Created
January 28, 2015 15:08
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Ambiguous parse: 5 alternatives. | |
# Alternative 1: | |
['hex',['hex',['hex',['hex',['digit','0']],['hex',['digit','1']]],['hex',['letter','F']]],['hex',['letter','E']]] | |
# Alternative 2: | |
['hex',['hex',['hex',['digit','0']],['hex',['hex',['digit','1']],['hex',['letter','F']]]],['hex',['letter','E']]] | |
# Alternative 3: | |
['hex',['hex',['hex',['digit','0']],['hex',['digit','1']]],['hex',['hex',['letter','F']],['hex',['letter','E']]]] | |
# Alternative 4: | |
['hex',['hex',['digit','0']],['hex',['hex',['hex',['digit','1']],['hex',['letter','F']]],['hex',['letter','E']]]] | |
# Alternative 5: | |
['hex',['hex',['digit','0']],['hex',['hex',['digit','1']],['hex',['hex',['letter','F']],['hex',['letter','E']]]]] |
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use 5.010; | |
use strict; | |
use warnings; | |
use Data::Dumper; | |
$Data::Dumper::Indent = 0; | |
$Data::Dumper::Terse = 1; | |
$Data::Dumper::Deepcopy = 1; | |
use Carp::Always; # force stack trace | |
use Marpa::R2; | |
my $g = Marpa::R2::Scanless::G->new( { source => \(<<'END_OF_SOURCE'), | |
:default ::= action => [ name, value] | |
lexeme default = action => [ name, value] latm => 1 | |
#this is highly ambiguous: | |
<hex> ::= <digit> | <letter> | <hex> <hex> | |
#this is unambiguous: <hex> ::= <digit> | <letter> | <hex> <digit> | <hex> <letter> | |
<digit> ::= '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' | |
<letter> ::= 'A' | 'B' | 'C' | 'D' | 'E' | 'F' | |
:discard ~ whitespace | |
whitespace ~ [\s]+ | |
END_OF_SOURCE | |
} ); | |
my $input = <<EOI; | |
01FE | |
EOI | |
my $r = Marpa::R2::Scanless::R->new( { | |
max_parses => 100, | |
grammar => $g, | |
} ); | |
eval { $r->read(\$input) } || warn "$@\nProgress report is:\n" . $r->show_progress; | |
my $ast = $r->value; | |
unless (defined $ast){ | |
die "No parse"; | |
} | |
if ( $r->ambiguity_metric() > 1 ){ | |
# gather parses | |
my @asts; | |
my $v = $ast; | |
do { | |
push @asts, ${ $v }; | |
} until ( not $v = $r->value() ); | |
# push @asts, ${ $v }; | |
say "Ambiguous parse: ", $#asts + 1, " alternatives."; | |
for my $i (0..$#asts){ | |
say "# Alternative ", $i+1, ":\n", Dumper $asts[$i]; | |
} | |
} | |
else{ | |
say Dumper $ast; | |
} |
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['hex',['hex',['hex',['hex',['digit','0']],['digit','1']],['letter','F']],['letter','E']] |
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