[project @ 2004-08-13 13:04:50 by simonmar]

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

diff --git a/ghc/compiler/typecheck/TcHsSyn.lhs b/ghc/compiler/typecheck/TcHsSyn.lhs
index a0f779f..0670a0c 100644 (file)
--- a/ghc/compiler/typecheck/TcHsSyn.lhs
+++ b/ghc/compiler/typecheck/TcHsSyn.lhs
@@ -1,5 +1,5 @@
 %
 %

-% (c) The AQUA Project, Glasgow University, 1996
+% (c) The AQUA Project, Glasgow University, 1996-1998

 %
 \section[TcHsSyn]{Specialisations of the @HsSyn@ syntax for the typechecker}
 
 %
 \section[TcHsSyn]{Specialisations of the @HsSyn@ syntax for the typechecker}
 

@@ -7,140 +7,143 @@ This module is an extension of @HsSyn@ syntax, for use in the type
 checker.
 
 \begin{code}
 checker.
 
 \begin{code}

-#include "HsVersions.h"
-

 module TcHsSyn (
 module TcHsSyn (

-       TcIdBndr(..), TcIdOcc(..),
+       TcDictBinds,
+       mkHsTyApp, mkHsDictApp, mkHsConApp,
+       mkHsTyLam, mkHsDictLam, mkHsLet, mkHsApp,
+       hsLitType, hsPatType, mkHsAppTy, mkSimpleHsAlt,
+       nlHsIntLit, glueBindsOnGRHSs,

        
        

-       TcMonoBinds(..), TcHsBinds(..), TcBind(..), TcPat(..),
-       TcExpr(..), TcGRHSsAndBinds(..), TcGRHS(..), TcMatch(..),
-       TcQual(..), TcStmt(..), TcArithSeqInfo(..), TcRecordBinds(..),
-       TcHsModule(..),
-       
-       TypecheckedHsBinds(..), TypecheckedBind(..),
-       TypecheckedMonoBinds(..), TypecheckedPat(..),
-       TypecheckedHsExpr(..), TypecheckedArithSeqInfo(..),
-       TypecheckedQual(..), TypecheckedStmt(..),
-       TypecheckedMatch(..), TypecheckedHsModule(..),
-       TypecheckedGRHSsAndBinds(..), TypecheckedGRHS(..),
-       TypecheckedRecordBinds(..),
-
-       mkHsTyApp, mkHsDictApp,
-       mkHsTyLam, mkHsDictLam,
-       tcIdType, tcIdTyVars,
-
-       zonkBinds,
-       zonkDictBinds
+
+       -- Coercions
+       Coercion, ExprCoFn, PatCoFn, 
+       (<$>), (<.>), mkCoercion, 
+       idCoercion, isIdCoercion,
+
+       -- re-exported from TcMonad
+       TcId, TcIdSet,
+
+       zonkTopDecls, zonkTopExpr, zonkTopLExpr,
+       zonkId, zonkTopBndrs

   ) where
 
   ) where
 

-IMP_Ubiq(){-uitous-}
+#include "HsVersions.h"

 
 -- friends:
 import HsSyn   -- oodles of it
 
 -- friends:
 import HsSyn   -- oodles of it

-import Id      ( GenId(..), IdDetails, PragmaInfo,     -- Can meddle modestly with Ids
-                 SYN_IE(DictVar), idType,
-                 SYN_IE(IdEnv), growIdEnvList, lookupIdEnv
-               )

 
 -- others:
 
 -- others:

-import Name    ( Name{--O only-} )
-import TcMonad hiding ( rnMtoTcM )
-import TcType  ( TcType(..), TcMaybe, TcTyVar(..),
-                 zonkTcTypeToType, zonkTcTyVarToTyVar
-               )
-import Usage   ( SYN_IE(UVar) )
-import Util    ( zipEqual, panic, pprPanic, pprTrace )
-
-import PprType  ( GenType, GenTyVar )  -- instances
-import Type    ( mkTyVarTy, tyVarsOfType )
-import TyVar   ( GenTyVar {- instances -},
-                 SYN_IE(TyVarEnv), growTyVarEnvList, emptyTyVarSet )
-import TysPrim ( voidTy )
-import Unique  ( Unique )              -- instances
-import UniqFM
-import PprStyle
-import Pretty
+import Id      ( idType, setIdType, Id )
+
+import TcRnMonad
+import Type      ( Type )
+import TcType    ( TcType, TcTyVar, mkTyVarTy, tcGetTyVar, mkTyConApp )
+import Kind      ( isLiftedTypeKind, liftedTypeKind, isSubKind )
+import qualified  Type
+import TcMType   ( zonkTcTyVarToTyVar, zonkType, zonkTcType, zonkTcTyVars,
+                   putTcTyVar )
+import TysPrim   ( charPrimTy, intPrimTy, floatPrimTy,
+                   doublePrimTy, addrPrimTy
+                 )
+import TysWiredIn ( charTy, stringTy, intTy, 
+                   mkListTy, mkPArrTy, mkTupleTy, unitTy,
+                   voidTy, listTyCon, tupleTyCon )
+import TyCon     ( mkPrimTyCon, tyConKind, PrimRep(..) )
+import Kind      ( splitKindFunTys )
+import Name      ( getOccName, mkInternalName, mkDerivedTyConOcc )
+import Var       ( Var, isId, isLocalVar, tyVarKind )
+import VarSet
+import VarEnv
+import BasicTypes ( Boxity(..), IPName(..), ipNameName, mapIPName )
+import Maybes    ( orElse )
+import Maybe     ( isNothing )
+import Unique    ( Uniquable(..) )
+import SrcLoc    ( noSrcLoc, noLoc, Located(..), unLoc )
+import Bag
+import Outputable

 \end{code}
 
 
 \end{code}
 
 

-Type definitions
-~~~~~~~~~~~~~~~~
+\begin{code}
+type TcDictBinds = LHsBinds TcId       -- Bag of dictionary bindings
+\end{code}

 
 

-The @Tc...@ datatypes are the ones that apply {\em during} type checking.
-All the types in @Tc...@ things have mutable type-variables in them for
-unification.

 
 

-At the end of type checking we zonk everything to @Typechecked...@ datatypes,
-which have immutable type variables in them.
+%************************************************************************
+%*                                                                     *
+\subsection[mkFailurePair]{Code for pattern-matching and other failures}
+%*                                                                     *
+%************************************************************************

 
 

+Note: If @hsPatType@ doesn't bear a strong resemblance to @exprType@,
+then something is wrong.

 \begin{code}
 \begin{code}

-type TcIdBndr s = GenId  (TcType s)    -- Binders are all TcTypes
-data TcIdOcc  s = TcId   (TcIdBndr s)  -- Bindees may be either
-               | RealId Id
-
-type TcHsBinds s       = HsBinds (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcBind s          = Bind (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcMonoBinds s     = MonoBinds (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcPat s           = OutPat (TcTyVar s) UVar (TcIdOcc s)
-type TcExpr s          = HsExpr (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcGRHSsAndBinds s = GRHSsAndBinds (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcGRHS s          = GRHS (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcMatch s         = Match (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcQual s          = Qualifier (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcStmt s          = Stmt (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcArithSeqInfo s  = ArithSeqInfo (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcRecordBinds s   = HsRecordBinds (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-type TcHsModule s      = HsModule (TcTyVar s) UVar (TcIdOcc s) (TcPat s)
-
-type TypecheckedPat            = OutPat        TyVar UVar Id
-type TypecheckedMonoBinds      = MonoBinds     TyVar UVar Id TypecheckedPat
-type TypecheckedHsBinds                = HsBinds       TyVar UVar Id TypecheckedPat
-type TypecheckedBind           = Bind          TyVar UVar Id TypecheckedPat
-type TypecheckedHsExpr         = HsExpr        TyVar UVar Id TypecheckedPat
-type TypecheckedArithSeqInfo   = ArithSeqInfo  TyVar UVar Id TypecheckedPat
-type TypecheckedQual           = Qualifier     TyVar UVar Id TypecheckedPat
-type TypecheckedStmt           = Stmt          TyVar UVar Id TypecheckedPat
-type TypecheckedMatch          = Match         TyVar UVar Id TypecheckedPat
-type TypecheckedGRHSsAndBinds  = GRHSsAndBinds TyVar UVar Id TypecheckedPat
-type TypecheckedGRHS           = GRHS          TyVar UVar Id TypecheckedPat
-type TypecheckedRecordBinds    = HsRecordBinds TyVar UVar Id TypecheckedPat
-type TypecheckedHsModule       = HsModule      TyVar UVar Id TypecheckedPat
+hsPatType :: OutPat Id -> Type
+hsPatType pat = pat_type (unLoc pat)
+
+pat_type (ParPat pat)            = hsPatType pat
+pat_type (WildPat ty)            = ty
+pat_type (VarPat var)            = idType var
+pat_type (LazyPat pat)           = hsPatType pat
+pat_type (LitPat lit)            = hsLitType lit
+pat_type (AsPat var pat)         = idType (unLoc var)
+pat_type (ListPat _ ty)                  = mkListTy ty
+pat_type (PArrPat _ ty)                  = mkPArrTy ty
+pat_type (TuplePat pats box)     = mkTupleTy box (length pats) (map hsPatType pats)
+pat_type (ConPatOut _ _ ty _ _)   = ty
+pat_type (SigPatOut _ ty _)      = ty
+pat_type (NPatOut lit ty _)      = ty
+pat_type (NPlusKPatOut id _ _ _)  = idType (unLoc id)
+pat_type (DictPat ds ms)          = case (ds ++ ms) of
+                                      []  -> unitTy
+                                      [d] -> idType d
+                                      ds  -> mkTupleTy Boxed (length ds) (map idType ds)
+
+
+hsLitType :: HsLit -> TcType
+hsLitType (HsChar c)       = charTy
+hsLitType (HsCharPrim c)   = charPrimTy
+hsLitType (HsString str)   = stringTy
+hsLitType (HsStringPrim s) = addrPrimTy
+hsLitType (HsInt i)       = intTy
+hsLitType (HsIntPrim i)    = intPrimTy
+hsLitType (HsInteger i ty) = ty
+hsLitType (HsRat _ ty)    = ty
+hsLitType (HsFloatPrim f)  = floatPrimTy
+hsLitType (HsDoublePrim d) = doublePrimTy

