[project @ 2003-12-30 16:29:17 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcHsSyn.lhs b/ghc/compiler/typecheck/TcHsSyn.lhs
index e7805cf..df44a06 100644 (file)
--- a/ghc/compiler/typecheck/TcHsSyn.lhs
+++ b/ghc/compiler/typecheck/TcHsSyn.lhs
@@ -8,28 +8,23 @@ checker.
 
 \begin{code}
 module TcHsSyn (
 
 \begin{code}
 module TcHsSyn (

-       TcMonoBinds, TcHsBinds, TcPat,
-       TcExpr, TcGRHSs, TcGRHS, TcMatch,
-       TcStmt, TcArithSeqInfo, TcRecordBinds,
-       TcHsModule, TcCoreExpr, TcDictBinds,
-       TcForeignExportDecl,
+       TcDictBinds,
+       mkHsTyApp, mkHsDictApp, mkHsConApp,
+       mkHsTyLam, mkHsDictLam, mkHsLet, mkHsApp,
+       hsLitType, hsPatType, mkHsAppTy, mkSimpleHsAlt,
+       nlHsIntLit, glueBindsOnGRHSs,

        
        

-       TypecheckedHsBinds, TypecheckedRuleDecl,
-       TypecheckedMonoBinds, TypecheckedPat,
-       TypecheckedHsExpr, TypecheckedArithSeqInfo,
-       TypecheckedStmt, TypecheckedForeignDecl,
-       TypecheckedMatch, TypecheckedHsModule,
-       TypecheckedGRHSs, TypecheckedGRHS,
-       TypecheckedRecordBinds, TypecheckedDictBinds,

 
 

-       mkHsTyApp, mkHsDictApp, mkHsConApp,
-       mkHsTyLam, mkHsDictLam, mkHsLet,
+       -- Coercions
+       Coercion, ExprCoFn, PatCoFn, 
+       (<$>), (<.>), mkCoercion, 
+       idCoercion, isIdCoercion,

 
 

-       -- re-exported from TcEnv
-       TcId, 
+       -- re-exported from TcMonad
+       TcId, TcIdSet,

 
 

-       zonkTopBinds, zonkId, zonkIdBndr, zonkIdOcc, zonkExpr,
-       zonkForeignExports, zonkRules
+       zonkTopDecls, zonkTopExpr, zonkTopLExpr,
+       zonkId, zonkTopBndrs

   ) where
 
 #include "HsVersions.h"
   ) where
 
 #include "HsVersions.h"

@@ -38,93 +33,137 @@ module TcHsSyn (
 import HsSyn   -- oodles of it
 
 -- others:
 import HsSyn   -- oodles of it
 
 -- others:

-import Id      ( idName, idType, isLocalId, setIdType, Id )
-import DataCon ( dataConWrapId )       
-import TcEnv   ( tcLookupGlobal_maybe, tcExtendGlobalValEnv,
-                 TcEnv, TcId
-               )
-
-import TcMonad
-import TcType  ( zonkTcTypeToType, zonkTcTyVarToTyVar, zonkTcType, zonkTcSigTyVars
-               )
-import CoreSyn  ( Expr )
-import BasicTypes ( RecFlag(..) )
+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 )
+import Kind      ( splitKindFunTys )
+import PrimRep   ( PrimRep(VoidRep) )
+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
 import Bag
 import Outputable

-import HscTypes        ( TyThing(..) )

 \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 TcHsBinds         = HsBinds TcId TcPat
-type TcMonoBinds       = MonoBinds TcId TcPat
-type TcDictBinds       = TcMonoBinds
-type TcPat             = OutPat TcId
-type TcExpr            = HsExpr TcId TcPat
-type TcGRHSs           = GRHSs TcId TcPat
-type TcGRHS            = GRHS TcId TcPat
-type TcMatch           = Match TcId TcPat
-type TcStmt            = Stmt TcId TcPat
-type TcArithSeqInfo    = ArithSeqInfo TcId TcPat
-type TcRecordBinds     = HsRecordBinds TcId TcPat
-type TcHsModule        = HsModule TcId TcPat
-
-type TcCoreExpr        = Expr TcId
-type TcForeignExportDecl = ForeignDecl TcId
-type TcRuleDecl         = RuleDecl    TcId TcPat
-
-type TypecheckedPat            = OutPat        Id
-type TypecheckedMonoBinds      = MonoBinds     Id TypecheckedPat
-type TypecheckedDictBinds      = TypecheckedMonoBinds
-type TypecheckedHsBinds                = HsBinds       Id TypecheckedPat
-type TypecheckedHsExpr         = HsExpr        Id TypecheckedPat
-type TypecheckedArithSeqInfo   = ArithSeqInfo  Id TypecheckedPat
-type TypecheckedStmt           = Stmt          Id TypecheckedPat
-type TypecheckedMatch          = Match         Id TypecheckedPat
-type TypecheckedGRHSs          = GRHSs         Id TypecheckedPat
-type TypecheckedGRHS           = GRHS          Id TypecheckedPat
-type TypecheckedRecordBinds    = HsRecordBinds Id TypecheckedPat
-type TypecheckedHsModule       = HsModule      Id TypecheckedPat
-type TypecheckedForeignDecl     = ForeignDecl Id
-type TypecheckedRuleDecl       = RuleDecl      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
+
+type ExprCoFn = Coercion (HsExpr TcId)
+type PatCoFn  = Coercion (Pat    TcId)

