Method iter_subtrees_topdown added

docs/classes.md

@@ -76,7 +76,11 @@ Returns all nodes of the tree whose data equals the given data.
 
 #### iter_subtrees(self)
 
-Iterates over all the subtrees, never returning to the same node twice (Lark's parse-tree is actually a DAG)
+Iterates over all the subtrees, never returning to the same node twice (Lark's parse-tree is actually a DAG).
+
+#### iter_subtrees_topdown(self)
+
+Iterates over all the subtrees, return nodes in order like pretty() does.
 
 #### \_\_eq\_\_, \_\_hash\_\_
 

lark/tree.py

@@ -5,6 +5,7 @@ except ImportError:
 
 from copy import deepcopy
 
+
 ###{standalone
 class Meta:
     pass
@@ -42,6 +43,7 @@ class Tree(object):
 
     def pretty(self, indent_str='  '):
         return ''.join(self._pretty(0, indent_str))
+
     def __eq__(self, other):
         try:
             return self.data == other.data and self.children == other.children
@@ -99,12 +101,25 @@ class Tree(object):
                 yield x
                 seen.add(id(x))
 
+    def iter_subtrees_topdown(self):
+        if not self.children:
+            return self
+
+        stack = [self]
+        while stack:
+            node = stack.pop()
+            if not isinstance(node, Tree):
+                continue
+            yield node
+            for n in reversed(node.children):
+                stack.append(n)
 
     def __deepcopy__(self, memo):
         return type(self)(self.data, deepcopy(self.children, memo))
 
     def copy(self):
         return type(self)(self.data, self.children)
+
     def set(self, data, children):
         self.data = data
         self.children = children