 \end{code}
 
 \end{code}
 

+%************************************************************************
+%*                                                                     *
+\subsection{Coercion functions}
+%*                                                                     *
+%************************************************************************
+

 \begin{code}
 \begin{code}

-mkHsTyApp expr []  = expr
-mkHsTyApp expr tys = TyApp expr tys
+type Coercion a = Maybe (a -> a)
+       -- Nothing => identity fn

 
 

-mkHsDictApp expr []     = expr
-mkHsDictApp expr dict_vars = DictApp expr dict_vars
+type ExprCoFn = Coercion (HsExpr TcId)
+type PatCoFn  = Coercion (Pat    TcId)

 
 

-mkHsTyLam []     expr = expr
-mkHsTyLam tyvars expr = TyLam tyvars expr
+(<.>) :: Coercion a -> Coercion a -> Coercion a        -- Composition
+Nothing <.> Nothing = Nothing
+Nothing <.> Just f  = Just f
+Just f  <.> Nothing = Just f
+Just f1 <.> Just f2 = Just (f1 . f2)

 
 

-mkHsDictLam []    expr = expr
-mkHsDictLam dicts expr = DictLam dicts expr
+(<$>) :: Coercion a -> a -> a
+Just f  <$> e = f e
+Nothing <$> e = e

 
 

-tcIdType :: TcIdOcc s -> TcType s
-tcIdType (TcId   id) = idType id
-tcIdType (RealId id) = pprPanic "tcIdType:" (ppr PprDebug id)
+mkCoercion :: (a -> a) -> Coercion a
+mkCoercion f = Just f

 
 

-tcIdTyVars (TcId id)  = tyVarsOfType (idType id)
-tcIdTyVars (RealId _) = emptyTyVarSet          -- Top level Ids have no free type variables
-\end{code}
+idCoercion :: Coercion a
+idCoercion = Nothing

 
 

-\begin{code}
-instance Eq (TcIdOcc s) where
-  (TcId id1)   == (TcId id2)   = id1 == id2
-  (RealId id1) == (RealId id2) = id1 == id2
-  _           == _            = False
-
-instance Outputable (TcIdOcc s) where
-  ppr sty (TcId id)   = ppr sty id
-  ppr sty (RealId id) = ppr sty id
-
-instance NamedThing (TcIdOcc s) where
-  getName (TcId id)   = getName id
-  getName (RealId id) = getName id
+isIdCoercion :: Coercion a -> Bool
+isIdCoercion = isNothing

 \end{code}
 
 
 \end{code}
 
 

@@ -150,192 +153,213 @@ instance NamedThing (TcIdOcc s) where
 %*                                                                     *
 %************************************************************************
 
 %*                                                                     *
 %************************************************************************
 

-This zonking pass runs over the bindings
+\begin{code}
+-- zonkId is used *during* typechecking just to zonk the Id's type
+zonkId :: TcId -> TcM TcId
+zonkId id
+  = zonkTcType (idType id) `thenM` \ ty' ->
+    returnM (setIdType id ty')
+\end{code}
+
+The rest of the zonking is done *after* typechecking.
+The main zonking pass runs over the bindings

 
  a) to convert TcTyVars to TyVars etc, dereferencing any bindings etc
  b) convert unbound TcTyVar to Void
 
  a) to convert TcTyVars to TyVars etc, dereferencing any bindings etc
  b) convert unbound TcTyVar to Void

+ c) convert each TcId to an Id by zonking its type

 
 

-We pass an environment around so that
- a) we know which TyVars are unbound
- b) we maintain sharing; eg an Id is zonked at its binding site and they
-    all occurrences of that Id point to the common zonked copy
+The type variables are converted by binding mutable tyvars to immutable ones
+and then zonking as normal.
+
+The Ids are converted by binding them in the normal Tc envt; that
+way we maintain sharing; eg an Id is zonked at its binding site and they
+all occurrences of that Id point to the common zonked copy

 
 It's all pretty boring stuff, because HsSyn is such a large type, and 
 the environment manipulation is tiresome.
 
 
 It's all pretty boring stuff, because HsSyn is such a large type, and 
 the environment manipulation is tiresome.
 

-

 \begin{code}
 \begin{code}

-zonkIdBndr :: TyVarEnv Type -> TcIdOcc s -> NF_TcM s Id
-zonkIdBndr te (TcId (Id u n ty details prags info))
-  = zonkTcTypeToType te ty     `thenNF_Tc` \ ty' ->
-    returnNF_Tc (Id u n ty' details prags info)
-
-zonkIdBndr te (RealId id) = returnNF_Tc id
-
-zonkIdOcc :: IdEnv Id -> TcIdOcc s -> Id
-zonkIdOcc ve (RealId id) = id
-zonkIdOcc ve (TcId id)   = case (lookupIdEnv ve id) of
-                               Just id' -> id'
-                               Nothing  -> pprTrace "zonkIdOcc: " (ppr PprDebug id) $
-                                           Id u n voidTy details prags info
-                                        where
-                                           Id u n _ details prags info = id
-
-extend_ve ve ids    = growIdEnvList ve [(id,id) | id <- ids]
-extend_te te tyvars = growTyVarEnvList te [(tyvar, mkTyVarTy tyvar) | tyvar <- tyvars]
+data ZonkEnv = ZonkEnv (TcType -> TcM Type)    -- How to zonk a type
+                       (IdEnv Id)              -- What variables are in scope
+       -- Maps an Id to its zonked version; both have the same Name
+       -- Is only consulted lazily; hence knot-tying
+
+emptyZonkEnv = ZonkEnv zonkTypeZapping emptyVarEnv
+
+extendZonkEnv :: ZonkEnv -> [Id] -> ZonkEnv
+extendZonkEnv (ZonkEnv zonk_ty env) ids 
+  = ZonkEnv zonk_ty (extendVarEnvList env [(id,id) | id <- ids])
+
+setZonkType :: ZonkEnv -> (TcType -> TcM Type) -> ZonkEnv
+setZonkType (ZonkEnv _ env) zonk_ty = ZonkEnv zonk_ty env
+
+mkZonkEnv :: [Id] -> ZonkEnv
+mkZonkEnv ids = extendZonkEnv emptyZonkEnv ids
+
+zonkIdOcc :: ZonkEnv -> TcId -> Id
+-- Ids defined in this module should be in the envt; 
+-- ignore others.  (Actually, data constructors are also
+-- not LocalVars, even when locally defined, but that is fine.)
+--
+-- Actually, Template Haskell works in 'chunks' of declarations, and
+-- an earlier chunk won't be in the 'env' that the zonking phase 
+-- carries around.  Instead it'll be in the tcg_gbl_env, already fully
+-- zonked.  There's no point in looking it up there (except for error 
+-- checking), and it's not conveniently to hand; hence the simple
+-- 'orElse' case in the LocalVar branch.
+--
+-- Even without template splices, in module Main, the checking of
+-- 'main' is done as a separte chunk.
+zonkIdOcc (ZonkEnv zonk_ty env) id 
+  | isLocalVar id = lookupVarEnv env id `orElse` id
+  | otherwise    = id
+
+zonkIdOccs env ids = map (zonkIdOcc env) ids
+
+-- zonkIdBndr is used *after* typechecking to get the Id's type
+-- to its final form.  The TyVarEnv give 
+zonkIdBndr :: ZonkEnv -> TcId -> TcM Id
+zonkIdBndr env id
+  = zonkTcTypeToType env (idType id)   `thenM` \ ty' ->
+    returnM (setIdType id ty')
+
+zonkIdBndrs :: ZonkEnv -> [TcId] -> TcM [Id]
+zonkIdBndrs env ids = mappM (zonkIdBndr env) ids
+
+zonkTopBndrs :: [TcId] -> TcM [Id]
+zonkTopBndrs ids = zonkIdBndrs emptyZonkEnv ids

 \end{code}
 
 \end{code}
 

-\begin{code}
-       -- Implicitly mutually recursive, which is overkill,
-       -- but it means that later ones see earlier ones
-zonkDictBinds te ve dbs 
-  = fixNF_Tc (\ ~(_,new_ve) ->
-       zonkDictBindsLocal te new_ve dbs        `thenNF_Tc` \ (new_binds, dict_ids) ->
-        returnNF_Tc (new_binds, extend_ve ve dict_ids)
-    )
-
-       -- The ..Local version assumes the caller has set up
-       -- a ve that contains all the things bound here
-zonkDictBindsLocal te ve [] = returnNF_Tc ([], [])
-
-zonkDictBindsLocal te ve ((dict,rhs) : binds)
-  = zonkIdBndr te dict                 `thenNF_Tc` \ new_dict ->
-    zonkExpr te ve rhs                 `thenNF_Tc` \ new_rhs ->
-    zonkDictBindsLocal te ve binds     `thenNF_Tc` \ (new_binds, dict_ids) ->
-    returnNF_Tc ((new_dict,new_rhs) : new_binds, 
-                new_dict:dict_ids)
-\end{code}

 
 \begin{code}
 
 \begin{code}

-zonkBinds :: TyVarEnv Type -> IdEnv Id 
-         -> TcHsBinds s -> NF_TcM s (TypecheckedHsBinds, IdEnv Id)
-
-zonkBinds te ve EmptyBinds = returnNF_Tc (EmptyBinds, ve)
-
-zonkBinds te ve (ThenBinds binds1 binds2)
-  = zonkBinds te ve binds1   `thenNF_Tc` \ (new_binds1, ve1) ->
-    zonkBinds te ve1 binds2  `thenNF_Tc` \ (new_binds2, ve2) ->
-    returnNF_Tc (ThenBinds new_binds1 new_binds2, ve2)
-
-zonkBinds te ve (SingleBind bind)
-  = fixNF_Tc (\ ~(_,new_ve) ->
-       zonkBind te new_ve bind  `thenNF_Tc` \ (new_bind, new_ids) ->
-       returnNF_Tc (SingleBind new_bind, extend_ve ve new_ids)
+zonkTopExpr :: HsExpr TcId -> TcM (HsExpr Id)
+zonkTopExpr e = zonkExpr emptyZonkEnv e
+
+zonkTopLExpr :: LHsExpr TcId -> TcM (LHsExpr Id)
+zonkTopLExpr e = zonkLExpr emptyZonkEnv e
+
+zonkTopDecls :: Bag (LHsBind TcId) -> [LRuleDecl TcId] -> [LForeignDecl TcId]
+            -> TcM ([Id], 
+                    Bag (LHsBind  Id),
+                    [LForeignDecl Id],
+                    [LRuleDecl    Id])
+zonkTopDecls binds rules fords -- Top level is implicitly recursive
+  = fixM (\ ~(new_ids, _, _, _) ->
+       let
+          zonk_env = mkZonkEnv new_ids
+       in
+       zonkMonoBinds zonk_env binds            `thenM` \ binds' ->
+       zonkRules zonk_env rules                `thenM` \ rules' ->
+       zonkForeignExports zonk_env fords       `thenM` \ fords' ->
+       
+       returnM (collectHsBindBinders binds', binds', fords', rules')

