Refactoring of hsXxxBinders

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

diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs
index 2aba527..af68408 100644 (file)
--- a/compiler/typecheck/TcDeriv.lhs
+++ b/compiler/typecheck/TcDeriv.lhs
@@ -436,10 +436,7 @@ makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
 
     all_tydata :: [(LHsType Name, LTyClDecl Name)]
        -- Derived predicate paired with its data type declaration
-    all_tydata = extractTyDataPreds tycl_decls ++
-                [ pd                -- Traverse assoc data families
-                 | L _ (InstDecl _ _ _ ats) <- inst_decls
-                , pd <- extractTyDataPreds ats ]
+    all_tydata = extractTyDataPreds (instDeclATs inst_decls ++ tycl_decls)
 
     deriv_locs = map (getLoc . snd) all_tydata
                 ++ map getLoc deriv_decls
@@ -743,7 +740,7 @@ inferConstraints :: [TyVar] -> Class -> [TcType] -> TyCon -> [TcType] -> ThetaTy
 -- Generate a sufficiently large set of constraints that typechecking the
 -- generated method definitions should succeed.   This set will be simplified
 -- before being used in the instance declaration
-inferConstraints tvs cls inst_tys rep_tc rep_tc_args
+inferConstraints _ cls inst_tys rep_tc rep_tc_args
   = ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr rep_tc )
     stupid_constraints ++ extra_constraints
     ++ sc_constraints ++ con_arg_constraints
@@ -784,15 +781,20 @@ inferConstraints tvs cls inst_tys rep_tc rep_tc_args
     stupid_constraints = substTheta subst (tyConStupidTheta rep_tc)
     subst = zipTopTvSubst rep_tc_tvs all_rep_tc_args
              
-       -- Extra constraints
+       -- Extra Data constraints
        -- The Data class (only) requires that for 
-       --    instance (...) => Data (T a b) 
-       -- then (Data a, Data b) are among the (...) constraints
-       -- Reason: that's what you need to typecheck the method
-       --             dataCast1 f = gcast1 f
+       --    instance (...) => Data (T t1 t2) 
+       -- IF   t1:*, t2:*
+       -- THEN (Data t1, Data t2) are among the (...) constraints
+       -- Reason: when the IF holds, we generate a method
+       --             dataCast2 f = gcast2 f
+       --         and we need the Data constraints to typecheck the method
     extra_constraints 
-      | cls `hasKey` dataClassKey = [mkClassPred cls [mkTyVarTy tv] | tv <- tvs]
-      | otherwise                = []
+      | cls `hasKey` dataClassKey
+      , all (isLiftedTypeKind . typeKind) rep_tc_args 
+      = [mkClassPred cls [ty] | ty <- rep_tc_args]
+      | otherwise 
+      = []
 
 ------------------------------------------------------------------
 -- Check side conditions that dis-allow derivability for particular classes
@@ -1295,6 +1297,7 @@ inferInstanceContexts oflag infer_specs
                 weird_preds = [pred | pred <- theta, not (tyVarsOfPred pred `subVarSet` tv_set)]  
           ; mapM_ (addErrTc . badDerivedPred) weird_preds      
 
+           ; traceTc (text "TcDeriv" <+> (ppr deriv_rhs $$ ppr theta))
                -- Claim: the result instance declaration is guaranteed valid
                -- Hence no need to call:
                --   checkValidInstance tyvars theta clas inst_tys