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#!/usr/bin/env perl
# Copyright 2022 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 searches for recursively nested braces --
# curly, square and round -- in a "salad" of other things.
# It's to show general BNF search -- sort of a grep or an ack,
# but for general BNF, instead of regexes. The term
# "salad" I picked up from Michael Roberts, to suggest
# that the targets occur in a sort of "lexeme salad".
# In the literature, this is called a supersequence
# search.
use 5.010001;
use strict;
use warnings;
use Marpa::R2 2.097_002;
use Data::Dumper;
use Test::More tests => 3;
use Getopt::Long ();
my $verbose;
die if not Getopt::Long::GetOptions( verbose => \$verbose );
my $grammar = << '=== GRAMMAR ===';
:default ::= action => [ name, value ]
lexeme default = action => [ name, value ] latm => 1 # to add token names to ast
<prefixed target> ::= prefix target
prefix ::= <prefix lexeme>*
target ::= balanced
event target = completed target
balanced ::=
lparen contents rparen
| lcurly contents rcurly
| lsquare contents rsquare
contents ::= <content item>*
<content item> ::= balanced | filler
<prefix lexeme> ~ <deep filler>
filler ~ <deep filler>
# x5b is left square bracket
# x5d is right square bracket
<deep filler> ~ [^(){}\x5B\x5D]+
<prefix lexeme> ~ <deep lparen>
lparen ~ <deep lparen>
<deep lparen> ~ '('
<prefix lexeme> ~ <deep rparen>
rparen ~ <deep rparen>
<deep rparen> ~ ')'
<prefix lexeme> ~ <deep lcurly>
lcurly ~ <deep lcurly>
<deep lcurly> ~ '{'
<prefix lexeme> ~ <deep rcurly>
rcurly ~ <deep rcurly>
<deep rcurly> ~ '}'
<prefix lexeme> ~ <deep lsquare>
lsquare ~ <deep lsquare>
<deep lsquare> ~ '['
<prefix lexeme> ~ <deep rsquare>
rsquare ~ <deep rsquare>
<deep rsquare> ~ ']'
=== GRAMMAR ===
my $g = Marpa::R2::Scanless::G->new( { source => \($grammar) } );
my @tests = (
[ 'z}ab)({[]})))(([]))zz', ( join "\n", '({[]})', '(([]))', '' ) ],
[ '9\090]{[][][9]89]8[][]90]{[]\{}{}09[]}[',
join "\n", '[]', '[]', '[9]', '[]', '[]', '{[]\{}{}09[]}', ''
],
[ '([]([])([]([]', join "\n", '[]', '([])', '[]', '[]', '' ],
);
for my $test (@tests) {
my ( $string, $expected_result ) = @{$test};
my $actual_result = test( $g, $string );
diag("Input: $string") if $verbose;
Test::More::is( $actual_result, $expected_result,
qq{Result of "$string"} );
} ## end for my $test (@tests)
sub test {
my ($g, $string) = @_;
my @found = ();
diag( "Input: $string" ) if $verbose;
my $input_length = length $string;
my $target_start = 0;
# my $recce_debug_args = { trace_terminals => 1, trace_values => 1 };
state $recce_debug_args = {};
# One pass through this loop for every target found,
# until we reach end of string without finding a target
TARGET: while ( $target_start < $input_length ) {
# First we find the "shortest span" -- the one which ends earliest.
# This tells us where the prefix should end.
# No prefix should go beyond the first location of the shortest span.
# Marpa::R2::Display
# name: SLIF exhaustion recognizer setting synopsis
my @shortest_span = ();
my $recce = Marpa::R2::Scanless::R->new(
{ grammar => $g,
exhaustion => 'event',
},
$recce_debug_args
);
my $pos = $recce->read( \$string, $target_start );
EVENT:
for my $event ( @{ $recce->events() } ) {
my ($name) = @{$event};
if ( $name eq 'target' ) {
@shortest_span = $recce->last_completed_span('target');
diag(
"Preliminary target at $pos: ",
$recce->literal(@shortest_span)
) if $verbose;
next EVENT;
} ## end if ( $name eq 'target' )
# Not all exhaustion has an exhaustion event,
# so we look for exhaustion explicitly below.
next EVENT if $name eq q('exhausted);
die join q{ }, "Spurious event at position $pos: '$name'";
} ## end EVENT: for my $event ( @{ $recce->events() } )
# Marpa::R2::Display::End
last TARGET if not scalar @shortest_span;
# We now have found the longest allowed prefix.
# Our "longest match" will begin at the end of this prefix,
# or before it.
# We just run until exhausted, the look for the last
# completed <target>. This will be our longest match.
diag( join q{ }, @shortest_span ) if $verbose;
my $prefix_end = $shortest_span[0];
$recce = Marpa::R2::Scanless::R->new(
{ grammar => $g,
exhaustion => 'event',
rejection => 'event',
},
$recce_debug_args
);
$recce->activate( 'target', 0 );
$recce->read( \$string, $target_start, $prefix_end - $target_start );
# Marpa::R2::Display
# name: SLIF recognizer lexeme_priority_set() synopsis
$recce->lexeme_priority_set( 'prefix lexeme', -1 );
# Marpa::R2::Display::End
$pos = $recce->resume($prefix_end);
# Marpa::R2::Display
# name: SLIF recognizer last_completed_span() synopsis
my @longest_span = $recce->last_completed_span('target');
diag( "Actual target at $pos: ", $recce->literal(@longest_span) ) if $verbose;
# Marpa::R2::Display::End
last TARGET if not scalar @longest_span;
push @found, $recce->literal(@longest_span);
diag( "Found target at $pos: ", $recce->literal(@longest_span) ) if $verbose;
# Move the search location forward,
# in preparation for looking for the next target
$target_start = $longest_span[0] + $longest_span[1];
} ## end TARGET: while ( $target_start < $input_length )
return join "\n", @found, q{};
} ## end sub test
# vim: expandtab shiftwidth=4:
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