This is a calculator using polish prefix notation with parentheses. It will properly parse and calculate when given input such as:

(+ 1 2 3 (* 4 3 (- 2 1) (% 5 2)) 3 4)
#NOTE: % is the modulo operator, / is for dividing.
[download]

It can do this, because I implemented it using recursive ascent parsing. If you want to try it, I would recommend running it in verbose mode to see what it is doing. You can do this by putting a space followed by 1,v,V,verbose,VERBOSE, or similar after the program name when you run it. Enjoy.

#!/usr/bin/perl
use warnings;
use strict;
use Data::Dump qw(dump);
sub arith;
sub solvepart($);
sub testiterations;
sub reformat;
my $VERBOSE=shift//0;
my $MAXITERATIONS=500;
my $iterations;
my @stack;
my $num=qr/(-?\d++\.?\d*?)/;
while(<>){
    $iterations=0;
    my $given = $_;
    if ($given ~~ /exit|end|quit/i){
        die "PROGRAM TERMINATED\n";
    }
    if ($given !~ /^(\((?:[^()]++|(?-1))*+\))/){
        die "IMPROPER INPUT\n";
    }
    until ($given !~ /[()]/){
        reformat $given;
        $given =~ s/(.*)(\(\S++ ++$num ++($num)?\))/$1.solvepart($2)/e
+;
        testiterations;
    }
    print "\nANSWER: ".$given."\n\n";
}
sub testiterations{
    $iterations++;
    if ($iterations==$MAXITERATIONS){
        die "MAX ITERATIONS ACHIEVED: ABORTING\n";
    }
}
sub reformat($){
1 while $_[0] =~        s/(?<leading>   \((?<op>\S++)\s++$num [^()]*?\
+s++)
                                        (?<nums>$num\s++$num)
                                        \)
                        /$+{leading}\($+{op}\ $+{nums}\)\)/x;
}
sub solvepart($){
    my $given = shift;
    unshift(@stack, [$2,$3,$4]) while $given =~ s/(.*)\((\S++) ++(-?\d
+++\.?\d*?) ++(-?\d++\.?\d*?)?\)/$1/;
    if ($VERBOSE or $VERBOSE ~~ /v(?:erbose)?/i){
        print "\nDATA:\n";
        dump @stack;
    }
    return arith;
}
sub arith{
    my $value=0;
    while(@stack){
        #my @level = map{handleneg($_)}@{pop @stack};
        my @level = @{pop @stack};
        if ($level[0]eq'+'){
            $level[2]
                ?($value=$level[1]+$level[2])
                :($value+=$level[1]);
        }
        elsif ($level[0]eq'-'){
                        $level[2]
                                ?($value=$level[1]-$level[2])
                                :($value=$level[1]-$value);
                }
        elsif ($level[0]eq'/'){
                        $level[2]
                                ?($value=$level[1]/$level[2])
                                :($value=$level[1]/$value);
                }
        elsif ($level[0]eq'*'){
                        $level[2]
                                ?($value=$level[1]*$level[2])
                                :($value*=$level[1]);
                }
        elsif ($level[0]eq'**'or$level[0]eq'^'){
                        $level[2]
                                ?($value=$level[1]**$level[2])
                                :($value=$level[1]**$value);
                }
        elsif ($level[0]eq'%'){
                        $level[2]
                                ?($value=$level[1] % $level[2])
                                :($value=$level[1] % $value);
                }
        else {
            die "IMPROPER INPUT\n";
        }
    }
    return $value;
}
[download]

You can exit by inputing eXiT, end, QUIT, or similar.

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