First cut at scalar vectorisation of class instances

7 files changed, 228 insertions, 81 deletions

diff --git a/compiler/vectorise/Vectorise.hs b/compiler/vectorise/Vectorise.hs
index 3ba247dfbe..7d2415caf2 100644
--- a/compiler/vectorise/Vectorise.hs
+++ b/compiler/vectorise/Vectorise.hs
@@ -81,25 +81,15 @@ vectModule guts@(ModGuts { mg_tcs        = tycons
           -- array types.
       ; (new_tycons, new_fam_insts, tc_binds) <- vectTypeEnv tycons ty_vect_decls cls_vect_decls
 
-{- TODO:
-
-instance Num Int where
-  (+) = primAdd
-{-# VECTORISE SCALAR instance Num Int #-}
-
-==> $dNumInt :: Num Int; $dNumInt = Num primAdd
-=>> $v$dNumInt :: $vNum Int
-    $v$dNumInt = $vNum (closure1 (scalar_zipWith primAdd) (scalar_zipWith primAdd))
-  $dNumInt -v> $v$dNumInt
--}
-
           -- Family instance environment for /all/ home-package modules including those instances
           -- generated by 'vectTypeEnv'.
       ; (_, fam_inst_env) <- readGEnv global_fam_inst_env
 
           -- Vectorise all the top level bindings and VECTORISE declarations on imported identifiers
+      ; let impBinds = [imp_id | Vect          imp_id _ <- vect_decls, isGlobalId imp_id] ++
+                       [imp_id | VectInst True imp_id   <- vect_decls, isGlobalId imp_id]
       ; binds_top <- mapM vectTopBind binds
-      ; binds_imp <- mapM vectImpBind [imp_id | Vect imp_id _ <- vect_decls, isGlobalId imp_id]
+      ; binds_imp <- mapM vectImpBind impBinds
 
       ; return $ guts { mg_tcs          = tycons ++ new_tycons
                         -- we produce no new classes or instances, only new class type constructors
@@ -283,21 +273,63 @@ vectTopBinder var inline expr
     unfolding = case inline of
                   Inline arity -> mkInlineUnfolding (Just arity) expr
                   DontInline   -> noUnfolding
+{-
+!!!TODO: dfuns and unfoldings:
+           -- Do not inline the dfun; instead give it a magic DFunFunfolding
+           -- See Note [ClassOp/DFun selection]
+           -- See also note [Single-method classes]
+        dfun_id_w_fun
+           | isNewTyCon class_tc
+           = dfun_id `setInlinePragma` alwaysInlinePragma { inl_sat = Just 0 }
+           | otherwise
+           = dfun_id `setIdUnfolding`  mkDFunUnfolding dfun_ty dfun_args
+                     `setInlinePragma` dfunInlinePragma
+ -}
 
 -- | Vectorise the RHS of a top-level binding, in an empty local environment.
 --
--- We need to distinguish three cases:
+-- We need to distinguish four cases:
 --
 -- (1) We have a (non-scalar) vectorisation declaration for the variable (which explicitly provides
 --     vectorised code implemented by the user)
 --     => no automatic vectorisation & instead use the user-supplied code
 -- 
--- (2) We have a scalar vectorisation declaration for the variable
+-- (2) We have a scalar vectorisation declaration for a variable that is no dfun
 --     => generate vectorised code that uses a scalar 'map'/'zipWith' to lift the computation
 -- 
--- (3) There is no vectorisation declaration for the variable
+-- (3) We have a scalar vectorisation declaration for a variable that *is* a dfun
+--     => generate vectorised code according to the the "Note [Scalar dfuns]" below
+-- 
+-- (4) There is no vectorisation declaration for the variable
 --     => perform automatic vectorisation of the RHS
 --
+-- Note [Scalar dfuns]
+-- ~~~~~~~~~~~~~~~~~~~
+--
+-- Here is the translation scheme for scalar dfuns — assume the instance declaration:
+--
+--   instance Num Int where
+--     (+) = primAdd
+--   {-# VECTORISE SCALAR instance Num Int #-}
+--
+-- It desugars to
+--
+--   $dNumInt :: Num Int
+--   $dNumInt = D:Num primAdd
+--
+-- We vectorise it to
+--
+--   $v$dNumInt :: V:Num Int
+--   $v$dNumInt = D:V:Num (closure2 ((+) $dNumInt) (scalar_zipWith ((+) $dNumInt))))
+--
+-- while adding the following entry to the vectorisation map: '$dNumInt' --> '$v$dNumInt'.
+--
+-- See "Note [Vectorising classes]" in 'Vectorise.Type.Env' for the definition of 'V:Num'.
+--
+-- NB: The outlined vectorisation scheme does not require the right-hand side of the original dfun.
+--     In fact, we definitely want to refer to the dfn variable instead of the right-hand side to 
+--     ensure that the dictionary selection rules fire.
+--
 vectTopRhs :: [Var]           -- ^ Names of all functions in the rec block
            -> Var             -- ^ Name of the binding.
            -> CoreExpr        -- ^ Body of the binding.
@@ -308,19 +340,24 @@ vectTopRhs recFs var expr
   = closedV
   $ do { globalScalar <- isGlobalScalar var
        ; vectDecl     <- lookupVectDecl var
+       ; let isDFun = isDFunId var
 
