Copyright	(c) The University of Glasgow 2009
License	see libraries/ghc-prim/LICENSE
Maintainer	ghc-devs@haskell.org
Stability	internal
Portability	non-portable (GHC Extensions)
Safe Haskell	Unsafe
Language	Haskell2010

GHC.Magic.Dict

Description

Defines the withDict function. For more information, see Note [withDict] in GHC.Tc.Instance.Class in GHC. The definition of withDict is located in a separate module from GHC.Magic because withDict is Unsafe (it threatens type class coherence) while GHC.Magic is Trustworthy.

Use GHC.Exts from the base package instead of importing this module directly.

Synopsis

class WithDict cls meth where
- withDict :: forall {rr :: RuntimeRep} (r :: TYPE rr). meth -> (cls => r) -> r

Documentation

class WithDict cls meth where Source #

The constraint WithDict cls meth can be solved when evidence for the constraint cls can be provided in the form of a dictionary of type meth. This requires cls to be a class constraint whose single method has type meth.

For more (important) details on how this works, see Note [withDict] in GHC.Tc.Instance.Class in GHC.

Since: ghc-prim-0.9.0

Methods

withDict :: forall {rr :: RuntimeRep} (r :: TYPE rr). meth -> (cls => r) -> r Source #