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module JoinList where
import Sized
import Scrabble
data JoinList m a = Empty
| Single m a
| Append m (JoinList m a) (JoinList m a)
deriving (Eq, Show)
-- Exercise 1
tag :: Monoid m => JoinList m a -> m
tag Empty = mempty
tag (Single m _) = m
tag (Append m _ _) = m
(+++) :: Monoid m => JoinList m a -> JoinList m a -> JoinList m a
(+++) jl1 jl2 = Append (mappend (tag jl1) (tag jl2)) jl1 jl2
-- Exercise 2
indexJ :: (Sized b, Monoid b) => Int -> JoinList b a -> Maybe a
indexJ _ Empty = Nothing
indexJ n (Single _ a)
| n == 0 = Just a
| otherwise = Nothing
indexJ n (Append m jl1 jl2)
| n < 0 || n >= (getSize $ size m) = Nothing
| n < s1 = indexJ n jl1
| n >= s1 = indexJ (n - s1) jl2
where s1 = getSize $ size $ tag jl1
dropJ :: (Sized b, Monoid b) => Int -> JoinList b a -> JoinList b a
dropJ _ Empty = Empty
dropJ n jl@(Single _ _)
| n >= 1 = Empty
| otherwise = jl
dropJ n jl@(Append m jl1 jl2)
| n <= 0 = jl
| n >= m' = Empty
| n < s1 = dropJ n jl1 +++ jl2
| n >= s1 = dropJ (n - s1) jl2
where
s1 = getSize $ size $ tag jl1
m' = getSize $ size m
takeJ :: (Sized b, Monoid b) => Int -> JoinList b a -> JoinList b a
takeJ _ Empty = Empty
takeJ n _ | n <= 0 = Empty
takeJ n jl@(Single _ _) = jl
takeJ n jl@(Append m jl1 jl2)
| n >= m' = jl
| n < s1 = takeJ n jl1
| n >= s1 = jl1 +++ takeJ (n - s1) jl2
where
s1 = getSize $ size $ tag jl1
m' = getSize $ size m
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