map_leaf method for tree

mapytex/calculus/core/tree.py

@@ -194,15 +194,27 @@ class Tree(object):
         ...    ("*", (3, 4)),
         ...    2))
         >>> t = Tree.from_nested_parenthesis(nested_par)
+        >>> print(t)
+        +
+         > *
+         | > 3
+         | > 4
+         > 2
+        >>> print(t.map_leaf(lambda x:2*x))
+        +
+         > *
+         | > 6
+         | > 8
+         > 4
 
         """
         try:
-            left_applied = self.left_value.apply(function)
+            left_applied = self.left_value.map_leaf(function)
         except AttributeError:
             left_applied = function(self.left_value)
 
         try:
-            right_applied = self.right_value.apply(function)
+            right_applied = self.right_value.map_leaf(function)
         except AttributeError:
             right_applied = function(self.right_value)