[Haskell-cafe] foldMap for semigroups

[Henning Thielemann]

On Fri, 14 May 2021, coot at coot.me wrote:

> Base has:
> * foldMap :: (Foldable t, Monoid a) => (x -> a) -> t x -> a
> * foldr1  :: (Foldable t) => (a -> a -> a) -> t x -> a
> Is there a good reason why it does not have:
> ```
> foldMap1 :: (Foldable t, Semigroup a, Functor f) => (a -> a) -> t x -> a
> foldMap1 = fodlr1 (<>) . fmap f
> ```
> Like `foldr1` it is partial for any foldable that can be empty.

I do not think we should extend support for partial functions.
foldMap1 should be restricted to non-empty Foldable (i.e. Foldable1).