Barbies.Constraints

Support for operating on Barbie-types with constrained functions.

Instance dictionaries

data Dict c a where

Dict c a is evidence that there exists an instance of c a.

It is essentially equivalent to Dict (c a) from the constraints package, but because of its kind, it allows us to define things like Dict Show.

Constructors

Dict :: c a => Dict c a

Instances

Show1 (Dict c)

Defined in Barbies.Internal.Dicts

Methods

liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Dict c a -> ShowS

liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [Dict c a] -> ShowS

Show (Dict c a)

Defined in Barbies.Internal.Dicts

Methods

showsPrec :: Int -> Dict c a -> ShowS

show :: Dict c a -> String

showList :: [Dict c a] -> ShowS

Eq (Dict c a)

Defined in Barbies.Internal.Dicts

Methods

(==) :: Dict c a -> Dict c a -> Bool

(/=) :: Dict c a -> Dict c a -> Bool

requiringDict :: (c a => r) -> Dict c a -> r

Turn a constrained-function into an unconstrained one that uses the packed instance dictionary instead.

Getting constraints

type AllBF c f b = AllB (ClassF c f) b

Similar to AllB but will put the functor argument f between the constraint c and the type a. For example:

  AllB  Show   Person ~ (Show    String,  Show    Int)
  AllBF Show f Person ~ (Show (f String), Show (f Int))
  

class c (f a) => ClassF c f a

ClassF has one universal instance that makes ClassF c f a equivalent to c (f a). However, we have

'ClassF c f :: k -> Constraint

This is useful since it allows to define constraint-constructors like ClassF Monoid Maybe

Instances

c (f a) => ClassF (c :: k1 -> Constraint) (f :: k2 -> k1) (a :: k2)

Defined in Barbies.Internal.Dicts

class c (f a) (g a) => ClassFG c f g a

Like ClassF but for binary relations.

Instances

c (f a) (g a) => ClassFG (c :: k1 -> k2 -> Constraint) (f :: k3 -> k1) (g :: k3 -> k2) (a :: k3)

Defined in Barbies.Internal.Dicts