Remove old, redundant note

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

diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs
index e7c472b..96e63aa 100644 (file)
--- a/compiler/typecheck/TcInstDcls.lhs
+++ b/compiler/typecheck/TcInstDcls.lhs
@@ -21,17 +21,19 @@ import FamInst
 import FamInstEnv
 import TcDeriv
 import TcEnv
 import FamInstEnv
 import TcDeriv
 import TcEnv

-import RnEnv   ( lookupImportedName )
+import RnEnv   ( lookupGlobalOccRn )
+import RnSource ( addTcgDUs )

 import TcHsType
 import TcUnify
 import TcSimplify
 import Type
 import Coercion
 import TyCon
 import TcHsType
 import TcUnify
 import TcSimplify
 import Type
 import Coercion
 import TyCon

-import TypeRep

 import DataCon
 import Class
 import Var
 import DataCon
 import Class
 import Var

+import CoreUnfold ( mkDFunUnfolding )
+import PrelNames  ( inlineIdName )

 import Id
 import MkId
 import Name
 import Id
 import MkId
 import Name

@@ -91,6 +93,7 @@ Running example:
 
        -- A top-level definition for each instance method
        -- Here op1_i, op2_i are the "instance method Ids"
 
        -- A top-level definition for each instance method
        -- Here op1_i, op2_i are the "instance method Ids"

+       -- The INLINE pragma comes from the user pragma

        {-# INLINE [2] op1_i #-}  -- From the instance decl bindings
        op1_i, op2_i :: forall a. C a => forall b. Ix b => [a] -> b -> b
        op1_i = /\a. \(d:C a). 
        {-# INLINE [2] op1_i #-}  -- From the instance decl bindings
        op1_i, op2_i :: forall a. C a => forall b. Ix b => [a] -> b -> b
        op1_i = /\a. \(d:C a). 

@@ -109,24 +112,26 @@ Running example:
        op2_i = /\a \d:C a. $dmop2 [a] (df_i a d) 
 
        -- The dictionary function itself
        op2_i = /\a \d:C a. $dmop2 [a] (df_i a d) 
 
        -- The dictionary function itself

-       {-# INLINE df_i #-}     -- Always inline dictionary functions
+       {-# NOINLINE CONLIKE df_i #-}   -- Never inline dictionary functions

        df_i :: forall a. C a -> C [a]
        df_i :: forall a. C a -> C [a]

-       df_i = /\a. \d:C a. letrec d' = MkC (op1_i  a   d)
-                                            ($dmop2 [a] d')
-                           in d'
+       df_i = /\a. \d:C a. MkC (op1_i a d) (op2_i a d)

                -- But see Note [Default methods in instances]
                -- We can't apply the type checker to the default-method call
 
                -- But see Note [Default methods in instances]
                -- We can't apply the type checker to the default-method call
 

-* The dictionary function itself is inlined as vigorously as we
+        -- Use a RULE to short-circuit applications of the class ops
+       {-# RULE "op1@C[a]" forall a, d:C a. 
+                            op1 [a] (df_i d) = op1_i a d #-}
+
+* We want to inline the dictionary function itself as vigorously as we

   possibly can, so that we expose that dictionary constructor to
   possibly can, so that we expose that dictionary constructor to

-  selectors as much as poss.  That is why the op_i stuff is in 
-  *separate* bindings, so that the df_i binding is small enough
-  to inline.  See Note [Inline dfuns unconditionally].
+  selectors as much as poss.  We don't actually inline it; rather, we
+  use a Builtin RULE for the ClassOps (see MkId.mkDictSelId) to short
+  circuit such applications.  But the RULE only applies if it can "see"
+  the dfun's DFunUnfolding. 

 
 * Note that df_i may be mutually recursive with both op1_i and op2_i.
   It's crucial that df_i is not chosen as the loop breaker, even 
   though op1_i has a (user-specified) INLINE pragma.
 
 * Note that df_i may be mutually recursive with both op1_i and op2_i.
   It's crucial that df_i is not chosen as the loop breaker, even 
   though op1_i has a (user-specified) INLINE pragma.

-  Not even once!  Else op1_i, op2_i may be inlined into df_i.

 
 * Instead the idea is to inline df_i into op1_i, which may then select
   methods from the MkC record, and thereby break the recursion with
 
 * Instead the idea is to inline df_i into op1_i, which may then select
   methods from the MkC record, and thereby break the recursion with

@@ -137,8 +142,10 @@ Running example:
 * If op1_i is marked INLINE by the user there's a danger that we won't
   inline df_i in it, and that in turn means that (since it'll be a
   loop-breaker because df_i isn't), op1_i will ironically never be 
 * If op1_i is marked INLINE by the user there's a danger that we won't
   inline df_i in it, and that in turn means that (since it'll be a
   loop-breaker because df_i isn't), op1_i will ironically never be 

-  inlined.  We need to fix this somehow -- perhaps allowing inlining
-  of INLINE funcitons inside other INLINE functions.
+  inlined.  But this is OK: the recursion breaking happens by way of
+  a RULE (the magic ClassOp rule above), and RULES work inside InlineRule
+  unfoldings. See Note [RULEs enabled in SimplGently] in SimplUtils
+

 
 Note [Subtle interaction of recursion and overlap]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Note [Subtle interaction of recursion and overlap]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

@@ -180,7 +187,7 @@ to have C [a] available.  That is why we have the strange local
 definition for 'this' in the definition of op1_i in the example above.
 We can typecheck the defintion of local_op1, and when doing tcSimplifyCheck
 we supply 'this' as a given dictionary.  Only needed, though, if there
 definition for 'this' in the definition of op1_i in the example above.
 We can typecheck the defintion of local_op1, and when doing tcSimplifyCheck
 we supply 'this' as a given dictionary.  Only needed, though, if there

-are some type variales involved; otherwise there can be no overlap and
+are some type variables involved; otherwise there can be no overlap and

 none of this arises.
 
 Note [Tricky type variable scoping]
 none of this arises.
 
 Note [Tricky type variable scoping]

@@ -201,93 +208,6 @@ which brings appropriate tyvars into scope. This happens for both
 <dm-rhs> and for <rhs>, but that doesn't matter: the *renamer* will have
 complained if 'b' is mentioned in <rhs>.
 
 <dm-rhs> and for <rhs>, but that doesn't matter: the *renamer* will have
 complained if 'b' is mentioned in <rhs>.
 