     )
 
     )
 

-zonkBinds te ve (AbsBinds tyvars dicts locprs dict_binds val_bind)
-  = mapNF_Tc zonkTcTyVarToTyVar tyvars `thenNF_Tc` \ new_tyvars ->
-    let
-       new_te = extend_te te new_tyvars
-    in
-    mapNF_Tc (zonkIdBndr new_te) dicts         `thenNF_Tc` \ new_dicts ->
-    mapNF_Tc (zonkIdBndr new_te) globals       `thenNF_Tc` \ new_globals ->
+---------------------------------------------
+zonkGroup :: ZonkEnv -> HsBindGroup TcId -> TcM (ZonkEnv, HsBindGroup Id)
+zonkGroup env (HsBindGroup bs sigs is_rec)
+  = ASSERT( null sigs )
+    do  { (env1, bs') <- fixM (\ ~(_, new_binds) -> do 
+                   { let env1 = extendZonkEnv env (collectHsBindBinders new_binds)
+                   ; bs' <- zonkMonoBinds env1 bs
+                   ; return (env1, bs') })
+          ; return (env1, HsBindGroup bs' [] is_rec) }
+ 
+
+zonkGroup env (HsIPBinds binds)
+  = mappM (wrapLocM zonk_ip_bind) binds        `thenM` \ new_binds ->

     let
     let

-       ve1 = extend_ve ve  new_globals
-        ve2 = extend_ve ve1 new_dicts
+       env1 = extendZonkEnv env [ipNameName n | L _ (IPBind n _) <- new_binds]

     in
     in

-    fixNF_Tc (\ ~(_, ve3) ->
-       zonkDictBindsLocal new_te ve3 dict_binds  `thenNF_Tc` \ (new_dict_binds, ds) ->
-       zonkBind new_te ve3 val_bind              `thenNF_Tc` \ (new_val_bind, ls) ->
+    returnM (env1, HsIPBinds new_binds)
+  where
+    zonk_ip_bind (IPBind n e)
+       = mapIPNameTc (zonkIdBndr env) n        `thenM` \ n' ->
+         zonkLExpr env e                       `thenM` \ e' ->
+         returnM (IPBind n' e')
+
+---------------------------------------------
+zonkNestedBinds :: ZonkEnv -> [HsBindGroup TcId] -> TcM (ZonkEnv, [HsBindGroup Id])
+zonkNestedBinds env []     = return (env, [])
+zonkNestedBinds env (b:bs) = do        { (env1, b') <- zonkGroup env b
+                               ; (env2, bs') <- zonkNestedBinds env1 bs
+                               ; return (env2, b':bs') }
+
+---------------------------------------------
+zonkMonoBinds :: ZonkEnv -> Bag (LHsBind TcId) -> TcM (Bag (LHsBind Id))
+zonkMonoBinds env binds = mapBagM (wrapLocM (zonk_bind env)) binds
+
+zonk_bind :: ZonkEnv -> HsBind TcId -> TcM (HsBind Id)
+zonk_bind env (PatBind pat grhss)
+  = zonkPat env pat    `thenM` \ (new_pat, _) ->
+    zonkGRHSs env grhss        `thenM` \ new_grhss ->
+    returnM (PatBind new_pat new_grhss)
+
+zonk_bind env (VarBind var expr)
+  = zonkIdBndr env var                         `thenM` \ new_var ->
+    zonkLExpr env expr                 `thenM` \ new_expr ->
+    returnM (VarBind new_var new_expr)
+
+zonk_bind env (FunBind var inf ms)
+  = wrapLocM (zonkIdBndr env) var      `thenM` \ new_var ->
+    mappM (zonkMatch env) ms           `thenM` \ new_ms ->
+    returnM (FunBind new_var inf new_ms)
+
+zonk_bind env (AbsBinds tyvars dicts exports inlines val_binds)
+  = mappM zonkTcTyVarToTyVar tyvars    `thenM` \ new_tyvars ->
+       -- No need to extend tyvar env: the effects are
+       -- propagated through binding the tyvars themselves
+
+    zonkIdBndrs env dicts              `thenM` \ new_dicts ->
+    fixM (\ ~(new_val_binds, _) ->

        let
        let

-           new_locprs = zipEqual "zonkBinds" (map (zonkIdOcc ve3) locals) new_globals
-        in
-        returnNF_Tc (AbsBinds new_tyvars new_dicts new_locprs new_dict_binds new_val_bind,
-                    extend_ve ve2 (ds++ls))
-    )                                          `thenNF_Tc` \ (binds, _) ->
-    returnNF_Tc (binds, ve1)   -- Yes, the "ve1" is right (SLPJ)
+         env1 = extendZonkEnv (extendZonkEnv env new_dicts)
+                              (collectHsBindBinders new_val_binds)
+       in
+       zonkMonoBinds env1 val_binds            `thenM` \ new_val_binds ->
+        mappM (zonkExport env1) exports                `thenM` \ new_exports ->
+       returnM (new_val_binds, new_exports)
+    )                                          `thenM` \ (new_val_bind, new_exports) ->
+    returnM (AbsBinds new_tyvars new_dicts new_exports inlines new_val_bind)

   where
   where

-    (locals, globals) = unzip locprs
-\end{code}
-
-\begin{code}
--------------------------------------------------------------------------
-zonkBind :: TyVarEnv Type -> IdEnv Id 
-        -> TcBind s -> NF_TcM s (TypecheckedBind, [Id])
-
-zonkBind te ve EmptyBind = returnNF_Tc (EmptyBind, [])
-
-zonkBind te ve (NonRecBind mbinds)
-  = zonkMonoBinds te ve mbinds `thenNF_Tc` \ (new_mbinds, new_ids) ->
-    returnNF_Tc (NonRecBind new_mbinds, new_ids)
-
-zonkBind te ve (RecBind mbinds)
-  = zonkMonoBinds te ve mbinds `thenNF_Tc` \ (new_mbinds, new_ids) ->
-    returnNF_Tc (RecBind new_mbinds, new_ids)
-
--------------------------------------------------------------------------
-zonkMonoBinds :: TyVarEnv Type -> IdEnv Id 
-             -> TcMonoBinds s -> NF_TcM s (TypecheckedMonoBinds, [Id])
-
-zonkMonoBinds te ve EmptyMonoBinds = returnNF_Tc (EmptyMonoBinds, [])
-
-zonkMonoBinds te ve (AndMonoBinds mbinds1 mbinds2)
-  = zonkMonoBinds te ve mbinds1  `thenNF_Tc` \ (new_mbinds1, ids1) ->
-    zonkMonoBinds te ve mbinds2  `thenNF_Tc` \ (new_mbinds2, ids2) ->
-    returnNF_Tc (AndMonoBinds new_mbinds1 new_mbinds2, ids1 ++ ids2)
-
-zonkMonoBinds te ve (PatMonoBind pat grhss_w_binds locn)
-  = zonkPat te ve pat                          `thenNF_Tc` \ (new_pat, ids) ->
-    zonkGRHSsAndBinds te ve grhss_w_binds      `thenNF_Tc` \ new_grhss_w_binds ->
-    returnNF_Tc (PatMonoBind new_pat new_grhss_w_binds locn, ids)
-
-zonkMonoBinds te ve (VarMonoBind var expr)
-  = zonkIdBndr te var          `thenNF_Tc` \ new_var ->
-    zonkExpr te ve expr                `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (VarMonoBind new_var new_expr, [new_var])
-
-zonkMonoBinds te ve (FunMonoBind var inf ms locn)
-  = zonkIdBndr te var                  `thenNF_Tc` \ new_var ->
-    mapNF_Tc (zonkMatch te ve) ms      `thenNF_Tc` \ new_ms ->
-    returnNF_Tc (FunMonoBind new_var inf new_ms locn, [new_var])
+    zonkExport env (tyvars, global, local)
+       = zonkTcTyVars tyvars           `thenM` \ tys ->
+         let
+               new_tyvars = map (tcGetTyVar "zonkExport") tys
+               -- This isn't the binding occurrence of these tyvars
+               -- but they should *be* tyvars.  Hence tcGetTyVar.
+         in
+         zonkIdBndr env global         `thenM` \ new_global ->
+         returnM (new_tyvars, new_global, zonkIdOcc env local)

 \end{code}
 
 %************************************************************************
 %*                                                                     *
 \end{code}
 
 %************************************************************************
 %*                                                                     *

-\subsection[BackSubst-Match-GRHSs]{Match and GRHSsAndBinds}
+\subsection[BackSubst-Match-GRHSs]{Match and GRHSs}

