Name

Marpa::R2::Scanless::G - Scanless interface grammars

Synopsis

    my $grammar = Marpa::R2::Scanless::G->new(
        {   
            action_object  => 'My_Actions',
            default_action => 'do_first_arg',
            source          => \(<<'END_OF_SOURCE'),
    :start ::= Script
    Script ::= Expression+ separator => comma action => do_script
    comma ~ [,]
    Expression ::=
        Number
        | '(' Expression ')' action => do_parens assoc => group
       || Expression '**' Expression action => do_pow assoc => right
       || Expression '*' Expression action => do_multiply
        | Expression '/' Expression action => do_divide
       || Expression '+' Expression action => do_add
        | Expression '-' Expression action => do_subtract
    Number ~ [\d]+

    :discard ~ whitespace
    whitespace ~ [\s]+
    # allow comments
    :discard ~ <hash comment>
    <hash comment> ~ <terminated hash comment> | <unterminated
       final hash comment>
    <terminated hash comment> ~ '#' <hash comment body> <vertical space char>
    <unterminated final hash comment> ~ '#' <hash comment body>
    <hash comment body> ~ <hash comment char>*
    <vertical space char> ~ [\x{A}\x{B}\x{C}\x{D}\x{2028}\x{2029}]
    <hash comment char> ~ [^\x{A}\x{B}\x{C}\x{D}\x{2028}\x{2029}]
    END_OF_SOURCE
        }
    );

About this document

This page is the reference for the grammar objects of Marpa's Scanless interface.

Constructor

The new() method is the constructor for Scanless grammars. An example of its use is above. The new() constructor accepts a hash of named arguments. The following named arguments are allowed:

action_object

Specifies the action_object named argument that will be used for the G1 grammar. For details, see "action_object" in Marpa::R2::Grammar.

bless_package

Specifies the name of a Perl package. The package is used for blessing node values into a Perl class, in conjunction with the bless adverb.

default_action

Specifies the default_action named argument that will be used for the G1 grammar. For details, see "default_action" in Marpa::R2::Grammar.

source

The value of the source named argument must be a reference to a string which contains a description of the grammar. The string's format is a domain-specific language, described in its own document.

trace_file_handle

The value is a file handle. Trace output and warning messages go to the trace file handle. By default the trace file handle is STDERR.

Accessor

rule()

Given a G1 rule ID as its argument, returns an array containing the names of the symbols of that rule. The rule() method returns a Perl false if no G1 rule with that rule ID exists. If the rule ID exists, rule() returns a list of one or more symbol names. The first symbol name will be that of the rule's LHS symbol. The rest of the list will be the names of the rule's RHS symbols, in order.

The SLIF rule() corresponds to the rule() method of grammars in Marpa's standard interface. The SLIF's rule() method is useful in combination with the SLIF's of the progress method, whose output identifies rules by rule ID.

Trace method

show_rules()

    my $show_rules_output = $grammar->show_rules();

The show_rules() method is the equivalent of calling Marpa::R2::Grammar's show_rules() method for both the G0 and G1 grammars. It is useful for showing the rules as they will appear in trace and debugging outputs.

Copyright and License

  Copyright 2013 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/.