diff options
| -rw-r--r-- | compiler/main/DynFlags.hs | 1 | ||||
| -rw-r--r-- | compiler/typecheck/TcType.lhs | 3 | ||||
| -rw-r--r-- | docs/users_guide/flags.xml | 5 |
3 files changed, 7 insertions, 2 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] diff --git a/docs/users_guide/flags.xml b/docs/users_guide/flags.xml index c8e5dfc1d6..2bcb5e6d93 100644 --- a/docs/users_guide/flags.xml +++ b/docs/users_guide/flags.xml @@ -990,8 +990,9 @@ </row> <row> <entry><option>-XFlexibleInstances</option></entry> - <entry>Enable <link linkend="instance-rules">flexible instances</link>.</entry> - <entry>dynamic</entry> + <entry>Enable <link linkend="instance-rules">flexible instances</link>. + Implies <option>-XTypeSynonymInstances</option> </entry> + <entry>dynamic</entry> <entry><option>-XNoFlexibleInstances</option></entry> </row> <row> |