diff options
| author | Simon Peyton Jones <simonpj@microsoft.com> | 2017-04-13 09:23:39 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2017-04-13 09:26:45 +0100 |
| commit | 87078efd7d517a69f6737b4c40a73c063684c5cf (patch) | |
| tree | c99fe5afbd4c2d5fa9513464a336a26d76886a4d | |
| parent | fbb27d77b9c707008344f4c49fbb8d1015efb739 (diff) | |
| download | haskell-87078efd7d517a69f6737b4c40a73c063684c5cf.tar.gz | |
Comments only in Type.isPredTy
| -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 |