Feature request: deriveFmap for functor compositions

[guoshimin]

Just a thought: seems it would be feasible to derive fmap for functors that are the composition of two or more functors, such as deriveFmap(func(A) B, func() ([A], error)) ([B], error)

[awalterschulze]

Interesting. I can see this example working.
Maybe you can provide a few more which include some joins, to see how we would handle stacked monads as well.
Just to make sure our theory is sound, before we start implementing.
What do you think?

[awalterschulze]

Hello?

[awalterschulze]

I think what we want here is traverse:

traverse :: Applicative f => (a -> f b) -> t a -> f (t b)

where f is (b, error) and t is a slice

[awalterschulze]

Oh no thats not what you were referring to, my bad.