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#!/usr/bin/perl
# 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/.
# This example is from Ralf Muschall, who clearly knows English
# grammar better than most native speakers. I've reworked the
# terminology to follow _A Comprehensive Grammar of the English
# Language_, by Quirk, Greenbaum, Leech and Svartvik. My edition
# was the "Seventh (corrected) impression 1989".
#
# When it is not a verb, I treat "like"
# as a preposition in an adjunct of manner,
# as per 8.79, p. 557; 9.4, pp. 661; and 9.48, pp. 698-699.
#
# The saying "time flies like an arrow; fruit flies like a banana"
# is attributed to Groucho Marx, but there is no reason to believe
# he ever said it. Apparently, the saying
# first appeared on the Usenet on net.jokes in 1982.
# I've documented this whole thing on Wikipedia:
# http://en.wikipedia.org/wiki/Time_flies_like_an_arrow
#
# The permalink is:
# http://en.wikipedia.org/w/index.php?title=Time_flies_like_an_arrow&oldid=311163283
use 5.010;
use strict;
use warnings;
use English qw( -no_match_vars );
use Test::More tests => 1;
use lib 'inc';
use Marpa::R2::Test;
use Marpa::R2;
## no critic (Subroutines::RequireArgUnpacking)
sub do_sva_sentence { return "sva($_[1];$_[2];$_[3])" }
sub do_svo_sentence { return "svo($_[1];$_[2];$_[3])" }
sub do_adjunct { return "adju($_[1];$_[2])" }
sub do_adjective { return "adje($_[1])" }
sub do_qualified_subject { return "s($_[1];$_[2])" }
sub do_bare_subject { return "s($_[1])" }
sub do_noun { return "n($_[1])" }
sub do_verb { return "v($_[1])" }
sub do_object { return "o($_[1];$_[2])" }
sub do_article { return "art($_[1])" }
sub do_preposition { return "pr($_[1])" }
## use critic
my $grammar = Marpa::R2::Grammar->new(
{ start => 'sentence',
actions => 'main',
rules => [
[ 'sentence', [qw(subject verb adjunct)], 'do_sva_sentence' ],
[ 'sentence', [qw(subject verb object)], 'do_svo_sentence' ],
[ 'adjunct', [qw(preposition object)], 'do_adjunct' ],
[ 'adjective', [qw(adjective_noun_lex)], 'do_adjective' ],
[ 'subject', [qw(adjective noun)], 'do_qualified_subject' ],
[ 'subject', [qw(noun)], 'do_bare_subject' ],
[ 'noun', [qw(adjective_noun_lex)], 'do_noun' ],
[ 'verb', [qw(verb_lex)], 'do_verb' ],
[ 'object', [qw(article noun)], 'do_object' ],
[ 'article', [qw(article_lex)], 'do_article' ],
[ 'preposition', [qw(preposition_lex)], 'do_preposition' ],
],
}
);
my $expected = <<'EOS';
sva(s(n(fruit));v(flies);adju(pr(like);o(art(a);n(banana))))
sva(s(n(time));v(flies);adju(pr(like);o(art(an);n(arrow))))
svo(s(adje(fruit);n(flies));v(like);o(art(a);n(banana)))
svo(s(adje(time);n(flies));v(like);o(art(an);n(arrow)))
EOS
my @actual = ();
$grammar->precompute();
my %lexical_class = (
'preposition_lex' => 'like',
'verb_lex' => 'like flies',
'adjective_noun_lex' => 'fruit banana time arrow flies',
'article_lex' => 'a an',
);
my %vocabulary = ();
for my $lexical_class (keys %lexical_class) {
my $words = $lexical_class{$lexical_class};
for my $word ( split q{ }, $words ) {
push @{ $vocabulary{$word} }, $lexical_class;
}
} ## end for my $lexical_class (%lexical_class)
for my $data ( 'time flies like an arrow', 'fruit flies like a banana' ) {
my $recce = Marpa::R2::Recognizer->new( { grammar => $grammar } );
die 'Failed to create recognizer' if not $recce;
for my $word ( split q{ }, $data ) {
# Marpa::R2::Display
# name: Recognizer exhausted Synopsis
$recce->exhausted() and die 'Recognizer exhausted';
# Marpa::R2::Display::End
for my $type ( @{ $vocabulary{$word} } ) {
$recce->alternative( $type, \$word, 1 )
or die 'Recognition failed';
}
$recce->earleme_complete();
} ## end for my $word ( split q{ }, $data )
# Marpa::R2::Display
# name: Recognizer end_input Synopsis
$recce->end_input();
# Marpa::R2::Display::End
while ( defined( my $value_ref = $recce->value() ) ) {
my $value = $value_ref ? ${$value_ref} : 'No parse';
push @actual, $value;
}
} ## end for my $data ( 'time flies like an arrow', ...)
Marpa::R2::Test::is( ( join "\n", sort @actual ) . "\n",
$expected, 'Ambiguous English sentences' );
1; # In case used as "do" file
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