pt::peg::to::cparam(n)						   Parser Tools 					    pt::peg::to::cparam(n)

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NAME

       pt::peg::to::cparam - PEG Conversion. Write CPARAM format

SYNOPSIS

       package require Tcl  8.5

       package require pt::peg::to::cparam  ?1.0.1?

       pt::peg::to::cparam reset

       pt::peg::to::cparam configure

       pt::peg::to::cparam configure option

       pt::peg::to::cparam configure option value...

       pt::peg::to::cparam convert serial

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DESCRIPTION

       Are  you  lost  ?  Do you have trouble understanding this document ?  In that case please read the overview provided by the Introduction to
       Parser Tools. This document is the entrypoint to the whole system the current package is a part of.

       This package implements the converter from parsing expression grammars to CPARAM markup.

       It resides in the Export section of the Core Layer of Parser Tools, and can be used either directly with the other packages of this  layer,
       or  indirectly  through	the  export manager provided by pt::peg::export. The latter is intented for use in untrusted environments and done
       through the corresponding export plugin pt::peg::export::cparam sitting between converter and export manager.

       IMAGE: arch_core_eplugins

API

       The API provided by this package satisfies the specification of the Converter API found in the Parser Tools Export API specification.

       pt::peg::to::cparam reset
	      This command resets the configuration of the package to its default settings.

       pt::peg::to::cparam configure
	      This command returns a dictionary containing the current configuration of the package.

       pt::peg::to::cparam configure option
	      This command returns the current value of the specified configuration option of the package. For the set of  legal  options,  please
	      read the section Options.

       pt::peg::to::cparam configure option value...
	      This command sets the given configuration options of the package, to the specified values. For the set of legal options, please read
	      the section Options.

       pt::peg::to::cparam convert serial
	      This command takes the canonical serialization of a parsing expression grammar, as specified in section  PEG  serialization  format,
	      and  contained  in  serial,  and	generates  CPARAM markup encoding the grammar, per the current package configuration.  The created
	      string is then returned as the result of the command.

OPTIONS

       The converter to C code recognizes the following configuration variables and changes its behaviour as they specify.

       -file string
	      The value of this option is the name of the file or other entity from which the grammar came, for which  the  command  is  run.  The
	      default value is unknown.

       -name string
	      The value of this option is the name of the grammar we are processing.  The default value is a_pe_grammar.

       -user string
	      The value of this option is the name of the user for which the command is run. The default value is unknown.

       -template string
	      The  value  of  this option is a string into which to put the generated text and the other configuration settings. The various loca-
	      tions for user-data are expected to be specified with the placeholders listed below. The default value is "@code@".

	      @user@ To be replaced with the value of the option -user.

	      @format@
		     To be replaced with the the constant C/PARAM.

	      @file@ To be replaced with the value of the option -file.

	      @name@ To be replaced with the value of the option -name.

	      @code@ To be replaced with the generated Tcl code.
       The following options are special, in that they will occur within the generated code, and are replaced there as well.

	      @statedecl@
		     To be replaced with the value of the option state-decl.

	      @stateref@
		     To be replaced with the value of the option state-ref.

	      @strings@
		     To be replaced with the value of the option string-varname.

	      @self@ To be replaced with the value of the option self-command.

	      @def@  To be replaced with the value of the option fun-qualifier.

	      @ns@   To be replaced with the value of the option namespace.

	      @main@ To be replaced with the value of the option main.

	      @prelude@
		     To be replaced with the value of the option prelude.

       -state-decl string
	      A C string representing the argument declaration to use in the generated parsing functions to refer to the parsing state. In essence
	      type and argument name.  The default value is the string RDE_PARAM p.

       -state-ref string
	      A C string representing the argument named used in the generated parsing functions to refer to the parsing state.  The default value
	      is the string p.

       -self-command string
	      A C string representing the reference needed to call the generated parser function (methods ...) from another parser  fonction,  per
	      the chosen framework (template).	The default value is the empty string.

       -fun-qualifier string
	      A  C  string  containing	the attributes to give to the generated functions (methods ...), per the chosen framework (template).  The
	      default value is static.

       -namespace string
	      The name of the C namespace the parser functions (methods, ...) shall reside in, or a general prefix to add to the  function  names.
	      The default value is the empty string.

       -main string
	      The  name  of  the  main function (method, ...) to be called by the chosen framework (template) to start parsing input.  The default
	      value is __main.

       -string-varname string
	      The name of the variable used for the table of strings used by the generated parser, i.e. error messages, symbol	names,	etc.   The
	      default value is p_string.

       -prelude string
	      A snippet of code to be inserted at the head of each generated parsing function.	The default value is the empty string.

       -indent integer
	      The number of characters to indent each line of the generated code by.  The default value is 0.

       While  the  high  parameterizability  of  this converter, as shown by the multitude of options it supports, is an advantage to the advanced
       user, allowing her to customize the output of the converter as needed, a novice user will likely not see the forest for the trees.

       To help these latter users an adjunct package is provided, containing a canned configuration which will generate  immediately  useful  full
       parsers. It is

       pt::cparam::configuration::critcl
	      Generated parsers are embedded into a Critcl-based framework.

