%functions = (
  '?' => 0,
  'HELLO' => sub { print "Hello, world.\n" },
  'HELP' => sub { print "Type 'hello' or 'goodbye'\n" },
  'GOODBYE' => sub { print "Goodbye...\n"; exit(0) }
);
# have to initialize this outside declaration of %functions
$functions{'?'} = $functions{'HELP'};