%
% (c) The AQUA Project, Glasgow University, 1993-1998
%
This is useful, general stuff for the Native Code Generator.
Provide trees (of instructions), so that lists of instructions
can be appended in linear time.
\begin{code}
module OrdList (
OrdList,
nilOL, isNilOL, unitOL, appOL, consOL, snocOL, concatOL,
fromOL, toOL, foldrOL, foldlOL
) where
infixl 5 `appOL`
infixl 5 `snocOL`
infixr 5 `consOL`
data OrdList a
= Many [a]
| Two (OrdList a) (OrdList a)
| One a
| None
nilOL :: OrdList a
isNilOL :: OrdList a -> Bool
unitOL :: a -> OrdList a
snocOL :: OrdList a -> a -> OrdList a
consOL :: a -> OrdList a -> OrdList a
appOL :: OrdList a -> OrdList a -> OrdList a
concatOL :: [OrdList a] -> OrdList a
nilOL = None
unitOL as = One as
snocOL as b = Two as (One b)
consOL a bs = Two (One a) bs
concatOL aas = foldr Two None aas
isNilOL None = True
isNilOL (One _) = False
isNilOL (Two as bs) = isNilOL as && isNilOL bs
isNilOL (Many xs) = null xs
appOL None bs = bs
appOL as None = as
appOL as bs = Two as bs
mapOL :: (a -> b) -> OrdList a -> OrdList b
mapOL f None = None
mapOL f (One x) = One (f x)
mapOL f (Two x y) = Two (mapOL f x) (mapOL f y)
mapOL f (Many xs) = Many (map f xs)
instance Functor OrdList where
fmap = mapOL
foldrOL :: (a->b->b) -> b -> OrdList a -> b
foldrOL k z None = z
foldrOL k z (One x) = k x z
foldrOL k z (Two b1 b2) = foldrOL k (foldrOL k z b2) b1
foldrOL k z (Many xs) = foldr k z xs
foldlOL :: (b->a->b) -> b -> OrdList a -> b
foldlOL k z None = z
foldlOL k z (One x) = k z x
foldlOL k z (Two b1 b2) = foldlOL k (foldlOL k z b1) b2
foldlOL k z (Many xs) = foldl k z xs
fromOL :: OrdList a -> [a]
fromOL ol
= flat ol []
where
flat None rest = rest
flat (One x) rest = x:rest
flat (Two a b) rest = flat a (flat b rest)
flat (Many xs) rest = xs ++ rest
toOL :: [a] -> OrdList a
toOL xs = Many xs
\end{code}