Hi, I declared a multi param type class as below: *class MyString m c where zIndex :: m -> Int -> c zLength :: m -> Int zPack :: [c] -> m zEquals :: c ->c -> Bool zWrap :: [c] -> (m,AnExistingDataType)* In the end I did not needed it for my program, but for those few minutes I played with the idea, I came across a zillion questions. Can some body help me here please? When I defined a function like below, \begin{code} compareStr::(MyString m c) => (m,Int) ->(m,Int)->Int->Int compareStr (s1,pos1) (s2,pos2) soFar | (pos1 < zLength s1) && (pos2 < zLength s2) = let c1 = zIndex s1 pos1 c2 = zIndex s2 pos2 in if(zEquals c1 c2) then compareStr (s1,(pos1 + 1)) (s2, (pos2 + 1)) (soFar + 1) else soFar | otherwise = soFar \end{code} when I loaded it on ghci ( invoked with -XMultiParamTypeClasses ), I got an essay in greek (or is it latin?), which started something like below: Could not deduce (MyString m c) from the context (MyString m c4) arising from a use of `zLength' at GenericZAlgo.lhs:42:21-31 Possible fix: add (MyString m c) to the context of the type signature for `compareStr' In the second argument of `(<)', namely `zLength s1' In the first argument of `(&&)', namely `(pos1 < zLength s1)' In a pattern guard for the definition of `compareStr': (pos1 < zLength s1) && (pos2 < zLength s2) And if I let the type inference run the show, the type it shows is : compareStr :: (MyString t c2, MyString m c2, Num a, MyString t1 c2, MyString t c, MyString t1 c1) => (t, Int) -> (t1, Int) -> a -> a And puzzlingly, if I try the same thing myself and reload it on the ghci,I still get similar error. I can go on about other 'puzzles'. Can some one please tell me whats going on here? Apologies, if it is something that's been documented left to right, top to bottom, but I could not get anywhere readily. Any pointers to the right documentation will be much appreciated. On the surface it looks like something that n00bs like yours truly better stay away. But I have a feeling that this one may throw some more light on type inference. Many thanks