Use 3-argument dict-map mapping function.

dictionary.scm

@@ -100,15 +100,27 @@
    (map car d))
 
  ;; Maps dictionary values, the procedure gets key-value pairs if it
- ;; accepts more than one argument.
+ ;; accepts more than one argument. If it accepts a third argument,
+ ;; index gets passed as well.
  (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)))
+   (let* ((lpi (length (procedure-information proc)))
+	  (both? (> lpi 2))
+	  (index? (> lpi 3)))
+     (let loop ((d d)
+		(r '())
+		(i 0))
+       (if (null? d)
+	   r ; No reverse needed, order does not matter
+	   (loop (cdr d)
+		 (let ((k (caar d))
+		       (v (cdar d)))
+		   (cons (cons k (if both?
+				     (if index?
+					 (proc k v i)
+					 (proc k v))
+				     (proc v)))
+			 r))
+		 (add1 i))))))
 
  ;; Returns a dictionary containing only kv pairs matching the
  ;; predicate which must accept two arguments. Unlike list filter,