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



______________________________________________________________________________

NAME
       pt::peg::container - PEG Storage

SYNOPSIS
       package require Tcl  8.5

       package require snit

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

       ::pt::peg objectName ?=|:=|<--|as|deserialize src?

       objectName destroy

       objectName clear

       objectName importer

       objectName importer object

       objectName exporter

       objectName exporter object

       objectName = source

       objectName --> destination

       objectName serialize ?format?

       objectName deserialize = data ?format?

       objectName deserialize += data ?format?

       objectName start

       objectName start pe

       objectName nonterminals

       objectName modes

       objectName modes dict

       objectName rules

       objectName rules dict

       objectName add ?nt...?

       objectName remove ?nt...?

       objectName exists nt

       objectName rename ntold ntnew

       objectName mode nt

       objectName mode nt mode

       objectName rule nt

       objectName rule nt pe

_________________________________________________________________

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 container class for parsing expression
       grammars, with each instance storing a single grammar and allowing the
       user to manipulate and query its definition.

       It resides in the Storage 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_container

       The other two pillars are, as shown above

       [1]    PEG Import, and

       [2]    PEG Export

       Packages related to this are:

       pt::rde
              This package provides an implementation of PARAM, a virtual
              machine for the parsing of a channel, geared towards the needs
              of handling PEGs.

       pt::peg::interp
              This package implements an interpreter for PEGs on top of the
              virtual machine provided by pt::peg::rde

   CLASS API
       The package exports the API described here.

       ::pt::peg objectName ?=|:=|<--|as|deserialize src?
              The command creates a new container object for a parsing
              expression grammar and returns the fully qualified name of the
              object command as its result. The API of this object command is
              described in the section Object API. It may be used to invoke
              various operations on the object.

              The new container will be empty if no src is specified.
              Otherwise it will contain a copy of the grammar contained in the
              src.  All operators except deserialize interpret src as a
              container object command. The deserialize operator interprets
              src as the serialization of a parsing expression grammar
              instead, as specified in section PEG serialization format.

              An empty grammar has no nonterminal symbols, and the start
              expression is the empty expression, i.e. epsilon. It is valid,
              but not useful.

   OBJECT API
       All objects created by this package provide the following methods for
       the manipulation and querying of their contents:

       objectName destroy
              This method destroys the object, releasing all claimed memory,
              and deleting the associated object command.

       objectName clear
              This method resets the object to contain the empty grammar. It
              does not destroy the object itself.

       objectName importer
              This method returns the import manager object currently attached
              to the container, if any.

       objectName importer object
              This method attaches the object as import manager to the
              container, and returns it as the result of the command.  Note
              that the object is not put into ownership of the container.
              I.e., destruction of the container will not destroy the object.

              It is expected that object provides a method named import text
              which takes a text and a format name, and returns the canonical
              serialization of the table of contents contained in the text,
              assuming the given format.

       objectName exporter
              This method returns the export manager object currently attached
              to the container, if any.

       objectName exporter object
              This method attaches the object as export manager to the
              container, and returns it as the result of the command.  Note
              that the object is not put into ownership of the container.
              I.e., destruction of the container will not destroy the object.

              It is expected that object provides a method named export object
              which takes the container and a format name, and returns a text
              encoding table of contents stored in the container, in the given
              format. It is further expected that the object will use the
              container's method serialize to obtain the serialization of the
              table of contents from which to generate the text.

       objectName = source
              This method assigns the contents of the PEG object source to
              ourselves, overwriting the existing definition. This is the
              assignment operator for grammars.

              This operation is in effect equivalent to



                  objectName deserialize = [source serialize]


       objectName --> destination
              This method assigns our contents to the PEG object destination,
              overwriting the existing definition. This is the reverse
              assignment operator for grammars.

              This operation is in effect equivalent to



                  destination deserialize = [objectName serialize]


       objectName serialize ?format?
              This method returns our grammar in some textual form usable for
              transfer, persistent storage, etc. If no format is not specified
              the returned result is the canonical serialization of the
              grammar, as specified in the section PEG serialization format.

              Otherwise the object will use the attached export manager to
              convert the data to the specified format. In that case the
              method will fail with an error if the container has no export
              manager attached to it.

       objectName deserialize = data ?format?
              This is the complementary method to serialize.  It replaces the
              current definition with the grammar contained in the data. If no
              format was specified it is assumed to be the regular
              serialization of a grammar, as specified in the section PEG
              serialization format

              Otherwise the object will use the attached import manager to
              convert the data from the specified format to a serialization it
              can handle.  In that case the method will fail with an error if
              the container has no import manager attached to it.

              The result of the method is the empty string.

       objectName deserialize += data ?format?
              This method behaves like deserialize = in its essentials, except
              that it merges the grammar in the data to its contents instead
              of replacing it.  The method will fail with an error and leave
              the grammar unchanged if merging is not possible, i.e. would
              produce an invalid grammar.

              The result of the method is the empty string.

       objectName start
              This method returns the current start expression of the grammar.

       objectName start pe
              This method defines the start expression of the grammar. It
              replaces the current start expression with the parsing
              expression pe, and returns the new start expression.

              The method will fail with an error and leave the grammar
              unchanged if pe does not contain a valid parsing expression as
              specified in the section PE serialization format.

       objectName nonterminals
              This method returns the set of all nonterminal symbols known to
              the grammar.

       objectName modes
              This method returns a dictionary mapping the set of all
              nonterminal symbols known to the grammar to their semantic
              modes.

       objectName modes dict
              This method takes a dictionary mapping a set of nonterminal
              symbols known to the grammar to their semantic modes, and
              returns the new full mapping of nonterminal symbols to semantic
              modes.

              The method will fail with an error if any of the nonterminal
              symbols in the dictionary is not known to the grammar, or the
              empty string, i.e. an invalid nonterminal symbol, or if any the
              chosen modes is not one of the legal values.

       objectName rules
              This method returns a dictionary mapping the set of all
              nonterminal symbols known to the grammar to their parsing
              expressions (right-hand sides).

       objectName rules dict
              This method takes a dictionary mapping a set of nonterminal
              symbols known to the grammar to their parsing expressions
              (right-hand sides), and returns the new full mapping of
              nonterminal symbols to parsing expressions.

              The method will fail with an error any of the nonterminal
              symbols in the dictionary is not known to the grammar, or the
              empty string, i.e. an invalid nonterminal symbol, or any of the
              chosen parsing expressions is not a valid parsing expression as
              specified in the section PE serialization format.

       objectName add ?nt...?
              This method adds the nonterminal symbols nt, etc. to the
              grammar, and defines default semantic mode and expression for it
              (value and epsilon respectively).  The method returns the empty
              string as its result.

              The method will fail with an error and leaves the grammar
              unchanged if any of the nonterminal symbols are either already
              defined in our grammar, or are the empty string (an invalid
              nonterminal symbol).

              The method does nothing if no symbol was specified as argument.

       objectName remove ?nt...?
              This method removes the named nonterminal symbols nt, etc. from
              the set of nonterminal symbols known to our grammar.  The method
              returns the empty string as its result.

              The method will fail with an error and leave the grammar
              unchanged if any of the nonterminal symbols is not known to the
              grammar, or is the empty string, i.e. an invalid nonterminal
              symbol.

       objectName exists nt
              This method tests whether the nonterminal symbol nt is known to
              our grammar or not.  The result is a boolean value. It will be
              set to true if nt is known, and false otherwise.

              The method will fail with an error if nt is the empty string,
              i.e. an invalid nonterminal symbol.

       objectName rename ntold ntnew
              This method renames the nonterminal symbol ntold to ntnew.  The
              method returns the empty string as its result.

              The method will fail with an error and leave the grammar
              unchanged if either ntold is not known to the grammar, or ntnew
              is already known, or any of them is the empty string, i.e. an
              invalid nonterminal symbol.

       objectName mode nt
              This method returns the current semantic mode for the
              nonterminal symbol nt.

              The method will fail with an error if nt is not known to the
              grammar, or the empty string, i.e. an invalid nonterminal
              symbol.

       objectName mode nt mode
              This mode sets the semantic mode for the nonterminal symbol nt,
              and returns the new mode.  The method will fail with an error if
              nt is not known to the grammar, or the empty string, i.e. an
              invalid nonterminal symbol, or the chosen mode is not one of the
              legal values.

              The following modes are legal:

              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).

       objectName rule nt
              This method returns the current parsing expression (right-hand
              side) for the nonterminal symbol nt.

              The method will fail with an error if nt is not known to the
              grammar, or the empty string, i.e. an invalid nonterminal
              symbol.

       objectName rule nt pe
              This method set the parsing expression (right-hand side) of the
              nonterminal nt to pe, and returns the new parsing expression.

              The method will fail with an error if nt is not known to the
              grammar, or the empty string, i.e. an invalid nonterminal
              symbol, or pe does not contain a valid parsing expression as
              specified in the section PE serialization format.

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::container(n)
