GHC chooses an instance between two overlapping, but cannot resolve a clause within the similar closed type family
We hoped that closed type families could replace overlapping instances. It is not currently the case: GHC can resolve overlapping instances but cannot resolve the similar closed type family.
I'm attaching a minimized example of program where it can be observed. This is reproducible on ghc-7.8.3 and HEAD.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.8.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |