Haskell Language Lists Zipping and Unzipping Lists
Example
zip takes two lists and returns a list of corresponding pairs:
zip [] _ = []
zip _ [] = []
zip (a:as) (b:bs) = (a,b) : zip as bs
> zip [1,3,5] [2,4,6]
> [(1,2),(3,4),(5,6)]
Zipping two lists with a function:
zipWith f [] _ = []
zipWith f _ [] = []
zipWith f (a:as) (b:bs) = f a b : zipWith f as bs
> zipWith (+) [1,3,5] [2,4,6]
> [3,7,11]
Unzipping a list:
unzip = foldr (\(a,b) ~(as,bs) -> (a:as,b:bs)) ([],[])
> unzip [(1,2),(3,4),(5,6)]
> ([1,3,5],[2,4,6])
