X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Fvectorise%2FVectUtils.hs;h=0789688c43ed8c7b976c9c77f13080a63da84550;hp=545460d1d5321d631a685f3eb3b0807809bb8dce;hb=9396c0736a7e7d73c2a13f1a18104e0c43b924b0;hpb=544f0afeea1c2f9ee146bd0a6a3583fee0acad5a

diff --git a/compiler/vectorise/VectUtils.hs b/compiler/vectorise/VectUtils.hs
index 545460d..0789688 100644
--- a/compiler/vectorise/VectUtils.hs
+++ b/compiler/vectorise/VectUtils.hs
@@ -1,16 +1,22 @@
 module VectUtils (
   collectAnnTypeBinders, collectAnnTypeArgs, isAnnTypeArg,
+  collectAnnValBinders,
+  mkDataConTag,
   splitClosureTy,
-  mkPADictType, mkPArrayType,
-  paDictArgType, paDictOfType,
-  paMethod, lengthPA, replicatePA, emptyPA,
-  polyAbstract, polyApply,
-  lookupPArrayFamInst,
-  hoistExpr, takeHoisted
+  mkPRepr, mkToPRepr, mkFromPRepr,
+  mkPADictType, mkPArrayType, mkPReprType,
+  parrayReprTyCon, parrayReprDataCon, mkVScrut,
+  paDictArgType, paDictOfType, paDFunType,
+  paMethod, lengthPA, replicatePA, emptyPA, liftPA,
+  polyAbstract, polyApply, polyVApply,
+  hoistBinding, hoistExpr, hoistPolyVExpr, takeHoisted,
+  buildClosure, buildClosures,
+  mkClosureApp
 ) where
 
 #include "HsVersions.h"
 
+import VectCore
 import VectMonad
 
 import DsUtils
@@ -19,10 +25,11 @@ import CoreUtils
 import Type
 import TypeRep
 import TyCon
-import DataCon            ( dataConWrapId )
+import DataCon            ( DataCon, dataConWrapId, dataConTag )
 import Var
 import Id                 ( mkWildId )
 import MkId               ( unwrapFamInstScrut )
+import Name               ( Name )
 import PrelNames
 import TysWiredIn
 import BasicTypes         ( Boxity(..) )
@@ -30,7 +37,7 @@ import BasicTypes         ( Boxity(..) )
 import Outputable
 import FastString
 
-import Control.Monad         ( liftM, zipWithM_ )
+import Control.Monad         ( liftM, liftM2, zipWithM_ )
 
 collectAnnTypeArgs :: AnnExpr b ann -> (AnnExpr b ann, [Type])
 collectAnnTypeArgs expr = go expr []
@@ -44,43 +51,215 @@ collectAnnTypeBinders expr = go [] expr
     go bs (_, AnnLam b e) | isTyVar b = go (b:bs) e
     go bs e                           = (reverse bs, e)
 
+collectAnnValBinders :: AnnExpr Var ann -> ([Var], AnnExpr Var ann)
+collectAnnValBinders expr = go [] expr
+  where
+    go bs (_, AnnLam b e) | isId b = go (b:bs) e
+    go bs e                        = (reverse bs, e)
+
 isAnnTypeArg :: AnnExpr b ann -> Bool
 isAnnTypeArg (_, AnnType t) = True
 isAnnTypeArg _              = False
 
-isClosureTyCon :: TyCon -> Bool
-isClosureTyCon tc = tyConName tc == closureTyConName
+mkDataConTag :: DataCon -> CoreExpr
+mkDataConTag dc = mkConApp intDataCon [mkIntLitInt $ dataConTag dc]
 
-splitClosureTy :: Type -> (Type, Type)
-splitClosureTy ty
-  | Just (tc, [arg_ty, res_ty]) <- splitTyConApp_maybe ty
-  , isClosureTyCon tc
-  = (arg_ty, res_ty)
+splitUnTy :: String -> Name -> Type -> Type
+splitUnTy s name ty
+  | Just (tc, [ty']) <- splitTyConApp_maybe ty
+  , tyConName tc == name
+  = ty'
+
+  | otherwise = pprPanic s (ppr ty)
 
-  | otherwise = pprPanic "splitClosureTy" (ppr ty)
+splitBinTy :: String -> Name -> Type -> (Type, Type)
+splitBinTy s name ty
+  | Just (tc, [ty1, ty2]) <- splitTyConApp_maybe ty
+  , tyConName tc == name
+  = (ty1, ty2)
 
