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use strict;
use FindBin;
use lib "$FindBin::Bin/lib";
use Pegex;
use Runner;
my $grammar = <<'...';
# Precedence Climbing grammar:
expr: add-sub
add-sub: mul-div+ % /- ( [ '+-' ])/
mul-div: power+ % /- ([ '*/' ])/
power: token+ % /- '^' /
token: /- '(' -/ expr /- ')'/ | number
number: /- ( '-'? DIGIT+ )/
...
{
package Calculator;
use base 'Pegex::Tree';
sub gotrule {
my ($self, $list) = @_;
return $list unless ref $list;
# Right associative:
if ($self->rule eq 'power') {
while (@$list > 1) {
my ($a, $b) = splice(@$list, -2, 2);
push @$list, $a ** $b;
}
}
# Left associative:
else {
while (@$list > 1) {
my ($a, $op, $b) = splice(@$list, 0, 3);
unshift @$list,
($op eq '+') ? ($a + $b) :
($op eq '-') ? ($a - $b) :
($op eq '*') ? ($a * $b) :
($op eq '/') ? ($a / $b) :
die;
}
}
return @$list;
}
}
Runner->new(args => \@ARGV)->run(
sub { pegex($grammar, 'Calculator')->parse($_[0]) }
);
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