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



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NAME
       pt::peg::to::container - PEG Conversion. Write CONTAINER format

SYNOPSIS
       package require Tcl  8.5

       package require pt::peg::to::container  ?1?

       package require pt::peg

       package require text::write

       package require char

       pt::peg::to::container reset

       pt::peg::to::container configure

       pt::peg::to::container configure option

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

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

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

       pt::peg::to::container 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::container 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::container 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 CONTAINER 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 the CONTAINER format recognizes the following options
       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.

       -mode bulk|incremental
              The value of this option controls which methods of
              pt::peg::container instances are used to specify the grammar,
              i.e. preload it into the container. There are two legal values,
              as listed below. The default is bulk.

              bulk   In this mode the methods start, add, modes, and rules are
                     used to specify the grammar in a bulk manner, i.e. as a
                     set of nonterminal symbols, and two dictionaries mapping
                     from the symbols to their semantic modes and parsing
                     expressions.

                     This mode is the default.

              incremental
                     In this mode the methods start, add, mode, and rule are
                     used to specify the grammar piecemal, with each
                     nonterminal having its own block of defining commands.

       -template string
              The value of this option is a string into which to put the
              generated code and the other configuration settings. The various
              locations 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 CONTAINER.

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

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

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

              @code@ To be replaced with the generated code.

GRAMMAR CONTAINER
       The container format is another form of describing parsing expression
       grammars. While data in this format is executable it does not
       constitute a parser for the grammar. It always has to be used in
       conjunction with the package pt::peg::interp, a grammar interpreter.

       The format represents grammars by a snit::type, i.e. class, whose
       instances are API-compatible to the instances of the pt::peg::container
       package, and which are preloaded with the grammar in question.

       It has no direct formal specification beyond what was said above.

   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;


       one possible CONTAINER serialization for it is

              snit::type a_pe_grammar {
                  constructor {} {
                      install myg using pt::peg::container ${selfns}::G
                      $myg start {n Expression}
                      $myg add   AddOp Digit Expression Factor MulOp Number Sign Term
                      $myg modes {
                          AddOp      value
                          Digit      value
                          Expression value
                          Factor     value
                          MulOp      value
                          Number     value
                          Sign       value
                          Term       value
                      }
                      $myg rules {
                          AddOp      {/ {t -} {t +}}
                          Digit      {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}
                          Expression {/ {x {t \50} {n Expression} {t \51}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}}
                          Factor     {x {n Term} {* {x {n AddOp} {n Term}}}}
                          MulOp      {/ {t *} {t /}}
                          Number     {x {? {n Sign}} {+ {n Digit}}}
                          Sign       {/ {t -} {t +}}
                          Term       {n Number}
                      }
                      return
                  }

                  component myg
                  delegate method * to myg
              }


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 relevant 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 serialization 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 constraints 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 superfluous 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 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
                            expression. 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
                            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 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 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 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 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 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
                     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://sourceforge.net/tracker/?group_id=12883].
       Please also report any ideas for enhancements you may have for either
       package and/or documentation.

KEYWORDS
       CONTAINER, 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, transducer

CATEGORY
       Parsing and Grammars

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




pt                                     1             pt::peg::to::container(n)