-isPArrayTyCon :: TyCon -> Bool
-isPArrayTyCon tc = tyConName tc == parrayTyConName
+  | otherwise = pprPanic s (ppr ty)
+
+splitCrossTy :: Type -> (Type, Type)
+splitCrossTy = splitBinTy "splitCrossTy" ndpCrossTyConName
+
+splitPlusTy :: Type -> (Type, Type)
+splitPlusTy = splitBinTy "splitSumTy" ndpPlusTyConName
+
+splitEmbedTy :: Type -> Type
+splitEmbedTy = splitUnTy "splitEmbedTy" embedTyConName
+
+splitClosureTy :: Type -> (Type, Type)
+splitClosureTy = splitBinTy "splitClosureTy" closureTyConName
 
 splitPArrayTy :: Type -> Type
-splitPArrayTy ty
-  | Just (tc, [arg_ty]) <- splitTyConApp_maybe ty
-  , isPArrayTyCon tc
-  = arg_ty
+splitPArrayTy = splitUnTy "splitPArrayTy" parrayTyConName
 
-  | otherwise = pprPanic "splitPArrayTy" (ppr ty)
+mkBuiltinTyConApp :: (Builtins -> TyCon) -> [Type] -> VM Type
+mkBuiltinTyConApp get_tc tys
+  = do
+      tc <- builtin get_tc
+      return $ mkTyConApp tc tys
 