-Note [Inline dfuns unconditionally]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The code above unconditionally inlines dict funs.  Here's why.
-Consider this program:
-
-    test :: Int -> Int -> Bool
-    test x y = (x,y) == (y,x) || test y x
-    -- Recursive to avoid making it inline.
-
-This needs the (Eq (Int,Int)) instance.  If we inline that dfun
-the code we end up with is good:
-
-    Test.$wtest =
-        \r -> case ==# [ww ww1] of wild {
-                PrelBase.False -> Test.$wtest ww1 ww;
-                PrelBase.True ->
-                  case ==# [ww1 ww] of wild1 {
-                    PrelBase.False -> Test.$wtest ww1 ww;
-                    PrelBase.True -> PrelBase.True [];
-                  };
-            };
-    Test.test = \r [w w1]
-            case w of w2 {
-              PrelBase.I# ww ->
-                  case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
-            };
-
-If we don't inline the dfun, the code is not nearly as good:
-
-    (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
-              PrelBase.:DEq tpl1 tpl2 -> tpl2;
-            };
-
-    Test.$wtest =
-        \r [ww ww1]
-            let { y = PrelBase.I#! [ww1]; } in
-            let { x = PrelBase.I#! [ww]; } in
-            let { sat_slx = PrelTup.(,)! [y x]; } in
-            let { sat_sly = PrelTup.(,)! [x y];
-            } in
-              case == sat_sly sat_slx of wild {
-                PrelBase.False -> Test.$wtest ww1 ww;
-                PrelBase.True -> PrelBase.True [];
-              };
-
-    Test.test =
-        \r [w w1]
-            case w of w2 {
-              PrelBase.I# ww ->
-                  case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
-            };
-
-Why didn't GHC inline $fEq in those days?  Because it looked big:
-
-    PrelTup.zdfEqZ1T{-rcX-}
-        = \ @ a{-reT-} :: * @ b{-reS-} :: *
-            zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
-            zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
-            let {
-              zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
-              zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
-            let {
-              zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
-              zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
-            let {
-              zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
-              zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
-                               ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
-                             case ds{-rf5-}
-                             of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
-                             case ds1{-rf4-}
-                             of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
-                             PrelBase.zaza{-r4e-}
-                               (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
-                               (zeze{-rf0-} a2{-reZ-} b2{-reY-})
-                             }
-                             } } in
-            let {
-              a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
-              a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
-                            b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
-                          PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
-            } in
-              PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
-
-and it's not as bad as it seems, because it's further dramatically
-simplified: only zeze2 is extracted and its body is simplified.

 
 
 %************************************************************************
 
 
 %************************************************************************

@@ -321,14 +241,15 @@ tcInstDecls1 tycl_decls inst_decls deriv_decls
 
        ; let { (local_info,
                 at_tycons_s)   = unzip local_info_tycons
 
        ; let { (local_info,
                 at_tycons_s)   = unzip local_info_tycons

-             ; at_idx_tycon    = concat at_tycons_s ++ idx_tycons
+             ; at_idx_tycons   = concat at_tycons_s ++ idx_tycons

              ; clas_decls      = filter (isClassDecl.unLoc) tycl_decls
              ; clas_decls      = filter (isClassDecl.unLoc) tycl_decls

-             ; implicit_things = concatMap implicitTyThings at_idx_tycon
+             ; implicit_things = concatMap implicitTyThings at_idx_tycons
+            ; aux_binds       = mkAuxBinds at_idx_tycons

              }
 
                 -- (2) Add the tycons of indexed types and their implicit
                 --     tythings to the global environment
              }
 
                 -- (2) Add the tycons of indexed types and their implicit
                 --     tythings to the global environment

-       ; tcExtendGlobalEnv (at_idx_tycon ++ implicit_things) $ do {
+       ; tcExtendGlobalEnv (at_idx_tycons ++ implicit_things) $ do {

 
                 -- (3) Instances from generic class declarations
        ; generic_inst_info <- getGenericInstances clas_decls
 
                 -- (3) Instances from generic class declarations
        ; generic_inst_info <- getGenericInstances clas_decls

@@ -338,9 +259,9 @@ tcInstDecls1 tycl_decls inst_decls deriv_decls
                 --   a) local instance decls
                 --   b) generic instances
                 --   c) local family instance decls
                 --   a) local instance decls
                 --   b) generic instances
                 --   c) local family instance decls

-       ; addInsts local_info         $ do {
-       ; addInsts generic_inst_info  $ do {
-       ; addFamInsts at_idx_tycon    $ do {
+       ; addInsts local_info         $
+         addInsts generic_inst_info  $
+         addFamInsts at_idx_tycons   $ do {

 
                 -- (4) Compute instances from "deriving" clauses;
                 -- This stuff computes a context for the derived instance
 
                 -- (4) Compute instances from "deriving" clauses;
                 -- This stuff computes a context for the derived instance

@@ -350,15 +271,13 @@ tcInstDecls1 tycl_decls inst_decls deriv_decls
         failIfErrsM            -- If the addInsts stuff gave any errors, don't
                                -- try the deriving stuff, becuase that may give
                                -- more errors still
         failIfErrsM            -- If the addInsts stuff gave any errors, don't
                                -- try the deriving stuff, becuase that may give
                                -- more errors still

-       ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls inst_decls
-                                                      deriv_decls
-       ; addInsts deriv_inst_info   $ do {
-
-       ; gbl_env <- getGblEnv
-       ; return (gbl_env,
+       ; (deriv_inst_info, deriv_binds, deriv_dus) 
+              <- tcDeriving tycl_decls inst_decls deriv_decls
+       ; gbl_env <- addInsts deriv_inst_info getGblEnv
+       ; return ( addTcgDUs gbl_env deriv_dus,

                   generic_inst_info ++ deriv_inst_info ++ local_info,
                   generic_inst_info ++ deriv_inst_info ++ local_info,

-                  deriv_binds)
-    }}}}}}
+                  aux_binds `plusHsValBinds` deriv_binds)
+    }}}

   where
     -- Make sure that toplevel type instance are not for associated types.
     -- !!!TODO: Need to perform this check for the TyThing of type functions,
   where
     -- Make sure that toplevel type instance are not for associated types.
     -- !!!TODO: Need to perform this check for the TyThing of type functions,

@@ -433,7 +352,7 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats))
               ispec          = mkLocalInstance dfun overlap_flag
 
         ; return (InstInfo { iSpec  = ispec,
               ispec          = mkLocalInstance dfun overlap_flag
 
         ; return (InstInfo { iSpec  = ispec,

-                              iBinds = VanillaInst binds uprags },
+                             iBinds = VanillaInst binds uprags False },

                   idx_tycons)
         }
   where
                   idx_tycons)
         }
   where

@@ -461,11 +380,11 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats))
            ; mapM_ (checkIndexes clas inst_tys) ats
            }
 
            ; mapM_ (checkIndexes clas inst_tys) ats
            }
 

-    checkIndexes clas inst_tys (hsAT, ATyCon tycon) =
+    checkIndexes clas inst_tys (hsAT, ATyCon tycon)

 -- !!!TODO: check that this does the Right Thing for indexed synonyms, too!
 -- !!!TODO: check that this does the Right Thing for indexed synonyms, too!

