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

my @actions = qw( add subtract quit );
my %dispatch = (
                 add => sub {
                     my ($x, $y) = map int rand 10, 1, 2;
                     print "$x + $y = ", $x + $y, "\n";
                 },
                 subtract => sub {
                     my ($x, $y) = map int rand 10, 1, 2;
                     print "$x - $y = ", $x - $y, "\n";
                 },
                 quit => sub { exit },
               );

while (1) {
    for my $idx (0 .. $#actions) {
        print "$idx) $actions[$idx]\n";
    }

    chomp(my $choice = <>);

    $choice = $actions[$choice] if $choice =~ /^[0-9]$/;
    if (exists $dispatch{$choice}) {
        $dispatch{$choice}->();
        next
    }

    print "Invalid option.\n";
}
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