function approveAndCall(
  address _spender,
  uint256 _value,
  bytes _extraData
) public returns (bool success) {
  allowed[msg.sender][_spender] = _value;
  Approval(msg.sender, _spender, _value);

  //call the receiveApproval function on the contract you want to be notified. This crafts the function signature manually so one doesn't have to include a contract in here just for this.
  //receiveApproval(address _from, uint256 _value, address _tokenContract, bytes _extraData)
  //it is assumed that when does this that the call *should* succeed, otherwise one would use vanilla approve instead.
  if (
    !_spender.call(
      bytes4(
        bytes32(keccak256("receiveApproval(address,uint256,address,bytes)"))
      ),
      msg.sender,
      _value,
      this,
      _extraData
    )
  ) {
    throw;
  }
  return true;
}