chickadee » srfi-179 » make-array

Assume first that the optional argument setter is not given.

If interval is an interval and getter is a function from interval to Scheme objects, then make-array returns an array with domain interval and getter getter.

It is an error to call make-array if interval and getter do not satisfy these conditions.

If now setter is specified, assume that it is a procedure such that getter and setter satisfy: If

(i1,...,in) $\neq$ (j1,...,jn)

are elements of interval and

(getter j1 ... jn) => x

then "after"

 (setter v i1 ... in)

we have

(getter j1 ... jn) => x

and

(getter i1,...,in) => v

Then make-array builds a mutable array with domain interval, getter getter, and setter setter. It is an error to call make-array if its arguments do not satisfy these conditions.

Example:

  (define a (make-array (make-interval '#(1 1) '#(11 11))
                        (lambda (i j)
                          (if (= i j)
                              1
                              0))))

defines an array for which (array-getter a) returns 1 when i=j and 0 otherwise.

Example:

(define a   ;; a sparse array
  (let ((domain
         (make-interval '#(1000000 1000000)))
        (sparse-rows
         (make-vector 1000000 '())))
    (make-array
     domain
     (lambda (i j)
       (cond ((assv j (vector-ref sparse-rows i))
              => cdr)
             (else
              0.0)))
     (lambda (v i j)
       (cond ((assv j (vector-ref sparse-rows i))
              => (lambda (pair)
                   (set-cdr! pair v)))
             (else
              (vector-set!
               sparse-rows
               i
               (cons (cons j v)
                     (vector-ref sparse-rows i)))))))))

(define a_ (array-getter a))
(define a! (array-setter a))

(a_ 12345 6789)  => 0.
(a_ 0 0) => 0.
(a! 1.0 0 0) => undefined
(a_ 12345 6789)  => 0.
(a_ 0 0) => 1.