Data.Comp.Multi.Projection

This module provides a generic projection function pr for arbitrary nested binary products.

Documentation

pr :: forall p q a. p :< q => q a -> p a

This function projects the component of type e out or the compound value of type p.

type (:<) f g = Proj (ComprEmb (Elem f g)) f g infixl 5

The constraint e :< p expresses that e is a component of the type p. That is, p is formed by binary products using the type e. The occurrence of e must be unique. For example we have Int :< (Bool,(Int,Bool)) but not Bool :< (Bool,(Int,Bool)).

data (f :*: g) a infixr 8

Formal product of signatures (functors).

Constructors

(f a) :*: (g a) infixr 8

Instances

(Functor f, Functor g) => Functor ((:*:) * f g)

(Foldable f, Foldable g) => Foldable ((:*:) * f g)

(Traversable f, Traversable g) => Traversable ((:*:) * f g)

ffst :: (f :*: g) a -> f a

fsnd :: (f :*: g) a -> g a