pt_peg_export(3)



pt::peg::export(3tcl)            Parser Tools            pt::peg::export(3tcl)

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NAME
       pt::peg::export - PEG Export

SYNOPSIS
       package require Tcl  8.5

       package require snit

       package require struct::map

       package require pt::peg

       package require pluginmgr

       package require pt::peg::export  ?1.0.1?

       ::pt::peg::export objectName

       objectName method ?arg arg ...?

       objectName destroy

       objectName export serial serial ?format?

       objectName export object object ?format?

       objectName configuration names

       objectName configuration get

       objectName configuration set name ?value?

       objectName configuration unset pattern...

______________________________________________________________________________

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 export of them to other
       formats, i.e. their conversion to, for example nroff, HTML, etc.

       It resides in the Export section of the Core Layer of Parser Tools, and
       is  one of the three pillars the management of parsing expression gram-
       mars resides on.

       IMAGE: arch_core_export

       The other two pillars are, as shown above

       [1]    PEG Import, and

       [2]    PEG Storage

       For information about the data structure which is the  major  input  to
       the  manager objects provided by this package see the section PEG seri-
       alization format.

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

       [1]    the environment variable GRAMMAR_PEG_EXPORT_PLUGINS,

       [2]    the environment variable GRAMMAR_PEG_PLUGINS,

       [3]    the environment variable GRAMMAR_PLUGINS,

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

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

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

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

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

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

       [10]   the  registry  entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\EX-
              PORT\PLUGINS"

       [11]   the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\PLUG-
              INS"

       [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  export  plugins,
       namely

       container
              See PEG Export Plugin. To CONTAINER format for details.

       json   See PEG Export Plugin. To JSON format for details.

       peg    See PEG Export Plugin. To PEG format for details.

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

API
   PACKAGE COMMANDS
       ::pt::peg::export objectName
              This command creates a new export manager object with an associ-
              ated  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::export command have the following
       general form:

       objectName method ?arg arg ...?
              The method method and its arg'uments determine the exact  behav-
              ior 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 export serial serial ?format?
              This method takes the canonical serialization of a  parsing  ex-
              pression  grammar stored in serial and converts it to the speci-
              fied format, using the export plugin for the format.  This  will
              fail  with  an error if no plugin could be found for the format.
              The string 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 Export API specification.

       objectName export object object ?format?
              This  method  is  a  convenient wrapper around the export serial
              method described by the previous item.  It expects  that  object
              is an object command supporting a serialize method returning the
              canonical serialization of a parsing expression grammar. It  in-
              vokes  that  method, feeds the result into export serial and re-
              turns the resulting string as its own result.

       objectName configuration names
              This method returns a list containing the names of all  configu-
              ration options currently known to the object.

       objectName configuration get
              This method returns a dictionary containing the names and values
              of all configuration options currently known to the object.

       objectName configuration set name ?value?
              This method sets the configuration option name to the  specified
              value and returns the new value of the option.

              If  no  value  is specified it simply returns the current value,
              without changing it.

              Note that these configuration options and their values are  sim-
              ply  passed  to a plugin when the actual export is performed. It
              is the plugin which checks the validity, not the manager.

       objectName configuration unset pattern...
              This method unsets all configuration options matching the speci-
              fied glob patterns. If no pattern is specified it will unset all
              currently defined configuration options.

PEG SERIALIZATION FORMAT
       Here we specify the format used by the Parser Tools to serialize  Pars-
       ing  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  expres-
                     sion. 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 dictio-
                                   nary 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  serial-
                                          ization format.

                                   mode   The value can be one of three values
                                          specifying how a parser should  han-
                                          dle  the  semantic value produced by
                                          the symbol.

                                          value  The  semantic  value  of  the
                                                 nonterminal  symbol is an ab-
                                                 stract 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  chil-
                                                 dren.

                                          leaf   The  semantic  value  of  the
                                                 nonterminal symbol is an  ab-
                                                 stract 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 seman-
                                                 tic value. Any ASTs generated
                                                 by the  symbol's  right  hand
                                                 side are discarded (as well).

                     start  The  value is the serialization of the start pars-
                            ing expression of the grammar, as specified in the
                            section PE serialization format.

              [4]    The terminal symbols of the grammar are specified implic-
                     itly 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 spec-
              ified 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 con-
                     tain 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  Pars-
       ing 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 expres-
                            sion. 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  charac-
                            ter.  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  expres-
                            sion.  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 charac-
                            ter. 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, includ-
                            ing 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 charac-
                            ter. This is a custom extension of  PEs  based  on
                            Tcl's builtin command string is.

                     [14]   The  string  wordchar is an atomic parsing expres-
                            sion. It matches any Unicode word character.  This
                            is any alphanumeric character (see alnum), and any
                            connector  punctuation  characters  (e.g.   under-
                            score). 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 ex-
                            pression. It matches the terminal string x.

                     [18]   The expression [list n A] is an atomic parsing ex-
                            pression. 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 repeti-
                            tions.

                     [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 for-
              mat 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 con-
                     tain 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 out-
       put 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>

tcllib                               1.0.1               pt::peg::export(3tcl)

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