use strict;

my %variable;
my %operation;

$operation{eq} = sub {
  my ($op1, $op2) = @_;
  return $op1 eq $op2;
};

$operation{ne} = sub {
  my ($op1, $op2) = @_;
  return $op1 ne $op2;
};

sub evaluate {
  my ($var,$op,$value) = @_;

  if (defined $operation{$op}) {
    my $code = $operation{$op};
    return $code->( $variable{$var}, $value );
  } else {
    die "Unknown operator : $op\n";
  };
};

$variable{foo} = 'FOO';
$variable{bar} = 'BAR';

my ($var,$op,$val);
foreach $var (keys %variable) {
  foreach $op (keys %operation) {
    foreach $val ('FOO','BAR','neither') {
      print "$var $op $val :", evaluate( $var, $op, $val ), "\n";
    };
  };
};