mapi: similar to standard map in Scheme, but function has index of elements as second parameter.

sumimus (Sumimus L) — Wed, 16 Apr 2008 22:03:41 GMT



;;;  mapi: similar to standard map in Scheme, but function has index of elements as parameter.

;;;

(define (mapi p l)

  (let loop ((l l) (i 0) (r '()))

    (if (pair? l)

	(loop (cdr l) (+ i 1) (cons (p (car l) i) r))

	(reverse r))))



;; Example: converting a binary number given as a list of binary digits. 

;; (apply + (mapi (lambda (x i) (* x (expt 2 i))) '(0 1 1)))

;; => 6

DZone Snippets: Sumimus's Code Snippets

mapi: similar to standard map in Scheme, but function has index of elements as second parameter.