 %*                                                                     *
 %************************************************************************
 
 \begin{code}
 %*                                                                     *
 %************************************************************************
 
 \begin{code}

-zonkMatch :: TyVarEnv Type -> IdEnv Id 
-         -> TcMatch s -> NF_TcM s TypecheckedMatch
-
-zonkMatch te ve (PatMatch pat match)
-  = zonkPat te ve pat          `thenNF_Tc` \ (new_pat, ids) ->
-    let
-       new_ve = extend_ve ve ids
-    in
-    zonkMatch te new_ve match          `thenNF_Tc` \ new_match ->
-    returnNF_Tc (PatMatch new_pat new_match)
-
-zonkMatch te ve (GRHSMatch grhss_w_binds)
-  = zonkGRHSsAndBinds te ve grhss_w_binds `thenNF_Tc` \ new_grhss_w_binds ->
-    returnNF_Tc (GRHSMatch new_grhss_w_binds)
+zonkMatch :: ZonkEnv -> LMatch TcId-> TcM (LMatch Id)

 
 

-zonkMatch te ve (SimpleMatch expr)
-  = zonkExpr te ve expr   `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (SimpleMatch new_expr)
+zonkMatch env (L loc (Match pats _ grhss))
+  = zonkPats env pats                                          `thenM` \ (new_pats, new_ids) ->
+    zonkGRHSs (extendZonkEnv env (bagToList new_ids)) grhss    `thenM` \ new_grhss ->
+    returnM (L loc (Match new_pats Nothing new_grhss))

 
 -------------------------------------------------------------------------
 
 -------------------------------------------------------------------------

-zonkGRHSsAndBinds :: TyVarEnv Type -> IdEnv Id 
-                 -> TcGRHSsAndBinds s
-                 -> NF_TcM s TypecheckedGRHSsAndBinds
+zonkGRHSs :: ZonkEnv -> GRHSs TcId -> TcM (GRHSs Id)

 
 

-zonkGRHSsAndBinds te ve (GRHSsAndBindsOut grhss binds ty)
-  = zonkBinds te ve binds              `thenNF_Tc` \ (new_binds, new_ve) ->
+zonkGRHSs env (GRHSs grhss binds ty)
+  = zonkNestedBinds env binds          `thenM` \ (new_env, new_binds) ->

     let
     let

-       zonk_grhs (GRHS guard expr locn)
-         = zonkExpr te new_ve guard  `thenNF_Tc` \ new_guard ->
-           zonkExpr te new_ve expr   `thenNF_Tc` \ new_expr  ->
-           returnNF_Tc (GRHS new_guard new_expr locn)
-
-        zonk_grhs (OtherwiseGRHS expr locn)
-          = zonkExpr te new_ve expr   `thenNF_Tc` \ new_expr  ->
-           returnNF_Tc (OtherwiseGRHS new_expr locn)
+       zonk_grhs (GRHS guarded)
+         = zonkStmts new_env guarded   `thenM` \ new_guarded ->
+           returnM (GRHS new_guarded)

     in
     in

-    mapNF_Tc zonk_grhs grhss   `thenNF_Tc` \ new_grhss ->
-    zonkTcTypeToType te ty     `thenNF_Tc` \ new_ty ->
-    returnNF_Tc (GRHSsAndBindsOut new_grhss new_binds new_ty)
+    mappM (wrapLocM zonk_grhs) grhss   `thenM` \ new_grhss ->
+    zonkTcTypeToType env ty            `thenM` \ new_ty ->
+    returnM (GRHSs new_grhss new_binds new_ty)

 \end{code}
 
 %************************************************************************
 \end{code}
 
 %************************************************************************

@@ -345,261 +369,309 @@ zonkGRHSsAndBinds te ve (GRHSsAndBindsOut grhss binds ty)
 %************************************************************************
 
 \begin{code}
 %************************************************************************
 
 \begin{code}

-zonkExpr :: TyVarEnv Type -> IdEnv Id 
-        -> TcExpr s -> NF_TcM s TypecheckedHsExpr
-
-zonkExpr te ve (HsVar name)
-  = returnNF_Tc (HsVar (zonkIdOcc ve name))
-
-zonkExpr te ve (HsLit _) = panic "zonkExpr te ve:HsLit"
-
-zonkExpr te ve (HsLitOut lit ty)
-  = zonkTcTypeToType te ty         `thenNF_Tc` \ new_ty  ->
-    returnNF_Tc (HsLitOut lit new_ty)
-
-zonkExpr te ve (HsLam match)
-  = zonkMatch te ve match      `thenNF_Tc` \ new_match ->
-    returnNF_Tc (HsLam new_match)
-
-zonkExpr te ve (HsApp e1 e2)
-  = zonkExpr te ve e1  `thenNF_Tc` \ new_e1 ->
-    zonkExpr te ve e2  `thenNF_Tc` \ new_e2 ->
-    returnNF_Tc (HsApp new_e1 new_e2)
-
-zonkExpr te ve (OpApp e1 op e2)
-  = zonkExpr te ve e1  `thenNF_Tc` \ new_e1 ->
-    zonkExpr te ve op  `thenNF_Tc` \ new_op ->
-    zonkExpr te ve e2  `thenNF_Tc` \ new_e2 ->
-    returnNF_Tc (OpApp new_e1 new_op new_e2)
-
-zonkExpr te ve (NegApp _ _) = panic "zonkExpr te ve:NegApp"
-zonkExpr te ve (HsPar _)    = panic "zonkExpr te ve:HsPar"
-
-zonkExpr te ve (SectionL expr op)
-  = zonkExpr te ve expr        `thenNF_Tc` \ new_expr ->
-    zonkExpr te ve op          `thenNF_Tc` \ new_op ->
-    returnNF_Tc (SectionL new_expr new_op)
-
-zonkExpr te ve (SectionR op expr)
-  = zonkExpr te ve op          `thenNF_Tc` \ new_op ->
-    zonkExpr te ve expr                `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (SectionR new_op new_expr)
-
-zonkExpr te ve (HsCase expr ms src_loc)
-  = zonkExpr te ve expr            `thenNF_Tc` \ new_expr ->
-    mapNF_Tc (zonkMatch te ve) ms   `thenNF_Tc` \ new_ms ->
-    returnNF_Tc (HsCase new_expr new_ms src_loc)
-
-zonkExpr te ve (HsIf e1 e2 e3 src_loc)
-  = zonkExpr te ve e1  `thenNF_Tc` \ new_e1 ->
-    zonkExpr te ve e2  `thenNF_Tc` \ new_e2 ->
-    zonkExpr te ve e3  `thenNF_Tc` \ new_e3 ->
-    returnNF_Tc (HsIf new_e1 new_e2 new_e3 src_loc)
-
-zonkExpr te ve (HsLet binds expr)
-  = zonkBinds te ve binds      `thenNF_Tc` \ (new_binds, new_ve) ->
-    zonkExpr  te new_ve expr   `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (HsLet new_binds new_expr)
-
-zonkExpr te ve (HsDo _ _) = panic "zonkExpr te ve:HsDo"
-
-zonkExpr te ve (HsDoOut stmts then_id zero_id src_loc)
-  = zonkStmts te ve stmts      `thenNF_Tc` \ new_stmts ->
-    returnNF_Tc (HsDoOut new_stmts (zonkIdOcc ve then_id) (zonkIdOcc ve zero_id) src_loc)
-
-zonkExpr te ve (ListComp expr quals)
-  = zonkQuals te ve quals      `thenNF_Tc` \ (new_quals, new_ve) ->
-    zonkExpr te new_ve expr    `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (ListComp new_expr new_quals)
-
-zonkExpr te ve (ExplicitList _) = panic "zonkExpr te ve:ExplicitList"
-
-zonkExpr te ve (ExplicitListOut ty exprs)
-  = zonkTcTypeToType te ty             `thenNF_Tc` \ new_ty ->
-    mapNF_Tc (zonkExpr te ve) exprs    `thenNF_Tc` \ new_exprs ->
-    returnNF_Tc (ExplicitListOut new_ty new_exprs)
-
-zonkExpr te ve (ExplicitTuple exprs)
-  = mapNF_Tc (zonkExpr te ve) exprs  `thenNF_Tc` \ new_exprs ->
-    returnNF_Tc (ExplicitTuple new_exprs)
-
-zonkExpr te ve (RecordCon con rbinds)
-  = zonkExpr te ve con         `thenNF_Tc` \ new_con ->
-    zonkRbinds te ve rbinds    `thenNF_Tc` \ new_rbinds ->
-    returnNF_Tc (RecordCon new_con new_rbinds)
-
-zonkExpr te ve (RecordUpd _ _) = panic "zonkExpr te ve:RecordUpd"
-
-zonkExpr te ve (RecordUpdOut expr dicts rbinds)
-  = zonkExpr te ve expr                `thenNF_Tc` \ new_expr ->
-    zonkRbinds te ve rbinds    `thenNF_Tc` \ new_rbinds ->
-    returnNF_Tc (RecordUpdOut new_expr new_dicts new_rbinds)
-  where
-    new_dicts = map (zonkIdOcc ve) dicts
+zonkLExprs :: ZonkEnv -> [LHsExpr TcId] -> TcM [LHsExpr Id]
+zonkLExpr  :: ZonkEnv -> LHsExpr TcId   -> TcM (LHsExpr Id)
+zonkExpr   :: ZonkEnv -> HsExpr TcId    -> TcM (HsExpr Id)

 
 

-zonkExpr te ve (ExprWithTySig _ _) = panic "zonkExpr te ve:ExprWithTySig"
-zonkExpr te ve (ArithSeqIn _) = panic "zonkExpr te ve:ArithSeqIn"
+zonkLExprs env exprs = mappM (zonkLExpr env) exprs
+zonkLExpr  env expr  = wrapLocM (zonkExpr env) expr

 
 