 
 

-mkHsDictApp expr []     = expr
-mkHsDictApp expr dict_vars = DictApp expr dict_vars
+(<.>) :: 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)

 
 

-mkHsTyLam []     expr = expr
-mkHsTyLam tyvars expr = TyLam tyvars expr
+(<$>) :: Coercion a -> a -> a
+Just f  <$> e = f e
+Nothing <$> e = e

 
 

-mkHsDictLam []    expr = expr
-mkHsDictLam dicts expr = DictLam dicts expr
+mkCoercion :: (a -> a) -> Coercion a
+mkCoercion f = Just f

 
 

-mkHsLet EmptyMonoBinds expr = expr
-mkHsLet mbinds        expr = HsLet (MonoBind mbinds [] Recursive) expr
+idCoercion :: Coercion a
+idCoercion = Nothing

 
 

-mkHsConApp data_con tys args = foldl HsApp (HsVar (dataConWrapId data_con) `mkHsTyApp` tys) args
+isIdCoercion :: Coercion a -> Bool
+isIdCoercion = isNothing

 \end{code}
 
 \end{code}
 

+

 %************************************************************************
 %*                                                                     *
 \subsection[BackSubst-HsBinds]{Running a substitution over @HsBinds@}
 %*                                                                     *
 %************************************************************************
 
 %************************************************************************
 %*                                                                     *
 \subsection[BackSubst-HsBinds]{Running a substitution over @HsBinds@}
 %*                                                                     *
 %************************************************************************
 

-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

@@ -141,138 +180,158 @@ It's all pretty boring stuff, because HsSyn is such a large type, and
 the environment manipulation is tiresome.
 
 \begin{code}
 the environment manipulation is tiresome.
 
 \begin{code}

--- zonkId is used *during* typechecking just to zonk the Id's type
-zonkId :: TcId -> NF_TcM TcId
-zonkId id
-  = zonkTcType (idType id) `thenNF_Tc` \ ty' ->
-    returnNF_Tc (setIdType id ty')
+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 is used *after* typechecking to get the Id's type
 -- to its final form.  The TyVarEnv give 

-zonkIdBndr :: TcId -> NF_TcM Id
-zonkIdBndr id
-  = zonkTcTypeToType (idType id)       `thenNF_Tc` \ ty' ->
-    returnNF_Tc (setIdType id ty')
-
-zonkIdOcc :: TcId -> NF_TcM Id
-zonkIdOcc id 
-  = tcLookupGlobal_maybe (idName id)   `thenNF_Tc` \ maybe_id' ->
-       -- We're even look up up superclass selectors and constructors; 
-       -- even though zonking them is a no-op anyway, and the
-       -- superclass selectors aren't in the environment anyway.
-       -- But we don't want to call isLocalId to find out whether
-       -- it's a superclass selector (for example) because that looks
-       -- at the IdInfo field, which in turn be in a knot because of
-       -- the big knot in typecheckModule
-    let
-       new_id = case maybe_id' of
-                   Just (AnId id') -> id'
-                   other           -> WARN( isLocalId id, ppr id ) id
-    in
-    returnNF_Tc new_id
-\end{code}
+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

 
 

-\begin{code}
-zonkTopBinds :: TcMonoBinds -> NF_TcM (TypecheckedMonoBinds, TcEnv)
-zonkTopBinds binds     -- Top level is implicitly recursive
-  = fixNF_Tc (\ ~(_, new_ids) ->
-       tcExtendGlobalValEnv (bagToList new_ids)        $
-       zonkMonoBinds binds                     `thenNF_Tc` \ (binds', new_ids) ->
-       tcGetEnv                                `thenNF_Tc` \ env ->
-       returnNF_Tc ((binds', env), new_ids)
-    )                                  `thenNF_Tc` \ (stuff, _) ->
-    returnNF_Tc stuff
-
-zonkBinds :: TcHsBinds -> NF_TcM (TypecheckedHsBinds, TcEnv)
-
-zonkBinds binds 
-  = go binds (\ binds' -> tcGetEnv `thenNF_Tc` \ env -> 
-                         returnNF_Tc (binds', env))
-  where
-    -- go :: TcHsBinds
-    --    -> (TypecheckedHsBinds
-    --       -> NF_TcM (TypecheckedHsBinds, TcEnv)
-    --       ) 
-    --   -> NF_TcM (TypecheckedHsBinds, TcEnv)
-
-    go (ThenBinds b1 b2) thing_inside = go b1  $ \ b1' -> 
-                                       go b2   $ \ b2' ->
-                                       thing_inside (b1' `ThenBinds` b2')
-
-    go EmptyBinds thing_inside = thing_inside EmptyBinds
-
-    go (MonoBind bind sigs is_rec) thing_inside
-         = ASSERT( null sigs )
-           fixNF_Tc (\ ~(_, new_ids) ->
-               tcExtendGlobalValEnv (bagToList new_ids)        $
-               zonkMonoBinds bind                              `thenNF_Tc` \ (new_bind, new_ids) ->
-               thing_inside (mkMonoBind new_bind [] is_rec)    `thenNF_Tc` \ stuff ->
-               returnNF_Tc (stuff, new_ids)
-           )                                                   `thenNF_Tc` \ (stuff, _) ->
-          returnNF_Tc stuff
+zonkTopBndrs :: [TcId] -> TcM [Id]
+zonkTopBndrs ids = zonkIdBndrs emptyZonkEnv ids

