"Illegal type synonym family application in instance" error is unnecessary, should be removed
GHC shouldn't complain about "Illegal type synonym family application in instance", since there's an obvious workaround:
type family Fam t
instance C (Fam Int)
can become
type family Fam t
instance (Fam Int ~ famint) => C famint
The programmer ought to be smart enough to notice that Fam is not a type-constructor, so "Fam Int" is going to overlap like a type-variable.
Trac metadata
Trac field | Value |
---|---|
Version | 6.10.4 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |