksb{/the/yy(2)}{/the/yy(4)}/the/yy(5)/the/yy(6){/the/toksa}}/on/astarray" );@]@;
+    @[TeX_( "/yy0{/astarraylastcs}" );@]@;
+    @[TeX_( "/let/astformat@@flaction/empty" );@]@; /* reset the format */
+
+@ @<Add a group of rules to section~2@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flactiongroup{/the/yy(2)}/the/yy(3){/the/yy(4)}/the/yy(5)}" );@]@;
+
+@ @<Start an empty section~2@>=
+  @[TeX_( "/yy0{}" );@]@;
+
+@ @<Add a bare action@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flbareaction/the/yy(2)}" );@]@;
+
+@ @<Productions for \flex\ section~2 parser@>=
+@G
+@t}\vb{\inline\flatten}{@>
+scon_stk_ptr:
+                                   {@> @=}
+ ;
+@t}\vb{\resetf}{@>
+scon:
+   '<' scon_stk_ptr namelist2 '>'  {@> @<Create a list of start conditions@> @=}
+ | '<' '*' '>'                     {@> @<Create a universal start condition@> @=}
+ |                                 {@> @<Create an empty start condition@> @=}
+ ;
+
+namelist2:
+   namelist2 ',' sconname          {@> @<Add a start condition to a list@> @=}
+ | sconname                        {@> @<Start a list with a start condition name@> @=}
+ | error                           {@> @<Report an error compiling a start condition list@> @=}
+ ;
+@t}\vb{\inline\flatten}{@>
+sconname:
+   NAME                            {@> @<Make a \prodstylens{NAME}{\flexnamespace} into a start condition@> @=}
+ ;
+
+@ @<Create a list of start conditions@>=
+  @[TeX_( "/yy0{/nx/flsconlist{/the/yy(1)}{/the/yy(3)}{/the/yy(4)}}" );@]@;
+
+@ @<Create a universal start condition@>=
+  @[TeX_( "/yy0{/nx/flsconuniv/the/yy(3)}" );@]@;
+
+@ @<Create an empty start condition@>=
+  @[TeX_( "/yy0{}" );@]@;
+
+@ @<Add a start condition to a list@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flnamesep/the/yy(2)/the/yy(3)}" );@]@;
+
+@ @<Start a list with a start condition name@>=
+  @<Copy the value@>@;
+
+@ @<Report an error compiling a start condition list@>=
+  @[TeX_( "/yyerror" );@]@;
+
+@ @<Make a \prodstylens{NAME}{\flexnamespace} into a start condition@>=
+  @[TeX_( "/yy0{/nx/flname/the/yy(1)}" );@]@;
+
+@ @<Productions for \flex\ section~2 parser@>=
+    @<Rules for \flex\ regular expressions@>@;
+
+@ @<Special productions for regular expressions@>=
+@G
+goal:
+   flexrule                        {@> @<Output a regular expression@> @=}
+ ;
+@g
+
+@ The parsed regular expression is output in the \.{\\table}
+register. It is important to ensure that whenever this parser is used
+inside another parser that uses \.{\\table} for output, the changes to
+this register stay local. The \.{\\frexproc} macro in \.{yyunion.sty}
+ensures that all the changes are local to the parsing macro.
+@<Output a regular expression@>=
+  @[TeX_( "/table/yy(1)" );@]@;
+
+@ @<Rules for \flex\ regular expressions@>=
+@G
+flexrule:
+   '^' rule                        {@> @<Match a rule at the beginning of the line@> @=}
+ | rule                            {@> @<Match an ordinary rule@> @=}
+ | EOF_OP                          {@> @<Match an end of file@> @=}
+ | error                           {@> @<Report an error and quit@> @=}
+ ;
+
+@ @<Match a rule at the beginning of the line@>=
+    @[TeX_( "/toksa/expandafter{/astformat@@flrule}" );@]@;
+    @[TeX_( "/let/astformat@@flrule/empty" );@]@;
+    @[TeX_( "/yy0{/nx/flbolrule{/the/yy(2)}{/the/toksa}}" );@]@;
+
+@ @<Match an ordinary rule@>=
+    @[TeX_( "/toksa/expandafter{/astformat@@flrule}" );@]@;
+    @[TeX_( "/let/astformat@@flrule/empty" );@]@;
+    @[TeX_( "/yy0{/nx/flrule{/the/yy(1)}{/the/toksa}}" );@]@;
+
+@ @<Match an end of file@>=
+  @[TeX_( "/yy0{/nx/fleof/the/yy(1)}" );@]@;
+
+@ @<Report an error and quit@>=
+  @[TeX_( "/yyerror" );@]@;
+  
+@ @<Rules for \flex\ regular expressions@>=
+@G
+rule:
+   re2 re                          {@> @<Match a regular expression with a trailing context@> @=}
+ | re2 re '$'                      {@> @<Disallow a repeated trailing context@> @=}
+ | re '$'                          {@> @<Match a regular expression at the end of the line@> @=}
+ | re                              {@> @<Match an ordinary regular expression@> @=}
+ ;
+
+re:
+   re '|' series                   {@> @<Match a sequence of alternatives@> @=}
+ | series                          {@> @<Match a sequence of singletons@> @=}
+ ;
+@t}\vb{\inline\flatten}{@>
+re2:
+   re '/'                          {@> @<Prepare to match a trailing context@> @=}
+ ;
+@g
+
+@ @<Match a regular expression with a trailing context@>=
+  @[TeX_( "/getsecond{/yy(1)}/to/toksa/getthird{/yy(1)}/to/toksb" );@]@;
+  @[TeX_( "/yy0{/nx/flretrail{/the/toksa}{/the/toksb}{/the/yy(2)}}" );@]@;
+  
+@ @<Disallow a repeated trailing context@>=
+  @[TeX_( "/yyerror" );@]@;
+  
+@ @<Match a regular expression at the end of the line@>=
+  @[TeX_( "/yy0{/nx/flreateol{/the/yy(1)}/the/yy(2)}" );@]@;
+
+@ @<Match an ordinary regular expression@>=
+  @<Copy the value@>@;
+  
+@ @<Match a sequence of alternatives@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flor/the/yy(2)/the/yy(3)}" );@]@;
+
+@ @<Match a sequence of singletons@>=
+  @<Copy the value@>@;
+
+@ @<Prepare to match a trailing context@>=
+  @[TeX_( "/yy0{/nx/fltrail{/the/yy(1)}{/the/yy(2)}}" );@]@;
+  
+@ @<Rules for \flex\ regular expressions@>=
+@G
+series:
+   series singleton                     {@> @<Extend a series by a singleton@> @=}
+ | singleton                            {@> @<Match a singleton@> @=}
+ | series BEGIN_REPEAT_POSIX                     
+     NUMBER ',' NUMBER END_REPEAT_POSIX {@> @<Match a series of specific length@> @=}                 
+ | series BEGIN_REPEAT_POSIX
+     NUMBER ',' END_REPEAT_POSIX        {@> @<Match a series of minimal length@> @=}
+ | series BEGIN_REPEAT_POSIX
+     NUMBER END_REPEAT_POSIX            {@> @<Match a series of exact length@> @=}
+ ;                                               
+@g
+
+@ @<Extend a series by a singleton@>=
+  @[TeX_( "/yy0{/the/yy(1)/the/yy(2)}" );@]@;
+  
+@ @<Match a singleton@>=
+  @<Copy the value@>@;
+