-mkPADictType :: Type -> VM Type
-mkPADictType ty
+mkBuiltinTyConApps :: (Builtins -> TyCon) -> [Type] -> Type -> VM Type
+mkBuiltinTyConApps get_tc tys ty
+  = do
+      tc <- builtin get_tc
+      return $ foldr (mk tc) ty tys
+  where
+    mk tc ty1 ty2 = mkTyConApp tc [ty1,ty2]
+
+mkBuiltinTyConApps1 :: (Builtins -> TyCon) -> Type -> [Type] -> VM Type
+mkBuiltinTyConApps1 get_tc dft [] = return dft
+mkBuiltinTyConApps1 get_tc dft tys
+  = do
+      tc <- builtin get_tc
+      case tys of
+        [] -> pprPanic "mkBuiltinTyConApps1" (ppr tc)
+        _  -> return $ foldr1 (mk tc) tys
+  where
+    mk tc ty1 ty2 = mkTyConApp tc [ty1,ty2]
+
+mkPRepr :: [[Type]] -> VM Type
+mkPRepr [] = return unitTy
+mkPRepr tys
   = do
-      tc <- builtin paDictTyCon
-      return $ TyConApp tc [ty]
+      embed <- builtin embedTyCon
+      cross <- builtin crossTyCon
+      plus  <- builtin plusTyCon
+
+      let mk_embed ty      = mkTyConApp embed [ty]
+          mk_cross ty1 ty2 = mkTyConApp cross [ty1, ty2]
+          mk_plus  ty1 ty2 = mkTyConApp plus  [ty1, ty2]
+
+          mk_tup   []      = unitTy
+          mk_tup   tys     = foldr1 mk_cross tys
+
+          mk_sum   []      = unitTy
+          mk_sum   tys     = foldr1 mk_plus  tys
+
+      return . mk_sum
+             . map (mk_tup . map mk_embed)
+             $ tys
+
+mkToPRepr :: [[CoreExpr]] -> VM ([CoreExpr], Type)
+mkToPRepr ess
+  = do
+      embed_tc <- builtin embedTyCon
+      embed_dc <- builtin embedDataCon
+      cross_tc <- builtin crossTyCon
+      cross_dc <- builtin crossDataCon
+      plus_tc  <- builtin plusTyCon
+      left_dc  <- builtin leftDataCon
+      right_dc <- builtin rightDataCon
+
+      let mk_embed (expr, ty, pa)
+            = (mkConApp   embed_dc [Type ty, pa, expr],
+               mkTyConApp embed_tc [ty])
+
+          mk_cross (expr1, ty1) (expr2, ty2)
+            = (mkConApp   cross_dc [Type ty1, Type ty2, expr1, expr2],
+               mkTyConApp cross_tc [ty1, ty2])
+
+          mk_tup [] = (Var unitDataConId, unitTy)
+          mk_tup es = foldr1 mk_cross es
+
+          mk_sum []           = ([Var unitDataConId], unitTy)
+          mk_sum [(expr, ty)] = ([expr], ty)
+          mk_sum ((expr, lty) : es)
+            = let (alts, rty) = mk_sum es
+              in
+              (mkConApp left_dc [Type lty, Type rty, expr]
+                 : [mkConApp right_dc [Type lty, Type rty, alt] | alt <- alts],
+               mkTyConApp plus_tc [lty, rty])
+      
+      liftM (mk_sum . map (mk_tup . map mk_embed))
+            (mapM (mapM init) ess)
+  where
+    init expr = let ty = exprType expr
+                in do
+                     pa <- paDictOfType ty
+                     return (expr, ty, pa)
+
+mkFromPRepr :: CoreExpr -> Type -> [([Var], CoreExpr)] -> VM CoreExpr
+mkFromPRepr scrut res_ty alts
+  = do
+      embed_dc <- builtin embedDataCon
+      cross_dc <- builtin crossDataCon
+      left_dc  <- builtin leftDataCon
+      right_dc <- builtin rightDataCon
+      pa_tc    <- builtin paTyCon
+
+      let un_embed expr ty var res
+            = do
+                pa <- newLocalVar FSLIT("pa") (mkTyConApp pa_tc [idType var])
+                return $ Case expr (mkWildId ty) res_ty
+                         [(DataAlt embed_dc, [pa, var], res)]
+
+          un_cross expr ty var1 var2 res
+            = Case expr (mkWildId ty) res_ty
+                [(DataAlt cross_dc, [var1, var2], res)]
+
+          un_tup expr ty []    res = return res
+          un_tup expr ty [var] res = un_embed expr ty var res
+          un_tup expr ty (var : vars) res
+            = do
+                lv <- newLocalVar FSLIT("x") lty
+                rv <- newLocalVar FSLIT("y") rty
+                liftM (un_cross expr ty lv rv)
+                        (un_embed (Var lv) lty var
+                         =<< un_tup (Var rv) rty vars res)
+            where
+              (lty, rty) = splitCrossTy ty
+
+          un_plus expr ty var1 var2 res1 res2
+            = Case expr (mkWildId ty) res_ty
+                [(DataAlt left_dc,  [var1], res1),
+                 (DataAlt right_dc, [var2], res2)]
+
+          un_sum expr ty [(vars, res)] = un_tup expr ty vars res
+          un_sum expr ty ((vars, res) : alts)
+            = do
+                lv <- newLocalVar FSLIT("l") lty
+                rv <- newLocalVar FSLIT("r") rty
+                liftM2 (un_plus expr ty lv rv)
+                         (un_tup (Var lv) lty vars res)
+                         (un_sum (Var rv) rty alts)
+            where
+              (lty, rty) = splitPlusTy ty
+
+      un_sum scrut (exprType scrut) alts
+
+mkClosureType :: Type -> Type -> VM Type
+mkClosureType arg_ty res_ty = mkBuiltinTyConApp closureTyCon [arg_ty, res_ty]
+
+mkClosureTypes :: [Type] -> Type -> VM Type
+mkClosureTypes = mkBuiltinTyConApps closureTyCon
+
+mkPReprType :: Type -> VM Type
+mkPReprType ty = mkBuiltinTyConApp preprTyCon [ty]
+
+mkPADictType :: Type -> VM Type
+mkPADictType ty = mkBuiltinTyConApp paTyCon [ty]
 
 mkPArrayType :: Type -> VM Type
-mkPArrayType ty
+mkPArrayType ty = mkBuiltinTyConApp parrayTyCon [ty]
+
+parrayReprTyCon :: Type -> VM (TyCon, [Type])
+parrayReprTyCon ty = builtin parrayTyCon >>= (`lookupFamInst` [ty])
+
+parrayReprDataCon :: Type -> VM (DataCon, [Type])
+parrayReprDataCon ty
   = do
-      tc <- builtin parrayTyCon
-      return $ TyConApp tc [ty]
+      (tc, arg_tys) <- parrayReprTyCon ty
+      let [dc] = tyConDataCons tc
+      return (dc, arg_tys)
+
+mkVScrut :: VExpr -> VM (VExpr, TyCon, [Type])
+mkVScrut (ve, le)
+  = do
+      (tc, arg_tys) <- parrayReprTyCon (exprType ve)
+      return ((ve, unwrapFamInstScrut tc arg_tys le), tc, arg_tys)
 
 paDictArgType :: TyVar -> VM (Maybe Type)
 paDictArgType tv = go (TyVarTy tv) (tyVarKind tv)
@@ -116,11 +295,21 @@ paDictOfTyApp (TyVarTy tv) ty_args
       paDFunApply dfun ty_args
 paDictOfTyApp (TyConApp tc _) ty_args
   = do
-      pa_class <- builtin paClass
-      (dfun, ty_args') <- lookupInst pa_class [TyConApp tc ty_args]
-      paDFunApply (Var dfun) ty_args'
+      dfun <- traceMaybeV "paDictOfTyApp" (ppr tc) (lookupTyConPA tc)
+      paDFunApply (Var dfun) ty_args
 paDictOfTyApp ty ty_args = pprPanic "paDictOfTyApp" (ppr ty)
 
+paDFunType :: TyCon -> VM Type
+paDFunType tc
+  = do
+      margs <- mapM paDictArgType tvs
+      res   <- mkPADictType (mkTyConApp tc arg_tys)
+      return . mkForAllTys tvs
+             $ mkFunTys [arg | Just arg <- margs] res
+  where
+    tvs = tyConTyVars tc
+    arg_tys = mkTyVarTys tvs
+
 paDFunApply :: CoreExpr -> [Type] -> VM CoreExpr
 paDFunApply dfun tys
   = do
@@ -146,6 +335,20 @@ replicatePA len x = liftM (`mkApps` [len,x])
 emptyPA :: Type -> VM CoreExpr
 emptyPA = paMethod emptyPAVar
 
+liftPA :: CoreExpr -> VM CoreExpr
+liftPA x
+  = do
+      lc <- builtin liftingContext
+      replicatePA (Var lc) x
+
+newLocalVVar :: FastString -> Type -> VM VVar
+newLocalVVar fs vty
+  = do
+      lty <- mkPArrayType vty
+      vv  <- newLocalVar fs vty
+      lv  <- newLocalVar fs lty
+      return (vv,lv)
+
 polyAbstract :: [TyVar] -> ((CoreExpr -> CoreExpr) -> VM a) -> VM a
 polyAbstract tvs p
   = localV
@@ -168,23 +371,38 @@ polyApply expr tys
       dicts <- mapM paDictOfType tys
       return $ expr `mkTyApps` tys `mkApps` dicts
 
-lookupPArrayFamInst :: Type -> VM (TyCon, [Type])
-lookupPArrayFamInst ty = builtin parrayTyCon >>= (`lookupFamInst` [ty])
+polyVApply :: VExpr -> [Type] -> VM VExpr
+polyVApply expr tys
+  = do
+      dicts <- mapM paDictOfType tys
+      return $ mapVect (\e -> e `mkTyApps` tys `mkApps` dicts) expr
+
+hoistBinding :: Var -> CoreExpr -> VM ()
+hoistBinding v e = updGEnv $ \env ->
+  env { global_bindings = (v,e) : global_bindings env }
 
 hoistExpr :: FastString -> CoreExpr -> VM Var
 hoistExpr fs expr
   = do
       var <- newLocalVar fs (exprType expr)
-      updGEnv $ \env ->
-        env { global_bindings = (var, expr) : global_bindings env }
+      hoistBinding var expr
       return var
 
-hoistPolyExpr :: FastString -> [TyVar] -> CoreExpr -> VM CoreExpr
-hoistPolyExpr fs tvs expr
+hoistVExpr :: VExpr -> VM VVar
+hoistVExpr (ve, le)
   = do
-      poly_expr <- closedV . polyAbstract tvs $ \abstract -> return (abstract expr)
-      fn        <- hoistExpr fs poly_expr
-      polyApply (Var fn) (mkTyVarTys tvs)
+      fs <- getBindName
+      vv <- hoistExpr ('v' `consFS` fs) ve
+      lv <- hoistExpr ('l' `consFS` fs) le
+      return (vv, lv)
+
+hoistPolyVExpr :: [TyVar] -> VM VExpr -> VM VExpr
+hoistPolyVExpr tvs p
+  = do
+      expr <- closedV . polyAbstract tvs $ \abstract ->
+              liftM (mapVect abstract) p
+      fn   <- hoistVExpr expr
+      polyVApply (vVar fn) (mkTyVarTys tvs)
 
 takeHoisted :: VM [(Var, CoreExpr)]
 takeHoisted
@@ -193,59 +411,79 @@ takeHoisted
       setGEnv $ env { global_bindings = [] }
       return $ global_bindings env
 
-
-mkClosure :: Type -> Type -> Type -> CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr -> VM CoreExpr
-mkClosure arg_ty res_ty env_ty pa_dict vfn lfn env
+mkClosure :: Type -> Type -> Type -> VExpr -> VExpr -> VM VExpr
+mkClosure arg_ty res_ty env_ty (vfn,lfn) (venv,lenv)
   = do
-      mk <- builtin mkClosureVar
-      return $ Var mk `mkTyApps` [arg_ty, res_ty, env_ty] `mkApps` [pa_dict, vfn, lfn, env]
-
-mkClosureP :: Type -> Type -> Type -> CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr -> VM CoreExpr
-mkClosureP arg_ty res_ty env_ty pa_dict vfn lfn env
+      dict <- paDictOfType env_ty
+      mkv  <- builtin mkClosureVar
+      mkl  <- builtin mkClosurePVar
+      return (Var mkv `mkTyApps` [arg_ty, res_ty, env_ty] `mkApps` [dict, vfn, lfn, venv],
+              Var mkl `mkTyApps` [arg_ty, res_ty, env_ty] `mkApps` [dict, vfn, lfn, lenv])
+
+mkClosureApp :: VExpr -> VExpr -> VM VExpr
+mkClosureApp (vclo, lclo) (varg, larg)
+  = do
+      vapply <- builtin applyClosureVar
+      lapply <- builtin applyClosurePVar
+      return (Var vapply `mkTyApps` [arg_ty, res_ty] `mkApps` [vclo, varg],
+              Var lapply `mkTyApps` [arg_ty, res_ty] `mkApps` [lclo, larg])
+  where
+    (arg_ty, res_ty) = splitClosureTy (exprType vclo)
+
+buildClosures :: [TyVar] -> [VVar] -> [Type] -> Type -> VM VExpr -> VM VExpr
+buildClosures tvs vars [] res_ty mk_body
+  = mk_body
+buildClosures tvs vars [arg_ty] res_ty mk_body
+  = buildClosure tvs vars arg_ty res_ty mk_body
+buildClosures tvs vars (arg_ty : arg_tys) res_ty mk_body
   = do
-      mk <- builtin mkClosurePVar
-      return $ Var mk `mkTyApps` [arg_ty, res_ty, env_ty] `mkApps` [pa_dict, vfn, lfn, env]
+      res_ty' <- mkClosureTypes arg_tys res_ty
+      arg <- newLocalVVar FSLIT("x") arg_ty
+      buildClosure tvs vars arg_ty res_ty'
+        . hoistPolyVExpr tvs
+        $ do
+            lc <- builtin liftingContext
+            clo <- buildClosures tvs (vars ++ [arg]) arg_tys res_ty mk_body
+            return $ vLams lc (vars ++ [arg]) clo
 
 -- (clo <x1,...,xn> <f,f^>, aclo (Arr lc xs1 ... xsn) <f,f^>)
 --   where
 --     f  = \env v -> case env of <x1,...,xn> -> e x1 ... xn v
 --     f^ = \env v -> case env of Arr l xs1 ... xsn -> e^ l x1 ... xn v
-
-buildClosure :: [TyVar] -> [(Var,Var)] -> (Var,Var) -> Var -> CoreExpr -> CoreExpr -> VM (CoreExpr, CoreExpr)
-buildClosure tvs env (varg, larg) lv vbody lbody
+--
+buildClosure :: [TyVar] -> [VVar] -> Type -> Type -> VM VExpr -> VM VExpr
+buildClosure tvs vars arg_ty res_ty mk_body
   = do
-      let (venv_ty, venv, bind_venv) = mkVectEnv tys vs
-      (lenv, bind_lenv) <- mkLiftEnv (Var lv) tys ls
-      lenv_ty <- mkPArrayType venv_ty
-
-      venv_bndr <- newLocalVar FSLIT("env") venv_ty
-      lenv_bndr <- newLocalVar FSLIT("env") lenv_ty
-
-      let mono_vfn = mkLams [venv_bndr, varg]
-                   . bind_venv (Var venv_bndr)
-                   $ vbody `mkVarApps` vs `mkVarApps` [varg]
-          mono_lfn = mkLams [lenv_bndr, larg]
-                   . bind_lenv (Var lenv_bndr) lv
-                   $ lbody `mkVarApps` (lv:ls) `mkVarApps` [larg]
-
-      vfn <- hoistPolyExpr FSLIT("vfn") tvs mono_vfn
-      lfn <- hoistPolyExpr FSLIT("lfn") tvs mono_lfn
-
-      pa_dict <- paDictOfType venv_ty
-
-      vclo <- mkClosure  arg_ty res_ty venv_ty pa_dict vfn lfn venv
-      lclo <- mkClosureP arg_ty res_ty venv_ty pa_dict vfn lfn lenv
-
-      return (vclo, lclo)
-
+      (env_ty, env, bind) <- buildEnv vars
+      env_bndr <- newLocalVVar FSLIT("env") env_ty
+      arg_bndr <- newLocalVVar FSLIT("arg") arg_ty
+
+      fn <- hoistPolyVExpr tvs
+          $ do
+              lc    <- builtin liftingContext
+              body  <- mk_body
+              body' <- bind (vVar env_bndr)
+                            (vVarApps lc body (vars ++ [arg_bndr]))
+              return (vLamsWithoutLC [env_bndr, arg_bndr] body')
+
+      mkClosure arg_ty res_ty env_ty fn env
+
+buildEnv :: [VVar] -> VM (Type, VExpr, VExpr -> VExpr -> VM VExpr)
+buildEnv vvs
+  = do
+      lc <- builtin liftingContext
+      let (ty, venv, vbind) = mkVectEnv tys vs
+      (lenv, lbind) <- mkLiftEnv lc tys ls
+      return (ty, (venv, lenv),
+              \(venv,lenv) (vbody,lbody) ->
+              do
+                let vbody' = vbind venv vbody
+                lbody' <- lbind lenv lbody
+                return (vbody', lbody'))
   where
-    vs  = map fst env
-    ls  = map snd env
-    tys = map idType vs
+    (vs,ls) = unzip vvs
+    tys     = map idType vs
 
-    arg_ty = idType varg
-    res_ty = exprType vbody
-    
 mkVectEnv :: [Type] -> [Var] -> (Type, CoreExpr, CoreExpr -> CoreExpr -> CoreExpr)
 mkVectEnv []   []  = (unitTy, Var unitDataConId, \env body -> body)
 mkVectEnv [ty] [v] = (ty, Var v, \env body -> Let (NonRec v env) body)
@@ -255,29 +493,33 @@ mkVectEnv tys  vs  = (ty, mkCoreTup (map Var vs),
   where
     ty = mkCoreTupTy tys
 
-mkLiftEnv :: CoreExpr -> [Type] -> [Var]
-          -> VM (CoreExpr, CoreExpr -> Var -> CoreExpr -> CoreExpr)
+mkLiftEnv :: Var -> [Type] -> [Var] -> VM (CoreExpr, CoreExpr -> CoreExpr -> VM CoreExpr)
 mkLiftEnv lc [ty] [v]
-  = do
-      len <- lengthPA (Var v)
-      return (Var v, \env lv body -> Let (NonRec v env)
-                                   $ Case len lv (exprType body) [(DEFAULT, [], body)])
+  = return (Var v, \env body ->
+                   do
+                     len <- lengthPA (Var v)
+                     return . Let (NonRec v env)
+                            $ Case len lc (exprType body) [(DEFAULT, [], body)])
 
 -- NOTE: this transparently deals with empty environments
 mkLiftEnv lc tys vs
   = do
-      (env_tc, env_tyargs) <- lookupPArrayFamInst vty
+      (env_tc, env_tyargs) <- parrayReprTyCon vty
       let [env_con] = tyConDataCons env_tc
           
           env = Var (dataConWrapId env_con)
-                `mkTyApps` env_tyargs
-                `mkApps`   (lc : map Var vs)
-
-          bind env lv body = let scrut = unwrapFamInstScrut env_tc env_tyargs env
-                             in
-                             Case scrut (mkWildId (exprType scrut)) (exprType body)
-                               [(DataAlt env_con, lv : vs, body)]
+                `mkTyApps`  env_tyargs
+                `mkVarApps` (lc : vs)
+
+          bind env body = let scrut = unwrapFamInstScrut env_tc env_tyargs env
+                          in
+                          return $ Case scrut (mkWildId (exprType scrut))
+                                        (exprType body)
+                                        [(DataAlt env_con, lc : bndrs, body)]
       return (env, bind)
   where
     vty = mkCoreTupTy tys
 
+    bndrs | null vs   = [mkWildId unitTy]
+          | otherwise = vs
+