module Text.LParse.TokenStream where
import Data.Either
import Data.Maybe
import Data.Traversable
class (Functor t, Foldable t) => TokenStream t where
top :: t a -> a
rest :: t a -> t a
nil :: t a
cons :: a -> t a -> t a
instance TokenStream [] where
top = head
rest = tail
nil = []
cons = (:)
instance TokenStream Maybe where
top = fromJust
rest = const Nothing
nil = Nothing
cons a _ = Just a
instance TokenStream (Either a) where
top = head . rights . return
rest x = if isLeft x then x else nil
nil = Left undefined
cons a _ = Right a
skipN :: (TokenStream s) => Int -> s a -> s a
skipN = sDrop
sDrop :: (TokenStream s) => Int -> s a -> s a
sDrop 0 x = x
sDrop n x = rest $ sDrop (n1) x
sZip :: (TokenStream s) => s a -> s b -> s (a,b)
sZip = sZipWith (,)
sZipWith :: (TokenStream s) => (a -> b -> c) -> s a -> s b -> s c
sZipWith f l r | null l || null r = nil
| otherwise = f (top l) (top r) `cons` (sZipWith f (rest l) (rest r))
sFilter :: (TokenStream s) => (a -> Bool) -> s a -> s a
sFilter c x | null x = nil
| c (top x) = (top x) `cons` sFilter c (rest x)
| otherwise = sFilter c (rest x)