Re: Another code review perhaps?

Arthur Lemmens wrote:

Define iterative and recursive versions of a function that takes an
object x and a vector v, and returns a list of all the objects that
immediately precede x in v.

 
Graham doesn't like LOOP, but I do. So here's a LOOP-version:
 
(defun precedes (object vector)
  (loop for x across vector
        and i from 0
        when (and (equal x object) (> i 0))
        collect (elt vector (1-i))))

Look at that:

(1-i)

Don't you think that that should be:

(1- i)

or

(- i 1)

?

It's shorter when you use a Lispy language instead of CL.

Gauche Scheme

(use srfi-42) ; list-ec

(define (precedes obj vec)
  (list-ec (: x (index i) vec)
    (if (and (> i 0) (equal? x obj)))
    (ref vec (- i 1))))

(precedes 5 #(5 0 4 5 8 9 5))
  ===>
(4 9)

Another way:

(define (precedes o v)
  (let ((l (vector->list vec)))
    (filter-map
      (^(a b) (and (equal? o a) b))
      (cdr l)
      l)))