-       ; traceVt ("vectTopRhs of " ++ show var ++ info globalScalar vectDecl) $ ppr expr
+       ; traceVt ("vectTopRhs of " ++ show var ++ info globalScalar isDFun vectDecl) $ ppr expr
 
-       ; rhs globalScalar vectDecl
+       ; rhs globalScalar isDFun vectDecl
        }
   where
-    rhs _globalScalar (Just (_, expr'))               -- Case (1)
+    rhs _globalScalar _isDFun (Just (_, expr'))               -- Case (1)
       = return (inlineMe, False, expr')
-    rhs True          Nothing                         -- Case (2)
+    rhs True          False   Nothing                         -- Case (2)
       = do { expr' <- vectScalarFun True recFs expr
            ; return (inlineMe, True, vectorised expr')
            }
-    rhs False         Nothing                         -- Case (3)
+    rhs True          True    Nothing                         -- Case (3)
+      = do { expr' <- vectScalarDFun var recFs
+           ; return (DontInline, True, expr')
+           }
+    rhs False         _isDFun Nothing                         -- Case (4)
       = do { let fvs = freeVars expr
            ; (inline, isScalar, vexpr) 
                <- inBind var $
@@ -328,9 +365,10 @@ vectTopRhs recFs var expr
            ; return (inline, isScalar, vectorised vexpr)
            }
     
-    info True  _                          = " [VECTORISE SCALAR]"
-    info False vectDecl | isJust vectDecl = " [VECTORISE]"
-                        | otherwise       = " (no pragma)"
+    info True  False _                          = " [VECTORISE SCALAR]"
+    info True  True  _                          = " [VECTORISE SCALAR instance]"
+    info False _     vectDecl | isJust vectDecl = " [VECTORISE]"
+                              | otherwise       = " (no pragma)"
 
 -- |Project out the vectorised version of a binding from some closure,
 -- or return the original body if that doesn't work or the binding is scalar. 
diff --git a/compiler/vectorise/Vectorise/Env.hs b/compiler/vectorise/Vectorise/Env.hs
index 2f20bb4067..2de71a5e3f 100644
--- a/compiler/vectorise/Vectorise/Env.hs
+++ b/compiler/vectorise/Vectorise/Env.hs
@@ -145,7 +145,8 @@ initGlobalEnv info vectDecls instEnvs famInstEnvs
                                         -- FIXME: we currently only allow RHSes consisting of a
                                         --   single variable to be able to obtain the type without
                                         --   inference — see also 'TcBinds.tcVect'
-    scalar_vars   = [var              | Vect     var   Nothing                  <- vectDecls]
+    scalar_vars   = [var              | Vect     var   Nothing                  <- vectDecls] ++
+                    [var              | VectInst True var                       <- vectDecls]
     novects       = [var              | NoVect   var                            <- vectDecls]
     scalar_tycons = [tyConName tycon  | VectType True tycon _                   <- vectDecls]
 
diff --git a/compiler/vectorise/Vectorise/Exp.hs b/compiler/vectorise/Vectorise/Exp.hs
index 3959a947bd..1a5701cc0f 100644
--- a/compiler/vectorise/Vectorise/Exp.hs
+++ b/compiler/vectorise/Vectorise/Exp.hs
@@ -1,30 +1,33 @@
+-- |Vectorisation of expressions.
 
