Overhaul of the rewrite rules

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

diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs
index fadc054..5d1e63a 100644 (file)
--- a/compiler/typecheck/TcInstDcls.lhs
+++ b/compiler/typecheck/TcInstDcls.lhs
@@ -6,11 +6,11 @@
 TcInstDecls: Typechecking instance declarations
 
 \begin{code}
 TcInstDecls: Typechecking instance declarations
 
 \begin{code}

-{-# OPTIONS_GHC -w #-}
+{-# OPTIONS -w #-}

 -- The above warning supression flag is a temporary kludge.
 -- While working on this module you are encouraged to remove it and fix
 -- any warnings in the module. See
 -- The above warning supression flag is a temporary kludge.
 -- While working on this module you are encouraged to remove it and fix
 -- any warnings in the module. See

---     http://hackage.haskell.org/trac/ghc/wiki/WorkingConventions#Warnings
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings

 -- for details
 
 module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where
 -- for details
 
 module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where

@@ -403,39 +403,37 @@ tcInstDecls2 tycl_decls inst_decls
 
 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
 the dictionary function for this instance declaration. For example
 
 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
 the dictionary function for this instance declaration. For example

-\begin{verbatim}
+

        instance Foo a => Foo [a] where
                op1 x = ...
                op2 y = ...
        instance Foo a => Foo [a] where
                op1 x = ...
                op2 y = ...

-\end{verbatim}
+

 might generate something like
 might generate something like

-\begin{verbatim}
+

        dfun.Foo.List dFoo_a = let op1 x = ...
                                   op2 y = ...
                               in
                                   Dict [op1, op2]
        dfun.Foo.List dFoo_a = let op1 x = ...
                                   op2 y = ...
                               in
                                   Dict [op1, op2]

-\end{verbatim}

 
 HOWEVER, if the instance decl has no context, then it returns a
 bigger @HsBinds@ with declarations for each method.  For example
 
 HOWEVER, if the instance decl has no context, then it returns a
 bigger @HsBinds@ with declarations for each method.  For example

-\begin{verbatim}
+

        instance Foo [a] where
                op1 x = ...
                op2 y = ...
        instance Foo [a] where
                op1 x = ...
                op2 y = ...

-\end{verbatim}
+

 might produce
 might produce

-\begin{verbatim}
+

        dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
        const.Foo.op1.List a x = ...
        const.Foo.op2.List a y = ...
        dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
        const.Foo.op1.List a x = ...
        const.Foo.op2.List a y = ...

-\end{verbatim}
+

 This group may be mutually recursive, because (for example) there may
 be no method supplied for op2 in which case we'll get
 This group may be mutually recursive, because (for example) there may
 be no method supplied for op2 in which case we'll get

-\begin{verbatim}
+

        const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
        const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)

-\end{verbatim}
-that is, the default method applied to the dictionary at this type.

 
 

+that is, the default method applied to the dictionary at this type.

 What we actually produce in either case is:
 
        AbsBinds [a] [dfun_theta_dicts]
 What we actually produce in either case is:
 
        AbsBinds [a] [dfun_theta_dicts]

@@ -447,7 +445,6 @@ What we actually produce in either case is:
 
 The "maybe" says that we only ask AbsBinds to make global constant methods
 if the dfun_theta is empty.
 
 The "maybe" says that we only ask AbsBinds to make global constant methods
 if the dfun_theta is empty.

-

                
 For an instance declaration, say,
 
                
 For an instance declaration, say,
 

@@ -463,8 +460,6 @@ Notice that we pass it the superclass dictionaries at the instance type; this
 is the ``Mark Jones optimisation''.  The stuff before the "=>" here
 is the @dfun_theta@ below.
 
 is the ``Mark Jones optimisation''.  The stuff before the "=>" here
 is the @dfun_theta@ below.
 

-First comes the easy case of a non-local instance decl.
-

 
 \begin{code}
 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
 
 \begin{code}
 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)

@@ -473,23 +468,23 @@ tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
 ------------------------
 -- Derived newtype instances; surprisingly tricky!
 --
 ------------------------
 -- Derived newtype instances; surprisingly tricky!
 --

--- In the case of a newtype, things are rather easy

 --     class Show a => Foo a b where ...
 --     class Show a => Foo a b where ...

