Provide Control.Applicative.Combinators.Expr

[turion]

The definitions in Control.Monad.Combinators.Expr are the only ones that don't exist as an Alternative version. Is it possible to create those as well?

[mrkkrp]

I would merge a PR adding that.

[turion]

I read the source a bit closer:

addPrecLevel :: MonadPlus m => m a -> [Operator m a] -> m a
addPrecLevel term ops =
  term' >>= \x -> choice [ras' x, las' x, nas' x, tern' x, return x]
  where
    ...

It seems to me that this is a usage of >>= that can't be replicated only with Applicative, right? But requiring a constraint (Monad m, Alternative m) without MonadPlus m seems silly. So I guess it actually can't be done?

We could still try and reduce MonadPlus m usage here and there (e.g. pTerm only needs Alternative I believe), but I guess we can't get rid of it completely?

[mrkkrp]

Indeed, perhaps that's the reason there is no applicative version.

[turion]

Ok I guess I'll close then until I have a better idea on what we could do.