-zonkExpr te ve (ArithSeqOut expr info)
-  = zonkExpr te ve expr        `thenNF_Tc` \ new_expr ->
-    zonkArithSeq te ve info    `thenNF_Tc` \ new_info ->
-    returnNF_Tc (ArithSeqOut new_expr new_info)
+zonkExpr env (HsVar id)
+  = returnM (HsVar (zonkIdOcc env id))

 
 

-zonkExpr te ve (CCall fun args may_gc is_casm result_ty)
-  = mapNF_Tc (zonkExpr te ve) args     `thenNF_Tc` \ new_args ->
-    zonkTcTypeToType te result_ty      `thenNF_Tc` \ new_result_ty ->
-    returnNF_Tc (CCall fun new_args may_gc is_casm new_result_ty)
+zonkExpr env (HsIPVar id)
+  = returnM (HsIPVar (mapIPName (zonkIdOcc env) id))

 
 

-zonkExpr te ve (HsSCC label expr)
-  = zonkExpr te ve expr        `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (HsSCC label new_expr)
+zonkExpr env (HsLit (HsRat f ty))
+  = zonkTcTypeToType env ty       `thenM` \ new_ty  ->
+    returnM (HsLit (HsRat f new_ty))

 
 

-zonkExpr te ve (TyLam tyvars expr)
-  = mapNF_Tc zonkTcTyVarToTyVar tyvars `thenNF_Tc` \ new_tyvars ->
-    let
-       new_te = extend_te te new_tyvars
-    in
-    zonkExpr new_te ve expr            `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (TyLam new_tyvars new_expr)
+zonkExpr env (HsLit lit)
+  = returnM (HsLit lit)
+
+-- HsOverLit doesn't appear in typechecker output
+
+zonkExpr env (HsLam match)
+  = zonkMatch env match        `thenM` \ new_match ->
+    returnM (HsLam new_match)

 
 

-zonkExpr te ve (TyApp expr tys)
-  = zonkExpr te ve expr                `thenNF_Tc` \ new_expr ->
-    mapNF_Tc (zonkTcTypeToType te) tys `thenNF_Tc` \ new_tys ->
-    returnNF_Tc (TyApp new_expr new_tys)
+zonkExpr env (HsApp e1 e2)
+  = zonkLExpr env e1   `thenM` \ new_e1 ->
+    zonkLExpr env e2   `thenM` \ new_e2 ->
+    returnM (HsApp new_e1 new_e2)

 
 

-zonkExpr te ve (DictLam dicts expr)
-  = mapNF_Tc (zonkIdBndr te) dicts     `thenNF_Tc` \ new_dicts ->
+zonkExpr env (HsBracketOut body bs) 
+  = mappM zonk_b bs    `thenM` \ bs' ->
+    returnM (HsBracketOut body bs')
+  where
+    zonk_b (n,e) = zonkLExpr env e     `thenM` \ e' ->
+                  returnM (n,e')
+
+zonkExpr env (HsSpliceE s) = WARN( True, ppr s )       -- Should not happen
+                            returnM (HsSpliceE s)
+
+zonkExpr env (OpApp e1 op fixity e2)
+  = zonkLExpr env e1   `thenM` \ new_e1 ->
+    zonkLExpr env op   `thenM` \ new_op ->
+    zonkLExpr env e2   `thenM` \ new_e2 ->
+    returnM (OpApp new_e1 new_op fixity new_e2)
+
+zonkExpr env (NegApp _ _) = panic "zonkExpr env: NegApp"
+
+zonkExpr env (HsPar e)    
+  = zonkLExpr env e    `thenM` \new_e ->
+    returnM (HsPar new_e)
+
+zonkExpr env (SectionL expr op)
+  = zonkLExpr env expr `thenM` \ new_expr ->
+    zonkLExpr env op           `thenM` \ new_op ->
+    returnM (SectionL new_expr new_op)
+
+zonkExpr env (SectionR op expr)
+  = zonkLExpr env op           `thenM` \ new_op ->
+    zonkLExpr env expr         `thenM` \ new_expr ->
+    returnM (SectionR new_op new_expr)
+
+zonkExpr env (HsCase expr ms)
+  = zonkLExpr env expr         `thenM` \ new_expr ->
+    mappM (zonkMatch env) ms   `thenM` \ new_ms ->
+    returnM (HsCase new_expr new_ms)
+
+zonkExpr env (HsIf e1 e2 e3)
+  = zonkLExpr env e1   `thenM` \ new_e1 ->
+    zonkLExpr env e2   `thenM` \ new_e2 ->
+    zonkLExpr env e3   `thenM` \ new_e3 ->
+    returnM (HsIf new_e1 new_e2 new_e3)
+
+zonkExpr env (HsLet binds expr)
+  = zonkNestedBinds env binds  `thenM` \ (new_env, new_binds) ->
+    zonkLExpr new_env expr     `thenM` \ new_expr ->
+    returnM (HsLet new_binds new_expr)
+
+zonkExpr env (HsDo do_or_lc stmts ids ty)
+  = zonkStmts env stmts        `thenM` \ new_stmts ->
+    zonkTcTypeToType env ty    `thenM` \ new_ty   ->
+    zonkReboundNames env ids   `thenM` \ new_ids ->
+    returnM (HsDo do_or_lc new_stmts new_ids new_ty)
+
+zonkExpr env (ExplicitList ty exprs)
+  = zonkTcTypeToType env ty    `thenM` \ new_ty ->
+    zonkLExprs env exprs       `thenM` \ new_exprs ->
+    returnM (ExplicitList new_ty new_exprs)
+
+zonkExpr env (ExplicitPArr ty exprs)
+  = zonkTcTypeToType env ty    `thenM` \ new_ty ->
+    zonkLExprs env exprs       `thenM` \ new_exprs ->
+    returnM (ExplicitPArr new_ty new_exprs)
+
+zonkExpr env (ExplicitTuple exprs boxed)
+  = zonkLExprs env exprs       `thenM` \ new_exprs ->
+    returnM (ExplicitTuple new_exprs boxed)
+
+zonkExpr env (RecordConOut data_con con_expr rbinds)
+  = zonkLExpr env con_expr     `thenM` \ new_con_expr ->
+    zonkRbinds env rbinds      `thenM` \ new_rbinds ->
+    returnM (RecordConOut data_con new_con_expr new_rbinds)
+
+zonkExpr env (RecordUpd _ _) = panic "zonkExpr env:RecordUpd"
+
+zonkExpr env (RecordUpdOut expr in_ty out_ty rbinds)
+  = zonkLExpr env expr         `thenM` \ new_expr ->
+    zonkTcTypeToType env in_ty `thenM` \ new_in_ty ->
+    zonkTcTypeToType env out_ty        `thenM` \ new_out_ty ->
+    zonkRbinds env rbinds      `thenM` \ new_rbinds ->
+    returnM (RecordUpdOut new_expr new_in_ty new_out_ty new_rbinds)
+
+zonkExpr env (ExprWithTySig _ _) = panic "zonkExpr env:ExprWithTySig"
+zonkExpr env (ArithSeqIn _)      = panic "zonkExpr env:ArithSeqIn"
+zonkExpr env (PArrSeqIn _)       = panic "zonkExpr env:PArrSeqIn"
+
+zonkExpr env (ArithSeqOut expr info)
+  = zonkLExpr env expr         `thenM` \ new_expr ->
+    zonkArithSeq env info      `thenM` \ new_info ->
+    returnM (ArithSeqOut new_expr new_info)
+
+zonkExpr env (PArrSeqOut expr info)
+  = zonkLExpr env expr         `thenM` \ new_expr ->
+    zonkArithSeq env info      `thenM` \ new_info ->
+    returnM (PArrSeqOut new_expr new_info)
+
+zonkExpr env (HsSCC lbl expr)
+  = zonkLExpr env expr `thenM` \ new_expr ->
+    returnM (HsSCC lbl new_expr)
+
+-- hdaume: core annotations
+zonkExpr env (HsCoreAnn lbl expr)
+  = zonkLExpr env expr   `thenM` \ new_expr ->
+    returnM (HsCoreAnn lbl new_expr)
+
+zonkExpr env (TyLam tyvars expr)
+  = mappM zonkTcTyVarToTyVar tyvars    `thenM` \ new_tyvars ->
+       -- No need to extend tyvar env; see AbsBinds
+
+    zonkLExpr env expr                 `thenM` \ new_expr ->
+    returnM (TyLam new_tyvars new_expr)
+
+zonkExpr env (TyApp expr tys)
+  = zonkLExpr env expr                 `thenM` \ new_expr ->
+    mappM (zonkTcTypeToType env) tys   `thenM` \ new_tys ->
+    returnM (TyApp new_expr new_tys)
+
+zonkExpr env (DictLam dicts expr)
+  = zonkIdBndrs env dicts      `thenM` \ new_dicts ->

     let
     let

-       new_ve = extend_ve ve new_dicts
+       env1 = extendZonkEnv env new_dicts

     in
     in

-    zonkExpr te new_ve expr                    `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (DictLam new_dicts new_expr)
+    zonkLExpr env1 expr        `thenM` \ new_expr ->
+    returnM (DictLam new_dicts new_expr)

 
 

-zonkExpr te ve (DictApp expr dicts)
-  = zonkExpr te ve expr                `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (DictApp new_expr new_dicts)
-  where
-    new_dicts = map (zonkIdOcc ve) dicts
+zonkExpr env (DictApp expr dicts)
+  = zonkLExpr env expr                 `thenM` \ new_expr ->
+    returnM (DictApp new_expr (zonkIdOccs env dicts))

 
 

