;;; $Id: vector-generator-mod.scm,v 1.2 2006/01/05 22:24:09 leavens Exp $

;;; Springer-Friedman, Program 9.21, pg. 283 -

(module vector-generator-mod (lib "typedscm.ss" "typedscm")
 
(provide vector-generator)

(deftype add1 (-> (number) number))
(define add1 (lambda (n) (+ 1 n)))

(deftype vector-generator
  (forall (T) (-> ((-> (number) T)) (-> (number) (vector-of T)))))

(define vector-generator
  (lambda (gen-proc)
    (lambda (size)
      ;; ENSURES: result is a new vector of elements indexed 0...size-1
      ;; such that the ith element is (gen-proc i).  Note that the calls
      ;; to gen-proc are made in order from 0 to size-1.
      (let ((vec (make-vector size)))
        (letrec
          ((loop ; TYPE: integer -> void
            (lambda (i)
              ;; REQUIRES: 0 <= i <= size and for all 0 <= j < i,
              ;; (vector-ref vec j) = (gen-proc j)
              ;; MODIFIES: vec
              ;; EFFECT: initialize indexes i up to size-1
              (if (< i size)
                  (begin
                    (vector-set! vec i (gen-proc i))
                    (loop (add1 i)))))))
          (loop 0))
        vec))))

) ; end module