pt::peg::export(n)               Parser Tools               pt::peg::export(n)



______________________________________________________________________________

NAME
       pt::peg::export - PEG Export

SYNOPSIS
       package require Tcl  8.5

       package require snit

       package require configuration

       package require pt::peg

       package require pluginmgr

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

       ::pt::peg::export objectName

       objectName method ?arg arg ...?

       objectName destroy

       objectName export serial serial ?format?

       objectName export object object ?format?

       objectName configuration names

       objectName configuration get

       objectName configuration set name ?value?

       objectName configuration unset pattern...

_________________________________________________________________

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 a manager for parsing expression grammars, with
       each instance handling a set of plugins for the export of them to other
       formats, i.e. their conversion to, for example nroff, HTML, etc.

       It resides in the Export section of the Core Layer of Parser Tools, and
       is one of the three pillars the management of parsing expression
       grammars resides on.

       IMAGE: arch_core_export

       The other two pillars are, as shown above

       [1]    PEG Import, and

       [2]    PEG Storage

       For information about the data structure which is the major input to
       the manager objects provided by this package see the section PEG
       serialization format.

       The plugin system of this class is based on the package pluginmgr, and
       configured to look for plugins using

       [1]    the environment variable GRAMMAR_PEG_EXPORT_PLUGINS,

       [2]    the environment variable GRAMMAR_PEG_PLUGINS,

       [3]    the environment variable GRAMMAR_PLUGINS,

       [4]    the path "~/.grammar/peg/export/plugin"

       [5]    the path "~/.grammar/peg/plugin"

       [6]    the path "~/.grammar/plugin"

       [7]    the path "~/.grammar/peg/export/plugins"

       [8]    the path "~/.grammar/peg/plugins"

       [9]    the path "~/.grammar/plugins"

       [10]   the registry entry
              "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\EXPORT\PLUGINS"

       [11]   the registry entry
              "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\PLUGINS"

       [12]   the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PLUGINS"

       The last three are used only when the package is run on a machine using
       the Windows(tm) operating system.

       The whole system is delivered with three predefined export plugins,
       namely

       container
              See PEG Export Plugin. To CONTAINER format for details.

       json   See PEG Export Plugin. To JSON format for details.

       peg    See PEG Export Plugin. To PEG format for details.

       For readers wishing to write their own export plugin for some format,
       i.e. plugin writers, reading and understanding the Parser Tools Export
       API specification is an absolute necessity, as it documents the
       interaction between this package and its plugins in detail.

API
   PACKAGE COMMANDS
       ::pt::peg::export objectName
              This command creates a new export manager object with an
              associated Tcl command whose name is objectName. This object
              command is explained in full detail in the sections Object
              command and Object methods. The object command will be created
              under the current namespace if the objectName is not fully
              qualified, and in the specified namespace otherwise.

   OBJECT COMMAND
       All objects created by the ::pt::peg::export command have the following
       general form:

       objectName method ?arg arg ...?
              The method method and its arg'uments determine the exact
              behavior of the command.  See section Object methods for the
              detailed specifications.

   OBJECT METHODS
       objectName destroy
              This method destroys the object it is invoked for.

       objectName export serial serial ?format?
              This method takes the canonical serialization of a parsing
              expression grammar stored in serial and converts it to the
              specified format, using the export plugin for the format. This
              will fail with an error if no plugin could be found for the
              format.  The string generated by the conversion process is
              returned as the result of this method.

              If no format is specified the method defaults to text.

              The specification of what a canonical serialization is can be
              found in the section PEG serialization format.

              The plugin has to conform to the interface documented in the
              Parser Tools Export API specification.

       objectName export object object ?format?
              This method is a convenient wrapper around the export serial
              method described by the previous item.  It expects that object
              is an object command supporting a serialize method returning the
              canonical serialization of a parsing expression grammar. It
              invokes that method, feeds the result into export serial and
              returns the resulting string as its own result.

       objectName configuration names
              This method returns a list containing the names of all
              configuration options currently known to the object.

       objectName configuration get
              This method returns a dictionary containing the names and values
              of all configuration options currently known to the object.

       objectName configuration set name ?value?
              This method sets the configuration option name to the specified
              value and returns the new value of the option.

              If no value is specified it simply returns the current value,
              without changing it.

              Note that these configuration options and their values are
              simply passed to a plugin when the actual export is performed.
              It is the plugin which checks the validity, not the manager.

       objectName configuration unset pattern...
              This method unsets all configuration options matching the
              specified glob patterns. If no pattern is specified it will
              unset all currently defined configuration options.

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
       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::peg::export(n)