-zonkExpr te ve (ClassDictLam dicts methods expr)
-  = zonkExpr te ve expr            `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (ClassDictLam new_dicts new_methods new_expr)
-  where
-    new_dicts   = map (zonkIdOcc ve) dicts
-    new_methods = map (zonkIdOcc ve) methods
-    
+-- arrow notation extensions
+zonkExpr env (HsProc pat body)
+  = zonkPat env pat                    `thenM` \ (new_pat, new_ids) ->
+    let
+       env1 = extendZonkEnv env (bagToList new_ids)
+    in
+    zonkCmdTop env1 body               `thenM` \ new_body ->
+    returnM (HsProc new_pat new_body)
+
+zonkExpr env (HsArrApp e1 e2 ty ho rl)
+  = zonkLExpr env e1                   `thenM` \ new_e1 ->
+    zonkLExpr env e2                   `thenM` \ new_e2 ->
+    zonkTcTypeToType env ty            `thenM` \ new_ty ->
+    returnM (HsArrApp new_e1 new_e2 new_ty ho rl)
+
+zonkExpr env (HsArrForm op fixity args)
+  = zonkLExpr env op                   `thenM` \ new_op ->
+    mappM (zonkCmdTop env) args                `thenM` \ new_args ->
+    returnM (HsArrForm new_op fixity new_args)
+
+zonkCmdTop :: ZonkEnv -> LHsCmdTop TcId -> TcM (LHsCmdTop Id)
+zonkCmdTop env cmd = wrapLocM (zonk_cmd_top env) cmd
+
+zonk_cmd_top env (HsCmdTop cmd stack_tys ty ids)
+  = zonkLExpr env cmd                  `thenM` \ new_cmd ->
+    mappM (zonkTcTypeToType env) stack_tys
+                                       `thenM` \ new_stack_tys ->
+    zonkTcTypeToType env ty            `thenM` \ new_ty ->
+    zonkReboundNames env ids           `thenM` \ new_ids ->
+    returnM (HsCmdTop new_cmd new_stack_tys new_ty new_ids)

 
 

-zonkExpr te ve (Dictionary dicts methods)
-  = returnNF_Tc (Dictionary new_dicts new_methods)
+-------------------------------------------------------------------------
+zonkReboundNames :: ZonkEnv -> ReboundNames Id -> TcM (ReboundNames Id)
+zonkReboundNames env prs 
+  = mapM zonk prs

   where
   where

-    new_dicts   = map (zonkIdOcc ve) dicts
-    new_methods = map (zonkIdOcc ve) methods
+    zonk (n, e) = zonkExpr env e `thenM` \ new_e ->
+                 returnM (n, new_e)

 
 

-zonkExpr te ve (SingleDict name)
-  = returnNF_Tc (SingleDict (zonkIdOcc ve name))
-
-zonkExpr te ve (HsCon con tys vargs)
-  = mapNF_Tc (zonkTcTypeToType te) tys `thenNF_Tc` \ new_tys   ->
-    mapNF_Tc (zonkExpr te ve) vargs    `thenNF_Tc` \ new_vargs ->
-    returnNF_Tc (HsCon con new_tys new_vargs)

 
 -------------------------------------------------------------------------
 
 -------------------------------------------------------------------------

-zonkArithSeq :: TyVarEnv Type -> IdEnv Id 
-            -> TcArithSeqInfo s -> NF_TcM s TypecheckedArithSeqInfo
+zonkArithSeq :: ZonkEnv -> ArithSeqInfo TcId -> TcM (ArithSeqInfo Id)

 
 

-zonkArithSeq te ve (From e)
-  = zonkExpr te ve e           `thenNF_Tc` \ new_e ->
-    returnNF_Tc (From new_e)
+zonkArithSeq env (From e)
+  = zonkLExpr env e            `thenM` \ new_e ->
+    returnM (From new_e)

 
 

-zonkArithSeq te ve (FromThen e1 e2)
-  = zonkExpr te ve e1  `thenNF_Tc` \ new_e1 ->
-    zonkExpr te ve e2  `thenNF_Tc` \ new_e2 ->
-    returnNF_Tc (FromThen new_e1 new_e2)
+zonkArithSeq env (FromThen e1 e2)
+  = zonkLExpr env e1   `thenM` \ new_e1 ->
+    zonkLExpr env e2   `thenM` \ new_e2 ->
+    returnM (FromThen new_e1 new_e2)

 
 

-zonkArithSeq te ve (FromTo e1 e2)
-  = zonkExpr te ve e1  `thenNF_Tc` \ new_e1 ->
-    zonkExpr te ve e2  `thenNF_Tc` \ new_e2 ->
-    returnNF_Tc (FromTo new_e1 new_e2)
+zonkArithSeq env (FromTo e1 e2)
+  = zonkLExpr env e1   `thenM` \ new_e1 ->
+    zonkLExpr env e2   `thenM` \ new_e2 ->
+    returnM (FromTo new_e1 new_e2)

 
 

-zonkArithSeq te ve (FromThenTo e1 e2 e3)
-  = zonkExpr te ve e1  `thenNF_Tc` \ new_e1 ->
-    zonkExpr te ve e2  `thenNF_Tc` \ new_e2 ->
-    zonkExpr te ve e3  `thenNF_Tc` \ new_e3 ->
-    returnNF_Tc (FromThenTo new_e1 new_e2 new_e3)
+zonkArithSeq env (FromThenTo e1 e2 e3)
+  = zonkLExpr env e1   `thenM` \ new_e1 ->
+    zonkLExpr env e2   `thenM` \ new_e2 ->
+    zonkLExpr env e3   `thenM` \ new_e3 ->
+    returnM (FromThenTo new_e1 new_e2 new_e3)

 
 

--------------------------------------------------------------------------
-zonkQuals :: TyVarEnv Type -> IdEnv Id 
-         -> [TcQual s] -> NF_TcM s ([TypecheckedQual], IdEnv Id)

 
 

-zonkQuals te ve [] 
-  = returnNF_Tc ([], ve)
+-------------------------------------------------------------------------
+zonkStmts  :: ZonkEnv -> [LStmt TcId] -> TcM [LStmt Id]
+
+zonkStmts env stmts = zonk_stmts env stmts     `thenM` \ (_, stmts) ->
+                     returnM stmts
+
+zonk_stmts :: ZonkEnv -> [LStmt TcId] -> TcM (ZonkEnv, [LStmt Id])
+zonk_stmts env []     = return (env, [])
+zonk_stmts env (s:ss) = do { (env1, s')  <- wrapLocSndM (zonkStmt env) s
+                          ; (env2, ss') <- zonk_stmts env1 ss
+                          ; return (env2, s' : ss') }
+
+zonkStmt :: ZonkEnv -> Stmt TcId -> TcM (ZonkEnv, Stmt Id)
+zonkStmt env (ParStmt stmts_w_bndrs)
+  = mappM zonk_branch stmts_w_bndrs    `thenM` \ new_stmts_w_bndrs ->
+    let 
+       new_binders = concat (map snd new_stmts_w_bndrs)
+       env1 = extendZonkEnv env new_binders
+    in
+    return (env1, ParStmt new_stmts_w_bndrs)
+  where
+    zonk_branch (stmts, bndrs) = zonk_stmts env stmts  `thenM` \ (env1, new_stmts) ->
+                                returnM (new_stmts, zonkIdOccs env1 bndrs)

 
 

-zonkQuals te ve (GeneratorQual pat expr : quals)
-  = zonkPat te ve pat  `thenNF_Tc` \ (new_pat, ids) ->
-    zonkExpr te ve expr        `thenNF_Tc` \ new_expr ->
+zonkStmt env (RecStmt segStmts lvs rvs rets)
+  = zonkIdBndrs env rvs                `thenM` \ new_rvs ->
+    let
+       env1 = extendZonkEnv env new_rvs
+    in
+    zonk_stmts env1 segStmts   `thenM` \ (env2, new_segStmts) ->
+       -- Zonk the ret-expressions in an envt that 
+       -- has the polymorphic bindings in the envt
+    zonkLExprs env2 rets       `thenM` \ new_rets ->

     let
     let

-       new_ve = extend_ve ve ids
+       new_lvs = zonkIdOccs env2 lvs
+       env3 = extendZonkEnv env new_lvs        -- Only the lvs are needed

     in
     in

-    zonkQuals te new_ve quals  `thenNF_Tc` \ (new_quals, final_ve) ->
-    returnNF_Tc (GeneratorQual new_pat new_expr : new_quals, final_ve)
+    returnM (env3, RecStmt new_segStmts new_lvs new_rvs new_rets)

 
 

-zonkQuals te ve (FilterQual expr : quals)
-  = zonkExpr te ve expr        `thenNF_Tc` \ new_expr ->
-    zonkQuals te ve quals      `thenNF_Tc` \ (new_quals, final_ve) ->
-    returnNF_Tc (FilterQual new_expr : new_quals, final_ve)
+zonkStmt env (ResultStmt expr)
+  = zonkLExpr env expr `thenM` \ new_expr ->
+    returnM (env, ResultStmt new_expr)

 
 

-zonkQuals te ve (LetQual binds : quals)
-  = zonkBinds te ve binds      `thenNF_Tc` \ (new_binds, new_ve) ->
-    zonkQuals te new_ve quals  `thenNF_Tc` \ (new_quals, final_ve) ->
-    returnNF_Tc (LetQual new_binds : new_quals, final_ve)
+zonkStmt env (ExprStmt expr ty)
+  = zonkLExpr env expr         `thenM` \ new_expr ->
+    zonkTcTypeToType env ty    `thenM` \ new_ty ->
+    returnM (env, ExprStmt new_expr new_ty)

 
 

--------------------------------------------------------------------------
-zonkStmts :: TyVarEnv Type -> IdEnv Id 
-         -> [TcStmt s] -> NF_TcM s [TypecheckedStmt]
-
-zonkStmts te ve [] = returnNF_Tc []
-
-zonkStmts te ve [ExprStmt expr locn]
-  = zonkExpr te ve expr                `thenNF_Tc` \ new_expr ->
-    returnNF_Tc [ExprStmt new_expr locn]
-
-zonkStmts te ve (ExprStmtOut expr locn a b : stmts)
-  = zonkExpr te ve      expr   `thenNF_Tc` \ new_expr  ->
-    zonkTcTypeToType te a      `thenNF_Tc` \ new_a     ->
-    zonkTcTypeToType te b      `thenNF_Tc` \ new_b     ->
-    zonkStmts te ve    stmts   `thenNF_Tc` \ new_stmts ->
-    returnNF_Tc (ExprStmtOut new_expr locn new_a new_b : new_stmts)
-
-zonkStmts te ve (LetStmt binds : stmts)
-  = zonkBinds te ve     binds  `thenNF_Tc` \ (new_binds, new_ve) ->
-    zonkStmts te new_ve stmts  `thenNF_Tc` \ new_stmts ->
-    returnNF_Tc (LetStmt new_binds : new_stmts)
-
-zonkStmts te ve (BindStmtOut pat expr locn a b : stmts)
-  = zonkPat te ve pat          `thenNF_Tc` \ (new_pat, ids) ->
-    zonkExpr te ve expr                `thenNF_Tc` \ new_expr ->
-    zonkTcTypeToType te a      `thenNF_Tc` \ new_a     ->
-    zonkTcTypeToType te b      `thenNF_Tc` \ new_b     ->
+zonkStmt env (LetStmt binds)
+  = zonkNestedBinds env binds  `thenM` \ (env1, new_binds) ->
+    returnM (env1, LetStmt new_binds)
+
+zonkStmt env (BindStmt pat expr)
+  = zonkLExpr env expr                 `thenM` \ new_expr ->
+    zonkPat env pat                    `thenM` \ (new_pat, new_ids) ->

     let
     let

-       new_ve = extend_ve ve ids
+       env1 = extendZonkEnv env (bagToList new_ids)

     in
     in

-    zonkStmts te new_ve stmts  `thenNF_Tc` \ new_stmts ->
-    returnNF_Tc (BindStmtOut new_pat new_expr locn new_a new_b : new_stmts)
+    returnM (env1, BindStmt new_pat new_expr)

 
 
 
 -------------------------------------------------------------------------
 
 
 
 -------------------------------------------------------------------------

-zonkRbinds :: TyVarEnv Type -> IdEnv Id 
-          -> TcRecordBinds s -> NF_TcM s TypecheckedRecordBinds
+zonkRbinds :: ZonkEnv -> HsRecordBinds TcId -> TcM (HsRecordBinds Id)

 
 

-zonkRbinds te ve rbinds
-  = mapNF_Tc zonk_rbind rbinds
+zonkRbinds env rbinds
+  = mappM zonk_rbind rbinds

   where
   where

-    zonk_rbind (field, expr, pun)
-      = zonkExpr te ve expr    `thenNF_Tc` \ new_expr ->
-       returnNF_Tc (zonkIdOcc ve field, new_expr, pun)
+    zonk_rbind (field, expr)
+      = zonkLExpr env expr     `thenM` \ new_expr ->
+       returnM (fmap (zonkIdOcc env) field, new_expr)
+
+-------------------------------------------------------------------------
+mapIPNameTc :: (a -> TcM b) -> IPName a -> TcM (IPName b)
+mapIPNameTc f (Dupable n) = f n  `thenM` \ r -> returnM (Dupable r)
+mapIPNameTc f (Linear  n) = f n  `thenM` \ r -> returnM (Linear r)

 \end{code}
 
 \end{code}
 

+

 %************************************************************************
 %*                                                                     *
 \subsection[BackSubst-Pats]{Patterns}
 %************************************************************************
 %*                                                                     *
 \subsection[BackSubst-Pats]{Patterns}

@@ -607,77 +679,259 @@ zonkRbinds te ve rbinds
 %************************************************************************
 
 \begin{code}
 %************************************************************************
 
 \begin{code}

-zonkPat :: TyVarEnv Type -> IdEnv Id 
-       -> TcPat s -> NF_TcM s (TypecheckedPat, [Id])
-
-zonkPat te ve (WildPat ty)
-  = zonkTcTypeToType te ty         `thenNF_Tc` \ new_ty ->
-    returnNF_Tc (WildPat new_ty, [])
-
-zonkPat te ve (VarPat v)
-  = zonkIdBndr te v        `thenNF_Tc` \ new_v ->
-    returnNF_Tc (VarPat new_v, [new_v])
-
-zonkPat te ve (LazyPat pat)
-  = zonkPat te ve pat      `thenNF_Tc` \ (new_pat, ids) ->
-    returnNF_Tc (LazyPat new_pat, ids)
-
-zonkPat te ve (AsPat n pat)
-  = zonkIdBndr te n        `thenNF_Tc` \ new_n ->
-    zonkPat te ve pat      `thenNF_Tc` \ (new_pat, ids) ->
-    returnNF_Tc (AsPat new_n new_pat, new_n:ids)
-
-zonkPat te ve (ConPat n ty pats)
-  = zonkTcTypeToType te ty     `thenNF_Tc` \ new_ty ->
-    zonkPats te ve pats                `thenNF_Tc` \ (new_pats, ids) ->
-    returnNF_Tc (ConPat n new_ty new_pats, ids)
-
-zonkPat te ve (ConOpPat pat1 op pat2 ty)
-  = zonkPat te ve pat1     `thenNF_Tc` \ (new_pat1, ids1) ->
-    zonkPat te ve pat2     `thenNF_Tc` \ (new_pat2, ids2) ->
-    zonkTcTypeToType te ty  `thenNF_Tc` \ new_ty ->
-    returnNF_Tc (ConOpPat new_pat1 op new_pat2 new_ty, ids1 ++ ids2)
-
-zonkPat te ve (ListPat ty pats)
-  = zonkTcTypeToType te ty     `thenNF_Tc` \ new_ty ->
-    zonkPats te ve pats                `thenNF_Tc` \ (new_pats, ids) ->
-    returnNF_Tc (ListPat new_ty new_pats, ids)
-
-zonkPat te ve (TuplePat pats)
-  = zonkPats te ve pats                `thenNF_Tc` \ (new_pats, ids) ->
-    returnNF_Tc (TuplePat new_pats, ids)
-
-zonkPat te ve (RecPat n ty rpats)
-  = zonkTcTypeToType te ty             `thenNF_Tc` \ new_ty ->
-    mapAndUnzipNF_Tc zonk_rpat rpats   `thenNF_Tc` \ (new_rpats, ids_s) ->
-    returnNF_Tc (RecPat n new_ty new_rpats, concat ids_s)
+zonkPat :: ZonkEnv -> OutPat TcId -> TcM (OutPat Id, Bag Id)
+zonkPat env pat = wrapLocFstM (zonk_pat env) pat
+
+zonk_pat env (ParPat p)
+  = zonkPat env p      `thenM` \ (new_p, ids) ->
+    returnM (ParPat new_p, ids)
+
+zonk_pat env (WildPat ty)
+  = zonkTcTypeToType env ty   `thenM` \ new_ty ->
+    returnM (WildPat new_ty, emptyBag)
+
+zonk_pat env (VarPat v)
+  = zonkIdBndr env v       `thenM` \ new_v ->
+    returnM (VarPat new_v, unitBag new_v)
+
+zonk_pat env (LazyPat pat)
+  = zonkPat env pat        `thenM` \ (new_pat, ids) ->
+    returnM (LazyPat new_pat, ids)
+
+zonk_pat env (AsPat n pat)
+  = wrapLocM (zonkIdBndr env) n        `thenM` \ new_n ->
+    zonkPat env pat            `thenM` \ (new_pat, ids) ->
+    returnM (AsPat new_n new_pat, unLoc new_n `consBag` ids)
+
+zonk_pat env (ListPat pats ty)
+  = zonkTcTypeToType env ty    `thenM` \ new_ty ->
+    zonkPats env pats          `thenM` \ (new_pats, ids) ->
+    returnM (ListPat new_pats new_ty, ids)
+
+zonk_pat env (PArrPat pats ty)
+  = zonkTcTypeToType env ty    `thenM` \ new_ty ->
+    zonkPats env pats          `thenM` \ (new_pats, ids) ->
+    returnM (PArrPat new_pats new_ty, ids)
+
+zonk_pat env (TuplePat pats boxed)
+  = zonkPats env pats                  `thenM` \ (new_pats, ids) ->
+    returnM (TuplePat new_pats boxed, ids)
+
+zonk_pat env (ConPatOut n stuff ty tvs dicts)
+  = zonkTcTypeToType env ty            `thenM` \ new_ty ->
+    mappM zonkTcTyVarToTyVar tvs       `thenM` \ new_tvs ->
+    zonkIdBndrs env dicts              `thenM` \ new_dicts ->
+    let
+       env1 = extendZonkEnv env new_dicts
+    in
+    zonkConStuff env1 stuff            `thenM` \ (new_stuff, ids) ->
+    returnM (ConPatOut n new_stuff new_ty new_tvs new_dicts, 
+                listToBag new_dicts `unionBags` ids)
+
+zonk_pat env (LitPat lit) = returnM (LitPat lit, emptyBag)
+
+zonk_pat env (SigPatOut pat ty expr)
+  = zonkPat env pat            `thenM` \ (new_pat, ids) ->
+    zonkTcTypeToType env ty    `thenM` \ new_ty  ->
+    zonkExpr env expr          `thenM` \ new_expr ->
+    returnM (SigPatOut new_pat new_ty new_expr, ids)
+
+zonk_pat env (NPatOut lit ty expr)
+  = zonkTcTypeToType env ty    `thenM` \ new_ty   ->
+    zonkExpr env expr          `thenM` \ new_expr ->
+    returnM (NPatOut lit new_ty new_expr, emptyBag)
+
+zonk_pat env (NPlusKPatOut n k e1 e2)
+  = wrapLocM (zonkIdBndr env) n                `thenM` \ new_n ->
+    zonkExpr env e1                    `thenM` \ new_e1 ->
+    zonkExpr env e2                    `thenM` \ new_e2 ->
+    returnM (NPlusKPatOut new_n k new_e1 new_e2, unitBag (unLoc new_n))
+
+zonk_pat env (DictPat ds ms)
+  = zonkIdBndrs env ds      `thenM` \ new_ds ->
+    zonkIdBndrs env ms     `thenM` \ new_ms ->
+    returnM (DictPat new_ds new_ms,
+                listToBag new_ds `unionBags` listToBag new_ms)
+
+---------------------------
+zonkConStuff env (PrefixCon pats)
+  = zonkPats env pats          `thenM` \ (new_pats, ids) ->
+    returnM (PrefixCon new_pats, ids)
+
+zonkConStuff env (InfixCon p1 p2)
+  = zonkPat env p1             `thenM` \ (new_p1, ids1) ->
+    zonkPat env p2             `thenM` \ (new_p2, ids2) ->
+    returnM (InfixCon new_p1 new_p2, ids1 `unionBags` ids2)
+
+zonkConStuff env (RecCon rpats)
+  = mapAndUnzipM zonk_rpat rpats       `thenM` \ (new_rpats, ids_s) ->
+    returnM (RecCon new_rpats, unionManyBags ids_s)

