add a generating thunk for split

1 files changed, 6 insertions, 4 deletions

diff --git a/mcgoron.weight-balanced-trees.internal.scm b/mcgoron.weight-balanced-trees.internal.scm
index c657178..99be0bc 100644
--- a/mcgoron.weight-balanced-trees.internal.scm
+++ b/mcgoron.weight-balanced-trees.internal.scm
@@ -18,6 +18,7 @@
   (left get-left)
   (right get-right))
 
+(: wb-tree-node? (* -> boolean : node-type))
 (define (wb-tree-node? x)
   (or (null? x) (non-null-wb-tree-node? x)))
 
@@ -239,16 +240,16 @@
 
 ;;; XXX: The comparator library does not export the struct type for
 ;;; the comparator.
-(: split (* node-type * --> node-type boolean node-type))
-(define (split cmp tree key)
+(: split (* node-type * (-> *) --> node-type * node-type))
+(define (split cmp tree key default)
   (let split ((tree tree))
     (if (null? tree)
-        (values '() #f '())
+        (values '() (default) '())
         (with-node (tree data ("<" left) (">" right))
           (comparator-if<=> cmp key data
             (let-values (((new-left bool new-right) (split left)))
               (values new-left bool (join data new-right right)))
-            (values left #t right)
+            (values left data right)
             (let-values (((new-left bool new-right) (split right)))
               (values (join data left new-left) bool new-right)))))))
 
@@ -265,3 +266,4 @@
                data
                (search right))))))))
 
+