diff options
Diffstat (limited to 'compiler/GHC/Core/Predicate.hs')
| -rw-r--r-- | compiler/GHC/Core/Predicate.hs | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/compiler/GHC/Core/Predicate.hs b/compiler/GHC/Core/Predicate.hs index 9dd1a7b815..b3fde40055 100644 --- a/compiler/GHC/Core/Predicate.hs +++ b/compiler/GHC/Core/Predicate.hs @@ -19,7 +19,7 @@ module GHC.Core.Predicate ( mkHeteroPrimEqPred, mkHeteroReprPrimEqPred, -- Class predicates - mkClassPred, isDictTy, + mkClassPred, isDictTy, typeDeterminesValue, isClassPred, isEqPredClass, isCTupleClass, getClassPredTys, getClassPredTys_maybe, classMethodTy, classMethodInstTy, @@ -102,6 +102,10 @@ mkClassPred clas tys = mkTyConApp (classTyCon clas) tys isDictTy :: Type -> Bool isDictTy = isClassPred +typeDeterminesValue :: Type -> Bool +-- See Note [Type determines value] +typeDeterminesValue ty = isDictTy ty && not (isIPLikePred ty) + getClassPredTys :: HasDebugCallStack => PredType -> (Class, [Type]) getClassPredTys ty = case getClassPredTys_maybe ty of Just (clas, tys) -> (clas, tys) @@ -132,6 +136,19 @@ classMethodInstTy sel_id arg_tys = funResultTy $ piResultTys (varType sel_id) arg_tys +{- Note [Type determines value] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Only specialise on non-impicit-parameter predicates, because these +are the ones whose *type* determines their *value*. In particular, +with implicit params, the type args *don't* say what the value of the +implicit param is! See #7101. + +So we treat implicit params just like ordinary arguments for the +purposes of specialisation. Note that we still want to specialise +functions with implicit params if they have *other* dicts which are +class params; see #17930. +-} + -- --------------------- Equality predicates --------------------------------- -- | A choice of equality relation. This is separate from the type 'Role' |