Coercions from boxy splitters must be sym'ed in pattern matches

[ghc-hetmet.git] / compiler / typecheck / TcUnify.lhs

diff --git a/compiler/typecheck/TcUnify.lhs b/compiler/typecheck/TcUnify.lhs
index bd25c51..0893850 100644 (file)
--- a/compiler/typecheck/TcUnify.lhs
+++ b/compiler/typecheck/TcUnify.lhs
@@ -222,7 +222,7 @@ subFunTys error_herald n_pats res_ty thing_inside
 boxySplitTyConApp :: TyCon                     -- T :: k1 -> ... -> kn -> *
                  -> BoxyRhoType                -- Expected type (T a b c)
                  -> TcM ([BoxySigmaType],      -- Element types, a b c
-                          CoercionI)
+                          CoercionI)            -- T a b c ~ orig_ty
   -- It's used for wired-in tycons, so we call checkWiredInTyCon
   -- Precondition: never called with FunTyCon
   -- Precondition: input type :: *
@@ -314,7 +314,7 @@ boxySplitAppTy orig_ty
       | Just (fun_ty, arg_ty) <- tcSplitAppTy_maybe ty
       = return ((fun_ty, arg_ty), IdCo)
 
-    loop ty@(TyConApp tycon args)
+    loop ty@(TyConApp tycon _args)
       | isOpenSynTyCon tycon        -- try to normalise type family application
       = do { (coi1, ty') <- tcNormaliseFamInst ty
            ; case coi1 of