list-put

Description

Replaces the ordinalth value of vlist with value. If span > 1, replaces ordinal to ordinal+span-1 values starting at ordinal.

Example

(list-put (1 2 3 4 5) 2 0 2) returns (1 0 0 4 5).

Author

Norman Walsh, <ndw@nwalsh.com>

Source Code

(define (list-put vlist ordinal value #!optional (span 1))
  ;; Replace a specific member of a list
  (let loop ((result vlist) (count span) (k ordinal))
    (if (equal? count 0)
	result
	(let ((head (list-head result (- k 1)))
	      (tail (list-tail result k)))
	  (loop (append head (list value) tail) (- count 1) (+ k 1))))))