if ($not_in_shift) {
  if ($current || !$past) {
    print "Register for shift\n";
  }
}
else {
  if ($current) {
    print "Confirm in shift\n";
    print "Remove from shift\n";
  }
  if ($past) {
    print "Confirm in shift\n";
  }
}

##</code><code>##

#!/usr/bin/perl -w
use strict;

# These can be filled by some function
my %conditions = (
    Current => 1,
    Not_in_shift => 1,
    Past => 0,
);

# Menu item to print if any set of conditions satisfies
my %menu =
            (
                'Add Self' => [
                    "Current,Not_in_shift",
                    "!Past,Not_in_shift",
                ],
            );

# No need to touch this stuff ever
for my $item ( keys %menu ) {
    for my $set ( @{$menu{$item}} ) {
        my $result = 1;
        for my $condition ( split(/,/,$set) ) {
            # Negating condition is a convenient thing to have
            if (substr($condition,0,1) eq '!') {
                substr($condition,0,1,'');
                ($result &&= !$conditions{$condition}) || last;
            }
            else {
                ($result &&= $conditions{$condition}) || last;
            }
        }
        if ($result) {
            add_menu_item($item);
            last;
        }
    }
}

# Whatever we want to do with the menu item
sub add_menu_item {
    my $item = shift;
    print "$item\n";
}