-      checkIndexes' clas inst_tys hsAT
-                    (tyConTyVars tycon,
-                     snd . fromJust . tyConFamInst_maybe $ tycon)
+      = checkIndexes' clas inst_tys hsAT
+                      (tyConTyVars tycon,
+                       snd . fromJust . tyConFamInst_maybe $ tycon)

     checkIndexes _ _ _ = panic "checkIndexes"
 
     checkIndexes' clas (instTvs, instTys) hsAT (atTvs, atTys)
     checkIndexes _ _ _ = panic "checkIndexes"
 
     checkIndexes' clas (instTvs, instTys) hsAT (atTvs, atTys)

@@ -475,8 +394,8 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats))
         addErrCtxt (atInstCtxt atName) $
         case find ((atName ==) . tyConName) (classATs clas) of
           Nothing     -> addErrTc $ badATErr clas atName  -- not in this class
         addErrCtxt (atInstCtxt atName) $
         case find ((atName ==) . tyConName) (classATs clas) of
           Nothing     -> addErrTc $ badATErr clas atName  -- not in this class

-          Just atDecl ->
-            case assocTyConArgPoss_maybe atDecl of
+          Just atycon ->
+            case assocTyConArgPoss_maybe atycon of

               Nothing   -> panic "checkIndexes': AT has no args poss?!?"
               Just poss ->
 
               Nothing   -> panic "checkIndexes': AT has no args poss?!?"
               Just poss ->
 

@@ -487,6 +406,13 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats))
                 -- which must be type variables; and (3) variables in AT and
                 -- instance head will be different `Name's even if their
                 -- source lexemes are identical.
                 -- which must be type variables; and (3) variables in AT and
                 -- instance head will be different `Name's even if their
                 -- source lexemes are identical.

+               --
+               -- e.g.    class C a b c where 
+               --           data D b a :: * -> *           -- NB (1) b a, omits c
+               --         instance C [x] Bool Char where 
+               --           data D Bool [x] v = MkD x [v]  -- NB (2) v
+               --                -- NB (3) the x in 'instance C...' have differnt
+               --                --        Names to x's in 'data D...'

                 --
                 -- Re (1), `poss' contains a permutation vector to extract the
                 -- class parameters in the right order.
                 --
                 -- Re (1), `poss' contains a permutation vector to extract the
                 -- class parameters in the right order.

@@ -545,23 +471,34 @@ tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo Name]
 
 tcInstDecls2 tycl_decls inst_decls
   = do  { -- (a) Default methods from class decls
 
 tcInstDecls2 tycl_decls inst_decls
   = do  { -- (a) Default methods from class decls

-          (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
-                                    filter (isClassDecl.unLoc) tycl_decls
-        ; tcExtendIdEnv (concat dm_ids_s) $ do
+          let class_decls = filter (isClassDecl . unLoc) tycl_decls
+        ; (dm_ids_s, dm_binds_s) <- mapAndUnzipM tcClassDecl2 class_decls
+                                    
+       ; tcExtendIdEnv (concat dm_ids_s) $ do 

 
           -- (b) instance declarations
 
           -- (b) instance declarations

-        ; inst_binds_s <- mapM tcInstDecl2 inst_decls
+        { inst_binds_s <- mapM tcInstDecl2 inst_decls

 
           -- Done
         ; let binds = unionManyBags dm_binds_s `unionBags`
                       unionManyBags inst_binds_s
         ; tcl_env <- getLclEnv -- Default method Ids in here
 
           -- Done
         ; let binds = unionManyBags dm_binds_s `unionBags`
                       unionManyBags inst_binds_s
         ; tcl_env <- getLclEnv -- Default method Ids in here

-        ; return (binds, tcl_env) }
+        ; return (binds, tcl_env) } }
+
+tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id)
+tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = ibinds })
+  = recoverM (return emptyLHsBinds)             $
+    setSrcSpan loc                              $
+    addErrCtxt (instDeclCtxt2 (idType dfun_id)) $ 
+    tc_inst_decl2 dfun_id ibinds
+ where
+    dfun_id = instanceDFunId ispec
+    loc     = getSrcSpan dfun_id

 \end{code}
 
 
 \begin{code}
 \end{code}
 
 
 \begin{code}

-tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id)
+tc_inst_decl2 :: Id -> InstBindings Name -> TcM (LHsBinds Id)

 -- Returns a binding for the dfun
 
 ------------------------
 -- Returns a binding for the dfun
 
 ------------------------

@@ -583,11 +520,11 @@ tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id)
 -- If there are no superclasses, matters are simpler, because we don't need the case
 -- see Note [Newtype deriving superclasses] in TcDeriv.lhs
 
 -- If there are no superclasses, matters are simpler, because we don't need the case
 -- see Note [Newtype deriving superclasses] in TcDeriv.lhs
 

-tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived })
-  = do  { let dfun_id      = instanceDFunId ispec
-              rigid_info   = InstSkol
-              origin       = SigOrigin rigid_info
-              inst_ty      = idType dfun_id
+tc_inst_decl2 dfun_id (NewTypeDerived coi)
+  = do  { let rigid_info = InstSkol
+              origin     = SigOrigin rigid_info
+              inst_ty    = idType dfun_id
+             inst_tvs   = fst (tcSplitForAllTys inst_ty)

         ; (inst_tvs', theta, inst_head_ty) <- tcSkolSigType rigid_info inst_ty
                 -- inst_head_ty is a PredType
 
         ; (inst_tvs', theta, inst_head_ty) <- tcSkolSigType rigid_info inst_ty
                 -- inst_head_ty is a PredType
 

@@ -595,22 +532,41 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived })
               (class_tyvars, sc_theta, _, _) = classBigSig cls
               cls_tycon = classTyCon cls
               sc_theta' = substTheta (zipOpenTvSubst class_tyvars cls_inst_tys) sc_theta
               (class_tyvars, sc_theta, _, _) = classBigSig cls
               cls_tycon = classTyCon cls
               sc_theta' = substTheta (zipOpenTvSubst class_tyvars cls_inst_tys) sc_theta

-

               Just (initial_cls_inst_tys, last_ty) = snocView cls_inst_tys
               Just (initial_cls_inst_tys, last_ty) = snocView cls_inst_tys

-              (nt_tycon, tc_args) = tcSplitTyConApp last_ty     -- Can't fail
-              rep_ty              = newTyConInstRhs nt_tycon tc_args

 
 

-              rep_pred     = mkClassPred cls (initial_cls_inst_tys ++ [rep_ty])
-                                -- In our example, rep_pred is (Foo Int (Tree [a]))
-              the_coercion = make_coercion cls_tycon initial_cls_inst_tys nt_tycon tc_args
-                                -- Coercion of kind (Foo Int (Tree [a]) ~ Foo Int (N a)
+              (rep_ty, wrapper) 
+                = case coi of
+                    IdCo   -> (last_ty, idHsWrapper)
+                    ACo co -> (snd (coercionKind co'), WpCast (mk_full_coercion co'))
+                           where
+                              co' = substTyWith inst_tvs (mkTyVarTys inst_tvs') co
+                               -- NB: the free variable of coi are bound by the
+                               -- universally quantified variables of the dfun_id
+                               -- This is weird, and maybe we should make NewTypeDerived
+                               -- carry a type-variable list too; but it works fine
+
+                -----------------------
+                --        mk_full_coercion
+                -- The inst_head looks like (C s1 .. sm (T a1 .. ak))
+                -- But we want the coercion (C s1 .. sm (sym (CoT a1 .. ak)))
+                --        with kind (C s1 .. sm (T a1 .. ak)  ~  C s1 .. sm <rep_ty>)
+                --        where rep_ty is the (eta-reduced) type rep of T
+                -- So we just replace T with CoT, and insert a 'sym'
+                -- NB: we know that k will be >= arity of CoT, because the latter fully eta-reduced
+
+             mk_full_coercion co = mkTyConApp cls_tycon 
+                                        (initial_cls_inst_tys ++ [mkSymCoercion co])
+                 -- Full coercion : (Foo Int (Tree [a]) ~ Foo Int (N a)
+
+              rep_pred = mkClassPred cls (initial_cls_inst_tys ++ [rep_ty])
+                 -- In our example, rep_pred is (Foo Int (Tree [a]))

