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|
-----------------------------------------------------------------------------
-- Standard Library: List operations
--
-- Suitable for use with Hugs 1.4.
-----------------------------------------------------------------------------
module List (
elemIndex, elemIndices,
find, findIndex, findIndices,
nub, nubBy, delete, deleteBy, (\\), deleteFirstsBy,
union, unionBy, intersect, intersectBy,
intersperse, transpose, partition, group, groupBy,
inits, tails, isPrefixOf, isSuffixOf,
mapAccumL, mapAccumR,
sort, sortBy, insertBy, maximumBy, minimumBy,
genericLength, genericTake, genericDrop,
genericSplitAt, genericIndex, genericReplicate,
zip4, zip5, zip6, zip7,
zipWith4, zipWith5, zipWith6, zipWith7,
unzip4, unzip5, unzip6, unzip7
) where
import Maybe( listToMaybe )
infix 5 \\
elemIndex :: Eq a => a -> [a] -> Maybe Int
elemIndex x = findIndex (x ==)
elemIndices :: Eq a => a -> [a] -> [Int]
elemIndices x = findIndices (x ==)
find :: (a -> Bool) -> [a] -> Maybe a
find p = listToMaybe . filter p
findIndex :: (a -> Bool) -> [a] -> Maybe Int
findIndex p = listToMaybe . findIndices p
findIndices :: (a -> Bool) -> [a] -> [Int]
findIndices p xs = [ i | (x,i) <- zip xs [0..], p x ]
nub :: (Eq a) => [a] -> [a]
nub = nubBy (==)
nubBy :: (a -> a -> Bool) -> [a] -> [a]
nubBy eq [] = []
nubBy eq (x:xs) = x : nubBy eq (filter (\y -> not (eq x y)) xs)
delete :: (Eq a) => a -> [a] -> [a]
delete = deleteBy (==)
deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]
deleteBy eq x [] = []
deleteBy eq x (y:ys) = if x `eq` y then ys else y : deleteBy eq x ys
(\\) :: (Eq a) => [a] -> [a] -> [a]
(\\) = foldl (flip delete)
deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
deleteFirstsBy eq = foldl (flip (deleteBy eq))
union :: (Eq a) => [a] -> [a] -> [a]
union = unionBy (==)
unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
unionBy eq xs ys = xs ++ foldl (flip (deleteBy eq)) (nubBy eq ys) xs
intersect :: (Eq a) => [a] -> [a] -> [a]
intersect = intersectBy (==)
intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
intersectBy eq xs ys = [x | x <- xs, any (eq x) ys]
intersperse :: a -> [a] -> [a]
intersperse sep [] = []
intersperse sep [x] = [x]
intersperse sep (x:xs) = x : sep : intersperse sep xs
transpose :: [[a]] -> [[a]]
transpose = foldr
(\xs xss -> zipWith (:) xs (xss ++ repeat []))
[]
partition :: (a -> Bool) -> [a] -> ([a],[a])
partition p xs = foldr select ([],[]) xs
where select x (ts,fs) | p x = (x:ts,fs)
| otherwise = (ts,x:fs)
-- group splits its list argument into a list of lists of equal, adjacent
-- elements. e.g.,
-- group "Mississippi" == ["M","i","ss","i","ss","i","pp","i"]
group :: (Eq a) => [a] -> [[a]]
group = groupBy (==)
groupBy :: (a -> a -> Bool) -> [a] -> [[a]]
groupBy eq [] = []
groupBy eq (x:xs) = (x:ys) : groupBy eq zs
where (ys,zs) = span (eq x) xs
-- inits xs returns the list of initial segments of xs, shortest first.
-- e.g., inits "abc" == ["","a","ab","abc"]
inits :: [a] -> [[a]]
inits [] = [[]]
inits (x:xs) = [[]] ++ map (x:) (inits xs)
-- tails xs returns the list of all final segments of xs, longest first.
