parameters: (x,callback)
docstring: Traverse every node in the AST and run a callback(node,childrenNodes)
  
      For example: 
          ast=SeExprPy.AST(expr)
          allNodes=[]
          traverseCallback(ast.root(),lambda node,children: allNodes.append(node))
docstring_summary: Traverse every node in the AST and run a callback(node,childrenNodes)
docstring_tokens: Traverse every node in the AST and run a callback ( node childrenNodes )
function: def traverseCallback(x,callback):
      """Traverse every node in the AST and run a callback(node,childrenNodes)
  
      For example: 
          ast=SeExprPy.AST(expr)
          allNodes=[]
          traverseCallback(ast.root(),lambda node,children: allNodes.append(node))
      """
      children=x.children()
      callback(x,children)
      for childNode in children: traverseCallback(childNode,callback)
function_tokens: def traverseCallback ( x , callback ) : children = x . children ( ) callback ( x , children ) for childNode in children : traverseCallback ( childNode , callback )