Provided by: tcllib_1.14-dfsg-1_all bug

NAME

       pt::peg::export::container - PEG Export Plugin. Write CONTAINER format

SYNOPSIS

       package require Tcl  8.5

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

       package require pt::peg::to::container

       export serial configuration

_________________________________________________________________

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 parsing expression grammar export plugin for the generation of
       CONTAINER markup.

       It resides in the Export section of the Core Layer of Parser Tools and is intended  to  be
       used by pt::peg::export, the export manager, sitting between it and the corresponding core
       conversion functionality provided by pt::peg::to::container.

       IMAGE: arch_core_eplugins

       While the direct use of this package with a  regular  interpreter  is  possible,  this  is
       strongly  disrecommended  and  requires  a  number  of contortions to provide the expected
       environment.  The proper way to use this functionality depends on the situation:

       [1]    In  an  untrusted  environment  the  proper   access   is   through   the   package
              pt::peg::export and the export manager objects it provides.

       [2]    In  a trusted environment however simply use the package pt::peg::to::container and
              access the core conversion functionality directly.

API

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

       export serial configuration
              This  command takes the canonical serialization of a parsing expression grammar, as
              specified in section  PEG  serialization  format,  and  contained  in  serial,  the
              configuration,  a  dictionary, and generates CONTAINER markup encoding the grammar.
              The created string is then returned as the result of the command.

CONFIGURATION

       The CONTAINER export plugin recognizes the following configuration variables  and  changes
       its behaviour as they specify.

       enum mode
              The  value  of  this  configuration  variable  controls  which  methods  of pt::peg
              instances the plugin will use to specify the grammar. There are two legal values

              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.

       string template
              If  this configuration variable is set it is assumed to contain a string into which
              to put the generated code and other configuration data. The various  locations  are
              expected to be specified with the following placeholders:

              @user@ To be replaced with the value of the configuration variable user.

              @format@
                     To be replaced with the the constant CONTAINER.

              @file@ To be replaced with the value of the configuration variable file.

              @name@ To be replaced with the value of the configuration variable name.

              @mode@ To be replaced with the value of the configuration variable mode.

              @code@ To be replaced with the generated code.

       If  this  configuration  variable  is  not  set, or empty, then the plugin falls back to a
       standard template, which is defined as "@code@".

       Note that this plugin may ignore the standard configuration variables user, format,  file,
       and their values, depending on the chosen template.

       The  content  of  the standard configuration variable name, if set, is used as name of the
       grammar in the output. Otherwise the plugin falls back to the default name a_pe_grammar.

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 <- Term (AddOp Term)*                            ;
                  MulOp      <- '*' / '/'                                     ;
                  Term       <- Factor (MulOp Factor)*                        ;
                  AddOp      <- '+'/'-'                                       ;
                  Factor     <- '(' Expression ')' / 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 <- Term (AddOp Term)*                            ;
                  MulOp      <- '*' / '/'                                     ;
                  Term       <- Factor (MulOp Factor)*                        ;
                  AddOp      <- '+'/'-'                                       ;
                  Factor     <- '(' Expression ')' / 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 {n Term} {* {x {n AddOp} {n Term}}}}                                        mode value}
                      Factor     {is {/ {x {t (} {n Expression} {t )}} {n Number}}                                  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 {x {n Factor} {* {x {n MulOp} {n Factor}}}}                                    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 <- 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  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, export, expression, grammar,
       matching, parser, parsing  expression,  parsing  expression  grammar,  plugin,  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>