pt_to_api(3)



pt_export_api(3tcl)              Parser Tools              pt_export_api(3tcl)

______________________________________________________________________________

NAME
       pt_export_api - Parser Tools Export API

SYNOPSIS
       package require Tcl  8.5

       CONVERTER reset

       CONVERTER configure

       CONVERTER configure option

       CONVERTER configure option value...

       CONVERTER convert serial

       ::export serial configuration

______________________________________________________________________________

DESCRIPTION
       Are  you  lost ?  Do you have trouble understanding this document ?  In
       that case please read the overview  provided  by  the  Introduction  to
       Parser  Tools.  This document is the entrypoint to the whole system the
       current package is a part of.

       This document describes two APIs. First the API shared by all  packages
       for  the conversion of Parsing Expression Grammars into some other for-
       mat, and then the API shared by the packages which implement the export
       plugins sitting on top of the conversion packages.

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

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

       IMAGE: arch_core_export

CONVERTER API
       Any (grammar) export converter has to follow the rules set out below:

       [1]    A  converter  is a package. Its name is arbitrary, however it is
              recommended to put it under the ::pt::peg::to namespace.

       [2]    The package provides either a single Tcl command  following  the
              API  outlined  below,  or a class command whose instances follow
              the same API. The commands which follow the API are called  con-
              verter commands.

       [3]    A  converter  command has to provide the following three methods
              with the given signatures and semantics. Converter commands  are
              allowed  to provide more methods of their own, but not less, and
              they may not provide different semantics  for  the  standardized
              methods.

              CONVERTER reset
                     This  method  has  to reset the configuration of the con-
                     verter to its default settings. The result of the  method
                     has to be the empty string.

              CONVERTER configure
                     This  method,  in  this  form, has to return a dictionary
                     containing the current configuration of the converter.

              CONVERTER configure option
                     This method, in this form,  has  to  return  the  current
                     value  of  the specified configuration option of the con-
                     verter.

                     Please read the section Options for the set  of  standard
                     options  any  converter has to accept.  Any other options
                     accepted by a specific converter will be described in its
                     manpage.

              CONVERTER configure option value...
                     This command, in this form, sets the specified options of
                     the converter to the given values.

                     Please read the section Options for the set  of  standard
                     options a converter has to accept.  Any other options ac-
                     cepted by a specific converter will be described  in  its
                     manpage.

              CONVERTER convert serial
                     This  method has to accept the canonical serialization of
                     a parsing expression grammar, as specified in section PEG
                     serialization  format,  and contained in serial.  The re-
                     sult of the method has to be the result of converting the
                     input grammar into whatever the converter is for, per its
                     configuration.

PLUGIN API
       Any (grammar) export plugin has to follow the rules set out below:

       [1]    A plugin is a package.

       [2]    The name of a plugin package has the form  pt::peg::export::FOO,
              where  FOO  is  the  name of the format the plugin will generate
              output for.

       [3]    The plugin can expect that the  package  pt::peg::export::plugin
              is  present,  as  indicator  that  it was invoked from a genuine
              plugin manager.

              It is recommended that a plugin does check for the  presence  of
              this package.

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

              ::export serial configuration
                     This command has to accept the canonical serialization of
                     a  parsing  expression  grammar and the configuration for
                     the converter invoked by the plugin. The  result  of  the
                     command  has to be the result of the converter invoked by
                     the plugin for th input grammar and configuration.

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

                     dictionary configuration
                            This argument will contain  the  configuration  to
                            configure  the  converter with before invoking it,
                            as a dictionary mapping from options to values.

                            Please read the section Options  for  the  set  of
                            standard  options any converter has to accept, and
                            thus any plugin as well.  Any  other  options  ac-
                            cepted  by  a specific plugin will be described in
                            its manpage.

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

OPTIONS
       Each export converter and plugin for an export converter has to  accept
       the  options below in their configure method. Converters are allowed to
       ignore the contents of these options when performing a conversion,  but
       they  must  not  reject  them. Plugins are expected to pass the options
       given to them to the converter they are invoking.

       -file string
              The value of this option is the name of the file or other entity
              from  which  the grammar came, for which the command is run. The
              default value is unknown.

       -name string
              The value of this option is the name of the grammar we are  pro-
              cessing.  The default value is a_pe_grammar.

       -user string
              The  value  of this option is the name of the user for which the
              command is run. The default value is unknown.

USAGE
       To use a converter do

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

                  # Provide a configuration
                  theconverter configure ...

                  # Perform the conversion
                  set result [theconverter convert $thegrammarserial]

                  ... process the result ...

       To use a plugin FOO do

                  # Get an export plugin manager
                  package require pt::peg::export
                  pt::peg::export E

                  # Provide a configuration
                  E configuration set ...

                  # Run the plugin, and the converter inside.
                  set result [E export serial $grammarserial FOO]

                  ... process the result ...

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                   pt_export_api(3tcl)

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