Implement dict-map.

dictionary.scm

@@ -91,6 +91,17 @@
  (define (dict-keys d)
    (map car d))
 
+ ;; Maps dictionary values, the procedure gets key-value pairs if it
+ ;; accepts more than one argument.
+ (define (dict-map proc d)
+   (let ((both? (> (length (procedure-information proc)) 2)))
+     (map
+      (lambda (kv)
+	(let ((k (car kv))
+	      (v (cdr kv)))
+	  (cons k (if both? (proc k v) (proc v)))))
+      d)))
+
  ;; Performs self-tests of the dictionary module.
  (define (dictionary-tests!)
    (run-tests
@@ -103,6 +114,16 @@
    (test-exn dict-remove (dict-remove (make-dict) 'nonexistent))
    (test-true dict-remove (null? (dict-remove (dict-set (make-dict) 'existing 1) 'existing)))
    (test-equal? dict-keys (dict-keys (dict-set (make-dict) 'existing 1)) '(existing))
+   (test-equal? dict-map (dict-map (lambda (v) (* 2 v))
+				   '((a . 1)
+				     (b . 2)))
+		'((a . 2)
+		  (b . 4)))
+   (test-equal? dict-map (dict-map (lambda (k v) (* 2 v))
+				   '((a . 1)
+				     (b . 2)))
+		'((a . 2)
+		  (b . 4)))
    ))
 
  )