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Fix Trac #3261: make default types play nice with -Werror
[ghc-hetmet.git]
/
compiler
/
typecheck
/
TcSimplify.lhs
diff --git
a/compiler/typecheck/TcSimplify.lhs
b/compiler/typecheck/TcSimplify.lhs
index
7aaa1ae
..
cf29748
100644
(file)
--- a/
compiler/typecheck/TcSimplify.lhs
+++ b/
compiler/typecheck/TcSimplify.lhs
@@
-2903,12
+2903,16
@@
disambigGroup :: [Type] -- The default types
-> TcM () -- Just does unification, to fix the default types
disambigGroup default_tys dicts
-> TcM () -- Just does unification, to fix the default types
disambigGroup default_tys dicts
- = try_default default_tys
+ = do { mb_chosen_ty <- try_default default_tys
+ ; case mb_chosen_ty of
+ Nothing -> return ()
+ Just chosen_ty -> do { unifyType chosen_ty (mkTyVarTy tyvar)
+ ; warnDefault dicts chosen_ty } }
where
(_,_,tyvar) = ASSERT(not (null dicts)) head dicts -- Should be non-empty
classes = [c | (_,c,_) <- dicts]
where
(_,_,tyvar) = ASSERT(not (null dicts)) head dicts -- Should be non-empty
classes = [c | (_,c,_) <- dicts]
- try_default [] = return ()
+ try_default [] = return Nothing
try_default (default_ty : default_tys)
= tryTcLIE_ (try_default default_tys) $
do { tcSimplifyDefault [mkClassPred clas [default_ty] | clas <- classes]
try_default (default_ty : default_tys)
= tryTcLIE_ (try_default default_tys) $
do { tcSimplifyDefault [mkClassPred clas [default_ty] | clas <- classes]
@@
-2918,10
+2922,7
@@
disambigGroup default_tys dicts
-- For example, if Real a is reqd, but the only type in the
-- default list is Int.
-- For example, if Real a is reqd, but the only type in the
-- default list is Int.
- -- After this we can't fail
- ; warnDefault dicts default_ty
- ; unifyType default_ty (mkTyVarTy tyvar)
- ; return () -- TOMDO: do something with the coercion
+ ; return (Just default_ty) -- TOMDO: do something with the coercion
}
}