Racket Programming language(Scheme)
  

• You must use proper Scheme style.
• If a problem asks you to implement a recursive solution, your solution must be recursive or you will receive no credit. Remember, a recursive function is a function that calls itself.
• If a problem asks you to make a pure function, you must not use set! or any form of mutable state in your solution. If you do, you will receive no credit.
• No input error-checking is required; you may assume input obeys the constraints stated in the problem description. For example, if the problem says an argument is a positive integer, you do not have to handle negative arguments.
• Make sure you test your stream functions with infinite streams.

;; Stream Stream -> Stream
;;
;; zip for streams. Return a stream whose elements are pairs where the first
;; item in the pair is taken from xs and the second item in the pair is taken
;; from ys.
;;

(define (stream-zip xs ys)
 'not-implemented)
 

Define a pure, recursive function stream-zip that takes two arguments, each of which is a stream, and produces a stream of pairs, where the nth pair's car is the nth element of xs and the nth pair's cdr is the nth element of ys. If xs and ys do not have the same length, then stream-zip should return a stream that has as many elements as the "shortest" of xs and ys. That is, if stream-zip runs out of items in either xs or ys, it can stop producing pairs. The behavior of stream-zip is undefined if either xs or ys is not a stream. Note that stream-zip is like zip from Homework 1, but it operates on streams. Unlike zip, we cannot assume that the two streams have the same length. The stream-zip function must also potentially handle infinite streams-there is no guarantee that xs and ys are finite streams.