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



____________________________________________________________________________________________________________

NAME
       pt::pe - Parsing Expression Serialization

SYNOPSIS
       package require Tcl  8.5

       package require pt::pe  ?1?

       package require char

       ::pt::pe verify serial ?canonvar?

       ::pt::pe verify-as-canonical serial

       ::pt::pe canonicalize serial

       ::pt::pe print serial

       ::pt::pe bottomup cmdprefix pe

       cmdprefix pe op arguments

       ::pt::pe topdown cmdprefix pe

       ::pt::pe equal seriala serialb

       ::pt::pe epsilon

       ::pt::pe dot

       ::pt::pe alnum

       ::pt::pe alpha

       ::pt::pe ascii

       ::pt::pe control

       ::pt::pe digit

       ::pt::pe graph

       ::pt::pe lower

       ::pt::pe print

       ::pt::pe punct

       ::pt::pe space

       ::pt::pe upper

       ::pt::pe wordchar

       ::pt::pe xdigit

       ::pt::pe ddigit

       ::pt::pe terminal t

       ::pt::pe range ta tb

       ::pt::pe nonterminal nt

       ::pt::pe choice pe...

       ::pt::pe sequence pe...

       ::pt::pe repeat0 pe

       ::pt::pe repeat1 pe

       ::pt::pe optional pe

       ::pt::pe ahead pe

       ::pt::pe notahead pe

____________________________________________________________________________________________________________

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

       This  package  provides commands to work with the serializations of parsing expressions as managed by
       the Parser Tools, and specified in section PE serialization format.

       This is a supporting package in the Core Layer of Parser Tools.

       IMAGE: arch_core_support


API
       ::pt::pe verify serial ?canonvar?
              This command verifies that the content of serial is a valid serialization of a parsing expres-sion expression
              sion  and  will throw an error if that is not the case. The result of the command is the empty
              string.

              If the argument canonvar is specified it is interpreted as the name of a variable in the call-ing calling
              ing context. This variable will be written to if and only if serial is a valid regular serial-ization. serialization.
              ization. Its value will be a boolean, with True indicating that the serialization is not  only
              valid, but also canonical. False will be written for a valid, but non-canonical serialization.

              For the specification of serializations see the section PE serialization format.

       ::pt::pe verify-as-canonical serial
              This command verifies that the content of serial is a valid canonical serialization of a pars-ing parsing
              ing  expression  and will throw an error if that is not the case. The result of the command is
              the empty string.

              For the specification of canonical serializations see the section PE serialization format.

       ::pt::pe canonicalize serial
              This command assumes that the content of serial is a valid regular serialization of a  parsing
              expression and will throw an error if that is not the case.

              It will then convert the input into the canonical serialization of this parsing expression and
              return it as its result. If the input is already canonical it will be returned unchanged.

              For the specification of regular and canonical serializations see the section PE serialization
              format.

       ::pt::pe print serial
              This  command  assumes  that  the  argument serial contains a valid serialization of a parsing
              expression and returns a string containing that PE in a human readable form.

              The exact format of this form is not specified and cannot be relied on for  parsing  or  other
              machine-based activities.

              For the specification of serializations see the section PE serialization format.

       ::pt::pe bottomup cmdprefix pe
              This command walks the parsing expression pe from the bottom up to the root, invoking the com-mand command
              mand prefix cmdprefix for each partial expression. This implies that the children of a parsing
              expression PE are handled before PE.

              The command prefix has the signature

              cmdprefix pe op arguments
                     I.e. it is invoked with the parsing expression pe the walk is currently at, the op'era-tor op'erator
                     tor in the pe, and the operator's arguments.

                     The result returned by the command prefix replaces pe in the parsing expression it  was
                     a child of, allowing transformations of the expression tree.

                     This  also  means  that for all inner parsing expressions the contents of arguments are
                     the results of the command prefix invoked  for  the  children  of  this  inner  parsing
                     expression.

       ::pt::pe topdown cmdprefix pe
              This  command  walks  the parsing expression pe from the root down to the leaves, invoking the
              command prefix cmdprefix for each partial expression. This implies  that  the  children  of  a
              parsing expression PE are handled after PE.

              The command prefix has the same signature as for bottomup, see above.

              The result returned by the command prefix is ignored.