---     newtype T a = MkT (Tree [a]) deriving( Foo Int )
+--     newtype N a = MkN (Tree [a]) deriving( Foo Int )
+--

 -- The newtype gives an FC axiom looking like
 -- The newtype gives an FC axiom looking like

---     axiom CoT a ::  T a :=: Tree [a]
+--     axiom CoN a ::  N a :=: Tree [a]

 --   (see Note [Newtype coercions] in TyCon for this unusual form of axiom)
 --
 -- So all need is to generate a binding looking like: 
 --   (see Note [Newtype coercions] in TyCon for this unusual form of axiom)
 --
 -- So all need is to generate a binding looking like: 

---     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 (sym (CoT a))) of
+--     dfunFooT :: forall a. (Foo Int (Tree [a], Show (N a)) => Foo Int (N a)
+--     dfunFooT = /\a. \(ds:Show (N a)) (df:Foo (Tree [a])).
+--               case df `cast` (Foo Int (sym (CoN a))) of

 --                  Foo _ op1 .. opn -> Foo ds op1 .. opn
 --
 -- If there are no superclasses, matters are simpler, because we don't need the case
 -- see Note [Newtype deriving superclasses] in TcDeriv.lhs
 
 --                  Foo _ op1 .. opn -> Foo ds op1 .. opn
 --
 -- 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 mb_preds })
+tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived })

   = do { let dfun_id      = instanceDFunId ispec 
              rigid_info   = InstSkol
              origin       = SigOrigin rigid_info
   = do { let dfun_id      = instanceDFunId ispec 
              rigid_info   = InstSkol
              origin       = SigOrigin rigid_info

@@ -497,46 +492,43 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived mb_preds })
        ; (tvs, theta, inst_head_ty) <- tcSkolSigType rigid_info inst_ty
                -- inst_head_ty is a PredType
 
        ; (tvs, theta, inst_head_ty) <- tcSkolSigType rigid_info inst_ty
                -- inst_head_ty is a PredType
 

-       ; inst_loc <- getInstLoc origin
-       ; (rep_dict_id : sc_dict_ids, wrap_fn, sc_binds)
-               <- make_wrapper inst_loc tvs theta mb_preds
-               -- Here, we are relying on the order of dictionary 
-               -- arguments built by NewTypeDerived in TcDeriv; 
-               -- namely, that the rep_dict_id comes first
-          

         ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head_ty
         ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head_ty

-             cls_tycon           = classTyCon cls
-             the_coercion        = make_coercion cls_tycon cls_inst_tys
-              coerced_rep_dict           = mkHsWrap the_coercion (HsVar rep_dict_id)
-
-       ; body <- make_body cls_tycon cls_inst_tys sc_dict_ids coerced_rep_dict
+             (class_tyvars, sc_theta, _, op_items) = 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
+             (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)

               
               

-        ; return (sc_binds `snocBag` (noLoc $ VarBind dfun_id $ noLoc $ mkHsWrap wrap_fn body)) }
+       ; inst_loc   <- getInstLoc origin
+       ; sc_loc     <- getInstLoc InstScOrigin
+       ; dfun_dicts <- newDictBndrs inst_loc theta
+       ; sc_dicts   <- newDictBndrs sc_loc sc_theta'
+       ; this_dict  <- newDictBndr inst_loc (mkClassPred cls cls_inst_tys)
+       ; rep_dict   <- newDictBndr inst_loc rep_pred
+
+       -- Figure out bindings for the superclass context from dfun_dicts
+       -- Don't include this_dict in the 'givens', else
+       -- wanted_sc_insts get bound by just selecting from this_dict!!
+       ; sc_binds <- addErrCtxt superClassCtxt $
+                     tcSimplifySuperClasses inst_loc dfun_dicts (rep_dict:sc_dicts)
+
+       ; let coerced_rep_dict = mkHsWrap the_coercion (HsVar (instToId 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)
+
+       ; return (unitBag $ noLoc $
+                 AbsBinds  tvs (map instToId dfun_dicts)
+                           [(tvs, dfun_id, instToId this_dict, [])] 
+                           (dict_bind `consBag` sc_binds)) }

   where
   where

-
-      -----------------------
-      --       make_wrapper
-      -- We distinguish two cases:
-      -- (a) there is no tyvar abstraction in the dfun, so all dicts are constant,
-      --     and the new dict can just be a constant
-      --       (mb_preds = Just preds)
-      -- (b) there are tyvars, so we must make a dict *fun*
-      --       (mb_preds = Nothing)
-      -- See the defn of NewTypeDerived for the meaning of mb_preds
-    make_wrapper inst_loc tvs theta (Just preds)       -- Case (a)
-      = ASSERT( null tvs && null theta )
-       do { dicts <- newDictBndrs inst_loc preds
-          ; sc_binds <- addErrCtxt superClassCtxt $
-                        tcSimplifySuperClasses inst_loc [] dicts
-               -- Use tcSimplifySuperClasses to avoid creating loops, for the
-               -- same reason as Note [SUPERCLASS-LOOP 1] in TcSimplify
-          ; return (map instToId dicts, idHsWrapper, sc_binds) }
-
-    make_wrapper inst_loc tvs theta Nothing    -- Case (b)
-      = do { dicts <- newDictBndrs inst_loc theta
-          ; let dict_ids = map instToId dicts
-          ; return (dict_ids, mkWpTyLams tvs <.> mkWpLams dict_ids, emptyBag) }
-

