License | BSD-style (see the LICENSE file in the distribution) |
---|---|
Maintainer | libraries@haskell.org |
Stability | experimental |
Portability | not portable |
Safe Haskell | None |
Language | Haskell2010 |
Data.Type.Coercion
Description
Definition of representational equality (Coercion
).
Since: 4.7.0.0
Documentation
data Coercion a b where Source
Representational equality. If Coercion a b
is inhabited by some terminating
value, then the type a
has the same underlying representation as the type b
.
To use this equality in practice, pattern-match on the Coercion a b
to get out
the Coercible a b
instance, and then use coerce
to apply it.
Since: 4.7.0.0
Instances
Category k (Coercion k) | |
TestCoercion k (Coercion k a) | |
Coercible k a b => Bounded (Coercion k a b) | |
Coercible k a b => Enum (Coercion k a b) | |
Eq (Coercion k a b) | |
(Coercible (TYPE Lifted) a b, Data a, Data b) => Data (Coercion (TYPE Lifted) a b) | |
Ord (Coercion k a b) | |
Coercible k a b => Read (Coercion k a b) | |
Show (Coercion k a b) | |
coerceWith :: Coercion a b -> a -> b Source
Type-safe cast, using representational equality
trans :: Coercion a b -> Coercion b c -> Coercion a c Source
Transitivity of representational equality
repr :: (a :~: b) -> Coercion a b Source
Convert propositional (nominal) equality to representational equality
class TestCoercion f where Source
This class contains types where you can learn the equality of two types from information contained in terms. Typically, only singleton types should inhabit this class.
Minimal complete definition
Methods
testCoercion :: f a -> f b -> Maybe (Coercion a b) Source
Conditionally prove the representational equality of a
and b
.
Instances
TestCoercion k (Coercion k a) | |
TestCoercion k ((:~:) k a) | |