 
         ; sc_loc     <- getInstLoc InstScOrigin
         ; sc_dicts   <- newDictBndrs sc_loc sc_theta'
         ; inst_loc   <- getInstLoc origin
         ; dfun_dicts <- newDictBndrs inst_loc theta
 
         ; sc_loc     <- getInstLoc InstScOrigin
         ; sc_dicts   <- newDictBndrs sc_loc sc_theta'
         ; inst_loc   <- getInstLoc origin
         ; dfun_dicts <- newDictBndrs inst_loc theta

-        ; this_dict  <- newDictBndr inst_loc (mkClassPred cls cls_inst_tys)

         ; rep_dict   <- newDictBndr inst_loc rep_pred
         ; rep_dict   <- newDictBndr inst_loc rep_pred

+        ; this_dict  <- newDictBndr inst_loc (mkClassPred cls cls_inst_tys)

 
         -- Figure out bindings for the superclass context from dfun_dicts
         -- Don't include this_dict in the 'givens', else
 
         -- Figure out bindings for the superclass context from dfun_dicts
         -- Don't include this_dict in the 'givens', else

@@ -623,10 +579,10 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived })
        -- in the envt with one of the clas_tyvars
        ; checkSigTyVars inst_tvs'
 
        -- in the envt with one of the clas_tyvars
        ; checkSigTyVars inst_tvs'
 

-        ; let coerced_rep_dict = wrapId the_coercion (instToId rep_dict)
+        ; let coerced_rep_dict = wrapId wrapper (instToId rep_dict)

 
         ; body <- make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict
 
         ; body <- make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict

-        ; let dict_bind = noLoc $ VarBind (instToId this_dict) (noLoc body)
+       ; let dict_bind = mkVarBind (instToId this_dict) (noLoc body)

 
         ; return (unitBag $ noLoc $
                   AbsBinds inst_tvs' (map instToVar dfun_dicts)
 
         ; return (unitBag $ noLoc $
                   AbsBinds inst_tvs' (map instToVar dfun_dicts)

@@ -634,22 +590,6 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived })
                             (dict_bind `consBag` sc_binds)) }
   where
       -----------------------
                             (dict_bind `consBag` sc_binds)) }
   where
       -----------------------

-      --        make_coercion
-      -- The inst_head looks like (C s1 .. sm (T a1 .. ak))
-      -- But we want the coercion (C s1 .. sm (sym (CoT a1 .. ak)))
-      --        with kind (C s1 .. sm (T a1 .. ak)  ~  C s1 .. sm <rep_ty>)
-      --        where rep_ty is the (eta-reduced) type rep of T
-      -- So we just replace T with CoT, and insert a 'sym'
-      -- NB: we know that k will be >= arity of CoT, because the latter fully eta-reduced
-
-    make_coercion cls_tycon initial_cls_inst_tys nt_tycon tc_args
-        | Just co_con <- newTyConCo_maybe nt_tycon
-        , let co = mkSymCoercion (mkTyConApp co_con tc_args)
-        = WpCast (mkTyConApp cls_tycon (initial_cls_inst_tys ++ [co]))
-        | otherwise     -- The newtype is transparent; no need for a cast
-        = idHsWrapper
-
-      -----------------------

       --     (make_body C tys scs coreced_rep_dict)
       --                returns
       --     (case coerced_rep_dict of { C _ ops -> C scs ops })
       --     (make_body C tys scs coreced_rep_dict)
       --                returns
       --     (case coerced_rep_dict of { C _ ops -> C scs ops })

@@ -686,103 +626,137 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived })
 ------------------------
 -- Ordinary instances
 
 ------------------------
 -- Ordinary instances
 

-tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })
-  = let
-        dfun_id    = instanceDFunId ispec
-        rigid_info = InstSkol
-        inst_ty    = idType dfun_id
-        loc        = getSrcSpan dfun_id
-    in
-         -- Prime error recovery
-    recoverM (return emptyLHsBinds)             $
-    setSrcSpan loc                              $
-    addErrCtxt (instDeclCtxt2 (idType dfun_id)) $ do
+tc_inst_decl2 dfun_id (VanillaInst monobinds uprags standalone_deriv)
+  = do { let rigid_info = InstSkol
+             inst_ty    = idType dfun_id
+             loc        = getSrcSpan dfun_id

 
         -- Instantiate the instance decl with skolem constants
 
         -- Instantiate the instance decl with skolem constants

-    (inst_tyvars', dfun_theta', inst_head') <- tcSkolSigType rigid_info inst_ty
+       ; (inst_tyvars', dfun_theta', inst_head') <- tcSkolSigType rigid_info inst_ty

                 -- These inst_tyvars' scope over the 'where' part
                 -- Those tyvars are inside the dfun_id's type, which is a bit
                 -- bizarre, but OK so long as you realise it!
                 -- These inst_tyvars' scope over the 'where' part
                 -- Those tyvars are inside the dfun_id's type, which is a bit
                 -- bizarre, but OK so long as you realise it!

-    let
-        (clas, inst_tys') = tcSplitDFunHead inst_head'
-        (class_tyvars, sc_theta, _, op_items) = classBigSig clas
+       ; let
+            (clas, inst_tys') = tcSplitDFunHead inst_head'
+            (class_tyvars, sc_theta, sc_sels, op_items) = classBigSig clas

 
 

-        -- Instantiate the super-class context with inst_tys
-        sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
-        origin    = SigOrigin rigid_info
+             -- Instantiate the super-class context with inst_tys
+            sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
+            origin    = SigOrigin rigid_info

 
          -- Create dictionary Ids from the specified instance contexts.
 
          -- Create dictionary Ids from the specified instance contexts.

-    sc_loc      <- getInstLoc InstScOrigin
-    sc_dicts    <- newDictOccs sc_loc sc_theta'                -- These are wanted
-    inst_loc    <- getInstLoc origin
-    dfun_dicts  <- newDictBndrs inst_loc dfun_theta'   -- Includes equalities
-    this_dict   <- newDictBndr inst_loc (mkClassPred clas inst_tys')
+       ; inst_loc   <- getInstLoc origin
+       ; dfun_dicts <- newDictBndrs inst_loc dfun_theta'       -- Includes equalities
+       ; this_dict  <- newDictBndr inst_loc (mkClassPred clas inst_tys')

                 -- Default-method Ids may be mentioned in synthesised RHSs,
                 -- but they'll already be in the environment.
 
