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| author | simonpj@microsoft.com <unknown> | 2010-12-14 17:47:55 +0000 |
|---|---|---|
| committer | simonpj@microsoft.com <unknown> | 2010-12-14 17:47:55 +0000 |
| commit | 4d8c7c976104d2e39a1183967ec0f254a0fc0a47 (patch) | |
| tree | 48007aa4f9ebcef52a06c6bef6aa0e0e2db2dfbd /compiler | |
| parent | 492303f32eb179c14a095aa175541bdbff486179 (diff) | |
| download | haskell-4d8c7c976104d2e39a1183967ec0f254a0fc0a47.tar.gz | |
Fix Trac #4841: behave right with TypeSynonymInstances and NoFlexibleInstances
When we have TypeSynonymInstances without FlexibleInstances we should still
insist on a H98-style instance head, after looking through the synonym.
This patch also make FlexibleInstances imply TypeSynonymInstances. Anything
else is a bit awkward, and not very useful.
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/main/DynFlags.hs | 1 | ||||
| -rw-r--r-- | compiler/typecheck/TcType.lhs | 3 |
2 files changed, 4 insertions, 0 deletions
diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs index e3de00655f..8f6f45dc75 100644 --- a/compiler/main/DynFlags.hs +++ b/compiler/main/DynFlags.hs @@ -1658,6 +1658,7 @@ impliedFlags , (Opt_LiberalTypeSynonyms, turnOn, Opt_ExplicitForAll) , (Opt_ExistentialQuantification, turnOn, Opt_ExplicitForAll) , (Opt_PolymorphicComponents, turnOn, Opt_ExplicitForAll) + , (Opt_FlexibleInstances, turnOn, Opt_TypeSynonymInstances) , (Opt_RebindableSyntax, turnOff, Opt_ImplicitPrelude) -- NB: turn off! diff --git a/compiler/typecheck/TcType.lhs b/compiler/typecheck/TcType.lhs index 89aba6504f..50ac35ab50 100644 --- a/compiler/typecheck/TcType.lhs +++ b/compiler/typecheck/TcType.lhs @@ -956,6 +956,9 @@ tcInstHeadTyAppAllTyVars :: Type -> Bool -- Used in Haskell-98 mode, for the argument types of an instance head -- These must be a constructor applied to type variable arguments tcInstHeadTyAppAllTyVars ty + | Just ty' <- tcView ty -- Look through synonyms + = tcInstHeadTyAppAllTyVars ty' + | otherwise = case ty of TyConApp _ tys -> ok tys FunTy arg res -> ok [arg, res] |