--- | Vectorisation of expressions.
-module Vectorise.Exp (
-
-  -- Vectorise a polymorphic expression
-  vectPolyExpr, 
-  
-  -- Vectorise a scalar expression of functional type
-  vectScalarFun
-) where
+module Vectorise.Exp
+  (   -- * Vectorise polymorphic expressions with special cases for right-hand sides of particular 
+      --   variable bindings
+    vectPolyExpr
+  , vectScalarFun
+  , vectScalarDFun
+  ) 
+where
 
 #include "HsVersions.h"
 
 import Vectorise.Type.Type
 import Vectorise.Var
+import Vectorise.Convert
 import Vectorise.Vect
 import Vectorise.Env
 import Vectorise.Monad
 import Vectorise.Builtins
 import Vectorise.Utils
 
-import CoreSyn
 import CoreUtils
 import MkCore
+import CoreSyn
 import CoreFVs
+import Class
 import DataCon
 import TyCon
+import TcType
 import Type
 import NameSet
 import Var
@@ -38,6 +41,7 @@ import TysPrim
 import Outputable
 import FastString
 import Control.Monad
+import Control.Applicative
 import Data.List
 
 
@@ -82,6 +86,7 @@ vectExpr (_, AnnTick tickish expr)
 -- SPECIAL CASE: Vectorise/lift 'patError @ ty err' by only vectorising/lifting the type 'ty';
 --   its only purpose is to abort the program, but we need to adjust the type to keep CoreLint
 --   happy.
+-- FIXME: can't be do this with a VECTORISE pragma on 'pAT_ERROR_ID' now?
 vectExpr (_, AnnApp (_, AnnApp (_, AnnVar v) (_, AnnType ty)) err)
   | v == pAT_ERROR_ID
   = do { (vty, lty) <- vectAndLiftType ty
@@ -168,7 +173,7 @@ onlyIfV (isEmptyVarSet fvs) (vectScalarLam bs $ deAnnotate body)
 
 vectExpr e = cantVectorise "Can't vectorise expression (vectExpr)" (ppr $ deAnnotate e)
 
--- | Vectorise an expression with an outer lambda abstraction.
+-- |Vectorise an expression with an outer lambda abstraction.
 --
 vectFnExpr :: Bool             -- ^ If we process the RHS of a binding, whether that binding should
                                --   be inlined
@@ -201,7 +206,7 @@ vectScalarFun forceScalar recFns expr
       ; let scalarVars = gscalarVars `extendVarSetList` recFns
             (arg_tys, res_ty) = splitFunTys (exprType expr)
       ; MASSERT( not $ null arg_tys )
-      ; onlyIfV empty
+      ; onlyIfV (ptext (sLit "not a scalar function"))
                 (forceScalar                              -- user asserts the functions is scalar
                  ||
                  all (is_scalar_ty scalarTyCons) arg_tys  -- check whether the function is scalar
@@ -300,6 +305,109 @@ mkScalarFun arg_tys res_ty expr
        ; return (Var clo_var, lclo)
        }
 