 \end{code}
 
 \end{code}
 

-\begin{code}
--------------------------------------------------------------------------
-zonkMonoBinds :: TcMonoBinds
-             -> NF_TcM (TypecheckedMonoBinds, Bag Id)
-
-zonkMonoBinds EmptyMonoBinds = returnNF_Tc (EmptyMonoBinds, emptyBag)
-
-zonkMonoBinds (AndMonoBinds mbinds1 mbinds2)
-  = zonkMonoBinds mbinds1              `thenNF_Tc` \ (b1', ids1) ->
-    zonkMonoBinds mbinds2              `thenNF_Tc` \ (b2', ids2) ->
-    returnNF_Tc (b1' `AndMonoBinds` b2', 
-                ids1 `unionBags` ids2)
-
-zonkMonoBinds (PatMonoBind pat grhss locn)
-  = zonkPat pat                `thenNF_Tc` \ (new_pat, ids) ->
-    zonkGRHSs grhss    `thenNF_Tc` \ new_grhss ->
-    returnNF_Tc (PatMonoBind new_pat new_grhss locn, ids)
-
-zonkMonoBinds (VarMonoBind var expr)
-  = zonkIdBndr var     `thenNF_Tc` \ new_var ->
-    zonkExpr expr      `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (VarMonoBind new_var new_expr, unitBag new_var)
-
-zonkMonoBinds (CoreMonoBind var core_expr)
-  = zonkIdBndr var     `thenNF_Tc` \ new_var ->
-    returnNF_Tc (CoreMonoBind new_var core_expr, unitBag new_var)
-
-zonkMonoBinds (FunMonoBind var inf ms locn)
-  = zonkIdBndr var                     `thenNF_Tc` \ new_var ->
-    mapNF_Tc zonkMatch ms              `thenNF_Tc` \ new_ms ->
-    returnNF_Tc (FunMonoBind new_var inf new_ms locn, unitBag new_var)
-

 
 

-zonkMonoBinds (AbsBinds tyvars dicts exports inlines val_bind)
-  = mapNF_Tc zonkTcTyVarToTyVar tyvars `thenNF_Tc` \ new_tyvars ->
+\begin{code}
+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')
+    )
+
+---------------------------------------------
+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
+       env1 = extendZonkEnv env [ipNameName n | L _ (IPBind n _) <- new_binds]
+    in
+    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
 
        -- No need to extend tyvar env: the effects are
        -- propagated through binding the tyvars themselves
 

-    mapNF_Tc zonkIdBndr  dicts         `thenNF_Tc` \ new_dicts ->
-    tcExtendGlobalValEnv new_dicts                     $
-
-    fixNF_Tc (\ ~(_, _, val_bind_ids) ->
-       tcExtendGlobalValEnv (bagToList val_bind_ids)   $
-       zonkMonoBinds val_bind                          `thenNF_Tc` \ (new_val_bind, val_bind_ids) ->
-        mapNF_Tc zonkExport exports                    `thenNF_Tc` \ new_exports ->
-       returnNF_Tc (new_val_bind, new_exports,  val_bind_ids)
-    )                                          `thenNF_Tc ` \ (new_val_bind, new_exports, _) ->
-    let
-           new_globals = listToBag [global | (_, global, local) <- new_exports]
-    in
-    returnNF_Tc (AbsBinds new_tyvars new_dicts new_exports inlines new_val_bind,
-                new_globals)
+    zonkIdBndrs env dicts              `thenM` \ new_dicts ->
+    fixM (\ ~(new_val_binds, _) ->
+       let
+         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

-    zonkExport (tyvars, global, local)
-       = zonkTcSigTyVars tyvars        `thenNF_Tc` \ new_tyvars ->
+    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
                -- This isn't the binding occurrence of these tyvars

-               -- but they should *be* tyvars.  Hence zonkTcSigTyVars.
-         zonkIdBndr global             `thenNF_Tc` \ new_global ->
-         zonkIdOcc local               `thenNF_Tc` \ new_local -> 
-         returnNF_Tc (new_tyvars, new_global, new_local)
+               -- 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}
 
 %************************************************************************

@@ -282,29 +341,26 @@ zonkMonoBinds (AbsBinds tyvars dicts exports inlines val_bind)
 %************************************************************************
 
 \begin{code}
 %************************************************************************
 
 \begin{code}

-zonkMatch :: TcMatch -> NF_TcM TypecheckedMatch
+zonkMatch :: ZonkEnv -> LMatch TcId-> TcM (LMatch Id)

 
 

-zonkMatch (Match _ pats _ grhss)
-  = zonkPats pats                              `thenNF_Tc` \ (new_pats, new_ids) ->
-    tcExtendGlobalValEnv (bagToList new_ids)   $
-    zonkGRHSs grhss                            `thenNF_Tc` \ new_grhss ->
-    returnNF_Tc (Match [] new_pats Nothing new_grhss)
+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))

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

-zonkGRHSs :: TcGRHSs
-         -> NF_TcM TypecheckedGRHSs
+zonkGRHSs :: ZonkEnv -> GRHSs TcId -> TcM (GRHSs Id)

 
 

-zonkGRHSs (GRHSs grhss binds (Just ty))
-  = zonkBinds binds            `thenNF_Tc` \ (new_binds, new_env) ->
-    tcSetEnv new_env $
+zonkGRHSs env (GRHSs grhss binds ty)
+  = zonkNestedBinds env binds          `thenM` \ (new_env, new_binds) ->

     let
     let

-       zonk_grhs (GRHS guarded locn)
-         = zonkStmts guarded  `thenNF_Tc` \ new_guarded ->
-           returnNF_Tc (GRHS new_guarded 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 ty        `thenNF_Tc` \ new_ty ->
-    returnNF_Tc (GRHSs new_grhss new_binds (Just 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}
 
 %************************************************************************

@@ -314,234 +370,309 @@ zonkGRHSs (GRHSs grhss binds (Just ty))
 %************************************************************************
 
 \begin{code}
 %************************************************************************
 
 \begin{code}

-zonkExpr :: TcExpr -> NF_TcM TypecheckedHsExpr
+zonkLExprs :: ZonkEnv -> [LHsExpr TcId] -> TcM [LHsExpr Id]
+zonkLExpr  :: ZonkEnv -> LHsExpr TcId   -> TcM (LHsExpr Id)
+zonkExpr   :: ZonkEnv -> HsExpr TcId    -> TcM (HsExpr Id)

 
 

-zonkExpr (HsVar id)
-  = zonkIdOcc id       `thenNF_Tc` \ id' ->
-    returnNF_Tc (HsVar id')
+zonkLExprs env exprs = mappM (zonkLExpr env) exprs
+zonkLExpr  env expr  = wrapLocM (zonkExpr env) expr

 
 

-zonkExpr (HsIPVar id)
-  = zonkIdOcc id       `thenNF_Tc` \ id' ->
-    returnNF_Tc (HsIPVar id')
+zonkExpr env (HsVar id)
+  = returnM (HsVar (zonkIdOcc env id))

 
 

-zonkExpr (HsLit (HsRat f ty))
-  = zonkTcTypeToType ty            `thenNF_Tc` \ new_ty  ->
-    returnNF_Tc (HsLit (HsRat f new_ty))
+zonkExpr env (HsIPVar id)
+  = returnM (HsIPVar (mapIPName (zonkIdOcc env) id))

 
 

-zonkExpr (HsLit (HsLitLit lit ty))
-  = zonkTcTypeToType ty            `thenNF_Tc` \ new_ty  ->
-    returnNF_Tc (HsLit (HsLitLit lit new_ty))
+zonkExpr env (HsLit (HsRat f ty))
+  = zonkTcTypeToType env ty       `thenM` \ new_ty  ->
+    returnM (HsLit (HsRat f new_ty))

 
 

-zonkExpr (HsLit lit)
-  = returnNF_Tc (HsLit lit)
+zonkExpr env (HsLit lit)
+  = returnM (HsLit lit)

 
 -- HsOverLit doesn't appear in typechecker output
 
 
 -- HsOverLit doesn't appear in typechecker output
 

-zonkExpr (HsLam match)
-  = zonkMatch match    `thenNF_Tc` \ new_match ->
-    returnNF_Tc (HsLam new_match)
-
-zonkExpr (HsApp e1 e2)
-  = zonkExpr e1        `thenNF_Tc` \ new_e1 ->
-    zonkExpr e2        `thenNF_Tc` \ new_e2 ->
-    returnNF_Tc (HsApp new_e1 new_e2)
-
-zonkExpr (OpApp e1 op fixity e2)
-  = zonkExpr e1        `thenNF_Tc` \ new_e1 ->
-    zonkExpr op        `thenNF_Tc` \ new_op ->
-    zonkExpr e2        `thenNF_Tc` \ new_e2 ->
-    returnNF_Tc (OpApp new_e1 new_op fixity new_e2)
-
-zonkExpr (NegApp _) = panic "zonkExpr: NegApp"
-zonkExpr (HsPar _)  = panic "zonkExpr: HsPar"
-
-zonkExpr (SectionL expr op)
-  = zonkExpr expr      `thenNF_Tc` \ new_expr ->
-    zonkExpr op                `thenNF_Tc` \ new_op ->
-    returnNF_Tc (SectionL new_expr new_op)
-
-zonkExpr (SectionR op expr)
-  = zonkExpr op                `thenNF_Tc` \ new_op ->
-    zonkExpr expr              `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (SectionR new_op new_expr)
-
-zonkExpr (HsCase expr ms src_loc)
-  = zonkExpr expr          `thenNF_Tc` \ new_expr ->
-    mapNF_Tc zonkMatch ms   `thenNF_Tc` \ new_ms ->
-    returnNF_Tc (HsCase new_expr new_ms src_loc)
-
-zonkExpr (HsIf e1 e2 e3 src_loc)
-  = zonkExpr e1        `thenNF_Tc` \ new_e1 ->
-    zonkExpr e2        `thenNF_Tc` \ new_e2 ->
-    zonkExpr e3        `thenNF_Tc` \ new_e3 ->
-    returnNF_Tc (HsIf new_e1 new_e2 new_e3 src_loc)
-
-zonkExpr (HsLet binds expr)
-  = zonkBinds binds            `thenNF_Tc` \ (new_binds, new_env) ->
-    tcSetEnv new_env           $
-    zonkExpr expr      `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (HsLet new_binds new_expr)
-
-zonkExpr (HsWith expr binds)
-  = zonkIPBinds binds                          `thenNF_Tc` \ new_binds ->
-    tcExtendGlobalValEnv (map fst new_binds)   $
-    zonkExpr expr                              `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (HsWith new_expr new_binds)
-    where
-       zonkIPBinds = mapNF_Tc zonkIPBind
-       zonkIPBind (n, e) =
-           zonkIdBndr n        `thenNF_Tc` \ n' ->
-           zonkExpr e          `thenNF_Tc` \ e' ->
-           returnNF_Tc (n', e')
-
-zonkExpr (HsDo _ _ _) = panic "zonkExpr:HsDo"
-
-zonkExpr (HsDoOut do_or_lc stmts return_id then_id zero_id ty src_loc)
-  = zonkStmts stmts            `thenNF_Tc` \ new_stmts ->
-    zonkTcTypeToType ty        `thenNF_Tc` \ new_ty   ->
-    zonkIdOcc return_id                `thenNF_Tc` \ new_return_id ->
-    zonkIdOcc then_id          `thenNF_Tc` \ new_then_id ->
-    zonkIdOcc zero_id          `thenNF_Tc` \ new_zero_id ->
-    returnNF_Tc (HsDoOut do_or_lc new_stmts new_return_id new_then_id new_zero_id
-                        new_ty src_loc)
-
-zonkExpr (ExplicitList _) = panic "zonkExpr:ExplicitList"
-
-zonkExpr (ExplicitListOut ty exprs)
-  = zonkTcTypeToType ty                `thenNF_Tc` \ new_ty ->
-    mapNF_Tc zonkExpr exprs    `thenNF_Tc` \ new_exprs ->
-    returnNF_Tc (ExplicitListOut new_ty new_exprs)
-
-zonkExpr (ExplicitTuple exprs boxed)
-  = mapNF_Tc zonkExpr exprs    `thenNF_Tc` \ new_exprs ->
-    returnNF_Tc (ExplicitTuple new_exprs boxed)
-
-zonkExpr (RecordConOut data_con con_expr rbinds)
-  = zonkExpr con_expr  `thenNF_Tc` \ new_con_expr ->
-    zonkRbinds rbinds  `thenNF_Tc` \ new_rbinds ->
-    returnNF_Tc (RecordConOut data_con new_con_expr new_rbinds)
-
-zonkExpr (RecordUpd _ _) = panic "zonkExpr:RecordUpd"
-
-zonkExpr (RecordUpdOut expr ty dicts rbinds)
-  = zonkExpr expr              `thenNF_Tc` \ new_expr ->
-    zonkTcTypeToType ty        `thenNF_Tc` \ new_ty ->
-    mapNF_Tc zonkIdOcc dicts   `thenNF_Tc` \ new_dicts ->
-    zonkRbinds rbinds  `thenNF_Tc` \ new_rbinds ->
-    returnNF_Tc (RecordUpdOut new_expr new_ty new_dicts new_rbinds)
-
-zonkExpr (ExprWithTySig _ _) = panic "zonkExpr:ExprWithTySig"
-zonkExpr (ArithSeqIn _)      = panic "zonkExpr:ArithSeqIn"
-
-zonkExpr (ArithSeqOut expr info)
-  = zonkExpr expr      `thenNF_Tc` \ new_expr ->
-    zonkArithSeq info  `thenNF_Tc` \ new_info ->
-    returnNF_Tc (ArithSeqOut new_expr new_info)
-
-zonkExpr (HsCCall fun args may_gc is_casm result_ty)
-  = mapNF_Tc zonkExpr args     `thenNF_Tc` \ new_args ->
-    zonkTcTypeToType result_ty `thenNF_Tc` \ new_result_ty ->
-    returnNF_Tc (HsCCall fun new_args may_gc is_casm new_result_ty)
-
-zonkExpr (HsSCC lbl expr)
-  = zonkExpr expr      `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (HsSCC lbl new_expr)
-
-zonkExpr (TyLam tyvars expr)
-  = mapNF_Tc zonkTcTyVarToTyVar tyvars `thenNF_Tc` \ new_tyvars ->
+zonkExpr env (HsLam match)
+  = zonkMatch env match        `thenM` \ new_match ->
+    returnM (HsLam new_match)
+
+zonkExpr env (HsApp e1 e2)
+  = zonkLExpr env e1   `thenM` \ new_e1 ->
+    zonkLExpr env e2   `thenM` \ new_e2 ->
+    returnM (HsApp new_e1 new_e2)
+
+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
 
        -- No need to extend tyvar env; see AbsBinds
 

-    zonkExpr expr                      `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (TyLam new_tyvars new_expr)
+    zonkLExpr env expr                 `thenM` \ new_expr ->
+    returnM (TyLam new_tyvars new_expr)

 
 

-zonkExpr (TyApp expr tys)
-  = zonkExpr expr                      `thenNF_Tc` \ new_expr ->
-    mapNF_Tc zonkTcTypeToType tys      `thenNF_Tc` \ new_tys ->
-    returnNF_Tc (TyApp new_expr new_tys)
+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 (DictLam dicts expr)
-  = mapNF_Tc zonkIdBndr dicts          `thenNF_Tc` \ new_dicts ->
-    tcExtendGlobalValEnv new_dicts     $
-    zonkExpr expr                      `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (DictLam new_dicts new_expr)
+zonkExpr env (DictLam dicts expr)
+  = zonkIdBndrs env dicts      `thenM` \ new_dicts ->
+    let
+       env1 = extendZonkEnv env new_dicts
+    in
+    zonkLExpr env1 expr        `thenM` \ new_expr ->
+    returnM (DictLam new_dicts new_expr)
+
+zonkExpr env (DictApp expr dicts)
+  = zonkLExpr env expr                 `thenM` \ new_expr ->
+    returnM (DictApp new_expr (zonkIdOccs env dicts))

 
 

-zonkExpr (DictApp expr dicts)
-  = zonkExpr expr              `thenNF_Tc` \ new_expr ->
-    mapNF_Tc zonkIdOcc dicts   `thenNF_Tc` \ new_dicts ->
-    returnNF_Tc (DictApp new_expr new_dicts)
+-- 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)

 
 

+-------------------------------------------------------------------------
+zonkReboundNames :: ZonkEnv -> ReboundNames Id -> TcM (ReboundNames Id)
+zonkReboundNames env prs 
+  = mapM zonk prs
+  where
+    zonk (n, e) = zonkLExpr env e `thenM` \ new_e ->
+                 returnM (n, new_e)

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

-zonkArithSeq :: TcArithSeqInfo -> NF_TcM TypecheckedArithSeqInfo
+zonkArithSeq :: ZonkEnv -> ArithSeqInfo TcId -> TcM (ArithSeqInfo Id)
+
+zonkArithSeq env (From e)
+  = zonkLExpr env e            `thenM` \ new_e ->
+    returnM (From new_e)

 
 

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

 
 

-zonkArithSeq (FromThen e1 e2)
-  = zonkExpr e1        `thenNF_Tc` \ new_e1 ->
-    zonkExpr e2        `thenNF_Tc` \ new_e2 ->
-    returnNF_Tc (FromThen 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 (FromTo e1 e2)
-  = zonkExpr e1        `thenNF_Tc` \ new_e1 ->
-    zonkExpr e2        `thenNF_Tc` \ new_e2 ->
-    returnNF_Tc (FromTo new_e1 new_e2)
+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)

 
 

-zonkArithSeq (FromThenTo e1 e2 e3)
-  = zonkExpr e1        `thenNF_Tc` \ new_e1 ->
-    zonkExpr e2        `thenNF_Tc` \ new_e2 ->
-    zonkExpr e3        `thenNF_Tc` \ new_e3 ->
-    returnNF_Tc (FromThenTo new_e1 new_e2 new_e3)

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

-zonkStmts :: [TcStmt]
-         -> NF_TcM [TypecheckedStmt]
+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)

 
 

-zonkStmts [] = returnNF_Tc []
+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
+       new_lvs = zonkIdOccs env2 lvs
+       env3 = extendZonkEnv env new_lvs        -- Only the lvs are needed
+    in
+    returnM (env3, RecStmt new_segStmts new_lvs new_rvs new_rets)

 
 

-zonkStmts (ParStmtOut bndrstmtss : stmts)
-  = mapNF_Tc (mapNF_Tc zonkId) bndrss  `thenNF_Tc` \ new_bndrss ->
-    let new_binders = concat new_bndrss in
-    mapNF_Tc zonkStmts stmtss          `thenNF_Tc` \ new_stmtss ->
-    tcExtendGlobalValEnv new_binders   $ 
-    zonkStmts stmts                    `thenNF_Tc` \ new_stmts ->
-    returnNF_Tc (ParStmtOut (zip new_bndrss new_stmtss) : new_stmts)
-  where (bndrss, stmtss) = unzip bndrstmtss
+zonkStmt env (ResultStmt expr)
+  = zonkLExpr env expr `thenM` \ new_expr ->
+    returnM (env, ResultStmt new_expr)

 
 

-zonkStmts (ExprStmt expr locn : stmts)
-  = zonkExpr expr      `thenNF_Tc` \ new_expr ->
-    zonkStmts stmts    `thenNF_Tc` \ new_stmts ->
-    returnNF_Tc (ExprStmt new_expr locn : new_stmts)
+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 (LetStmt binds : stmts)
-  = zonkBinds binds            `thenNF_Tc` \ (new_binds, new_env) ->
-    tcSetEnv new_env           $
-    zonkStmts stmts            `thenNF_Tc` \ new_stmts ->
-    returnNF_Tc (LetStmt new_binds : new_stmts)
+zonkStmt env (LetStmt binds)
+  = zonkNestedBinds env binds  `thenM` \ (env1, new_binds) ->
+    returnM (env1, LetStmt new_binds)

 
 

-zonkStmts (BindStmt pat expr locn : stmts)
-  = zonkExpr expr                              `thenNF_Tc` \ new_expr ->
-    zonkPat pat                                        `thenNF_Tc` \ (new_pat, new_ids) ->
-    tcExtendGlobalValEnv (bagToList new_ids)   $ 
-    zonkStmts stmts                            `thenNF_Tc` \ new_stmts ->
-    returnNF_Tc (BindStmt new_pat new_expr locn : new_stmts)
+zonkStmt env (BindStmt pat expr)
+  = zonkLExpr env expr                 `thenM` \ new_expr ->
+    zonkPat env pat                    `thenM` \ (new_pat, new_ids) ->
+    let
+       env1 = extendZonkEnv env (bagToList new_ids)
+    in
+    returnM (env1, BindStmt new_pat new_expr)

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

-zonkRbinds :: TcRecordBinds -> NF_TcM TypecheckedRecordBinds
+zonkRbinds :: ZonkEnv -> HsRecordBinds TcId -> TcM (HsRecordBinds Id)

 
 

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

   where
   where

-    zonk_rbind (field, expr, pun)
-      = zonkExpr expr          `thenNF_Tc` \ new_expr ->
-       zonkIdOcc field         `thenNF_Tc` \ new_field ->
-       returnNF_Tc (new_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}

@@ -549,86 +680,106 @@ zonkRbinds rbinds
 %************************************************************************
 
 \begin{code}
 %************************************************************************
 
 \begin{code}

-zonkPat :: TcPat -> NF_TcM (TypecheckedPat, Bag Id)
-
-zonkPat (WildPat ty)
-  = zonkTcTypeToType ty            `thenNF_Tc` \ new_ty ->
-    returnNF_Tc (WildPat new_ty, emptyBag)
-
-zonkPat (VarPat v)
-  = zonkIdBndr v           `thenNF_Tc` \ new_v ->
-    returnNF_Tc (VarPat new_v, unitBag new_v)
-
-zonkPat (LazyPat pat)
-  = zonkPat pat            `thenNF_Tc` \ (new_pat, ids) ->
-    returnNF_Tc (LazyPat new_pat, ids)
-
-zonkPat (AsPat n pat)
-  = zonkIdBndr n           `thenNF_Tc` \ new_n ->
-    zonkPat pat            `thenNF_Tc` \ (new_pat, ids) ->
-    returnNF_Tc (AsPat new_n new_pat, new_n `consBag` ids)
-
-zonkPat (ListPat ty pats)
-  = zonkTcTypeToType ty        `thenNF_Tc` \ new_ty ->
-    zonkPats pats              `thenNF_Tc` \ (new_pats, ids) ->
-    returnNF_Tc (ListPat new_ty new_pats, ids)
-
-zonkPat (TuplePat pats boxed)
-  = zonkPats pats              `thenNF_Tc` \ (new_pats, ids) ->
-    returnNF_Tc (TuplePat new_pats boxed, ids)
-
-zonkPat (ConPat n ty tvs dicts pats)
-  = zonkTcTypeToType ty                `thenNF_Tc` \ new_ty ->
-    mapNF_Tc zonkTcTyVarToTyVar tvs    `thenNF_Tc` \ new_tvs ->
-    mapNF_Tc zonkIdBndr dicts          `thenNF_Tc` \ new_dicts ->
-    tcExtendGlobalValEnv new_dicts     $
-    zonkPats pats                      `thenNF_Tc` \ (new_pats, ids) ->
-    returnNF_Tc (ConPat n new_ty new_tvs new_dicts new_pats, 
+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)
 
                 listToBag new_dicts `unionBags` ids)
 

-zonkPat (RecPat n ty tvs dicts rpats)
-  = zonkTcTypeToType ty                        `thenNF_Tc` \ new_ty ->
-    mapNF_Tc zonkTcTyVarToTyVar tvs    `thenNF_Tc` \ new_tvs ->
-    mapNF_Tc zonkIdBndr dicts          `thenNF_Tc` \ new_dicts ->
-    tcExtendGlobalValEnv new_dicts     $
-    mapAndUnzipNF_Tc zonk_rpat rpats   `thenNF_Tc` \ (new_rpats, ids_s) ->
-    returnNF_Tc (RecPat n new_ty new_tvs new_dicts new_rpats, 
-                listToBag new_dicts `unionBags` unionManyBags ids_s)
-  where
-    zonk_rpat (f, pat, pun)
-      = zonkPat pat            `thenNF_Tc` \ (new_pat, ids) ->
-       returnNF_Tc ((f, new_pat, pun), ids)
-
-zonkPat (LitPat lit ty)
-  = zonkTcTypeToType ty            `thenNF_Tc` \ new_ty  ->
-    returnNF_Tc (LitPat lit new_ty, emptyBag)
-
-zonkPat (NPat lit ty expr)
-  = zonkTcTypeToType ty                `thenNF_Tc` \ new_ty   ->
-    zonkExpr expr              `thenNF_Tc` \ new_expr ->
-    returnNF_Tc (NPat lit new_ty new_expr, emptyBag)
-
-zonkPat (NPlusKPat n k ty e1 e2)
-  = zonkIdBndr n               `thenNF_Tc` \ new_n ->
-    zonkTcTypeToType ty        `thenNF_Tc` \ new_ty ->
-    zonkExpr e1                `thenNF_Tc` \ new_e1 ->
-    zonkExpr e2                `thenNF_Tc` \ new_e2 ->
-    returnNF_Tc (NPlusKPat new_n k new_ty new_e1 new_e2, unitBag new_n)
-
-zonkPat (DictPat ds ms)
-  = mapNF_Tc zonkIdBndr ds    `thenNF_Tc` \ new_ds ->
-    mapNF_Tc zonkIdBndr ms    `thenNF_Tc` \ new_ms ->
-    returnNF_Tc (DictPat new_ds new_ms,
+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)
 
                 listToBag new_ds `unionBags` listToBag new_ms)
 

+---------------------------
+zonkConStuff env (PrefixCon pats)
+  = zonkPats env pats          `thenM` \ (new_pats, ids) ->
+    returnM (PrefixCon new_pats, ids)

 
 

-zonkPats []
-  = returnNF_Tc ([], emptyBag)
+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)

 
 

-zonkPats (pat:pats) 
-  = zonkPat pat                `thenNF_Tc` \ (pat',  ids1) ->
-    zonkPats pats      `thenNF_Tc` \ (pats', ids2) ->
-    returnNF_Tc (pat':pats', ids1 `unionBags` ids2)
+zonkConStuff env (RecCon rpats)
+  = mapAndUnzipM zonk_rpat rpats       `thenM` \ (new_rpats, ids_s) ->
+    returnM (RecCon new_rpats, unionManyBags ids_s)
+  where
+    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}
 
 %************************************************************************
 \end{code}
 
 %************************************************************************

@@ -639,29 +790,149 @@ zonkPats (pat:pats)
 
 
 \begin{code}
 
 
 \begin{code}

-zonkForeignExports :: [TcForeignExportDecl] -> NF_TcM [TypecheckedForeignDecl]
-zonkForeignExports ls = mapNF_Tc zonkForeignExport ls
+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}

 
 

-zonkForeignExport :: TcForeignExportDecl -> NF_TcM (TypecheckedForeignDecl)
-zonkForeignExport (ForeignDecl i imp_exp hs_ty ext_nm cconv src_loc) =
-   zonkIdOcc i `thenNF_Tc` \ i' ->
-   returnNF_Tc (ForeignDecl i' imp_exp undefined ext_nm cconv src_loc)
+\begin{code}
+zonkRules :: ZonkEnv -> [LRuleDecl TcId] -> TcM [LRuleDecl Id]
+zonkRules env rs = mappM (wrapLocM (zonkRule env)) rs
+
+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}
 \begin{code}

-zonkRules :: [TcRuleDecl] -> NF_TcM [TypecheckedRuleDecl]
-zonkRules rs = mapNF_Tc zonkRule rs
-
-zonkRule (HsRule name tyvars vars lhs rhs loc)
-  = mapNF_Tc zonkTcTyVarToTyVar tyvars                 `thenNF_Tc` \ new_tyvars ->
-    mapNF_Tc zonkIdBndr [v | RuleBndr v <- vars]       `thenNF_Tc` \ new_bndrs ->
-    tcExtendGlobalValEnv new_bndrs                     $
-    zonkExpr lhs                                       `thenNF_Tc` \ new_lhs ->
-    zonkExpr rhs                                       `thenNF_Tc` \ new_rhs ->
-    returnNF_Tc (HsRule name new_tyvars (map RuleBndr new_bndrs) new_lhs new_rhs loc)
-       -- I hate this map RuleBndr stuff
-
-zonkRule (IfaceRuleOut fun rule)
-  = zonkIdOcc fun      `thenNF_Tc` \ fun' ->
-    returnNF_Tc (IfaceRuleOut fun' rule)
+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}
 \end{code}