diff options
Diffstat (limited to 'compiler/deSugar')
| -rw-r--r-- | compiler/deSugar/Check.hs | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/compiler/deSugar/Check.hs b/compiler/deSugar/Check.hs index c1c260d0c8..81832c8982 100644 --- a/compiler/deSugar/Check.hs +++ b/compiler/deSugar/Check.hs @@ -491,6 +491,10 @@ pmTopNormaliseType_maybe :: FamInstEnvs -> Bag EvVar -> Type -- Behaves exactly like `topNormaliseType_maybe`, but instead of returning a -- coercion, it returns useful information for issuing pattern matching -- warnings. See Note [Type normalisation for EmptyCase] for details. +-- +-- NB: Normalisation can potentially change kinds, if the head of the type +-- is a type family with a variable result kind. I (Richard E) can't think +-- of a way to cause trouble here, though. pmTopNormaliseType_maybe env ty_cs typ = do (_, mb_typ') <- liftD $ initTcDsForSolver $ tcNormalise ty_cs typ -- Before proceeding, we chuck typ into the constraint solver, in case @@ -536,7 +540,7 @@ pmTopNormaliseType_maybe env ty_cs typ tyFamStepper :: NormaliseStepper ([Type] -> [Type], [DataCon] -> [DataCon]) tyFamStepper rec_nts tc tys -- Try to step a type/data family - = let (_args_co, ntys) = normaliseTcArgs env Representational tc tys in + = let (_args_co, ntys, _res_co) = normaliseTcArgs env Representational tc tys in -- NB: It's OK to use normaliseTcArgs here instead of -- normalise_tc_args (which takes the LiftingContext described -- in Note [Normalising types]) because the reduceTyFamApp below @@ -747,7 +751,7 @@ then type we get if we rewrite type families but not data families or newtypes. (b) dcs is the list of data constructors "skipped", every time we normalise a - newtype to it's core representation, we keep track of the source data + newtype to its core representation, we keep track of the source data constructor. (c) core_ty is the rewritten type. That is, pmTopNormaliseType_maybe env ty_cs ty = Just (src_ty, dcs, core_ty) |