Can't unsafeCoerce a GADT with a coercion
type family Blah a
type instance Blah Int = Int
data E where
E :: (Blah a ~ Int) => a -> E
*Example Unsafe.Coerce GHC.Prim> (unsafeCoerce E) :: Any
<interactive>:1:15:
Couldn't match type `Blah a0' with `Int'
In the first argument of `unsafeCoerce', namely `E'
In the expression: (unsafeCoerce E) :: Any
In an equation for `it': it = (unsafeCoerce E) :: Any
This also doesn't work with less dangerous operators, like seq:
*Example Unsafe.Coerce GHC.Prim> (id E) `seq` ()
<interactive>:1:5:
Couldn't match type `Blah a0' with `Int'
In the first argument of `id', namely `E'
In the first argument of `seq', namely `(id E)'
In the expression: (id E) `seq` ()
Trac metadata
Trac field | Value |
---|---|
Version | 7.0.2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |