Use coercions to implement fmapDefault and foldMapDefault

We should be able to use

fmapDefault :: Traversable t => (a -> b) -> t a -> t b
fmapDefault = (getId .) #. traverse .# (Id .)

foldMapDefault :: (Traversable t, Monoid m) => (a -> m) -> t a -> m
foldMapDefault = (getConst .) #. traverse .# (Const .)

where .# and #. are coercion operators found in Data.Profunctor.Unsafe. This should help when the function passed in doesn't inline.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Core Libraries
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	ekmett
Operating system
Architecture