积累在Scheme Lang R5RS中不工作

Question

I solved a problem which involved using map and accumulate but it gave me this error: "accumulate: undefined;" cannot reference undefined identifier. "accumulate: undefined;" cannot reference undefined identifier.

This is my code:

;Procedure to test it with
(define (double x)
   (* 2 x))

(define (my-map proc sequence) 
   (accumulate (lambda (x y) (cons (proc x) y)) '() sequence))

Please can anyone tell me how to fix this problem?

Answer 1

The procedure accumulate is not defined in R5RS. But it's simple enough to define your own:

(define (accumulate proc init lst)
  (if (null? lst)
      init
      (proc (car lst)
            (accumulate proc init (cdr lst)))))

For future reference, accumulate is also known as foldr , fold-right , inject or reduce in other programming languages, consult your interpreter's documentation for more details.