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};
    }
}