diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/types/Type.hs | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/compiler/types/Type.hs b/compiler/types/Type.hs index 56fa938257..0b01f1db39 100644 --- a/compiler/types/Type.hs +++ b/compiler/types/Type.hs @@ -1662,6 +1662,7 @@ isPredTy ty = go ty [] -- -- 1. There is actually a kind error. Example in which this showed up: -- polykinds/T11399 + -- -- 2. A type constructor application appears to be oversaturated. An -- example of this occurred in GHC Trac #13187: -- @@ -1669,11 +1670,14 @@ isPredTy ty = go ty [] -- type Const a b = b -- f :: Const Int (,) Bool Char -> Char -- - -- This code is actually fine, since Const is polymorphic in its - -- return kind. It does show that isPredTy could possibly report a - -- false negative if a constraint is similarly oversaturated, but + -- We call isPredTy (Const k1 k2 Int (,) Bool Char + -- where k1,k2 are unification variables that have been + -- unified to *, and (*->*->*) resp, /but not zonked/. + -- This shows that isPredTy can report a false negative + -- if a constraint is similarly oversaturated, but -- it's hard to do better than isPredTy currently does without - -- zonking, so we punt on such cases for now. + -- zonking, so we punt on such cases for now. This only happens + -- during debug-printing, so it doesn't matter. isClassPred, isEqPred, isNomEqPred, isIPPred :: PredType -> Bool isClassPred ty = case tyConAppTyCon_maybe ty of |