Hello, I'm writing a little word game that consists of the following : between a consonant and a vowel, insert "AV" so "fabien" becomes "fAVabAVien". When i type : f "fabine", the result is ok ("fAVabAVinAVe") When i type : f "fabien", the result is fAVabAVie *** exception :prelude empty list Here's my program voyelles="aeiouy" consonnes="bcdfghjklmnpqrstvwxz" est_voyelle x = x `elem` voyelles est_consonne x = x `elem` consonnes --f []=[] ; unuseful - conflict with f a = a f (a:b:c) = case trait a b of True -> a : (" AV " ++ f (b:c)) False -> a : f (b:c) f (a:b) = case trait a (head b) of True -> a : (" EP " ++ f ( b) ) False -> a : f ( b) f a = a -- detect a vowel following a consonant trait a b = est_consonne a && est_voyelle b f (a:b) is never invoked (i wrote EP instead of AV to trace the problem). f(a:b:c) seems to always take precedence over the other patterns. I expect f(a:b:c) to treat words greater than or equal to 3 letters, f(a:b) the last two letters of the word (no third part) and f a the last letter. Another trick : how can i calculate consonnes with a method that makes the difference between the two lists [a..z] and voyelles, rather than writing each consonant. As we can append two lists (++), can we compute the difference between lists, i.e. delete from the first list the elements that are present in the second one ? Last, with Ghci, is it possible to debug my program, especially for recursive functions, because it's hard to follow the successive calls and the parameters that are passed each turn. Greetings, Didier.