Name

       Marpa::R2::BNF - BNF Interface (obsoleted)

Synopsis

           use Marpa::R2;

           my $grammar = Marpa::R2::Grammar->new(
               {
                   actions        => 'My_Actions',
                   default_action => 'do_first_arg',
                   source          => \(<<'END_OF_SOURCE'),
           :start ::= Script
           Script ::= Expression+ separator => <op comma> action => do_script
           Expression ::=
               Number
               | (<op lparen>) Expression (<op rparen>) action => do_parens assoc => group
              || Expression (<op pow>) Expression action => do_pow assoc => right
              || Expression (<op times>) Expression action => do_multiply
               | Expression (<op divide>) Expression action => do_divide
              || Expression (<op add>) Expression action => do_add
               | Expression (<op subtract>) Expression action => do_subtract
           END_OF_SOURCE
               }
           );

Overview

       This page is the reference for the Marpa's "BNF interface", also called its "Stuifzand
       interface".  Use of the Stuifzand interface is now discouraged, in favor of the SLIF
       interface.  Almost all of the functionality of the Stuifzand interface can be duplicated
       in the SLIF interface by switching immediately to external scanning, and never switching
       back to internal scanning.  To switch immediately to external scanning in the SLIF,
       specify a length of zero for its initial "read()".  For more details, see the document for
       the SLIF itself.

The source string

       Stuifzand interface  source strings are specified using the the "source" named argument of
       Marpa::R2's grammars.  BNF source strings perform the functions of the "rules" and the
       "start" named arguments of Marpa grammars.  When the "source" named argument is used to
       specify a grammar, the "rules" and "start" named arguments should not be used, and vice
       versa.  The syntax for the Stuifzand interface's source string is the same as the syntax
       for the SLIF DSL, except that features and syntax not relevant to the Stuifzand interface
       are not supported.

       Everything related to L0 grammars is unsupported.  L0 grammars do not exist in the
       Stuifzand interface.  Lexemes, character classes and quoted strings all implicitly require
       a L0 grammar to exist and therefore, they also are not supported.

       Since the Stuifzand interface does not implement internal scanning, everything to do with
       internal scanning is unsupported.  Events and pauses are the most visible of these
       features.

       In most cases, when features have introduced after the SLIF replaced the Stuifzand
       interface as Marpa's primary interface, those features have been retro-ported if they make
       sense in the Stuifzand context.  However, this will necessarily always be the case in the
       future.

       Here is a list of some of the unsupported SLIF DSL features,

       •   Character classes

           These implicitly use the L0 grammar.

       •   Quoted strings

           These implicitly use the L0 grammar.

       •   Discard rules

           ":discard" rules control the behavior of the L0 grammar.

       •   The lexeme and lexeme default statements

           The ":lexeme" pseudo-rule and the lexeme default statement define the behavior of
           lexemes.  Lexemes in the SLIF sense do not exist in the Stuifzand interface.

       •   L0 rules

           Rules with the tilde declarator (""~"") defined L0 rules.

       •   Event declarations

           Events exist to pause the SLIF internal scanning.

       •   The pause adverb

           The pause adverb exists to pause the SLIF internal scanning.

       •   The priority adverb

           The priority adverb defines lexeme priorities.  Lexemes in the SLIF sense do not exist
           in the Stuifzand interface.

       •   Actions specified as array descriptors

           Actions specified as array descriptors, for example,

               action => [start,length,value]

           exist primarily to support lexeme semantics.  They can also specify rule semantics,
           but their functionality has not been retro-ported to the Stuifzand interface, and
           probably never will be.

Copyright and License

         Copyright 2014 Jeffrey Kegler
         This file is part of Marpa::R2.  Marpa::R2 is free software: you can
         redistribute it and/or modify it under the terms of the GNU Lesser
         General Public License as published by the Free Software Foundation,
         either version 3 of the License, or (at your option) any later version.

         Marpa::R2 is distributed in the hope that it will be useful,
         but WITHOUT ANY WARRANTY; without even the implied warranty of
         MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
         Lesser General Public License for more details.

         You should have received a copy of the GNU Lesser
         General Public License along with Marpa::R2.  If not, see
         http://www.gnu.org/licenses/.