zip package:protolude

zip takes two lists and returns a list of corresponding pairs. zip is right-lazy:

>>> zip [] undefined
[]

>>> zip undefined []
*** Exception: Prelude.undefined
...

zip is capable of list fusion, but it is restricted to its first list argument and its resulting list.

Examples

>>> zip [1, 2, 3] ['a', 'b', 'c']
[(1,'a'),(2,'b'),(3,'c')]

If one input list is shorter than the other, excess elements of the longer list are discarded, even if one of the lists is infinite:

>>> zip [1] ['a', 'b']
[(1,'a')]

>>> zip [1, 2] ['a']
[(1,'a')]

>>> zip [] [1..]
[]

>>> zip [1..] []
[]

zipWith generalises zip by zipping with the function given as the first argument, instead of a tupling function.

zipWith (,) xs ys == zip xs ys
zipWith f [x1,x2,x3..] [y1,y2,y3..] == [f x1 y1, f x2 y2, f x3 y3..]

zipWith is right-lazy:

>>> let f = undefined

>>> zipWith f [] undefined
[]

zipWith is capable of list fusion, but it is restricted to its first list argument and its resulting list.

Examples

zipWith (+) can be applied to two lists to produce the list of corresponding sums:

>>> zipWith (+) [1, 2, 3] [4, 5, 6]
[5,7,9]

>>> zipWith (++) ["hello ", "foo"] ["world!", "bar"]
["hello world!","foobar"]

The zipWithM function generalizes zipWith to arbitrary applicative functors.

zipWithM_ is the extension of zipWithM which ignores the final result.

Lists, but with an Applicative functor based on zipping.

unzip transforms a list of pairs into a list of first components and a list of second components.

Examples

>>> unzip []
([],[])

>>> unzip [(1, 'a'), (2, 'b')]
([1,2],"ab")

The mapAndUnzipM function maps its first argument over a list, returning the result as a pair of lists. This function is mainly used with complicated data structures or a state monad.