+-- |Vectorise a dictionary function that has a 'VECTORISE SCALAR instance' pragma.
+-- 
+-- In other words, all methods in that dictionary are scalar functions — to be vectorised with
+-- 'vectScalarFun'.  The dictionary "function" itself may be a constant, though.
+--
+-- NB: You may think that we could implement this function guided by the struture of the Core
+--     expression of the right-hand side of the dictionary function.  We cannot proceed like this as
+--     'vectScalarDFun' must also work for *imported* dfuns, where we don't necessarily have access
+--     to the Core code of the unvectorised dfun.
+--
+-- Here an example — assume,
+--
+-- > class Eq a where { (==) :: a -> a -> Bool }
+-- > instance (Eq a, Eq b) => Eq (a, b) where { (==) = ... }
+-- > {-# VECTORISE SCALAR instance Eq (a, b) }
+--
+-- The unvectorised dfun for the above instance has the following signature:
+--
+-- > $dEqPair :: forall a b. Eq a -> Eq b -> Eq (a, b)
+--
+-- We generate the following (scalar) vectorised dfun (liberally using TH notation):
+--
+-- > $v$dEqPair :: forall a b. V:Eq a -> V:Eq b -> V:Eq (a, b)
+-- > $v$dEqPair = /\a b -> \dEqa :: V:Eq a -> \dEqb :: V:Eq b ->
+-- >                D:V:Eq $(vectScalarFun True recFns 
+-- >                         [| (==) @(a, b) ($dEqPair @a @b $(unVect dEqa) $(unVect dEqb)) |])
+--
+-- NB:
+-- * '(,)' vectorises to '(,)' — hence, the type constructor in the result type remains the same.
+-- * We share the '$(unVect di)' sub-expressions between the different selectors, but duplicate
+--   the application of the unvectorised dfun, to enable the dictionary selection rules to fire.
+--
+vectScalarDFun :: Var        -- ^ Original dfun
+               -> [Var]      -- ^ Functions names in same recursive binding group
+               -> VM CoreExpr
+vectScalarDFun var recFns
+  = do {   -- bring the type variables into scope
+       ; mapM_ defLocalTyVar tvs
+
+           -- vectorise dictionary argument types and generate variables for them
+       ; vTheta     <- mapM vectType theta
+       ; vThetaBndr <- mapM (newLocalVar (fsLit "vd")) vTheta
+       ; let vThetaVars = varsToCoreExprs vThetaBndr
+       
+           -- vectorise superclass dictionaries and methods as scalar expressions
+       ; thetaVars  <- mapM (newLocalVar (fsLit "d")) theta
+       ; thetaExprs <- zipWithM unVectDict theta vThetaVars
+       ; let thetaDictBinds = zipWith NonRec thetaVars thetaExprs
+             dict           = Var var `mkTyApps` (mkTyVarTys tvs) `mkVarApps` thetaVars
+             scsOps         = map (\selId -> varToCoreExpr selId `mkTyApps` tys `mkApps` [dict])
+                                  selIds
+       ; vScsOps <- mapM (\e -> vectorised <$> vectScalarFun True recFns e) scsOps
+
+           -- vectorised applications of the class-dictionary data constructor
+       ; Just vDataCon <- lookupDataCon dataCon
+       ; vTys          <- mapM vectType tys
+       ; let vBody = thetaDictBinds `mkLets` mkCoreConApps vDataCon (map Type vTys ++ vScsOps)
+
+       ; return $ mkLams (tvs ++ vThetaBndr) vBody
+       }
+  where
+    ty                = varType var
+    (tvs, theta, pty) = tcSplitSigmaTy  ty        -- 'theta' is the instance context
+    (cls, tys)        = tcSplitDFunHead pty       -- 'pty' is the instance head
+    selIds            = classAllSelIds cls
+    dataCon           = classDataCon cls
+
+-- Build a value of the dictionary before vectorisation from original, unvectorised type and an
+-- expression computing the vectorised dictionary.
+--
+-- Given the vectorised version of a dictionary 'vd :: V:C vt1..vtn', generate code that computes
+-- the unvectorised version, thus:
+--
+-- > D:C op1 .. opm
+-- > where
+-- >   opi = $(fromVect opTyi [| vSeli @vt1..vtk vd |])
+--
+-- where 'opTyi' is the type of the i-th superclass or op of the unvectorised dictionary.
+--
+unVectDict :: Type -> CoreExpr -> VM CoreExpr
+unVectDict ty e 
+  = do { vTys <- mapM vectType tys
+       ; let meths = map (\sel -> Var sel `mkTyApps` vTys `mkApps` [e]) selIds
+       ; scOps <- zipWithM fromVect methTys meths
+       ; return $ mkCoreConApps dataCon (map Type tys ++ scOps)
+       }
+  where
+    (tycon, tys, dataCon, methTys) = splitProductType "unVectDict: original type" ty
+    cls                            = case tyConClass_maybe tycon of
+                                       Just cls -> cls
+                                       Nothing  -> panic "Vectorise.Exp.unVectDict: no class"
+    selIds                         = classAllSelIds cls
+
+{-
+!!!How about 'isClassOpId_maybe'?  Do we need to treat them specially to get the class ops for
+!!!the vectorised instances or do they just work out?? (We may want to make sure that the
+!!!vectorised Ids at least get the right IdDetails...)
+!!!NB: For *locally defined* instances, the selector functions are part of the vectorised bindings,
+!!!    but not so for *imported* instances, where we need to generate the vectorised versions from
+!!!    scratch.
+!!!Also need to take care of the builtin rules for selectors (see mkDictSelId).
+ -}
+
 -- | Vectorise a lambda abstraction.
 --
 vectLam :: Bool             -- ^ When the RHS of a binding, whether that binding should be inlined.
diff --git a/compiler/vectorise/Vectorise/Monad/Global.hs b/compiler/vectorise/Vectorise/Monad/Global.hs
index c0dc97e403..bc68a5012f 100644
--- a/compiler/vectorise/Vectorise/Monad/Global.hs
+++ b/compiler/vectorise/Vectorise/Monad/Global.hs
@@ -137,7 +137,6 @@ lookupDataCon :: DataCon -> VM (Maybe DataCon)
 lookupDataCon dc
   | isTupleTyCon (dataConTyCon dc) 
   = return (Just dc)
-
   | otherwise 
   = readGEnv $ \env -> lookupNameEnv (global_datacons env) (dataConName dc)
 
