pt::pe::op(n)							   Parser Tools 						     pt::pe::op(n)

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NAME

       pt::pe::op - Parsing Expression Utilities

SYNOPSIS

       package require Tcl  8.5

       package require pt::pe::op  ?1?

       package require pt::pe  ?1?

       package require struct::set

       ::pt::pe::op drop dropset pe

       ::pt::pe::op rename nt ntnew pe

       ::pt::pe::op called pe

       ::pt::pe::op flatten pe

       ::pt::pe::op fusechars pe

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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 provides additional commands to work with the serializations of parsing expressions as managed by the PEG  and  related  pack-
       ages, and specified in section PE serialization format.

       This is an internal package, for use by the higher level packages handling PEGs, their conversion into and out of various other formats, or
       other uses.

API

       ::pt::pe::op drop dropset pe
	      This command removes all occurences of any of the nonterminals symbols in the set dropset from the parsing expression pe,  and  sim-
	      plifies it. This may result in the expression becoming "epsilon", i.e. matching nothing.

       ::pt::pe::op rename nt ntnew pe
	      This command renames all occurences of the nonterminal nt in the parsing expression pe into ntnew.

       ::pt::pe::op called pe
	      This command extracts the set of all nonterminal symbols used, i.e. 'called', in the parsing expression pe.

       ::pt::pe::op flatten pe
	      This  command  transforms  the  parsing expression by eliminating sequences nested in sequences, and choices in choices, lifting the
	      children of the nested expression into the parent. It further eliminates all sequences and choices with only one child, as these are
	      redundant.

	      The resulting parsing expression is returned as the result of the command.

       ::pt::pe::op fusechars pe
	      This  command  transforms  the  parsing  expression  by  fusing adjacent terminals in sequences and adjacent terminals and ranges in
	      choices, it (re)constructs highlevel strings and character classes.

	      The resulting pseudo-parsing expression is returned as the result of the command and may contain the pseudo-operators str for  char-
	      acter sequences, aka strings, and cl for character choices, aka character classes.

	      The  result  is  called  a pseudo-parsing expression because it is not a true parsing expression anymore, and will fail a check with
	      ::pt::peg verify if the new pseudo-operators are present in the result, but is otherwise of sound structure for  a  parsing  expres-
	      sion.  Notably, the commands ::pt::peg bottomup and ::pt::peg topdown will process them without trouble.

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

       EBNF, LL(k), PEG, TDPL, context-free languages, expression, grammar, matching, parser, parsing expression, parsing expression grammar, push
       down automaton, recursive descent, state, top-down parsing languages, transducer

CATEGORY

       Parsing and Grammars

COPYRIGHT

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

pt									 1							     pt::pe::op(n)