       -----------------------
       --       make_coercion
       -- The inst_head looks like (C s1 .. sm (T a1 .. ak))
       -----------------------
       --       make_coercion
       -- The inst_head looks like (C s1 .. sm (T a1 .. ak))

@@ -546,25 +538,24 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived mb_preds })
       -- 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
 
       -- 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 cls_inst_tys
-       | Just (all_tys_but_last, last_ty) <- snocView cls_inst_tys
-       , (tycon, tc_args) <- tcSplitTyConApp last_ty   -- Should not fail
-       , Just co_con <- newTyConCo_maybe tycon
+    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)
        , let co = mkSymCoercion (mkTyConApp co_con tc_args)

-        = WpCo (mkTyConApp cls_tycon (all_tys_but_last ++ [co]))
+        = WpCo (mkTyConApp cls_tycon (initial_cls_inst_tys ++ [co]))

         | otherwise    -- The newtype is transparent; no need for a cast
         = idHsWrapper
 
       -----------------------
         | otherwise    -- The newtype is transparent; no need for a cast
         = idHsWrapper
 
       -----------------------

-      --       make_body
-      -- Two cases; see Note [Newtype deriving superclasses] in TcDeriv.lhs
-      -- (a) no superclasses; then we can just use the coerced dict
-      -- (b) one or more superclasses; then new need to do the unpack/repack
+      --     (make_body C tys scs coreced_rep_dict)
+      --               returns 
+      --     (case coerced_rep_dict of { C _ ops -> C scs ops })
+      -- But if there are no superclasses, it returns just coerced_rep_dict
+      -- See Note [Newtype deriving superclasses] in TcDeriv.lhs

        
        

-    make_body cls_tycon cls_inst_tys sc_dict_ids coerced_rep_dict
-       | null sc_dict_ids              -- Case (a)
+    make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict
+       | null sc_dicts         -- Case (a)

        = return coerced_rep_dict
        = return coerced_rep_dict

-       | otherwise                     -- Case (b)
+       | otherwise             -- Case (b)

        = do { op_ids            <- newSysLocalIds FSLIT("op") op_tys
             ; dummy_sc_dict_ids <- newSysLocalIds FSLIT("sc") (map idType sc_dict_ids)
             ; let the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],
        = do { op_ids            <- newSysLocalIds FSLIT("op") op_tys
             ; dummy_sc_dict_ids <- newSysLocalIds FSLIT("sc") (map idType sc_dict_ids)
             ; let the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],

@@ -582,6 +573,7 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived mb_preds })
             ; return (HsCase (noLoc coerced_rep_dict) $
                       MatchGroup [the_match] (mkFunTy pat_ty pat_ty)) }
        where
             ; return (HsCase (noLoc coerced_rep_dict) $
                       MatchGroup [the_match] (mkFunTy pat_ty pat_ty)) }
        where

+         sc_dict_ids  = map instToId sc_dicts

          pat_ty       = mkTyConApp cls_tycon cls_inst_tys
           cls_data_con = head (tyConDataCons cls_tycon)
           cls_arg_tys  = dataConInstArgTys cls_data_con cls_inst_tys 
          pat_ty       = mkTyConApp cls_tycon cls_inst_tys
           cls_data_con = head (tyConDataCons cls_tycon)
           cls_arg_tys  = dataConInstArgTys cls_data_con cls_inst_tys 

@@ -696,23 +688,16 @@ tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })
     returnM (unitBag main_bind)
 
 mkCoVars :: [PredType] -> TcM [TyVar]
     returnM (unitBag main_bind)
 
 mkCoVars :: [PredType] -> TcM [TyVar]

-mkCoVars [] = return []
-mkCoVars (pred:preds) = 
-       do { uniq <- newUnique
-          ; let name = mkSysTvName uniq FSLIT("mkCoVars")
-          ; let tv = mkCoVar name (PredTy pred)
-          ; tvs <- mkCoVars preds
-          ; return (tv:tvs)
-          }
+mkCoVars = newCoVars . map unEqPred
+  where
+    unEqPred (EqPred ty1 ty2) = (ty1, ty2)
+    unEqPred _                = panic "TcInstDcls.mkCoVars"

 
 mkMetaCoVars :: [PredType] -> TcM [TyVar]
 
 mkMetaCoVars :: [PredType] -> TcM [TyVar]

-mkMetaCoVars [] = return []
-mkMetaCoVars (EqPred ty1 ty2:preds) = 
-       do { tv <- newMetaTyVar TauTv (mkCoKind ty1 ty2)          
-          ; tvs <- mkMetaCoVars preds
-          ; return (tv:tvs)
-          }
-
+mkMetaCoVars = mappM eqPredToCoVar
+  where
+    eqPredToCoVar (EqPred ty1 ty2) = newMetaCoVar ty1 ty2
+    eqPredToCoVar _                = panic "TcInstDcls.mkMetaCoVars"

 
 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys' 
          avail_insts op_items monobinds uprags
 
 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys' 
          avail_insts op_items monobinds uprags