   where
   where

-    zonk_rpat (f, pat, pun)
-      = zonkPat te ve pat           `thenNF_Tc` \ (new_pat, ids) ->
-       returnNF_Tc ((f, new_pat, pun), ids)
+    zonk_rpat (f, pat)
+      = zonkPat env pat                `thenM` \ (new_pat, ids) ->
+       returnM ((f, new_pat), ids)
+
+---------------------------
+zonkPats env []
+  = returnM ([], emptyBag)
+
+zonkPats env (pat:pats) 
+  = zonkPat env pat    `thenM` \ (pat',  ids1) ->
+    zonkPats env pats  `thenM` \ (pats', ids2) ->
+    returnM (pat':pats', ids1 `unionBags` ids2)
+\end{code}

 
 

-zonkPat te ve (LitPat lit ty)
-  = zonkTcTypeToType te ty         `thenNF_Tc` \ new_ty  ->
-    returnNF_Tc (LitPat lit new_ty, [])
+%************************************************************************
+%*                                                                     *
+\subsection[BackSubst-Foreign]{Foreign exports}
+%*                                                                     *
+%************************************************************************

 
 

-zonkPat te ve (NPat lit ty expr)
-  = zonkTcTypeToType te ty     `thenNF_Tc` \ new_ty   ->
-    zonkExpr te ve expr                `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (NPat lit new_ty new_expr, [])

 
 

-zonkPat te ve (DictPat ds ms)
-  = mapNF_Tc (zonkIdBndr te) ds    `thenNF_Tc` \ new_ds ->
-    mapNF_Tc (zonkIdBndr te) ms    `thenNF_Tc` \ new_ms ->
-    returnNF_Tc (DictPat new_ds new_ms, new_ds ++ new_ms)
+\begin{code}
+zonkForeignExports :: ZonkEnv -> [LForeignDecl TcId] -> TcM [LForeignDecl Id]
+zonkForeignExports env ls = mappM (wrapLocM (zonkForeignExport env)) ls
+
+zonkForeignExport :: ZonkEnv -> ForeignDecl TcId -> TcM (ForeignDecl Id)
+zonkForeignExport env (ForeignExport i hs_ty spec isDeprec) =
+   returnM (ForeignExport (fmap (zonkIdOcc env) i) undefined spec isDeprec)
+zonkForeignExport env for_imp 
+  = returnM for_imp    -- Foreign imports don't need zonking
+\end{code}

 
 

+\begin{code}
+zonkRules :: ZonkEnv -> [LRuleDecl TcId] -> TcM [LRuleDecl Id]
+zonkRules env rs = mappM (wrapLocM (zonkRule env)) rs

 
 

-zonkPats te ve [] 
-  = returnNF_Tc ([], [])
-zonkPats te ve (pat:pats) 
-  = zonkPat te ve pat  `thenNF_Tc` \ (pat', ids1) ->
-    zonkPats te ve pats        `thenNF_Tc` \ (pats', ids2) ->
-    returnNF_Tc (pat':pats', ids1 ++ ids2)
+zonkRule :: ZonkEnv -> RuleDecl TcId -> TcM (RuleDecl Id)
+zonkRule env (HsRule name act (vars::[RuleBndr TcId]) lhs rhs)
+  = mappM zonk_bndr vars               `thenM` \ new_bndrs ->
+    newMutVar emptyVarSet              `thenM` \ unbound_tv_set ->
+    let
+       env_rhs = extendZonkEnv env [id | b <- new_bndrs, let id = unLoc b, isId id]
+       -- Type variables don't need an envt
+       -- They are bound through the mutable mechanism
+
+       env_lhs = setZonkType env_rhs (zonkTypeCollecting unbound_tv_set)
+       -- We need to gather the type variables mentioned on the LHS so we can 
+       -- quantify over them.  Example:
+       --   data T a = C
+       -- 
+       --   foo :: T a -> Int
+       --   foo C = 1
+       --
+       --   {-# RULES "myrule"  foo C = 1 #-}
+       -- 
+       -- After type checking the LHS becomes (foo a (C a))
+       -- and we do not want to zap the unbound tyvar 'a' to (), because
+       -- that limits the applicability of the rule.  Instead, we
+       -- want to quantify over it!  
+       --
+       -- It's easiest to find the free tyvars here. Attempts to do so earlier
+       -- are tiresome, because (a) the data type is big and (b) finding the 
+       -- free type vars of an expression is necessarily monadic operation.
+       --      (consider /\a -> f @ b, where b is side-effected to a)
+    in
+    zonkLExpr env_lhs lhs              `thenM` \ new_lhs ->
+    zonkLExpr env_rhs rhs              `thenM` \ new_rhs ->

 
 

+    readMutVar unbound_tv_set          `thenM` \ unbound_tvs ->
+    let
+       final_bndrs :: [Located Var]
+       final_bndrs = map noLoc (varSetElems unbound_tvs) ++ new_bndrs
+    in
+    returnM (HsRule name act (map RuleBndr final_bndrs) new_lhs new_rhs)
+               -- I hate this map RuleBndr stuff
+  where
+   zonk_bndr (RuleBndr v) 
+       | isId (unLoc v) = wrapLocM (zonkIdBndr env)   v
+       | otherwise      = wrapLocM zonkTcTyVarToTyVar v

 \end{code}
 
 
 \end{code}
 
 

+%************************************************************************
+%*                                                                     *
+\subsection[BackSubst-Foreign]{Foreign exports}
+%*                                                                     *
+%************************************************************************
+
+\begin{code}
+zonkTcTypeToType :: ZonkEnv -> TcType -> TcM Type
+zonkTcTypeToType (ZonkEnv zonk_ty _) ty = zonk_ty ty
+
+zonkTypeCollecting :: TcRef TyVarSet -> TcType -> TcM Type
+-- This variant collects unbound type variables in a mutable variable
+zonkTypeCollecting unbound_tv_set
+  = zonkType zonk_unbound_tyvar
+  where
+    zonk_unbound_tyvar tv 
+       = zonkTcTyVarToTyVar tv                                 `thenM` \ tv' ->
+         readMutVar unbound_tv_set                             `thenM` \ tv_set ->
+         writeMutVar unbound_tv_set (extendVarSet tv_set tv')  `thenM_`
+         return (mkTyVarTy tv')
+
+zonkTypeZapping :: TcType -> TcM Type
+-- This variant is used for everything except the LHS of rules
+-- It zaps unbound type variables to (), or some other arbitrary type
+zonkTypeZapping ty 
+  = zonkType zonk_unbound_tyvar ty
+  where
+       -- Zonk a mutable but unbound type variable to an arbitrary type
+       -- We know it's unbound even though we don't carry an environment,
+       -- because at the binding site for a type variable we bind the
+       -- mutable tyvar to a fresh immutable one.  So the mutable store
+       -- plays the role of an environment.  If we come across a mutable
+       -- type variable that isn't so bound, it must be completely free.
+    zonk_unbound_tyvar tv = putTcTyVar tv (mkArbitraryType tv)
+
+
+-- When the type checker finds a type variable with no binding,
+-- which means it can be instantiated with an arbitrary type, it
+-- usually instantiates it to Void.  Eg.
+-- 
+--     length []
+-- ===>
+--     length Void (Nil Void)
+-- 
+-- But in really obscure programs, the type variable might have
+-- a kind other than *, so we need to invent a suitably-kinded type.
+-- 
+-- This commit uses
+--     Void for kind *
+--     List for kind *->*
+--     Tuple for kind *->...*->*
+-- 
+-- which deals with most cases.  (Previously, it only dealt with
+-- kind *.)   
+-- 
+-- In the other cases, it just makes up a TyCon with a suitable
+-- kind.  If this gets into an interface file, anyone reading that
+-- file won't understand it.  This is fixable (by making the client
+-- of the interface file make up a TyCon too) but it is tiresome and
+-- never happens, so I am leaving it 
+
+mkArbitraryType :: TcTyVar -> Type
+-- Make up an arbitrary type whose kind is the same as the tyvar.
+-- We'll use this to instantiate the (unbound) tyvar.
+mkArbitraryType tv 
+  | liftedTypeKind `isSubKind` kind = voidTy           -- The vastly common case
+  | otherwise                      = mkTyConApp tycon []
+  where
+    kind       = tyVarKind tv
+    (args,res) = splitKindFunTys kind
+
+    tycon | kind == tyConKind listTyCon        -- *->*
+         = listTyCon                           -- No tuples this size
+
+         | all isLiftedTypeKind args && isLiftedTypeKind res
+         = tupleTyCon Boxed (length args)      -- *-> ... ->*->*
+
+         | otherwise
+         = pprTrace "Urk! Inventing strangely-kinded void TyCon:" (ppr tc_name $$ ppr kind) $
+           mkPrimTyCon tc_name kind 0 [] VoidRep
+               -- Same name as the tyvar, apart from making it start with a colon (sigh)
+               -- I dread to think what will happen if this gets out into an 
+               -- interface file.  Catastrophe likely.  Major sigh.
+
+    tc_name = mkInternalName (getUnique tv) (mkDerivedTyConOcc (getOccName tv)) noSrcLoc
+\end{code}