Fails to coerce between newtypes directly
import Data.Coerce
import Data.Type.Coercion
newtype W a = W a
newtype A = MkA (W A)
a :: Coercion A A
a = Coercion
b :: Coercion a a' -> Coercion a (W a')
b Coercion = Coercion
c :: Coercion A (W A)
c = b a
works just fine but the following fail:
-- • Couldn't match representation of type ‘A’ with that of ‘W A’
-- arising from a use of ‘Coercion’
-- • In the expression: Coercion
-- In an equation for ‘d’: d = Coercion
d :: Coercion A (W A)
d = Coercion
-- • Couldn't match representation of type ‘A’ with that of ‘W A’
-- arising from a use of ‘coerce’
-- • In the expression: coerce
-- In an equation for ‘e’: e = coerce
e :: A -> W A
e = coerce
Trac metadata
Trac field | Value |
---|---|
Version | 8.2.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |