diff options
Diffstat (limited to 'compiler/GHC/Tc/Solver/InertSet.hs')
| -rw-r--r-- | compiler/GHC/Tc/Solver/InertSet.hs | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/compiler/GHC/Tc/Solver/InertSet.hs b/compiler/GHC/Tc/Solver/InertSet.hs index b3dcb3f5b1..5dc3431b9a 100644 --- a/compiler/GHC/Tc/Solver/InertSet.hs +++ b/compiler/GHC/Tc/Solver/InertSet.hs @@ -1633,12 +1633,17 @@ mightEqualLater inert_set given_pred given_loc wanted_pred wanted_loc = False can_unify lhs_tv _other _rhs_ty = mentions_meta_ty_var lhs_tv -prohibitedSuperClassSolve :: CtLoc -> CtLoc -> Bool --- See Note [Solving superclass constraints] in GHC.Tc.TyCl.Instance -prohibitedSuperClassSolve from_loc solve_loc - | InstSCOrigin _ given_size <- ctLocOrigin from_loc - , ScOrigin wanted_size <- ctLocOrigin solve_loc - = given_size >= wanted_size +prohibitedSuperClassSolve :: CtLoc -- ^ is it loopy to use this one ... + -> CtLoc -- ^ ... to solve this one? + -> Bool -- ^ True ==> don't solve it +-- See Note [Solving superclass constraints] in GHC.Tc.TyCl.Instance, (sc2) +prohibitedSuperClassSolve given_loc wanted_loc + | GivenSCOrigin _ _ blocked <- ctLocOrigin given_loc + , blocked + , ScOrigin _ NakedSc <- ctLocOrigin wanted_loc + = True -- Prohibited if the Wanted is a superclass + -- and the Given has come via a superclass selection from + -- a predicate bigger than the head | otherwise = False |