+@ @<Match a series of specific length@>=
+  @<Create a series of specific length@>@;
+  
+@ @<Match a series of minimal length@>=
+  @<Create a series of minimal length@>@;
+  
+@ @<Match a series of exact length@>=
+  @<Create a series of exact length@>@;
+  
+@ @<Rules for \flex\ regular expressions@>=
+@G
+singleton:                                       
+   singleton '*'                        {@> @<Create a lazy series match@> @=}
+ | singleton '+'                        {@> @<Create a nonempty series match@> @=}
+ | singleton '?'                        {@> @<Create a possible single match@> @=}
+ | singleton BEGIN_REPEAT_FLEX                   
+     NUMBER ',' NUMBER END_REPEAT_FLEX  {@> @<Create a series of specific length@> @=}
+ | singleton BEGIN_REPEAT_FLEX                   
+     NUMBER ',' END_REPEAT_FLEX         {@> @<Create a series of minimal length@> @=}
+ | singleton BEGIN_REPEAT_FLEX
+     NUMBER END_REPEAT_FLEX             {@> @<Create a series of exact length@> @=}
+ | '.'                                  {@> @<Match (almost) any character@> @=}
+ | fullccl                              {@> @<Match a character class@> @=}
+ | PREVCCL                              {@> @<Match a \prodstylens{PREVCCL}{\flexnamespace}@> @=}
+ | '"' string '"'                       {@> @<Match a string@> @=}
+ | '(' re ')'                           {@> @<Match an atom@> @=}
+ | CHAR                                 {@> @<Match a specific character@> @=}
+ ;
+@g
+                                                 
+@ @<Create a lazy series match@>=
+  @[TeX_( "/yy0{/nx/flrepeat{/the/yy(1)}}" );@]@;
+  
+@ @<Create a nonempty series match@>=
+  @[TeX_( "/yy0{/nx/flrepeatstrict{/the/yy(1)}}" );@]@;
+  
+@ @<Create a possible single match@>=
+  @[TeX_( "/yy0{/nx/flrepeatonce{/the/yy(1)}}" );@]@;
+  
+@ @<Create a series of specific length@>=
+  @[TeX_( "/yy0{/nx/flrepeatnm{/the/yy(1)}{/the/yy(3)}{/the/yy(5)}}" );@]@;
+  
+@ @<Create a series of minimal length@>=
+  @[TeX_( "/yy0{/nx/flrepeatgen{/the/yy(1)}{/the/yy(3)}}" );@]@;
+  
+@ @<Create a series of exact length@>=
+  @[TeX_( "/yy0{/nx/flrepeatn{/the/yy(1)}{/the/yy(3)}}" );@]@;
+  
+@ @<Match (almost) any character@>=
+  @[TeX_( "/yy0{/nx/fldot/the/yy(1)}" );@]@;
+
+@ @<Match a character class@>=
+  @<Copy the value@>@;
+  
+@ @<Match a \prodstylens{PREVCCL}{\flexnamespace}@>=
+  @<Copy the value@>@;
+  
+@ @<Match a string@>=
+  @[TeX_( "/yy0{/nx/flstring{/the/yy(1)}{/the/yy(2)}{/the/yy(3)}}" );@]@;
+  
+@ @<Match an atom@>=
+    @[TeX_( "/toksa/expandafter{/astformat@@flparens}" );@]@;
+    @[TeX_( "/let/astformat@@flparens/empty" );@]@;
+    @[TeX_( "/yy0{/nx/flparens{/the/yy(1)}{/the/yy(2)}{/the/yy(3)}{/the/toksa}}" );@]@;
+  
+@ @<Match a specific character@>=
+  @[TeX_( "/yy0{/nx/flchar/the/yy(1)}" );@]@;
+
+@ @<Rules for \flex\ regular expressions@>=
+@G
+fullccl:                                         
+   fullccl CCL_OP_DIFF  braceccl        {@> @<Subtract a character class@> @=}
+ | fullccl CCL_OP_UNION braceccl        {@> @<Create a union of character classes@> @=}
+ | braceccl                             {@> @<Turn a basic character class into a character class@> @=}
+ ;
+
+braceccl:
+   '[' ccl ']'        {@> @<Create a character class@> @=}
+ | '[' '^' ccl ']'    {@> @<Create a complementary character class@> @=}
+ ;                             
+                               
+ccl:                           
+   ccl CHAR '-' CHAR  {@> @<Add a range to a character class@> @=}
+ | ccl CHAR           {@> @<Add a character to a character class@> @=}
+ | ccl ccl_expr       {@> @<Add an expression to a character class@> @=}
+ |                    {@> @<Create an empty character class@> @=}
+ ;
+@g
+
+@ @<Subtract a character class@>=
+  @[TeX_( "/yy0{/nx/flccldiff{/the/yy(1)}{/the/yy(3)}}" );@]@;
+  
+@ @<Create a union of character classes@>=
+  @[TeX_( "/yy0{/nx/flcclunion{/the/yy(1)}{/the/yy(3)}}" );@]@;
+
+@ @<Turn a basic character class into a character class@>=
+  @<Copy the value@>@;
+
+@ @<Create a character class@>=
+  @[TeX_( "/yy0{/nx/flbraceccl{/the/yy(1)}{/the/yy(2)}{/the/yy(3)}}" );@]@;
+  
+@ @<Create a complementary character class@>=
+  @[TeX_( "/yy0{/nx/flbracecclneg{/the/yy(1)}{/the/yy(3)}{/the/yy(4)}}" );@]@;
+  
+@ @<Add a range to a character class@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flcclrnge{/nx/flchar/the/yy(2)}{/nx/flchar/the/yy(4)}}" );@]@;
+
+@ @<Add a character to a character class@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flchar/the/yy(2)}" );@]@;
+
+@ @<Add an expression to a character class@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flcclexpr/the/yy(2)}" );@]@;
+
+@ @<Create an empty character class@>=
+  @[TeX_( "/yy0{}" );@]@;
+
+@ @<Rules for \flex\ regular expressions@>=
+@G
+ccl_expr:
+@t}\vb{\flatten}{@>
+   CCE_ALNUM      {@> @<Copy the value@> @=}
+ | CCE_ALPHA      {@> @<Copy the value@> @=}
+ | CCE_BLANK      {@> @<Copy the value@> @=}
+ | CCE_CNTRL      {@> @<Copy the value@> @=}
+ | CCE_DIGIT      {@> @<Copy the value@> @=}
+ | CCE_GRAPH      {@> @<Copy the value@> @=}
+ @t}\vb{\fold\flatten}{@>
+ | CCE_LOWER      {@> @<Copy the value@> @=}
+ | CCE_PRINT      {@> @<Copy the value@> @=}
+ | CCE_PUNCT      {@> @<Copy the value@> @=}
+ | CCE_SPACE      {@> @<Copy the value@> @=}
+ | CCE_XDIGIT     {@> @<Copy the value@> @=}
+ | CCE_UPPER      {@> @<Copy the value@> @=}
+@t}\vb{\fold\flatten}{@>
+ | CCE_NEG_ALNUM  {@> @<Copy the value@> @=}
+ | CCE_NEG_ALPHA  {@> @<Copy the value@> @=}
+ | CCE_NEG_BLANK  {@> @<Copy the value@> @=}
+ | CCE_NEG_CNTRL  {@> @<Copy the value@> @=}
+ | CCE_NEG_DIGIT  {@> @<Copy the value@> @=}
+ | CCE_NEG_GRAPH  {@> @<Copy the value@> @=}
+ @t}\vb{\fold\flatten}{@>
+ | CCE_NEG_PRINT  {@> @<Copy the value@> @=}
+ | CCE_NEG_PUNCT  {@> @<Copy the value@> @=}
+ | CCE_NEG_SPACE  {@> @<Copy the value@> @=}
+ | CCE_NEG_XDIGIT {@> @<Copy the value@> @=}
+ | CCE_NEG_LOWER  {@> @<Copy the value@> @=}
+ | CCE_NEG_UPPER  {@> @<Copy the value@> @=}
+ ;
+@t}\vb{\inline}{@>
+string:
+   string CHAR    {@> @<Extend a \flex\ string by a character@> @=}
+ |                {@> @<Make an empty regular expression string@> @=}
+ ;
+@g
+
+@ @<Copy the value@>=
+  @[TeX_( "/yy0{/the/yy(1)}" );@]@;
+
+@ @<Extend a \flex\ string by a character@>=
+  @[TeX_( "/yy0{/the/yy(1)/nx/flchar/the/yy(2)}" );@]@;
+
+@ @<Make an empty regular expression string@>=
+  @[TeX_( "/yy0{}" );@]@;
+
+@ This is needed to get the |yytoknum| array. A trivial declaration suffices.
+@<Postamble for \flex\ parser@>=
+#define YYPRINT(file, type, value)   @[yyprint (file, type, value)@]
+  static void yyprint (FILE *file, int type, YYSTYPE value){}