pt_import_api(i)                 Parser Tools                 pt_import_api(i)



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NAME
       pt_import_api - Parser Tools Import API

SYNOPSIS
       package require Tcl  8.5

       CONVERTER convert text

       IncludeFile currentfile path

       ::import text

_________________________________________________________________

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 some other format into Parsing Expression
       Grammars , and then the API shared by the packages which implement the
       import plugins sitting on top of the conversion packages.

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

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

       IMAGE: arch_core_import

CONVERTER API
       Any (grammar) import 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::from 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 single method
              with the given signature and semantic. Converter commands are
              allowed to provide more methods of their own, but not less, and
              they may not provide different semantics for the standardized
              method.

              CONVERTER convert text
                     This method has to accept some text, a parsing expression
                     grammar in some format.  The result of the method has to
                     be the canonical serialization of a parsing expression
                     grammar, as specified in section PEG serialization
                     format, the result of reading and converting the input
                     text.

PLUGIN API
       Any (grammar) import 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::import::FOO,
              where FOO is the name of the format the plugin will accept input
              for.

       [3]    The plugin can expect that the package pt::peg::import::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]    The plugin can expect that a command named IncludeFile is
              present, with the signature

              IncludeFile currentfile path
                     This command has to be invoked by the plugin when it has
                     to process an included file, if the format has the
                     concept of such.

                     The plugin has to supply the following arguments

                     string currentfile
                            The path of the file it is currently processing.
                            This may be the empty string if no such is known.

                     string path
                            The path of the include file as specified in the
                            include directive being processed.
              The result of the command will be a 5-element list containing

                     [1]    A boolean flag indicating the success (True) or
                            failure (False) of the operation.

                     [2]    In case of success the contents of the included
                            file, and the empty string otherwise.

                     [3]    The resolved, i.e. absolute path of the included
                            file, if possible, or the unchanged path argument.
                            This is for display in an error message, or as the
                            currentfile argument of another call to
                            IncludeFile should this file contain more files.

                     [4]    In case of success an empty string, and for
                            failure a code indicating the reason for it, one
                            of

                            notfound
                                   The specified file could not be found.

                            notread
                                   The specified file was found, but not be
                                   read into memory.

                     [5]    An empty string in case of success of a notfound
                            failure, and an additional error message
                            describing the reason for a notread error in more
                            detail.

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

              ::import text
                     This command has to accept the a text containing a
                     parsing expression grammar in some format. The result of
                     the command has to be the result of the converter invoked
                     by the plugin for the input grammar, the canonical
                     serialization of the parsing expression grammar contained
                     in the input.

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

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

USAGE
       To use a converter do

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

                  # Perform the conversion
                  set serial [theconverter convert $thegrammartext]

                  ... process the result ...

       To use a plugin FOO do

                  # Get an import plugin manager
                  package require pt::peg::import
                  pt::peg::import I

                  # Run the plugin, and the converter inside.
                  set serial [I import serial $thegrammartext 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 <- '(' 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_import_api(i)
