Copyright | (c) 2014 Patrick Bahr |
---|---|
License | BSD3 |
Maintainer | Patrick Bahr <paba@di.ku.dk> |
Stability | experimental |
Portability | non-portable (GHC Extensions) |
Safe Haskell | Safe-Inferred |
Language | Haskell2010 |
This module provides a generic projection function pr
for
arbitrary nested binary products.
Documentation
pr :: forall p q. p :< q => q -> p Source #
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 Source #
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))
.