X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcInstDcls.lhs;h=b05b5519429d7bf9f6e08c94255e0624355d0c03;hb=5c71a3bc3e9acfe3bee384a7948696aa5ac71646;hp=3e5584475fad2ce58176f07218d7478bbe27bcf8;hpb=c94408e522e5af3b79a5beadc7e6d15cee553ee7;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs
index 3e55844..b05b551 100644
--- a/compiler/typecheck/TcInstDcls.lhs
+++ b/compiler/typecheck/TcInstDcls.lhs
@@ -305,9 +305,13 @@ First comes the easy case of a non-local instance decl.
 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
 -- Returns a binding for the dfun
 
-		** Explain superclass stuff ***
-
+--
 -- Derived newtype instances
+--
+-- We need to make a copy of the dictionary we are deriving from
+-- because we may need to change some of the superclass dictionaries
+-- see Note [Newtype deriving superclasses] in TcDeriv.lhs
+--
 -- In the case of a newtype, things are rather easy
 -- 	class Show a => Foo a b where ...
 -- 	newtype T a = MkT (Tree [a]) deriving( Foo Int )
@@ -315,26 +319,50 @@ tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
 --	axiom CoT a :: Tree [a] = T a
 --
 -- So all need is to generate a binding looking like
--- 	dfunFooT :: forall a. (Show (T a), Foo Int (Tree [a]) => Foo Int (T a)
---	dfunFooT = /\a. \(ds:Show (T a) (df:Foo (Tree [a])).
+-- 	dfunFooT :: forall a. (Foo Int (Tree [a], Show (T a)) => Foo Int (T a)
+--	dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
 --		  case df `cast` (Foo Int (CoT a)) of
 --		     Foo _ op1 .. opn -> Foo ds op1 .. opn
 
 tcInstDecl2 (InstInfo { iSpec = ispec, 
-			iBinds = NewTypeDerived rep_tys })
-  = do	{ let dfun_id = instanceDFunId ispec 
-	      rigid_info = InstSkol dfun_id
-	      origin	 = SigOrigin rigid_info
-	      inst_ty    = idType dfun_id
+			iBinds = NewTypeDerived tycon rep_tys })
+  = do	{ let dfun_id      = instanceDFunId ispec 
+	      rigid_info   = InstSkol dfun_id
+	      origin	   = SigOrigin rigid_info
+	      inst_ty      = idType dfun_id
+              maybe_co_con = newTyConCo tycon
 	; (tvs, theta, inst_head) <- tcSkolSigType rigid_info inst_ty
-	; ASSERT( isSingleton theta )	-- Always the case for NewTypeDerived
-	  rep_dict <- newDict origin (head theta)
-
-	; let rep_dict_id = instToId rep_dict
-	      cast = 
-	      co_fn = CoTyLams tvs <.> CoLams [rep_dict_id] <.> ExprCoFn cast
-
-	; return (unitBag (VarBind dfun_id (HsCoerce co_fn (HsVar rep_dict_id))))
+	; dicts <- newDicts origin theta
+	; uniqs <- newUniqueSupply
+	; let (rep_dict_id:sc_dict_ids) = map instToId dicts
+		-- (Here, wee are relying on the order of dictionary 
+		-- arguments built by NewTypeDerived in TcDeriv.)
+
+              wrap_fn = CoTyLams tvs <.> CoLams dict_ids
+	 
+	      coerced_rep_dict = mkHsCoerce co_fn (HsVar rep_dict_id)
+
+	      body | null sc_dicts = coerced_rep_dict
+		   | otherwise = HsCase coerced_rep_dict $
+				 MatchGroup [the_match] inst_head
+	      the_match = mkSimpleMatch [the_pat] the_rhs
+	      op_ids = zipWith (mkSysLocal FSLIT("op"))
+			       (uniqsFromSupply uniqs) op_tys
+	      the_pat = ConPatOut { pat_con = cls_data_con, pat_tvs = [],
+				    pat_dicts = map (WildPat . idType) sc_dict_ids,
+				    pat_binds = emptyDictBinds,
+				    pat_args = PrefixCon (map VarPat op_ids), 
+				    pat_ty = <type of pattern> }
+	      the_rhs = mkHsApps (dataConWrapId cls_data_con) types sc_dict_ids (map HsVar op_ids)
+
+        ; return (unitBag (VarBind dfun_id (mkHsCoerce wrap_fn body))) }
+  where
+    co_fn :: ExprCoFn
+    co_fn | Just co_con <- newTyConCo tycon
+	  = ExprCoFn (mkAppCoercion (mkAppsCoercion tycon rep_tys) 
+                       		    (mkTyConApp co_con tvs))
+	  | otherwise
+	  = idCoerecion
 
 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys' 
 	  avail_insts op_items (NewTypeDerived rep_tys)
@@ -523,44 +551,6 @@ tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
     mapM tc_method_bind meth_infos		`thenM` \ meth_binds_s ->
    
     returnM (meth_ids, unionManyBags meth_binds_s)
-v v v v v v v
-*************
-
-
--- Derived newtype instances
-tcMethods origin clas inst_tyvars' dfun_theta' inst_tys' 
-	  avail_insts op_items (NewTypeDerived maybe_co rep_tys)
-  = getInstLoc origin				`thenM` \ inst_loc ->
-    mapAndUnzip3M (do_one inst_loc) op_items	`thenM` \ (meth_ids, meth_binds, rhs_insts) ->
-    
-    tcSimplifyCheck
-	 (ptext SLIT("newtype derived instance"))
-	 inst_tyvars' avail_insts rhs_insts	`thenM` \ lie_binds ->
-
-	-- I don't think we have to do the checkSigTyVars thing
-
-    returnM (meth_ids, lie_binds `unionBags` listToBag meth_binds)
-
-  where
-    do_one inst_loc (sel_id, _)
-	= -- The binding is like "op @ NewTy = op @ RepTy"
-		-- Make the *binder*, like in mkMethodBind
-	  tcInstClassOp inst_loc sel_id inst_tys'	`thenM` \ meth_inst ->
-
-		-- Make the *occurrence on the rhs*
-	  tcInstClassOp inst_loc sel_id rep_tys'	`thenM` \ rhs_inst ->
-	  let
-	     meth_id = instToId meth_inst
-	  in
-	  return (meth_id, noLoc (VarBind meth_id (nlHsVar (instToId rhs_inst))), rhs_inst)
-
-	-- Instantiate rep_tys with the relevant type variables
-	-- This looks a bit odd, because inst_tyvars' are the skolemised version
-	-- of the type variables in the instance declaration; but rep_tys doesn't
-	-- have the skolemised version, so we substitute them in here
-    rep_tys' = substTys subst rep_tys
-    subst    = zipOpenTvSubst inst_tyvars' (mkTyVarTys inst_tyvars')
-^ ^ ^ ^ ^ ^ ^
 \end{code}