; vec-search-up? : (any -> boolean) (vectorof any) -> boolean
; Purpose: Returns whether any element of the vector meets the given
;          predicate.
; Examples:
;   (vec-search-up? number? (vector true false))   = false
;   (vec-search-up? number? (vector true 3 false)) = true
;   (vec-search-up? number? (vector))              = false

(define (vec-search-up1? pred? a-vec)
  (local [;; search : natnum -> boolean
	  ;; Purpose: Returns whether any element
	  ;;          (vector-length a-vec)-num_elts..(vector-length a-vec)-1
	  ;;          of a-vec meets predicate pred?.
	  (define (search num_elts)
	    (cond
	      [(zero? num_elts)
	       false]
	      [else
		(or (pred? (vector-ref a-vec (- (vector-length a-vec)
						num_elts)))
		    (search (sub1 num_elts)))]))]
    (search (vector-length a-vec))))

(define (vec-search-up2? pred? a-vec)
  (local [;; search : natnum -> boolean
	  ;; Purpose: Returns whether any element
	  ;;          index..(vector-length a-vec)-1
	  ;;          of a-vec meets predicate pred?.
	  (define (search index)
	    (cond
	      [(= (vector-length a-vec) index)
	       false]
	      [else
		(or (pred? (vector-ref a-vec index))
		    (search (add1 index)))]))]
    (search 0)))

; Note:  vec-search-up2? does NOT work with zero-length vectors,
; i.e., (vector).  To make it work, you need to change the base case,
; e.g., to
;   [(<= (vector-length a-vec) index)  false]