       ::pt::pe equal seriala serialb
              This  command  tests  the two parsing expressions seriala and serialb for structural equality.
              The result of the command is a boolean value. It will be set to true if  the  expressions  are
              identical, and false otherwise.

              String  equality is usable only if we can assume that the two parsing expressions are pure Tcl
              lists.

       ::pt::pe epsilon
              This command constructs the atomic parsing expression for epsilon.

       ::pt::pe dot
              This command constructs the atomic parsing expression for dot.

       ::pt::pe alnum
              This command constructs the atomic parsing expression for alnum.

       ::pt::pe alpha
              This command constructs the atomic parsing expression for alpha.

       ::pt::pe ascii
              This command constructs the atomic parsing expression for ascii.

       ::pt::pe control
              This command constructs the atomic parsing expression for control.

       ::pt::pe digit
              This command constructs the atomic parsing expression for digit.

       ::pt::pe graph
              This command constructs the atomic parsing expression for graph.

       ::pt::pe lower
              This command constructs the atomic parsing expression for lower.

       ::pt::pe print
              This command constructs the atomic parsing expression for print.

       ::pt::pe punct
              This command constructs the atomic parsing expression for punct.

       ::pt::pe space
              This command constructs the atomic parsing expression for space.

       ::pt::pe upper
              This command constructs the atomic parsing expression for upper.

       ::pt::pe wordchar
              This command constructs the atomic parsing expression for wordchar.

       ::pt::pe xdigit
              This command constructs the atomic parsing expression for xdigit.

       ::pt::pe ddigit
              This command constructs the atomic parsing expression for ddigit.

       ::pt::pe terminal t
              This command constructs the atomic parsing expression for the terminal symbol t.

       ::pt::pe range ta tb
              This command constructs the atomic parsing expression for the range of terminal symbols ta ...
              tb.

       ::pt::pe nonterminal nt
              This command constructs the atomic parsing expression for the nonterminal symbol nt.

       ::pt::pe choice pe...
              This  command constructs the parsing expression representing the ordered or prioritized choice
              between the argument parsing expressions. The first argument has the highest priority.

       ::pt::pe sequence pe...
              This command constructs the parsing expression representing the sequence of the argument pars-ing parsing
              ing expression. The first argument is the first element of the sequence.

       ::pt::pe repeat0 pe
              This command constructs the parsing expression representing the zero or more repetition of the
              argument parsing expression pe, also known as the kleene closure.

       ::pt::pe repeat1 pe
              This command constructs the parsing expression representing the one or more repetition of  the
              argument parsing expression pe, also known as the positive kleene closure.

       ::pt::pe optional pe
              This  command  constructs  the parsing expression representing the optionality of the argument
              parsing expression pe.

       ::pt::pe ahead pe
              This command constructs the parsing expression representing  the  positive  lookahead  of  the
              argument parsing expression pe.

       ::pt::pe notahead pe
              This  command  constructs  the  parsing  expression representing the negative lookahead of the
              argument parsing expression pe.


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 alpha-bet alphabet
                            bet 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 alpha-bet alphabet
                            bet character. This is a custom extension of PEs based on Tcl's builtin  command
                            string is.

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

                     [6]    The  string control is an atomic parsing expression. It matches any Unicode con-trol control
                            trol character. This is a custom extension 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 print-ing printing
                            ing 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 lowercase
                            case alphabet character. This is a  custom  extension  of  PEs  based  on  Tcl's
                            builtin command string is.

                     [10]   The  string print is an atomic parsing expression. It matches any Unicode print-ing printing
                            ing 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 punctu-ation punctuation
                            ation character. This is a custom extension of PEs based on Tcl's  builtin  com-mand command
                            mand 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 uppercase
                            case alphabet character. This is a  custom  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 extension of PEs based on Tcl's builtin com-mand command
                            mand 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 reg-exp. regexp.
                            exp.

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

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

              Combined Parsing Expressions

                     [1]    For parsing expressions e1, e2, ... the result of [list / e1 e2 ... ] is a pars-ing parsing
                            ing 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 pars-ing parsing
                            ing 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 closure, 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 predicate.

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

                     [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  previ-ous previous
              ous  item,  and  then additionally satisfies 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 superfluous 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://source -
       forge.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 pars-ing parsing
       ing languages, transducer

CATEGORY
       Parsing and Grammars

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




pt                                                    1                                            pt::pe(n)