diff --git a/compiler/vectorise/Vectorise/Monad/Naming.hs b/compiler/vectorise/Vectorise/Monad/Naming.hs
index 54e292d397..adc2d0ca01 100644
--- a/compiler/vectorise/Vectorise/Monad/Naming.hs
+++ b/compiler/vectorise/Vectorise/Monad/Naming.hs
@@ -9,15 +9,18 @@ module Vectorise.Monad.Naming
   , newLocalVars
   , newDummyVar
   , newTyVar
-  ) where
+  )
+where
 
 import Vectorise.Monad.Base
 
 import DsMonad
+import TcType
 import Type
 import Var
 import Name
 import SrcLoc
+import MkId
 import Id
 import FastString
 
@@ -43,7 +46,8 @@ mkLocalisedName mk_occ name =
      ; return new_name
      }
 
--- |Produce the vectorised variant of an `Id` with the given type.
+-- |Produce the vectorised variant of an `Id` with the given type, while taking care that vectorised
+-- dfun ids must be dfuns again.
 --
 -- Force the new name to be a system name and, if the original was an external name, disambiguate
 -- the new name with the module name of the original.
@@ -51,10 +55,17 @@ mkLocalisedName mk_occ name =
 mkVectId :: Id -> Type -> VM Id
 mkVectId id ty
   = do { name <- mkLocalisedName mkVectOcc (getName id)
-       ; let id' | isExportedId id = Id.mkExportedLocalId name ty
+       ; let id' | isDFunId id     = MkId.mkDictFunId name tvs theta cls tys
+                 | isExportedId id = Id.mkExportedLocalId name ty
                  | otherwise       = Id.mkLocalId         name ty
        ; return id'
        }
+  where
+    -- Decompose a dictionary function signature: \forall tvs. theta -> cls tys
+    -- NB: We do *not* use closures '(:->)' for vectorised predicate abstraction as dictionary
+    --     functions are always fully applied.
+    (tvs, theta, pty) = tcSplitSigmaTy  ty
+    (cls, tys)        = tcSplitDFunHead pty
 
 -- |Make a fresh instance of this var, with a new unique.
 --
diff --git a/compiler/vectorise/Vectorise/Type/Env.hs b/compiler/vectorise/Vectorise/Type/Env.hs
index 2373bcaf00..a6112c714c 100644
--- a/compiler/vectorise/Vectorise/Type/Env.hs
+++ b/compiler/vectorise/Vectorise/Type/Env.hs
@@ -108,16 +108,16 @@ import Data.List
 --
 -- It desugars to
 --
---   data Num a = Num { (+) :: a -> a -> a }
+--   data Num a = D:Num { (+) :: a -> a -> a }
 --
 -- which we vectorise to
 --
---  data $vNum a = $vNum { ($v+) :: PArray a :-> PArray a :-> PArray a }
+--  data V:Num a = D:V:Num { ($v+) :: PArray a :-> PArray a :-> PArray a }
 --
 -- while adding the following entries to the vectorisation map:
 --
---   tycon  : Num --> $vNum
---   datacon: Num --> $vNum
+--   tycon  : Num   --> V:Num
+--   datacon: D:Num --> D:V:Num
 --   var    : (+) --> ($v+)
 
