Barbies.Bare.Layered

Bare values

type family Wear t (f :: Type -> Type) a where ...

The Wear type-function allows one to define a Barbie-type as

data B t f
  = B { f1 :: Wear t f Int
      , f2 :: Wear t f Bool
      }

This gives rise to two rather different types:

• B Covered f is a normal Barbie-type, in the sense that f1 :: B Covered f -> f Int, etc.
• B Bare f, on the other hand, is a normal record with no functor around the type:

B { f1 :: 5, f2 = True } :: B Bare f

Equations

Wear Bare f a = a

Wear Covered f a = f a

Wear (Param _1 t) f a = Wear t f a

Wear t _1 _2 = TypeError (('Text "`Wear` should only be used with " :<>: 'Text "`Bare` or `Covered`.") :$$: ((('Text "`" :<>: 'ShowType t) :<>: 'Text "`") :<>: 'Text " is not allowed in this context.")) :: Type

data Bare

data Covered

Covering and stripping

class FunctorB (b Covered) => BareB b where

Class of Barbie-types defined using Wear and can therefore have Bare versions. Must satisfy:

bcover . bstrip = id
bstrip . bcover = id

Methods

bstrip :: b Covered Identity -> b Bare Identity

bcover :: b Bare Identity -> b Covered Identity

bstripFrom :: (BareB b, Functor f) => (forall a. f a -> a) -> b Covered f -> b Bare Identity

Generalization of bstrip to arbitrary functors.

bcoverWith :: (BareB b, Functor f) => (forall a. a -> f a) -> b Bare Identity -> b Covered f

Generalization of bcover to arbitrary functors.