Re: yet another very simple overlapping instance example

Hi! Koen Claessen wrote:

| instance (Num a) => Op_plus a MyInt where | i `plus` (MyInt b) = i + b

Remember that b is of type Int, but you also say that i is of any Num type. This clashes, since + requires both if its arguments to hve the same types.

You are right! I did't notice that error. Here is a version of the example free (if a remove the last instance compiles cleanly) of this mistake. data MyInt = MyInt Integer deriving Show class Op_plus a b where plus :: a -> b -> Integer instance Op_plus MyInt MyInt where (MyInt a) `plus` (MyInt b) = a + b instance (Integral a) => Op_plus a MyInt where i `plus` (MyInt b) = (toInteger i) + b Obs: perhaps MyInt should be now MyInteger. :-) -- Razvan ME