Merge remote branch 'origin/master' into ghc-generics

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

diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs
index fd66cb8..dff85f3 100644 (file)
--- a/compiler/typecheck/TcDeriv.lhs
+++ b/compiler/typecheck/TcDeriv.lhs
@@ -1302,7 +1302,7 @@ inferInstanceContexts oflag infer_specs
     gen_soln (DS { ds_loc = loc, ds_orig = orig, ds_tvs = tyvars 
                 , ds_cls = clas, ds_tys = inst_tys, ds_theta = deriv_rhs })
       = setSrcSpan loc $
-       addErrCtxt (derivInstCtxt clas inst_tys) $ 
+       addErrCtxt (derivInstCtxt the_pred) $ 
        do {      -- Check for a bizarre corner case, when the derived instance decl should
                  -- have form  instance C a b => D (T a) where ...
                  -- Note that 'b' isn't a parameter of T.  This gives rise to all sorts
@@ -1317,7 +1317,7 @@ inferInstanceContexts oflag infer_specs
                                      , not (tyVarsOfPred pred `subVarSet` tv_set)]  
           ; mapM_ (addErrTc . badDerivedPred) weird_preds      
 
-           ; theta <- simplifyDeriv orig tyvars deriv_rhs
+           ; theta <- simplifyDeriv orig the_pred tyvars deriv_rhs
                -- checkValidInstance tyvars theta clas inst_tys
                -- Not necessary; see Note [Exotic derived instance contexts]
                --                in TcSimplify
@@ -1327,6 +1327,8 @@ inferInstanceContexts oflag infer_specs
                -- Hence no need to call:
                --   checkValidInstance tyvars theta clas inst_tys
           ; return (sortLe (<=) theta) }       -- Canonicalise before returning the solution
+      where
+        the_pred = mkClassPred clas inst_tys
 
 ------------------------------------------------------------------
 mkInstance :: OverlapFlag -> ThetaType -> DerivSpec -> Instance
@@ -1658,9 +1660,9 @@ standaloneCtxt :: LHsType Name -> SDoc
 standaloneCtxt ty = hang (ptext (sLit "In the stand-alone deriving instance for")) 
                       2 (quotes (ppr ty))
 
-derivInstCtxt :: Class -> [Type] -> Message
-derivInstCtxt clas inst_tys
-  = ptext (sLit "When deriving the instance for") <+> parens (pprClassPred clas inst_tys)
+derivInstCtxt :: PredType -> Message
+derivInstCtxt pred
+  = ptext (sLit "When deriving the instance for") <+> parens (ppr pred)
 
 badDerivedPred :: PredType -> Message
 badDerivedPred pred