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use v5.10;
use warnings;
use List::Util qw< reduce >;
use Data::Dumper qw< Dumper >;
use Regexp::Grammars;
my $calculator = qr{
\A
<Answer>
<objrule: Answer>
<[Operand=Mult]>+ % <[Operator=(\+|\-)]>
<objrule: Mult>
<[Operand=Pow]>+ % <[Operator=( [*/%] )]>
<objrule: Pow>
<[Operand=Term]>+ % <Operator=(\^)>
<objrule: Term>
<MATCH=Literal>
| <Sign=(-)> \( <Operand= Answer> \)
| <MATCH=Answer>
<token: Literal>
<MATCH=( [+-]? \d++ (?: \. \d++ )?+ )>
}xms;
while (my $input = <>) {
if ($input =~ $calculator) {
warn Dumper $/{Answer};
}
}
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