-- e.g., tails "abc" == ["abc", "bc", "c",""]
tails :: [a] -> [[a]]
tails [] = [[]]
tails xxs@(_:xs) = xxs : tails xs
isPrefixOf :: (Eq a) => [a] -> [a] -> Bool
isPrefixOf [] _ = True
isPrefixOf _ [] = False
isPrefixOf (x:xs) (y:ys) = x == y && isPrefixOf xs ys
isSuffixOf :: (Eq a) => [a] -> [a] -> Bool
isSuffixOf x y = reverse x `isPrefixOf` reverse y
mapAccumL :: (a -> b -> (a, c)) -> a -> [b] -> (a, [c])
mapAccumL f s [] = (s, [])
mapAccumL f s (x:xs) = (s'',y:ys)
where (s', y ) = f s x
(s'',ys) = mapAccumL f s' xs
mapAccumR :: (a -> b -> (a, c)) -> a -> [b] -> (a, [c])
mapAccumR f s [] = (s, [])
mapAccumR f s (x:xs) = (s'', y:ys)
where (s'',y ) = f s' x
(s', ys) = mapAccumR f s xs
sort :: (Ord a) => [a] -> [a]
sort = sortBy compare
sortBy :: (a -> a -> Ordering) -> [a] -> [a]
sortBy cmp = foldr (insertBy cmp) []
insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a]
insertBy cmp x [] = [x]
insertBy cmp x ys@(y:ys')
= case cmp x y of
GT -> y : insertBy cmp x ys'
_ -> x : ys
maximumBy :: (a -> a -> a) -> [a] -> a
maximumBy max [] = error "List.maximumBy: empty list"
maximumBy max xs = foldl1 max xs
minimumBy :: (a -> a -> a) -> [a] -> a
minimumBy min [] = error "List.minimumBy: empty list"
minimumBy min xs = foldl1 min xs
genericLength :: (Integral a) => [b] -> a
genericLength [] = 0
genericLength (x:xs) = 1 + genericLength xs
genericTake :: (Integral a) => a -> [b] -> [b]
genericTake 0 _ = []
genericTake _ [] = []
genericTake n (x:xs)
| n > 0 = x : genericTake (n-1) xs
| otherwise = error "List.genericTake: negative argument"
genericDrop :: (Integral a) => a -> [b] -> [b]
genericDrop 0 xs = xs
genericDrop _ [] = []
genericDrop n (_:xs)
| n > 0 = genericDrop (n-1) xs
| otherwise = error "List.genericDrop: negative argument"
genericSplitAt :: (Integral a) => a -> [b] -> ([b],[b])
genericSplitAt 0 xs = ([],xs)
genericSplitAt _ [] = ([],[])
genericSplitAt n (x:xs)
| n > 0 = (x:xs',xs'')
| otherwise = error "List.genericSplitAt: negative argument"
where (xs',xs'') = genericSplitAt (n-1) xs
genericIndex :: (Integral a) => [b] -> a -> b
genericIndex (x:_) 0 = x
genericIndex (_:xs) n
| n > 0 = genericIndex xs (n-1)
| otherwise = error "List.genericIndex: negative argument"
genericIndex _ _ = error "List.genericIndex: index too large"
genericReplicate :: (Integral a) => a -> b -> [b]
genericReplicate n x = genericTake n (repeat x)
zip4 :: [a] -> [b] -> [c] -> [d] -> [(a,b,c,d)]
zip4 = zipWith4 (,,,)
zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a,b,c,d,e)]
zip5 = zipWith5 (,,,,)
zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] ->
[(a,b,c,d,e,f)]
zip6 = zipWith6 (,,,,,)
zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] ->
[g] -> [(a,b,c,d,e,f,g)]
zip7 = zipWith7 (,,,,,,)
zipWith4 :: (a->b->c->d->e) -> [a]->[b]->[c]->[d]->[e]
zipWith4 z (a:as) (b:bs) (c:cs) (d:ds)
= z a b c d : zipWith4 z as bs cs ds
zipWith4 _ _ _ _ _ = []
zipWith5 :: (a->b->c->d->e->f) ->
[a]->[b]->[c]->[d]->[e]->[f]
zipWith5 z (a:as) (b:bs) (c:cs) (d:ds) (e:es)
= z a b c d e : zipWith5 z as bs cs ds es
zipWith5 _ _ _ _ _ _ = []
zipWith6 :: (a->b->c->d->e->f->g) ->
[a]->[b]->[c]->[d]->[e]->[f]->[g]
zipWith6 z (a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs)
= z a b c d e f : zipWith6 z as bs cs ds es fs
zipWith6 _ _ _ _ _ _ _ = []
zipWith7 :: (a->b->c->d->e->f->g->h) ->
[a]->[b]->[c]->[d]->[e]->[f]->[g]->[h]
zipWith7 z (a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs) (g:gs)
= z a b c d e f g : zipWith7 z as bs cs ds es fs gs
zipWith7 _ _ _ _ _ _ _ _ = []
unzip4 :: [(a,b,c,d)] -> ([a],[b],[c],[d])
unzip4 = foldr (\(a,b,c,d) ~(as,bs,cs,ds) ->
(a:as,b:bs,c:cs,d:ds))
([],[],[],[])
unzip5 :: [(a,b,c,d,e)] -> ([a],[b],[c],[d],[e])
unzip5 = foldr (\(a,b,c,d,e) ~(as,bs,cs,ds,es) ->
(a:as,b:bs,c:cs,d:ds,e:es))
([],[],[],[],[])
unzip6 :: [(a,b,c,d,e,f)] -> ([a],[b],[c],[d],[e],[f])
unzip6 = foldr (\(a,b,c,d,e,f) ~(as,bs,cs,ds,es,fs) ->
(a:as,b:bs,c:cs,d:ds,e:es,f:fs))
([],[],[],[],[],[])
unzip7 :: [(a,b,c,d,e,f,g)] -> ([a],[b],[c],[d],[e],[f],[g])
unzip7 = foldr (\(a,b,c,d,e,f,g) ~(as,bs,cs,ds,es,fs,gs) ->
(a:as,b:bs,c:cs,d:ds,e:es,f:fs,g:gs))
([],[],[],[],[],[],[])
-----------------------------------------------------------------------------
|
