pt_export_api(i)                 Parser Tools                 pt_export_api(i)



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NAME
       pt_export_api - Parser Tools Export API

SYNOPSIS
       package require Tcl  8.5

       CONVERTER reset

       CONVERTER configure

       CONVERTER configure option

       CONVERTER configure option value...

       CONVERTER convert serial

       ::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 document describes two APIs. First the API shared by all packages
       for the conversion of Parsing Expression Grammars into some other
       format, and then the API shared by the packages which implement the
       export plugins sitting on top of the conversion packages.

       Its intended audience are people who wish to create their own converter
       for some type of output, and/or an export plugin for their or some
       other converter.

       It resides in the Export section of the Core Layer of Parser Tools.

       IMAGE: arch_core_export

CONVERTER API
       Any (grammar) export converter has to follow the rules set out below:

       [1]    A converter is a package. Its name is arbitrary, however it is
              recommended to put it under the ::pt::peg::to namespace.

       [2]    The package provides either a single Tcl command following the
              API outlined below, or a class command whose instances follow
              the same API. The commands which follow the API are called
              converter commands.

       [3]    A converter command has to provide the following three methods
              with the given signatures and semantics. Converter commands are
              allowed to provide more methods of their own, but not less, and
              they may not provide different semantics for the standardized
              methods.

              CONVERTER reset
                     This method has to reset the configuration of the
                     converter to its default settings. The result of the
                     method has to be the empty string.

              CONVERTER configure
                     This method, in this form, has to return a dictionary
                     containing the current configuration of the converter.

              CONVERTER configure option
                     This method, in this form, has to return the current
                     value of the specified configuration option of the
                     converter.

                     Please read the section Options for the set of standard
                     options any converter has to accept.  Any other options
                     accepted by a specific converter will be described in its
                     manpage.

              CONVERTER configure option value...
                     This command, in this form, sets the specified options of
                     the converter to the given values.

                     Please read the section Options for the set of standard
                     options a converter has to accept.  Any other options
                     accepted by a specific converter will be described in its
                     manpage.

              CONVERTER convert serial
                     This method has to accept the canonical serialization of
                     a parsing expression grammar, as specified in section PEG
                     serialization format, and contained in serial.  The
                     result of the method has to be the result of converting
                     the input grammar into whatever the converter is for, per
                     its configuration.

PLUGIN API
       Any (grammar) export plugin has to follow the rules set out below:

       [1]    A plugin is a package.

       [2]    The name of a plugin package has the form pt::peg::export::FOO,
              where FOO is the name of the format the plugin will generate
              output for.

       [3]    The plugin can expect that the package pt::peg::export::plugin
              is present, as indicator that it was invoked from a genuine
              plugin manager.

              It is recommended that a plugin does check for the presence of
              this package.

       [4]    A plugin has to provide a single command, in the global
              namespace, with the signature shown below. Plugins are allowed
              to provide more command of their own, but not less, and they may
              not provide different semantics for the standardized command.

              ::export serial configuration
                     This command has to accept the canonical serialization of
                     a parsing expression grammar and the configuration for
                     the converter invoked by the plugin. The result of the
                     command has to be the result of the converter invoked by
                     the plugin for th input grammar and configuration.

                     string serial
                            This argument will contain the canonical
                            serialization of the parsing expression grammar
                            for which to generate the output.  The
                            specification of what a canonical serialization is
                            can be found in the section PEG serialization
                            format.

                     dictionary configuration
                            This argument will contain the configuration to
                            configure the converter with before invoking it,
                            as a dictionary mapping from options to values.

                            Please read the section Options for the set of
                            standard options any converter has to accept, and
                            thus any plugin as well.  Any other options
                            accepted by a specific plugin will be described in
                            its manpage.

       [5]    A single usage cycle of a plugin consists of an invokation of
              the command export. This call has to leave the plugin in a state
              where another usage cycle can be run without problems.

OPTIONS
       Each export converter and plugin for an export converter has to accept
       the options below in their configure method. Converters are allowed to
       ignore the contents of these options when performing a conversion, but
       they must not reject them. Plugins are expected to pass the options
       given to them to the converter they are invoking.

       -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.

USAGE
       To use a converter do


                  # Get the converter (single command here, not class)
                  package require the-converter-package

                  # Provide a configuration
                  theconverter configure ...

                  # Perform the conversion
                  set result [theconverter convert $thegrammarserial]

                  ... process the result ...

       To use a plugin FOO do


                  # Get an export plugin manager
                  package require pt::peg::export
                  pt::peg::export E

                  # Provide a configuration
                  E configuration set ...

                  # Run the plugin, and the converter inside.
                  set result [E export serial $grammarserial FOO]

                  ... process the result ...


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
       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_export_api(i)
