Modularised Prelude

[garyb]

This is not for merging just yet, as this formulation has some changes that will have impact elsewhere:

The following modules are currently defined in purescript-control but sans the actual classes. I've merged them in here, so I guess if we did this we'd want to remove them from control? Either that or reverse the dependency and Prelude would become something more like an even more minimal base.

• Data.Functor
• Control.Apply
• Control.Applicative
• Control.Bind
• Control.Monad

It seems like Data.Functor should belong in -functors now we have it, but that's not a great option without some work and dependency shuffling - it depends on tuples and foldable-traversable.

Other breaking changes we talked about:

• Removed the return alias for pure
• Removed the (++) alias for append

Some we didn't discuss, but seem worth considering:

• Renamed liftM1 to just liftM. I guess if we were going to include higher arity versions then keeping the 1 would make sense alternatively.
• Renamed the lift2...lift5 functions to liftAn to make them less ambiguous and to match liftA1.
• Moved when and unless into Control.Applicative and relaxed the Monad constraint to Applicative.

Some non-breaking changes/enhancements:

• Each Control module exports its Control dependencies, so if you import Applicative then you get Functor and associated operators in scope too.
• Same for the number hierarchy
• Added instances for functions in the style of (X b) => X (a -> b) as we had them on some classes and not others currently

There's a lot of stuff here, maybe we don't want any of it - that's fine, it was mainly to pass some time while on the road 😄

[paf31]

Whoa, this works now? 😄

[garyb]

Yep! You need to import qualified _ as _ though, import _ as _ doesn't work which perhaps should be added too.

[paf31]

👍 Looks nice.

[garyb]

I think I'll come back to this later. Perhaps we can squeeze in operator aliases just before we wrap up 0.8 - it'd be nice to not to have to break Prelude all over again when operator aliases land - probably can start tagging libraries as v1.0.0 once we get those in too?