Skeleton of generic BST removal with counting.

src/util-bst.scm

@@ -15,7 +15,7 @@
   bst-contains?
 
   bst-set
-  ;;bst-remove ;;
+  bst-remove
 
   ;;bst->kvv
   ;;kvv->bst
@@ -172,6 +172,36 @@
 			  new-root
 			  (+ (bst-count bst) count-add)))))
 
+ (define/doc (bst-remove bst k . nos)
+   ("Removes given key from the BST.")
+   (let-comparators
+    (EQ? <? bst)
+    (let-values
+	(((new-root sub-count)
+	  (let loop ((n (bst-root bst)))
+	    (if n
+		(let ((nk (bst-node-key n)))
+		  (if (EQ? nk k)
+		      #f ;; ... from line 212 in util-dict-bst
+		      (if (<? k nk)
+			  (let-values (((new-left-node sub-count)
+					(loop (bst-node-left n))))
+			    (values (set-bst-node-left n new-left-node)
+				    sub-count))
+			  (let-values (((new-right-node sub-count)
+					(loop (bst-node-right n))))
+			    (values (set-bst-node-right n new-right-node)
+				    sub-count)))))
+		(if (and (not (null? nos))
+			 (car nos))
+		    (values #f 0)
+		    (error 'bst-remove "Key does not exist" k))))))
+      (if (eq? sub-count 0)
+	  bst
+	  (set-bst-root+count bst
+			      new-root
+			      (- (bst-count bst) sub-count))))))
+
  ;; Module self-tests
  (define (util-bst-tests!)
    (run-tests