                 -- Default-method Ids may be mentioned in synthesised RHSs,
                 -- but they'll already be in the environment.
 

-        -- Typecheck the methods
-    let this_dict_id   = instToId this_dict
-       dfun_lam_vars   = map instToVar dfun_dicts      -- Includes equalities
-       prag_fn = mkPragFun uprags 
-       tc_meth = tcInstanceMethod loc clas inst_tyvars'
-                                  dfun_dicts
-                                  dfun_theta' inst_tys'
-                                  this_dict dfun_id
-                                  prag_fn monobinds
-    (meth_exprs, meth_binds) <- tcExtendTyVarEnv inst_tyvars'  $
-                               mapAndUnzipM tc_meth op_items 
-
-    -- Figure out bindings for the superclass context
-    -- Don't include this_dict in the 'givens', else
-    -- sc_dicts get bound by just selecting  from this_dict!!
-    sc_binds <- addErrCtxt superClassCtxt $
-                tcSimplifySuperClasses inst_loc this_dict dfun_dicts sc_dicts
-               -- Note [Recursive superclasses]
+       
+       -- Cook up a binding for "this = df d1 .. dn",
+       -- to use in each method binding
+       -- Need to clone the dict in case it is floated out, and
+       -- then clashes with its friends
+       ; cloned_this <- cloneDict this_dict
+       ; let cloned_this_bind = mkVarBind (instToId cloned_this) $ 
+                               L loc $ wrapId app_wrapper dfun_id
+            app_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars')
+            dfun_lam_vars = map instToVar dfun_dicts   -- Includes equalities
+            nested_this_pair 
+               | null inst_tyvars' && null dfun_theta' = (this_dict, emptyBag)
+               | otherwise = (cloned_this, unitBag cloned_this_bind)
+
+       -- Deal with 'SPECIALISE instance' pragmas
+       -- See Note [SPECIALISE instance pragmas]
+       ; let spec_inst_sigs = filter isSpecInstLSig uprags
+                    -- The filter removes the pragmas for methods
+       ; spec_inst_prags <- mapM (wrapLocM (tcSpecInst dfun_id)) spec_inst_sigs

 
 

-       -- It's possible that the superclass stuff might unified something
-       -- in the envt with one of the inst_tyvars'
-    checkSigTyVars inst_tyvars'
-
-    -- Deal with 'SPECIALISE instance' pragmas
-    prags <- tcPrags dfun_id (filter isSpecInstLSig uprags)
-
-    -- Create the result bindings
-    let
-        dict_constr   = classDataCon clas
-        inline_prag | null dfun_dicts  = []
-                    | otherwise        = [L loc (InlinePrag (Inline AlwaysActive True))]
-                -- Always inline the dfun; this is an experimental decision
-                -- because it makes a big performance difference sometimes.
-                -- Often it means we can do the method selection, and then
-                -- inline the method as well.  Marcin's idea; see comments below.
-                --
-                -- BUT: don't inline it if it's a constant dictionary;
-                -- we'll get all the benefit without inlining, and we get
-                -- a **lot** of code duplication if we inline it
-                --
-                --      See Note [Inline dfuns] below
-
-        sc_dict_vars  = map instToVar sc_dicts
-        dict_bind     = L loc (VarBind this_dict_id dict_rhs)
-        dict_rhs      = foldl (\ f a -> L loc (HsApp f (L loc a))) inst_constr meth_exprs
-       inst_constr   = L loc $ wrapId (mkWpApps sc_dict_vars <.> mkWpTyApps inst_tys')
-                                      (dataConWrapId dict_constr)
-                -- We don't produce a binding for the dict_constr; instead we
-                -- rely on the simplifier to unfold this saturated application
-                -- We do this rather than generate an HsCon directly, because
-                -- it means that the special cases (e.g. dictionary with only one
-                -- member) are dealt with by the common MkId.mkDataConWrapId code rather
-                -- than needing to be repeated here.
-
-
-        main_bind = noLoc $ AbsBinds
-                            inst_tyvars'
-                            dfun_lam_vars
-                            [(inst_tyvars', dfun_id, this_dict_id, inline_prag ++ prags)]
-                            (dict_bind `consBag` sc_binds)
-
-    showLIE (text "instance")
-    return (main_bind `consBag` unionManyBags meth_binds)
+        -- Typecheck the methods
+       ; let prag_fn = mkPragFun uprags 
+             tc_meth = tcInstanceMethod loc standalone_deriv
+                                        clas inst_tyvars'
+                                       dfun_dicts inst_tys'
+                                       nested_this_pair 
+                                       prag_fn spec_inst_prags monobinds
+
+       ; (meth_ids, meth_binds) <- tcExtendTyVarEnv inst_tyvars' $
+                                  mapAndUnzipM tc_meth op_items 
+
+         -- Figure out bindings for the superclass context
+       ; sc_loc   <- getInstLoc InstScOrigin
+       ; sc_dicts <- newDictOccs sc_loc sc_theta'              -- These are wanted
+       ; let tc_sc = tcSuperClass inst_loc inst_tyvars' dfun_dicts nested_this_pair
+       ; (sc_ids, sc_binds) <- mapAndUnzipM tc_sc (sc_sels `zip` sc_dicts)
+
+       -- It's possible that the superclass stuff might unified
+       -- something in the envt with one of the inst_tyvars'
+       ; checkSigTyVars inst_tyvars'
+
+       -- Create the result bindings
+       ; let dict_constr   = classDataCon clas
+             this_dict_id  = instToId this_dict
+            dict_bind     = mkVarBind this_dict_id dict_rhs
+             dict_rhs      = foldl mk_app inst_constr (sc_ids ++ meth_ids)
+            inst_constr   = L loc $ wrapId (mkWpTyApps inst_tys')
+                                           (dataConWrapId dict_constr)
+                     -- We don't produce a binding for the dict_constr; instead we
+                     -- rely on the simplifier to unfold this saturated application
+                     -- We do this rather than generate an HsCon directly, because
+                     -- it means that the special cases (e.g. dictionary with only one
+                     -- member) are dealt with by the common MkId.mkDataConWrapId code rather
+                     -- than needing to be repeated here.
+
+            mk_app :: LHsExpr Id -> Id -> LHsExpr Id
+            mk_app fun arg_id = L loc (HsApp fun (L loc (wrapId arg_wrapper arg_id)))
+            arg_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars')
+
+             dfun_id_w_fun = dfun_id 
+                             `setIdUnfolding` mkDFunUnfolding dict_constr (sc_ids ++ meth_ids)
+                             `setInlinePragma` dfunInlinePragma
+
+             main_bind = noLoc $ AbsBinds
+                                 inst_tyvars'
+                                 dfun_lam_vars
+                                 [(inst_tyvars', dfun_id_w_fun, this_dict_id, spec_inst_prags)]
+                                 (unitBag dict_bind)
+
+       ; showLIE (text "instance")
+       ; return (unitBag main_bind    `unionBags` 
+                listToBag meth_binds `unionBags` 
+                 listToBag sc_binds) }
+
+
+------------------------------
+tcSuperClass :: InstLoc -> [TyVar] -> [Inst]
+            -> (Inst, LHsBinds Id)
+            -> (Id, Inst) -> TcM (Id, LHsBind Id)
+-- Build a top level decl like
+--     sc_op = /\a \d. let this = ... in 
+--                     let sc = ... in
+--                     sc
+-- The "this" part is just-in-case (discarded if not used)
+-- See Note [Recursive superclasses]
+tcSuperClass inst_loc tyvars dicts (this_dict, this_bind)
+            (sc_sel, sc_dict)
+  = addErrCtxt superClassCtxt $
+    do { sc_binds <- tcSimplifySuperClasses inst_loc 
+                               this_dict dicts [sc_dict]
+         -- Don't include this_dict in the 'givens', else
+         -- sc_dicts get bound by just selecting  from this_dict!!
+
+       ; uniq <- newUnique
+       ; let sc_op_ty = mkSigmaTy tyvars (map dictPred dicts) 
+                                 (mkPredTy (dictPred sc_dict))
+            sc_op_name = mkDerivedInternalName mkClassOpAuxOcc uniq
+                                               (getName sc_sel)
+            sc_op_id   = mkLocalId sc_op_name sc_op_ty
+            sc_id      = instToVar sc_dict
+            sc_op_bind = AbsBinds tyvars 
+                            (map instToVar dicts) 
+                             [(tyvars, sc_op_id, sc_id, [])]
+                             (this_bind `unionBags` sc_binds)
+
+       ; return (sc_op_id, noLoc sc_op_bind) }

