coerce fails for Coercible type families
I want to bring attention to this reddit post that boils down to
type family X a
type instance X Int = String
type instance X Bool = String
data T a = T (X a)
but not being able to coerce
coerce :: T Int -> T Bool
This gives the error “Couldn't match type ‘Int
’ with ‘Bool
’ arising from a use of ‘coerce
’”.
Trac metadata
Trac field | Value |
---|---|
Version | 8.6.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |