Provided by: tcllib_1.21+dfsg-1_all bug

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   Trackers
       [http://core.tcl.tk/tcllib/reportlist].  Please also report any ideas for enhancements you
       may have for either package and/or documentation.

       When proposing code changes, please provide unified diffs, i.e the output of diff -u.

       Note further that attachments are strongly preferred over inlined patches. Attachments can
       be  made  by going to the Edit form of the ticket immediately after its creation, and then
       using the left-most button in the secondary navigation bar.

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>