Add a tree-fold function to iterate over the tree and build a single value.

src/collection/tree.rkt

@@ -4,7 +4,7 @@
   tree tree? tree-key tree-value tree-children
   make-tree tree-ref tree-set!
   tree-node tree-child tree->list
-  tree-for-each tree-find-path)
+  tree-for-each tree-find-path tree-fold)
 
 ; Tree structures, with key and possible value on nodes
 ; Like a table, with a list of keys as reference to a value
@@ -79,3 +79,14 @@
         (map
           (lambda (c) (tree-find-path c pred (cons (tree-key tr) path)))
           (tree-children tr)))))
+
+; Fold the tree into a single value
+; This works around the fun function who takes two arguments : the value of a node, the list of results of tree-fold applied recursively on all children
+(define (tree-fold tr fun)
+  (fun
+    (tree-value tr)
+    (map
+      (lambda (x)
+        (tree-fold x fun))
+      (tree-children tr))))
+