Do Racket streams memoize their elements?

Question

Does Racket use memoization when computing large amounts of numbers from an infinite stream? So, for example, if I printed out (aka, computed and displayed) the first 400 nu

Answer 1

You can use the memoize package.

GitHub source: https://github.com/jbclements/memoize/tree/master

raco pkg install memoize

Using it is as simple as replacing define with define/memo. To quote its example:

(define (fib n)                                     
  (if (<= n 1) 1 (+ (fib (- n 1)) (fib (- n 2)))))  

> (time (fib 35))                                   
cpu time: 513 real time: 522 gc time: 0             
14930352                                            

> (define/memo (fib n)                              
    (if (<= n 1) 1 (+ (fib (- n 1)) (fib (- n 2)))))

> (time (fib 35))                                   
cpu time: 0 real time: 0 gc time: 0                 
14930352      

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Also, it is generally quite easy to implement memoization yourself using a Racket hash-table.