[Haskell-beginners] doubt....plz help me out

I am new to haskell plz dnt mind scan :: [Char] -> Token scan ('i':'f':tl) = IfKeyword scan ('t':'h':'e':'n':tl) = ThenKeyword scanp :: [Char] -> [Token] scanp t = sequence (map scan t) when I call scan on my file which has "if then" then its just printing if as IfKeyword ..its nt talking the then word I tried using sequence but its nt working..Can you please help me out.. I have to get the output as a list of tokens [IfKeyword, ThenKeyword]