Desugarer needs an extra case for casts in coercions
Ganesh (via Darcs) found the code below crashes GHC 7.6rc1, thus:
ghc-stage1: panic! (the 'impossible' happened)
(GHC version 7.6.0 for x86_64-unknown-linux):
coVarsOfTcCo:Bind
cobox{v agK} [lid]
= cobox{v agY} [lid] `cast` (<main:Patch.WithState{tc reC}
(main:Patch.ModelOf{tc reH} prim{tv t1h} [tv])
prim{tv t1h} [tv]>
ghc-prim:GHC.Types.~{(w) tc 31Q} main:Patch.WithState{tc reC}
(main:Patch.ModelOf{tc reH}
(Sym cobox{v agV} [lid]))
<prim{tv t1h} [tv]>)
Problem is a missing case in DsBinds.ds_tc_coercion
.
Here's the test case
{-# LANGUAGE ImpredicativeTypes #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE TypeFamilies #-}
module Patch (qc_prim) where
class PrimPatch (prim :: * -> * -> *)
class PrimPatch (PrimOf p) => PrimPatchBase p where
type PrimOf (p :: * -> * -> *) :: * -> * -> *
type TestGenerator thing gen = (forall t ctx . (forall xx yy . thing xx yy -> t) -> (gen ctx -> t))
type family ModelOf (patch :: * -> * -> *) :: * -> *
data WithState s p x y = WithState {
_wsStartState :: s x
, _wsPatch :: p x y
, _wsEndState :: s y
}
arbitraryThing :: x -> TestGenerator thing (thing x)
arbitraryThing _ f p = f p
qc_prim :: forall prim x y .
(PrimPatch prim
, PrimOf prim ~ prim
) => prim x y -> [()]
qc_prim _ =
concat
[
patch_repo_properties (undefined :: prim x a) "arbitrary" arbitraryThing'
]
where arbitraryThing' = arbitraryThing (undefined :: a)
patch_repo_properties :: p x y -> String -> TestGenerator (WithState (ModelOf (PrimOf p)) p) gen -> [()]
patch_repo_properties _ _genname _gen = undefined
Thanks to Ganesh for isolating it out of Darcs.
Trac metadata
Trac field | Value |
---|---|
Version | 7.4.2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |