Re: [Haskell-cafe] Generalizing unionWithKey, unionWith, ...

Dne 28.5.2013 12:32, Johannes Waldmann napsal(a):

Jose A. Lopes writes:

...

unionWith :: Ord k => (a -> b -> c) -> Map k a -> Map k b -> Map k c

what should be the result of

unionWith undefined (M.singleton False 42) (M.singleton True "bar") ? Perhaps the generalized signature should be instead:

```haskell unionWith :: Ord k => (Maybe a -> Maybe b -> c) -> Map k a -> Map k b -> Map k c ``` (The function would always get at least one `Just`.) But this functionality can be achieved using `map`s and the current `unionWith`. P.P.