    -- |Simple vectorised constructors and projections.
    --
    module Vectorise.Vect
      ( Vect, VVar, VExpr, VBind

      , vectorised
      , lifted
      , mapVect

      , vVarType
      , vNonRec
      , vRec
      , vVar
      , vType
      , vTick
      , vLet
      , vLams
      , vVarApps
      , vCaseDEFAULT
      )
    where

    import CoreSyn
    import Type           ( Type )
    import Var

    -- |Contains the vectorised and lifted versions of some thing.
    --
    type Vect a = (a,a)
    type VVar   = Vect Var
    type VExpr  = Vect CoreExpr
    type VBind  = Vect CoreBind

    -- |Get the vectorised version of a thing.
    --
    vectorised :: Vect a -> a
    vectorised = fst

    -- |Get the lifted version of a thing.
    --
    lifted :: Vect a -> a
    lifted = snd

    -- |Apply some function to both the vectorised and lifted versions of a thing.
    --
    mapVect :: (a -> b) -> Vect a -> Vect b
    mapVect f (x, y) = (f x, f y)

    -- |Combine vectorised and lifted versions of two things componentwise.
    --
    zipWithVect :: (a -> b -> c) -> Vect a -> Vect b -> Vect c
    zipWithVect f (x1, y1) (x2, y2) = (f x1 x2, f y1 y2)

    -- |Get the type of a vectorised variable.
    --
    vVarType :: VVar -> Type
    vVarType = varType . vectorised

    -- |Wrap a vectorised variable as a vectorised expression.
    --
    vVar :: VVar -> VExpr
    vVar = mapVect Var

    -- |Wrap a vectorised type as a vectorised expression.
    --
    vType :: Type -> VExpr
    vType ty = (Type ty, Type ty)

    -- |Make a vectorised note.
    --
    vTick :: Tickish Id -> VExpr -> VExpr
    vTick = mapVect . Tick

    -- |Make a vectorised non-recursive binding.
    --
    vNonRec :: VVar -> VExpr -> VBind
    vNonRec = zipWithVect NonRec

    -- |Make a vectorised recursive binding.
    --
    vRec :: [VVar] -> [VExpr] -> VBind
    vRec vs es = (Rec (zip vvs ves), Rec (zip lvs les))
      where
        (vvs, lvs) = unzip vs
        (ves, les) = unzip es

    -- |Make a vectorised let expresion.
    --
    vLet :: VBind -> VExpr -> VExpr
    vLet = zipWithVect Let

    -- |Make a vectorised lambda abstraction.
    --
    -- The lifted version also binds the lifting context 'lc'.
    --
    vLams :: Var      -- ^ Var bound to the lifting context.
          -> [VVar]   -- ^ Parameter vars for the abstraction.
          -> VExpr    -- ^ Body of the abstraction.
          -> VExpr
    vLams lc vs (ve, le)
      = (mkLams vvs ve, mkLams (lc:lvs) le)
      where
        (vvs, lvs) = unzip vs

    -- |Apply an expression to a set of argument variables.
    --
    -- The lifted version is also applied to the variable of the lifting context.
    --
    vVarApps :: Var -> VExpr -> [VVar] -> VExpr
    vVarApps lc (ve, le) vvs
      = (ve `mkVarApps` vs, le `mkVarApps` (lc : ls))
      where
        (vs, ls) = unzip vvs

    vCaseDEFAULT :: VExpr  -- scrutiniy
                 -> VVar   -- bnder
                 -> Type   -- type of vectorised version
                 -> Type   -- type of lifted version
                 -> VExpr  -- body of alternative.
                 -> VExpr
    vCaseDEFAULT (vscrut, lscrut) (vbndr, lbndr) vty lty (vbody, lbody)
      = (Case vscrut vbndr vty (mkDEFAULT vbody),
         Case lscrut lbndr lty (mkDEFAULT lbody))
      where
        mkDEFAULT e = [(DEFAULT, [], e)]