On Sat, Mar 03, 2018 at 06:31:47PM -0800, Hilco Wijbenga wrote:
In any case, _when_ I flip "success" and "failure" the Functor instance no longer compiles. Which probably makes sense because I did not tell the compiler to interpret "Result failure" as "Result * failure"?
I wonder if you are talking about failure (type parameter) or Failure (data constructor). This instance obviously work instance Functor (Result success) where fmap f (Success value) = Success (f value) fmap _ (Failure error) = Failure error Flipping in `data` of course means you are to flip one of: a) instance or b) data constructor, e.g.: instance Functor (Result success) where fmap f (Failure error) = Failure (f error) fmap _ (Success value) = Success value