| 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 * a b, Data a, Data b) => Data (Coercion * 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.
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) |