I was reading "Arrows and Computation" http://www.soi.city.ac.uk/~ross/papers/fop.ps.gz (trying to lose my 'beginner' status) when I saw (on page one) add :: (b -> Int) -> (b -> Int) -> (b -> Int) add f g b = f b + g b It seemed like the type definition was wrong (short at least). I tried it anyway .. module Main where add :: (b -> Int) -> (b -> Int) -> (b -> Int) add f g b = f b + g b main = do x <- return $ add (+2) (+3) 7 print x The program compiles and runs and produces '19' ! For fun I loaded into ghci and got what I believe is the proper type .. *Main> :t add add :: (b -> Int) -> (b -> Int) -> b -> Int When I try the same thing with something simpler (leaving a bit off the type definition) I get the expected error (by me) .. module Main where dog :: Int -> Int dog a b = a + b main = do x <- return $ dog 2 3 print x Main.hs:5:0: The equation(s) for `dog' have two arguments, but its type `Int -> Int' has only one What am I missing? .. Apparently something fundamental about type definitions .. Any help appreciated. Tom