Curry: An Integrated Functional Logic Language

foldr1 _ [x] = x
foldr1 f (x1:x2:xs) = f x1 (foldr1 f (x2:xs))
-- Filter elements in a list
filter :: (a -> Bool) -> [a] -> [a]
filter _ [] = []
filter p (x:xs) = if p x then x : filter p xs
else filter p xs
-- Join two lists into one list of pairs. If one input list is shorter than
-- the other, the additional elements of the longer list are discarded.
zip :: [a] -> [b] -> [(a,b)]
zip [] _ = []
zip (_:_) [] = []
zip (x:xs) (y:ys) = (x,y) : zip xs ys
-- Join three lists into one list of triples. If one input list is shorter than
-- the other, the additional elements of the longer lists are discarded.
zip3 :: [a] -> [b] -> [c] -> [(a,b,c)]
zip3 [] _ _ = []
zip3 (_:_) [] _ = []
zip3 (_:_) (_:_) [] = []
zip3 (x:xs) (y:ys) (z:zs) = (x,y,z) : zip3 xs ys zs
-- Join two lists into one list by applying a combination function to
-- corresponding pairs of elements (i.e., zip = zipWith (,)):
zipWith :: (a->b->c) -> [a] -> [b] -> [c]
zipWith _ [] _ = []
zipWith _ (_:_) [] = []
zipWith f (x:xs) (y:ys) = f x y : zipWith f xs ys
-- Join three lists into one list by applying a combination function to
-- corresponding triples of elements (i.e., zip3 = zipWith3 (,,)):
zipWith3 :: (a->b->c->d) -> [a] -> [b] -> [c] -> [d]
zipWith3 _ [] _ _ = []
zipWith3 _ (_:_) [] _ = []
zipWith3 _ (_:_) (_:_) [] = []
zipWith3 f (x:xs) (y:ys) (z:zs) = f x y z : zipWith3 f xs ys zs
-- Transform a list of pairs into a pair of lists
unzip :: [(a,b)] -> ([a],[b])
unzip [] = ([],[])
unzip ((x,y):ps) = (x:xs,y:ys) where (xs,ys) = unzip ps
-- Transform a list of triples into a triple of lists
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