C
/PARAM CODE REPRESENTATION OF PARSING EXPRESSION GRAMMARS
       The c format is executable code, a parser for the grammar. The parser implementation is written in C and can be tweaked to the users' needs
       through a multitude of options.

       The critcl format, for example, is implemented as a canned configuration of these options on top of the generator for c.

       The bulk of such a framework has to be specified through the option -template. The additional options

       -fun-qualifier string

       -indent integer

       -main string

       -namespace string

       -prelude string

       -self-command string

       -state-decl string

       -state-ref string

       -string-varname string

       provide code snippets which help to glue framework and generated code together. Their placeholders are in the generated code.

   EXAMPLE
       We are forgoing an example of this representation, with apologies.  It would be way to large for this document.

PEG SERIALIZATION FORMAT

       Here we specify the format used by the Parser Tools to serialize Parsing Expression Grammars as immutable values for transport, comparison,
       etc.

       We  distinguish between regular and canonical serializations.  While a PEG may have more than one regular serialization only exactly one of
       them will be canonical.

       regular serialization

	      [1]    The serialization of any PEG is a nested Tcl dictionary.

	      [2]    This dictionary holds a single key, pt::grammar::peg, and its value. This value holds the contents of the grammar.

	      [3]    The contents of the grammar are a Tcl dictionary holding the set of nonterminal symbols and the starting expression. The rel-
		     evant keys and their values are

		     rules  The value is a Tcl dictionary whose keys are the names of the nonterminal symbols known to the grammar.

			    [1]    Each nonterminal symbol may occur only once.

			    [2]    The empty string is not a legal nonterminal symbol.

			    [3]    The value for each symbol is a Tcl dictionary itself. The relevant keys and their values in this dictionary are

				   is	  The value is the serialization of the parsing expression describing the symbols sentennial structure, as
					  specified in the section PE serialization format.

				   mode   The value can be one of three values specifying how a parser should handle the semantic  value  produced
					  by the symbol.

					  value  The  semantic	value  of the nonterminal symbol is an abstract syntax tree consisting of a single
						 node node for the nonterminal itself, which has the ASTs of the symbol's right hand side  as  its
						 children.

					  leaf	 The  semantic	value  of the nonterminal symbol is an abstract syntax tree consisting of a single
						 node node for the nonterminal, without any children. Any ASTs generated  by  the  symbol's  right
						 hand side are discarded.

					  void	 The  nonterminal  has	no  semantic value. Any ASTs generated by the symbol's right hand side are
						 discarded (as well).

		     start  The value is the serialization of the start parsing expression of the grammar, as specified in the section PE  serial-
			    ization format.

	      [4]    The  terminal symbols of the grammar are specified implicitly as the set of all terminal symbols used in the start expression
		     and on the RHS of the grammar rules.

       canonical serialization
	      The canonical serialization of a grammar has the format as specified in the previous item, and then additionally satisfies the  con-
	      straints below, which make it unique among all the possible serializations of this grammar.

	      [1]    The  keys	found  in  all the nested Tcl dictionaries are sorted in ascending dictionary order, as generated by Tcl's builtin
		     command lsort -increasing -dict.

	      [2]    The string representation of the value is the canonical representation of a Tcl dictionary. I.e. it does not  contain  super-
		     fluous whitespace.

   EXAMPLE
       Assuming the following PEG for simple mathematical expressions

       PEG calculator (Expression)
	   Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'   ;
	   Sign       <- '-' / '+'			 ;
	   Number     <- Sign? Digit+			      ;
	   Expression <- '(' Expression ')' / (Factor (MulOp Factor)*)	;
	   MulOp      <- '*' / '/'			 ;
	   Factor     <- Term (AddOp Term)*		      ;
	   AddOp      <- '+'/'-'			 ;
	   Term       <- Number 		    ;
       END;

       then its canonical serialization (except for whitespace) is

       pt::grammar::peg {
	   rules {
	    AddOp      {is {/ {t -} {t +}}								  mode value}
	    Digit      {is {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}		  mode value}
	    Expression {is {/ {x {t (} {n Expression} {t )}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}} mode value}
	    Factor     {is {x {n Term} {* {x {n AddOp} {n Term}}}}					  mode value}
	    MulOp      {is {/ {t *} {t /}}								  mode value}
	    Number     {is {x {? {n Sign}} {+ {n Digit}}}						  mode value}
	    Sign       {is {/ {t -} {t +}}								  mode value}
	    Term       {is  {n Number}									  mode value}
	   }
	   start {n Expression}
       }

PE SERIALIZATION FORMAT

       Here we specify the format used by the Parser Tools to serialize Parsing Expressions as immutable values for transport, comparison, etc.

       We  distinguish between regular and canonical serializations.  While a parsing expression may have more than one regular serialization only
       exactly one of them will be canonical.

       Regular serialization

	      Atomic Parsing Expressions

		     [1]    The string epsilon is an atomic parsing expression. It matches the empty string.

		     [2]    The string dot is an atomic parsing expression. It matches any character.

