Map on nested lists

General
1

I was in need of applying a function to a list of values that contains sub-lists. map can not works on nested lists and i can not find a procedure in the scheme library or SRFI so i wrote my own :

(module map-nested racket/base


  (provide map-nested )


  ;; (map-nested sin '(0.1 0.2 (0.3) 0.4))
  ;; '(0.09983341664682815 0.19866933079506122 (0.29552020666133955) 0.3894183423086505)

  (define (map-nested f L)

    (define (map-nested-aux x)
      (if (list? x)
	      (map map-nested-aux x)
	      (apply f (list x))))

    (map map-nested-aux L))

)
2

Check Shawn's collection of tree functions.

2 Likes
3

yes map-tree or walk-tree should make it, map-tree i suppose, but haven't test it as my solution is already good.

4

leaf-map in particular:

> (require soup-lib/tree)
> (leaf-map sin '(0.1 0.2 (0.3) 0.4))
'(0.09983341664682815
  0.19866933079506122
  (0.29552020666133955)
  0.3894183423086505)
1 Like
5

oh yes ,it is true it is exactly and only the leaf (leaves ?) i'm aiming.

6

FWIW, Instead of (apply f (list x)), (f x) should work and be more performant (since the argument list is fixed, we don't need the indirection of apply).

1 Like
7

:open_mouth: yes, i corrected the code (i do not know why i overcomplexified my code,sometimes things are so simple, we do not see them :sweat_smile:)

8

and another people outside Racket discourse provide me with this more concise solution:

(define (map-nested f L)

    (if (list? L)
      (map (lambda (x) (map-nested f x))
	       L)
      (f L)))