1. How would I convert capital letters into small letters?

2. How would I remove vowels from a string?

I expect the first problem is actually to convert the upper case letters in a string to lower case, as the single-character version isn't a very interesting problem. A little thought shows that the first problem can be expressed as both a catamorphism or an anamorphism. The anamorphic solution would be [(p,f)] where p as = as == [] and f (a:as) = (makeLowerCase a, bs). The solution to the second problem is clearly a catamorphism, and one solution might be (|[],g|) where g (a:as) = if isVowel a then as else a:as The definitions of 'makeLowerCase' and 'isVowel' are quite simple (assuming English/Ascii, as pointed out in other messages), while finding the prelude functions for the patterns of recursion might take a little more thought. Suitable, possible, as homework questions in an introductory Haskell course ... Robin