Curry: An Integrated Functional Logic Language

unzip3 :: [(a,b,c)] -> ([a],[b],[c])
unzip3 [] = ([],[],[])
unzip3 ((x,y,z):ts) = (x:xs,y:ys,z:zs) where (xs,ys,zs) = unzip3 ts
-- Concatenate a list of lists into one list
concat :: [[a]] -> [a]
concat l = foldr (++) [] l
-- Map a function from elements to lists and merge the result into one list
concatMap :: (a -> [b]) -> [a] -> [b]
concatMap f = concat . map f
-- Infinite list of repeated applications of a function f to an element x:
-- iterate f x = [x, f x, f (f x),...]
iterate :: (a -> a) -> a -> [a]
iterate f x = x : iterate f (f x)
-- Infinite list where all elements have the same value x:
repeat :: a -> [a]
repeat x = x : repeat x
-- List of length n where all elements have the same value x:
replicate :: Int -> a -> [a]
replicate n x = take n (repeat x)
-- Return prefix of length n
take :: Int -> [a] -> [a]
take n l = if n==0 then [] else takep n l
where takep _ [] = []
takep n (x:xs) = x : take (n-1) xs
-- Return suffix without first n elements
drop :: Int -> [a] -> [a]
drop n l = if n==0 then l else dropp n l
where dropp _ [] = []
dropp n (_:xs) = drop (n-1) xs
-- (splitAt n xs) is equivalent to (take n xs, drop n xs)
splitAt :: Int -> [a] -> ([a],[a])
splitAt n l = if n==0 then ([],l) else splitAtp n l
where splitAtp _ [] = ([],[])
splitAtp n (x:xs) = let (ys,zs) = splitAt (n-1) xs in (x:ys,zs)
-- Return longest prefix with elements satisfying a predicate
takeWhile :: (a -> Bool) -> [a] -> [a]
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