 \end{code}
 
 Note [Recursive superclasses]
 \end{code}
 
 Note [Recursive superclasses]

@@ -793,6 +767,62 @@ get satisfied by selection from this_dict, and that leads to an immediate
 loop.  What we need is to add this_dict to Avails without adding its 
 superclasses, and we currently have no way to do that.
 
 loop.  What we need is to add this_dict to Avails without adding its 
 superclasses, and we currently have no way to do that.
 

+Note [SPECIALISE instance pragmas]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+
+   instance (Ix a, Ix b) => Ix (a,b) where
+     {-# SPECIALISE instance Ix (Int,Int) #-}
+     range (x,y) = ...
+
+We do *not* want to make a specialised version of the dictionary
+function.  Rather, we want specialised versions of each method.
+Thus we should generate something like this:
+
+  $dfIx :: (Ix a, Ix x) => Ix (a,b)
+  {- DFUN [$crange, ...] -}
+  $dfIx da db = Ix ($crange da db) (...other methods...)
+
+  $dfIxPair :: (Ix a, Ix x) => Ix (a,b)
+  {- DFUN [$crangePair, ...] -}
+  $dfIxPair = Ix ($crangePair da db) (...other methods...)
+
+  $crange :: (Ix a, Ix b) -> ((a,b),(a,b)) -> [(a,b)]
+  {-# SPECIALISE $crange :: ((Int,Int),(Int,Int)) -> [(Int,Int)] #-}
+  $crange da db = <blah>
+
+  {-# RULE  range ($dfIx da db) = $crange da db #-}
+
+Note that  
+
+  * The RULE is unaffected by the specialisation.  We don't want to
+    specialise $dfIx, because then it would need a specialised RULE
+    which is a pain.  The single RULE works fine at all specialisations.
+    See Note [How instance declarations are translated] above
+
+  * Instead, we want to specialise the *method*, $crange
+
+In practice, rather than faking up a SPECIALISE pragama for each
+method (which is painful, since we'd have to figure out its
+specialised type), we call tcSpecPrag *as if* were going to specialise
+$dfIx -- you can see that in the call to tcSpecInst.  That generates a
+SpecPrag which, as it turns out, can be used unchanged for each method.
+The "it turns out" bit is delicate, but it works fine!
+
+\begin{code}
+tcSpecInst :: Id -> Sig Name -> TcM SpecPrag
+tcSpecInst dfun_id prag@(SpecInstSig hs_ty) 
+  = addErrCtxt (spec_ctxt prag) $
+    do  { let name = idName dfun_id
+        ; (tyvars, theta, tau) <- tcHsInstHead hs_ty   
+        ; let spec_ty = mkSigmaTy tyvars theta tau
+        ; co_fn <- tcSubExp (SpecPragOrigin name) (idType dfun_id) spec_ty
+        ; return (SpecPrag co_fn defaultInlinePragma) }
+  where
+    spec_ctxt prag = hang (ptext (sLit "In the SPECIALISE pragma")) 2 (ppr prag)
+
+tcSpecInst _  _ = panic "tcSpecInst"
+\end{code}

 
 %************************************************************************
 %*                                                                      *
 
 %************************************************************************
 %*                                                                      *

@@ -809,119 +839,218 @@ tcInstanceMethod
 - Use tcValBinds to do the checking
 
 \begin{code}
 - Use tcValBinds to do the checking
 
 \begin{code}

-tcInstanceMethod :: SrcSpan -> Class -> [TcTyVar] -> [Inst]
-                -> TcThetaType -> [TcType]
-                -> Inst -> Id
-                -> TcPragFun -> LHsBinds Name 
+tcInstanceMethod :: SrcSpan -> Bool -> Class -> [TcTyVar] -> [Inst]
+                -> [TcType]
+                -> (Inst, LHsBinds Id)  -- "This" and its binding
+                -> TcPragFun            -- Local prags
+                -> [LSpecPrag]          -- Arising from 'SPECLALISE instance'
+                 -> LHsBinds Name 

                 -> (Id, DefMeth)
                 -> (Id, DefMeth)

-                -> TcM (HsExpr Id, LHsBinds Id)
+                -> TcM (Id, LHsBind Id)

        -- The returned inst_meth_ids all have types starting
        --      forall tvs. theta => ...
 
        -- The returned inst_meth_ids all have types starting
        --      forall tvs. theta => ...
 

