pt_pexpr_op(3)



pt::pe::op(3tcl)                 Parser Tools                 pt::pe::op(3tcl)

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NAME
       pt::pe::op - Parsing Expression Utilities

SYNOPSIS
       package require Tcl  8.5

       package require pt::pe::op  ?1.0.1?

       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  serializa-
       tions  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  han-
       dling  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
              simplifies it. This may result in the expression  becoming  "ep-
              silon", 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 fur-
              ther 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  adja-
              cent 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 re-
              sult of the command and may contain the pseudo-operators str for
              character  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
              expression.   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 Pars-
       ing 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  expres-
                            sion. 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 charac-
                            ter. 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  extension 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 expres-
                            sion. It matches any  Unicode  control  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 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 charac-
                            ter.  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 printing character, includ-
                            ing 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 charac-
                            ter.  This  is  a custom extension of PEs based on
                            Tcl's builtin command string is.

                     [14]   The string wordchar is an atomic  parsing  expres-
                            sion.  It matches any Unicode word character. This
                            is any alphanumeric character (see alnum), and any
                            connector  punctuation  characters  (e.g.   under-
                            score). 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 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 ex-
                            pression. It matches the terminal string x.

                     [18]   The expression [list n A] is an atomic parsing ex-
                            pression. 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  repeti-
                            tions.

                     [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 for-
              mat  as  specified  in  the previous 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  con-
                     tain 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 <- Term (AddOp Term)*

       then its canonical serialization (except for whitespace) is

                  {x {n Term} {* {x {n AddOp} {n Term}}}}

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  Trackers  [http://core.tcl.tk/tcllib/reportlist].   Please also
       report any ideas for enhancements  you  may  have  for  either  package
       and/or documentation.

       When proposing code changes, please provide unified diffs, i.e the out-
       put of diff -u.

       Note further that  attachments  are  strongly  preferred  over  inlined
       patches.  Attachments  can  be  made  by  going to the Edit form of the
       ticket immediately after its creation, and  then  using  the  left-most
       button in the secondary navigation bar.

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>

tcllib                               1.0.1                    pt::pe::op(3tcl)

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