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



______________________________________________________________________________

NAME
       pt::peg::import - PEG Import

SYNOPSIS
       package require Tcl  8.5

       package require snit

       package require configuration

       package require pt::peg

       package require pluginmgr

       package require pt::peg::import  ?1?

       ::pt::peg::import objectName

       objectName method ?arg arg ...?

       objectName destroy

       objectName import text text ?format?

       objectName import file path ?format?

       objectName import object text object text ?format?

       objectName import object file object path ?format?

       objectName includes

       objectName include add path

       objectName include remove path

       objectName include clear

_________________________________________________________________

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 import of them from
       other formats, i.e. their conversion from, for example peg, container,
       json, etc.

       It resides in the Import 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_import

       The other two pillars are, as shown above

       [1]    PEG Export, and

       [2]    PEG Storage

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

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

       [1]    the environment variable GRAMMAR_PEG_IMPORT_PLUGINS,

       [2]    the environment variable GRAMMAR_PEG_PLUGINS,

       [3]    the environment variable GRAMMAR_PLUGINS,

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

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

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

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

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

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

       [10]   the registry entry
              "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\IMPORT\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 import plugins,
       namely

       container
              See PEG Import Plugin. From CONTAINER format for details.

       json   See PEG Import Plugin. From JSON format for details.

       peg    See PEG Import Plugin. From PEG format for details.

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

API
   PACKAGE COMMANDS
       ::pt::peg::import objectName
              This command creates a new import 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::import 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 import text text ?format?
              This method takes the text and converts it from the specified
              format to the canonical serialization of a parsing expression
              grammar using the import plugin for the format. An error is
              thrown if no plugin could be found for the format.  The
              serialization 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 Import API specification.

       objectName import file path ?format?
              This method is a convenient wrapper around the import text
              method described by the previous item.  It reads the contents of
              the specified file into memory, feeds the result into import
              text and returns the resulting serialization as its own result.

       objectName import object text object text ?format?
              This method is a convenient wrapper around the import text
              method described by the previous item.  It expects that object
              is an object command supporting a deserialize method expecting
              the canonical serialization of a parsing expression grammar.  It
              imports the text using import text and then feeds the resulting
              serialization into the object via deserialize.  This method
              returns the empty string as it result.

       objectName import object file object path ?format?
              This method behaves like import object text, except that it
              reads the text to convert from the specified file instead of
              being given it as argument.

       objectName includes
              This method returns a list containing the currently specified
              paths to use to search for include files when processing input.
              The order of paths in the list corresponds to the order in which
              they are used, from first to last, and also corresponds to the
              order in which they were added to the object.

       objectName include add path
              This methods adds the specified path to the list of paths to use
              to search for include files when processing input. The path is
              added to the end of the list, causing it to be searched after
              all previously added paths. The result of the command is the
              empty string.

              The method does nothing if the path is already known.

       objectName include remove path
              This methods removes the specified path from the list of paths
              to use to search for include files when processing input. The
              result of the command is the empty string.

              The method does nothing if the path is not known.

       objectName include clear
              This method clears the list of paths to use to search for
              include files when processing input. The result of the command
              is the empty string.

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::peg::import(n)