		     [3]    The string alnum is an atomic parsing expression. It matches any Unicode alphabet or digit character. This is a custom
			    extension of PEs based on Tcl's builtin command string is.

		     [4]    The  string  alpha is an atomic parsing expression. It matches any Unicode alphabet character. This is a custom exten-
			    sion of PEs based on Tcl's builtin command string is.

		     [5]    The string ascii is an atomic parsing expression. It matches any Unicode character	below  U0080.  This  is  a  custom
			    extension of PEs based on Tcl's builtin command string is.

		     [6]    The  string control is an atomic parsing expression. It matches any Unicode control character. This is a custom exten-
			    sion of PEs based on Tcl's builtin command string is.

		     [7]    The string digit is an atomic parsing expression. It matches any Unicode digit  character.	Note  that  this  includes
			    characters outside of the [0..9] range. This is a custom extension of PEs based on Tcl's builtin command string is.

		     [8]    The string graph is an atomic parsing expression. It matches any Unicode printing character, except for space. This is
			    a custom extension of PEs based on Tcl's builtin command string is.

		     [9]    The string lower is an atomic parsing expression. It matches any Unicode lower-case alphabet character. This is a cus-
			    tom extension of PEs based on Tcl's builtin command string is.

		     [10]   The  string print is an atomic parsing expression. It matches any Unicode printing character, including space. This is
			    a custom extension of PEs based on Tcl's builtin command string is.

		     [11]   The string punct is an atomic parsing expression. It matches any Unicode  punctuation  character.  This  is  a  custom
			    extension of PEs based on Tcl's builtin command string is.

		     [12]   The  string  space is an atomic parsing expression. It matches any Unicode space character. This is a custom extension
			    of PEs based on Tcl's builtin command string is.

		     [13]   The string upper is an atomic parsing expression. It matches any Unicode upper-case alphabet character. This is a cus-
			    tom extension of PEs based on Tcl's builtin command string is.

		     [14]   The  string  wordchar is an atomic parsing expression. It matches any Unicode word character. This is any alphanumeric
			    character (see alnum), and any connector punctuation characters (e.g.  underscore). This is a custom extension of  PEs
			    based on Tcl's builtin command string is.

		     [15]   The string xdigit is an atomic parsing expression. It matches any hexadecimal digit character. This is a custom exten-
			    sion of PEs based on Tcl's builtin command string is.

		     [16]   The string ddigit is an atomic parsing expression. It matches any decimal digit character. This is a custom  extension
			    of PEs based on Tcl's builtin command regexp.

		     [17]   The expression [list t x] is an atomic parsing expression. It matches the terminal string x.

		     [18]   The expression [list n A] is an atomic parsing expression. It matches the nonterminal A.

	      Combined Parsing Expressions

		     [1]    For  parsing  expressions  e1, e2, ... the result of [list / e1 e2 ... ] is a parsing expression as well.  This is the
			    ordered choice, aka prioritized choice.

		     [2]    For parsing expressions e1, e2, ... the result of [list x e1 e2 ... ] is a parsing expression as well.   This  is  the
			    sequence.

		     [3]    For  a  parsing  expression  e  the result of [list * e] is a parsing expression as well.  This is the kleene closure,
			    describing zero or more repetitions.

		     [4]    For a parsing expression e the result of [list + e] is a parsing expression as well.  This is the positive kleene clo-
			    sure, describing one or more repetitions.

		     [5]    For a parsing expression e the result of [list & e] is a parsing expression as well.  This is the and lookahead predi-
			    cate.

		     [6]    For a parsing expression e the result of [list ! e] is a parsing expression as well.  This is the not lookahead predi-
			    cate.

		     [7]    For a parsing expression e the result of [list ? e] is a parsing expression as well.  This is the optional input.

       Canonical serialization
	      The  canonical  serialization of a parsing expression has the format as specified in the previous item, and then additionally satis-
	      fies the constraints below, which make it unique among all the possible serializations of this parsing expression.

	      [1]    The string representation of the value is the canonical representation of a pure Tcl list. I.e. it does not contain superflu-
		     ous whitespace.

	      [2]    Terminals are not encoded as ranges (where start and end of the range are identical).

   EXAMPLE
       Assuming the parsing expression shown on the right-hand side of the rule

	   Expression <- '(' Expression ')'
		       / Factor (MulOp Factor)*

       then its canonical serialization (except for whitespace) is

	   {/ {x {t (} {n Expression} {t )}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}}

BUGS, IDEAS, FEEDBACK
       This  document,	and  the package it describes, will undoubtedly contain bugs and other problems.  Please report such in the category pt of
       the Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883].  Please also report any ideas for enhancements you  may  have  for
       either package and/or documentation.

KEYWORDS

       CPARAM,	EBNF,  LL(k),  PEG,  TDPL,  context-free  languages, conversion, expression, format conversion, grammar, matching, parser, parsing
       expression, parsing expression grammar, push down automaton, recursive descent, serialization, state, top-down  parsing	languages,  trans-
       ducer

CATEGORY

       Parsing and Grammars

COPYRIGHT

       Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>

pt								       1.0.1						    pt::peg::to::cparam(n)