#!/usr/bin/perl
use warnings;
use strict;

use Scalar::Util 'looks_like_number';

my $MAXITERATIONS = 500;

while ( <> ) {
    my $iterations = 0;
    1 while s/(\([^()]+\))/ die "MAX ITERATIONS ACHIEVED: ABORTING\n" if ++$iterations >= $MAXITERATIONS; solvepart( $1 ) /eg;
    print "\nANSWER: $_\n\n";
    }

sub solvepart {
    my $expression = shift;
    $expression =~ tr/()//d;
    $expression =~ s/\^/**/;
    my ( $operator, @values ) = split ' ', $expression;
    $operator =~ /\*\*|[+\-*\/%]/ && @values >= 2 && @values == grep looks_like_number( $_ ), @values
        or die "IMPROPER INPUT\n";
    eval join $operator, @values;
    }