my %description = (
   a => 'a vowel',
   b => 'a consonant',
   '' => 'not in the alphabet' #description of anything else
);

print("a is $description{'a'}\n");
print("b is $description{'b'}\n");
print("~ is $description{'~'}"); #Would like the following:
                                 #"~ is not in the alphabet"