-tcInstanceMethod loc clas tyvars dfun_dicts theta inst_tys 
-                this_dict dfun_id prag_fn binds_in (sel_id, dm_info)
-  = do { cloned_this <- cloneDict this_dict
-               -- Need to clone the dict in case it is floated out, and
-               -- then clashes with its friends
-       ; uniq1 <- newUnique
-       ; let local_meth_name = mkInternalName uniq1 sel_occ loc   -- Same OccName
-             this_dict_bind  = L loc $ VarBind (instToId cloned_this) $ 
-                               L loc $ wrapId meth_wrapper dfun_id
-             mb_this_bind | null tyvars = Nothing
-                          | otherwise   = Just (cloned_this, this_dict_bind)
-               -- Only need the this_dict stuff if there are type variables
-               -- involved; otherwise overlap is not possible
-               -- See Note [Subtle interaction of recursion and overlap]       
-
-             tc_body rn_bind = do { (meth_id, tc_binds) <- tcInstanceMethodBody 
-                                               InstSkol clas tyvars dfun_dicts theta inst_tys
-                                               mb_this_bind sel_id 
-                                               local_meth_name
-                                               meth_sig_fn meth_prag_fn rn_bind
-                                  ; return (wrapId meth_wrapper meth_id, tc_binds) }
-
-       ; case (findMethodBind sel_name local_meth_name binds_in, dm_info) of
-               -- There is a user-supplied method binding, so use it
-           (Just user_bind, _) -> tc_body user_bind
-
+tcInstanceMethod loc standalone_deriv clas tyvars dfun_dicts inst_tys 
+                (this_dict, this_dict_bind)
+                prag_fn spec_inst_prags binds_in (sel_id, dm_info)
+  = do  { uniq <- newUnique
+       ; let meth_name = mkDerivedInternalName mkClassOpAuxOcc uniq sel_name
+        ; local_meth_name <- newLocalName sel_name
+         -- Base the local_meth_name on the selector name, becuase
+         -- type errors from tcInstanceMethodBody come from here
+
+        ; let local_meth_ty = instantiateMethod clas sel_id inst_tys
+             meth_ty = mkSigmaTy tyvars (map dictPred dfun_dicts) local_meth_ty
+             meth_id       = mkLocalId meth_name meth_ty
+              local_meth_id = mkLocalId local_meth_name local_meth_ty
+
+           --------------
+             tc_body rn_bind 
+                = add_meth_ctxt rn_bind $
+                  do { (meth_id1, spec_prags) <- tcPrags NonRecursive False True 
+                                                    meth_id (prag_fn sel_name)
+                     ; tcInstanceMethodBody (instLoc this_dict)
+                                    tyvars dfun_dicts
+                                   ([this_dict], this_dict_bind)
+                                    meth_id1 local_meth_id
+                                   meth_sig_fn 
+                                    (spec_inst_prags ++ spec_prags) 
+                                    rn_bind }
+
+           --------------
+             tc_default :: DefMeth -> TcM (Id, LHsBind Id)

                -- The user didn't supply a method binding, so we have to make 
                -- up a default binding, in a way depending on the default-method info
 
                -- The user didn't supply a method binding, so we have to make 
                -- up a default binding, in a way depending on the default-method info
 

-           (Nothing, GenDefMeth) -> do         -- Derivable type classes stuff
-                       { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id local_meth_name
-                       ; tc_body meth_bind }
-
-           (Nothing, NoDefMeth) -> do          -- No default method in the class
-                       { warn <- doptM Opt_WarnMissingMethods          
-                        ; warnTc (warn  -- Warn only if -fwarn-missing-methods
-                                 && reportIfUnused (getOccName sel_id))
-                                       -- Don't warn about _foo methods
-                                omitted_meth_warn
-                       ; return (error_rhs, emptyBag) }
-
-           (Nothing, DefMeth) -> do    -- An polymorphic default method
-                       {   -- Build the typechecked version directly, 
-                           -- without calling typecheck_method; 
-                           -- see Note [Default methods in instances]
-                         dm_name <- lookupImportedName (mkDefMethRdrName sel_name)
+              tc_default NoDefMeth         -- No default method at all
+               = do { warnMissingMethod sel_id
+                    ; return (meth_id, mkVarBind meth_id $ 
+                                        mkLHsWrap lam_wrapper error_rhs) }
+             
+             tc_default GenDefMeth    -- Derivable type classes stuff
+                = do { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id local_meth_name
+                     ; tc_body meth_bind }
+                 
+             tc_default DefMeth        -- An polymorphic default method
+               = do {   -- Build the typechecked version directly, 
+                        -- without calling typecheck_method; 
+                        -- see Note [Default methods in instances]
+                        -- Generate   /\as.\ds. let this = df as ds 
+                         --                      in $dm inst_tys this
+                        -- The 'let' is necessary only because HsSyn doesn't allow
+                        -- you to apply a function to a dictionary *expression*.
+                      dm_name <- lookupGlobalOccRn (mkDefMethRdrName sel_name)

                                        -- Might not be imported, but will be an OrigName
                                        -- Might not be imported, but will be an OrigName

-                       ; dm_id   <- tcLookupId dm_name
-                       ; return (wrapId dm_wrapper dm_id, emptyBag) } }
+                    ; dm_id <- tcLookupId dm_name
+                    ; inline_id <- tcLookupId inlineIdName
+                     ; let dm_inline_prag = idInlinePragma dm_id
+                           dm_app = HsWrap (WpApp (instToId this_dict) <.> mkWpTyApps inst_tys) $
+                                   HsVar dm_id 
+                           rhs | isInlinePragma dm_inline_prag  -- See Note [INLINE and default methods]
+                               = HsApp (L loc (HsWrap (WpTyApp local_meth_ty) (HsVar inline_id)))
+                                       (L loc dm_app)
+                               | otherwise = dm_app
+
+                          meth_bind = L loc $ VarBind { var_id = local_meth_id
+                                                       , var_rhs = L loc rhs 
+                                                      , var_inline = False }
+                           meth_id1 = meth_id `setInlinePragma` dm_inline_prag
+                                   -- Copy the inline pragma (if any) from the default
+                                   -- method to this version. Note [INLINE and default methods]
+                                   
+                           bind = AbsBinds { abs_tvs = tyvars, abs_dicts =  dfun_lam_vars
+                                           , abs_exports = [( tyvars, meth_id1
+                                                            , local_meth_id, spec_inst_prags)]
+                                           , abs_binds = this_dict_bind `unionBags` unitBag meth_bind }
+                    -- Default methods in an instance declaration can't have their own 
+                    -- INLINE or SPECIALISE pragmas. It'd be possible to allow them, but
+                    -- currently they are rejected with 
+                    --           "INLINE pragma lacks an accompanying binding"
+
+                    ; return (meth_id1, L loc bind) } 
+
+        ; case findMethodBind sel_name local_meth_name binds_in of
+           Just user_bind -> tc_body user_bind    -- User-supplied method binding
+           Nothing        -> tc_default dm_info   -- None supplied
+       }

   where
     sel_name = idName sel_id
   where
     sel_name = idName sel_id

-    sel_occ  = nameOccName sel_name
-    this_dict_id = instToId this_dict
-
-    meth_prag_fn _ = prag_fn sel_name
-    meth_sig_fn _  = Just []   -- The 'Just' says "yes, there's a type sig"
-                       -- But there are no scoped type variables from local_method_id
-                       -- Only the ones from the instance decl itself, which are already
-                       -- in scope.  Example:
-                       --      class C a where { op :: forall b. Eq b => ... }
-                       --      instance C [c] where { op = <rhs> }
-                       -- In <rhs>, 'c' is scope but 'b' is not!
-
-    error_rhs    = HsApp error_fun error_msg
+
+    meth_sig_fn _ = Just []    -- The 'Just' says "yes, there's a type sig"
+       -- But there are no scoped type variables from local_method_id
+       -- Only the ones from the instance decl itself, which are already
+       -- in scope.  Example:
+       --      class C a where { op :: forall b. Eq b => ... }
+       --      instance C [c] where { op = <rhs> }
+       -- In <rhs>, 'c' is scope but 'b' is not!
+
+    error_rhs    = L loc $ HsApp error_fun error_msg

     error_fun    = L loc $ wrapId (WpTyApp meth_tau) nO_METHOD_BINDING_ERROR_ID
     error_msg    = L loc (HsLit (HsStringPrim (mkFastString error_string)))
     meth_tau     = funResultTy (applyTys (idType sel_id) inst_tys)
     error_string = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
 
     error_fun    = L loc $ wrapId (WpTyApp meth_tau) nO_METHOD_BINDING_ERROR_ID
     error_msg    = L loc (HsLit (HsStringPrim (mkFastString error_string)))
     meth_tau     = funResultTy (applyTys (idType sel_id) inst_tys)
     error_string = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
 

