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Marpa-R2-2.068000
River stage two • 39 direct dependents • 56 total dependents
48 ++
/ Marpa::R2::Scanless::G

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::NAIF::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::NAIF::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.

Mutator

set()

    $slg->set( { trace_file_handle => $trace_fh } );

This method allows the named arguments to be changed after an SLIF grammar is created. Currently, the only argument that may be changed in trace_file_handle.

Accessors

g1_rule_ids()

    my @g1_rule_ids = $slg->g1_rule_ids();
    for my $g1_rule_id (@g1_rule_ids) {
        $g1_rules_description .= "$g1_rule_id "
            . ( join q{ }, map {"<$_>"} $slg->rule($g1_rule_id) ) . "\n";
    }

Returns a list of the G1 rule ID's. The symbols for these can be queried using the the SLIF grammar's rule() method,

Trace methods

g0_rule()

    my @g0_rule_ids = $slg->g0_rule_ids();
    for my $g0_rule_id (@g0_rule_ids) {
        $g0_rules_description .= "$g0_rule_id "
            . ( join q{ }, map {"<$_>"} $slg->g0_rule($g0_rule_id) ) . "\n";
    }

Given a G0 rule ID as its argument, returns an array containing the names of the symbols of that rule. The g0_rule() method returns a Perl false if no G0 rule with that rule ID exists. If the G0 rule ID exists, g0_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.

g0_rule_ids()

    my @g0_rule_ids = $slg->g0_rule_ids();
    for my $g0_rule_id (@g0_rule_ids) {
        $g0_rules_description .= "$g0_rule_id "
            . ( join q{ }, map {"<$_>"} $slg->g0_rule($g0_rule_id) ) . "\n";
    }

Returns a list of the G0 rule ID's. The symbols for these can be queried using the the SLIF grammar's g0_rule() method,

show_rules()

    my $show_rules_output = $slg->show_rules();
    $show_rules_output .= $slg->show_rules(3, 'G0');

The show_rules() method returns a descripton of the rules for a subgrammar, by default G1. It is useful for understanding the rules as they appear in trace and debugging outputs. To allow for improvements in Marpa::R2, the output of show_rules() is subject to change.

The first optional argument can be a numeric verbosity level. The default verbosity is 1, which is adequate for most purposes. A verbosity of 2 prints additional information useful for those new to SLIF tracing and debugging. A verbosity of 3 prints additional information for experts, for those new to SLIF tracing and debugging.

The second, optional, argument is the name of a subgrammar. Currently there are G0 and G1 subgrammars.

show_symbols()

    $show_symbols_output .= $slg->show_symbols(3);
    $show_symbols_output .= $slg->show_symbols(3, 'G0');

The show_symbols() method returns a descripton of the symbols for a subgrammar, by default G1. It is useful for understanding the symbols as they appear in trace and debugging outputs. To allow for improvements in Marpa::R2, the output of show_symbols() is subject to change.

The first argument can be a numeric verbosity level. The default verbosity is 1, which is adequate for most purposes. A verbosity of 2 prints additional information useful for those new to SLIF tracing and debugging. A verbosity of 3 prints additional information for experts, for those new to SLIF tracing and debugging.

The second, optional, argument is the name of a subgrammar. Currently there are G0 and G1 subgrammars.

Discouraged methods

Discouraged methods are those that continue to be supported, but their use is discouraged for one reason or another.

rule()

    my @g1_rule_ids = $slg->g1_rule_ids();
    for my $g1_rule_id (@g1_rule_ids) {
        $g1_rules_description .= "$g1_rule_id "
            . ( join q{ }, map {"<$_>"} $slg->rule($g1_rule_id) ) . "\n";
    }

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's rule() method is useful in combination with the SLIF's of the progress method, whose output identifies rules by rule ID.

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/.