extract* Functions

[FintanH]

Add functions to extract out subclasses for more safety.

For example if foo takes an Applicative, i.e. { map = ..., ap = ..., pure ... } and a Monad is in scope the current approach is to do monad.{ map, ap, pure }. This should be available as Monad/extractApplicative. It should also exist for other typeclasses:

• Applicative/extractFunctor
• Monad/extractApplicative
• Traversable/extractFunctor
• Traversable/extractFoldable
• Monoid/extractSemigroup

[jkachmar]

With these functions in place, does it make sense to leave convenience functions in the package.dhall modules, or try to factor out all method usage in terms of extract*?

i.e. Applicative/Type would lose map = applicative.map and then usage would change from applicative.map to (extractFunctor f applicative).map

EDIT: Ah, nvm. I misinterpreted some of what this is