Should the signature of foldr1 (and similarly foldl1) be:
foldr1 :: forall f a b. Foldable1 f => (a -> b -> b) -> (a -> b) -> f a -> b
I understand the logic behind the current signature:
foldr1 :: forall f a b. Foldable1 f => (b -> b -> b) -> f b -> b
In that, if I have a mapping from a -> b, then I can pre-map unconditionally, and derive the latter signature. Unfortunately that's not actually what I want to do:
- I only want the mapping to apply to the terminal value.
- I want to otherwise combine with the combining function.
- I don't want to waste an entire traversal to make the signature work.
I feel like there's a missed opportunity with the current signature. To be honest, I almost never want the current signature.
Should the signature of foldr1 (and similarly foldl1) be:
I understand the logic behind the current signature:
In that, if I have a mapping from a -> b, then I can pre-map unconditionally, and derive the latter signature. Unfortunately that's not actually what I want to do:
I feel like there's a missed opportunity with the current signature. To be honest, I almost never want the current signature.