-    dm_wrapper   = WpApp this_dict_id <.> mkWpTyApps inst_tys 
-
-    omitted_meth_warn :: SDoc
-    omitted_meth_warn = ptext (sLit "No explicit method nor default method for")
-                        <+> quotes (ppr sel_id)
-

     dfun_lam_vars = map instToVar dfun_dicts
     dfun_lam_vars = map instToVar dfun_dicts

-    meth_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys tyvars)
+    lam_wrapper   = mkWpTyLams tyvars <.> mkWpLams dfun_lam_vars

 
 

+       -- For instance decls that come from standalone deriving clauses
+       -- we want to print out the full source code if there's an error
+       -- because otherwise the user won't see the code at all
+    add_meth_ctxt rn_bind thing 
+      | standalone_deriv = addLandmarkErrCtxt (derivBindCtxt clas inst_tys rn_bind) thing
+      | otherwise        = thing

 
 wrapId :: HsWrapper -> id -> HsExpr id
 wrapId wrapper id = mkHsWrap wrapper (HsVar id)
 
 wrapId :: HsWrapper -> id -> HsExpr id
 wrapId wrapper id = mkHsWrap wrapper (HsVar id)

+
+derivBindCtxt :: Class -> [Type ] -> LHsBind Name -> SDoc
+derivBindCtxt clas tys bind
+   = vcat [ ptext (sLit "When typechecking a standalone-derived method for")
+           <+> quotes (pprClassPred clas tys) <> colon
+         , nest 2 $ pprSetDepth AllTheWay $ ppr bind ]
+
+warnMissingMethod :: Id -> TcM ()
+warnMissingMethod sel_id
+  = do { warn <- doptM Opt_WarnMissingMethods          
+       ; warnTc (warn  -- Warn only if -fwarn-missing-methods
+                 && not (startsWithUnderscore (getOccName sel_id)))
+                                       -- Don't warn about _foo methods
+               (ptext (sLit "No explicit method nor default method for")
+                 <+> quotes (ppr sel_id)) }

 \end{code}
 
 \end{code}
 

+Note [Export helper functions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We arrange to export the "helper functions" of an instance declaration,
+so that they are not subject to preInlineUnconditionally, even if their
+RHS is trivial.  Reason: they are mentioned in the DFunUnfolding of
+the dict fun as Ids, not as CoreExprs, so we can't substitute a 
+non-variable for them.
+
+We could change this by making DFunUnfoldings have CoreExprs, but it
+seems a bit simpler this way.
+

 Note [Default methods in instances]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Consider this
 
    class Baz v x where
       foo :: x -> x
 Note [Default methods in instances]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Consider this
 
    class Baz v x where
       foo :: x -> x

-      foo y = y
+      foo y = <blah>

 
    instance Baz Int Int
 
 From the class decl we get
 
    $dmfoo :: forall v x. Baz v x => x -> x
 
    instance Baz Int Int
 
 From the class decl we get
 
    $dmfoo :: forall v x. Baz v x => x -> x

+   $dmfoo y = <blah>

 
 Notice that the type is ambiguous.  That's fine, though. The instance decl generates
 
 
 Notice that the type is ambiguous.  That's fine, though. The instance decl generates
 

-   $dBazIntInt = MkBaz ($dmfoo Int Int $dBazIntInt)
+   $dBazIntInt = MkBaz fooIntInt
+   fooIntInt = $dmfoo Int Int $dBazIntInt
+
+BUT this does mean we must generate the dictionary translation of
+fooIntInt directly, rather than generating source-code and
+type-checking it.  That was the bug in Trac #1061. In any case it's
+less work to generate the translated version!
+
+Note [INLINE and default methods]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We *copy* any INLINE pragma from the default method to the instance.
+Example:
+  class Foo a where
+    op1, op2 :: Bool -> a -> a
+
+    {-# INLINE op1 #-}
+    op1 b x = op2 (not b) x
+
+  instance Foo Int where
+    op2 b x = <blah>
+
+Then we generate:
+
+  {-# INLINE $dmop1 #-}
+  $dmop1 d b x = op2 d (not b) x
+
+  $fFooInt = MkD $cop1 $cop2
+
+  {-# INLINE $cop1 #-}
+  $cop1 = inline $dmop1 $fFooInt
+
+  $cop2 = <blah>
+
+Note carefully:
+  a) We copy $dmop1's inline pragma to $cop1.  Otherwise 
+     we'll just inline the former in the latter and stop, which 
+     isn't what the user expected
+
+  b) We use the magic 'inline' Id to ensure that $dmop1 really is
+     inlined in $cop1, even though the latter itself has an INLINE pragma
+     That is important to allow the mutual recursion between $fooInt and
+     $cop1 to be broken

 
 

-BUT this does mean we must generate the dictionary translation directly, rather
-than generating source-code and type-checking it.  That was the bug ing
-Trac #1061. In any case it's less work to generate the translated version!
+This is all regrettably delicate.

 
 
 %************************************************************************
 
 
 %************************************************************************

@@ -941,7 +1070,7 @@ instDeclCtxt2 :: Type -> SDoc
 instDeclCtxt2 dfun_ty
   = inst_decl_ctxt (ppr (mkClassPred cls tys))
   where
 instDeclCtxt2 dfun_ty
   = inst_decl_ctxt (ppr (mkClassPred cls tys))
   where

-    (_,_,cls,tys) = tcSplitDFunTy dfun_ty
+    (_,cls,tys) = tcSplitDFunTy dfun_ty

 
 inst_decl_ctxt :: SDoc -> SDoc
 inst_decl_ctxt doc = ptext (sLit "In the instance declaration for") <+> quotes doc
 
 inst_decl_ctxt :: SDoc -> SDoc
 inst_decl_ctxt doc = ptext (sLit "In the instance declaration for") <+> quotes doc

@@ -963,7 +1092,7 @@ mustBeVarArgErr ty =
 wrongATArgErr :: Type -> Type -> SDoc
 wrongATArgErr ty instTy =
   sep [ ptext (sLit "Type indexes must match class instance head")
 wrongATArgErr :: Type -> Type -> SDoc
 wrongATArgErr ty instTy =
   sep [ ptext (sLit "Type indexes must match class instance head")

-      , ptext (sLit "Found") <+> ppr ty <+> ptext (sLit "but expected") <+>
-         ppr instTy
+      , ptext (sLit "Found") <+> quotes (ppr ty)
+        <+> ptext (sLit "but expected") <+> quotes (ppr instTy)

       ]
 \end{code}
       ]
 \end{code}