"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 famintThe 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 |