 -- |Vectorise type constructor including class type constructors.
diff --git a/compiler/vectorise/Vectorise/Utils/Closure.hs b/compiler/vectorise/Vectorise/Utils/Closure.hs
index f3fe742aef..1f99ee5013 100644
--- a/compiler/vectorise/Vectorise/Utils/Closure.hs
+++ b/compiler/vectorise/Vectorise/Utils/Closure.hs
@@ -6,8 +6,7 @@ module Vectorise.Utils.Closure (
   buildClosure,
   buildClosures,
   buildEnv
-)
-where
+) where
 
 import Vectorise.Builtins
 import Vectorise.Vect
@@ -28,15 +27,14 @@ import BasicTypes( TupleSort(..) )
 import FastString
 
 
--- | Make a closure.
-mkClosure
-  :: Type   -- ^ Type of the argument.
-  -> Type   -- ^ Type of the result.
-  -> Type   -- ^ Type of the environment.
-  -> VExpr  -- ^ The function to apply.
-  -> VExpr  -- ^ The environment to use.
-  -> VM VExpr
-
+-- |Make a closure.
+--
+mkClosure :: Type       -- ^ Type of the argument.
+          -> Type       -- ^ Type of the result.
+          -> Type       -- ^ Type of the environment.
+          -> VExpr      -- ^ The function to apply.
+          -> VExpr      -- ^ The environment to use.
+          -> VM VExpr
 mkClosure arg_ty res_ty env_ty (vfn,lfn) (venv,lenv)
  = do dict <- paDictOfType env_ty
       mkv  <- builtin closureVar
@@ -44,15 +42,13 @@ mkClosure arg_ty res_ty env_ty (vfn,lfn) (venv,lenv)
       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])
 
-
--- | Make a closure application.
-mkClosureApp 
-  :: Type   -- ^ Type of the argument.
-  -> Type   -- ^ Type of the result.
-  -> VExpr  -- ^ Closure to apply.
-  -> VExpr  -- ^ Argument to use.
-  -> VM VExpr
-
+-- |Make a closure application.
+--
+mkClosureApp :: Type      -- ^ Type of the argument.
+             -> Type      -- ^ Type of the result.
+             -> VExpr     -- ^ Closure to apply.
+             -> VExpr     -- ^ Argument to use.
+             -> VM VExpr
 mkClosureApp arg_ty res_ty (vclo, lclo) (varg, larg)
  = do vapply <- builtin applyVar
       lapply <- builtin liftedApplyVar
@@ -60,21 +56,16 @@ mkClosureApp arg_ty res_ty (vclo, lclo) (varg, larg)
       return (Var vapply `mkTyApps` [arg_ty, res_ty] `mkApps` [vclo, varg],
               Var lapply `mkTyApps` [arg_ty, res_ty] `mkApps` [Var lc, lclo, larg])
 
-
-buildClosures 
-  :: [TyVar]
-  -> [VVar]
-  -> [Type] -- ^ Type of the arguments.
-  -> Type   -- ^ Type of result.
-  -> VM VExpr
-  -> VM VExpr
-
+buildClosures :: [TyVar]
+              -> [VVar]
+              -> [Type]   -- ^ Type of the arguments.
+              -> Type     -- ^ Type of result.
+              -> VM VExpr
+              -> VM VExpr
 buildClosures _   _    [] _ 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 res_ty' <- mkClosureTypes arg_tys res_ty
       arg     <- newLocalVVar (fsLit "x") arg_ty
@@ -85,7 +76,6 @@ buildClosures tvs vars (arg_ty : arg_tys) res_ty mk_body
             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
@@ -110,6 +100,7 @@ buildClosure tvs vars arg_ty res_ty mk_body
 
 
 -- Environments ---------------------------------------------------------------
+
 buildEnv :: [VVar] -> VM (Type, VExpr, VExpr -> VExpr -> VExpr)
 buildEnv [] 
  = do
@@ -117,10 +108,9 @@ buildEnv []
       void  <- builtin voidVar
       pvoid <- builtin pvoidVar
       return (ty, vVar (void, pvoid), \_ body -> body)
-
-buildEnv [v] = return (vVarType v, vVar v,
-                    \env body -> vLet (vNonRec v env) body)
-
+buildEnv [v] 
+ = return (vVarType v, vVar v,
+           \env body -> vLet (vNonRec v env) body)
 buildEnv vs
  = do (lenv_tc, lenv_tyargs) <- pdataReprTyCon ty