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| author | Krzysztof Gogolewski <krzysztof.gogolewski@tweag.io> | 2021-01-08 11:57:32 +0100 |
|---|---|---|
| committer | Krzysztof Gogolewski <krzysztof.gogolewski@tweag.io> | 2021-01-08 12:16:20 +0100 |
| commit | c1e24faa9579dd4b50a46c65ebe3f3a292139422 (patch) | |
| tree | 94890ed5c935804f22a0fcc2938321a627943dcd /compiler/GHC/Tc/Gen/Default.hs | |
| parent | bd877edd9499a351db947cd51ed583872b2facdf (diff) | |
| download | haskell-wip/better-default.tar.gz | |
Improve defaulting detection codewip/better-default
As suggested at https://gitlab.haskell.org/ghc/ghc/-/merge_requests/4701#note_322397
This makes sure that the code does not create an ill-kinded type.
Diffstat (limited to 'compiler/GHC/Tc/Gen/Default.hs')
| -rw-r--r-- | compiler/GHC/Tc/Gen/Default.hs | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/compiler/GHC/Tc/Gen/Default.hs b/compiler/GHC/Tc/Gen/Default.hs index d37f26df40..0a50f3e983 100644 --- a/compiler/GHC/Tc/Gen/Default.hs +++ b/compiler/GHC/Tc/Gen/Default.hs @@ -12,6 +12,7 @@ import GHC.Prelude import GHC.Hs import GHC.Core.Class +import GHC.Core.Type (typeKind) import GHC.Tc.Utils.Monad import GHC.Tc.Utils.Env import GHC.Tc.Gen.HsType @@ -85,10 +86,10 @@ check_instance :: Type -> Class -> TcM Bool -- Check that ty is an instance of cls -- We only care about whether it worked or not; return a boolean check_instance ty cls - = do { (_, success) <- discardErrs $ - askNoErrs $ - simplifyDefault [mkClassPred cls [ty]] - ; return success } + | eqType (typeKind $ mkTyConTy $ classTyCon cls) + (mkVisFunTyMany (typeKind ty) constraintKind) + = simplifyDefault [mkClassPred cls [ty]] + | otherwise = return False defaultDeclCtxt :: SDoc defaultDeclCtxt = text "When checking the types in a default declaration" |