Panic when wrongly using a type family as return types for GADTs
The following code causes the following panic:
{-# LANGUAGE TypeFamilies, GADTs #-}
type family F a
data G1 a where
G1C :: F Int
data G2 a where
G2C :: F Intghc: panic! (the 'impossible' happened)
(GHC version 7.6.0.20120810 for x86_64-apple-darwin):
compiler/typecheck/TcTyClsDecls.lhs:1081:5-62: Irrefutable pattern failed for pattern Data.Maybe.Just substAdmittedly, the code causing the panic is silly, but it happened to me as I was refactoring. Having two separate GADTs with the wrong return types seems necessary to cause the panic.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.6.1-rc1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |