my $key = ReadKey(-1);
next unless defined $key;  #next or return depending on your code structure
if ($key eq "\e") { #expecting more
   $key .= ReadKey(-1);  # should be a '['
   $key .= ReadKey(-1);
   }
my $callback= $keymap{$key};
if (defined $callback) {
   $callback->($key);
   }
else { beep(); }  #no such key is meaningful here