parameters: (self, fn, state=None)
docstring: Walks the tree of nodes, depth-first
docstring_summary: Walks the tree of nodes, depth-first
docstring_tokens: Walks the tree of nodes depth - first
function: def walk(self, fn, state=None):
          """ Walks the tree of nodes, depth-first """
          for e in self.e:
              e.walk(fn, state)
          fn(self, state)
function_tokens: def walk ( self , fn , state = None ) : for e in self . e : e . walk ( fn , state ) fn ( self , state )