Acting on an optional

Questions
1

I often want to use a function such as

optionalA : Action m => b -> (a -> m b) -> Optional a -> m b
optionalA n _ None  = pure n
optionalA _ f (Some x) = f x

but every time that I actually apply it, because the Optional a is the last argument it looks weird and I inline the case analysis instead. Should I break with convention and change the order of arguments? Are there other workarounds?

2

It is common in the stdlib to have two names for the same function with different argument orders. For example, in DA.Traversable, you have mapA, for which one instance is Action m => (a -> m b) -> Optional a -> m (Optional b), but the function forA is also provided, which has an instance Action m => Optional a -> (a -> m b) -> m (Optional b).

See also <$> vs <&>. There’s no problem having different names with different argument orders for the same function, though if one is a member of a typeclass, the other should not be (as it is with the stdlib examples).

import Prelude hiding (mapA)
import DA.Optional (fromOptional)
import DA.Traversable (mapA)

optionalA' : Action m => b -> (a -> m b) -> Optional a -> m b
optionalA' n f oa = fromOptional n <$> mapA f oa