Chain of packets in MathLink: are the packets always strictly ordered?

Question

The Documentation does not state clear the order of packets returned by slave kernel via MathLink. It is natural to suppose that (when sending an input expression with head EnterExpressionPacket and working in standard mode):

1) the last packet before the next InputNamePacket is always ReturnExpressionPacket

2) there may be always only one ReturnExpressionPacket and one OutputNamePacket for one EnterExpressionPacket

3) ReturnExpressionPacket is always the next after OutputNamePacket

4) after MessagePacket the next packet is always TextPacket with all contents of that message

5) there are only 7 types of returned packets in the standard mode: InputNamePacket, OutputNamePacket, ReturnExpressionPacket, DisplayPacket, DisplayEndPacket, MessagePacket, TextPacket.

Which of these statements are true?

Answer 1

• 1 is probably not guaranteed.
• 2 is definitely not true (evaluate: "2+2\n2+3").
• 3 is probably true but probably not guaranteed.
• I believe 4 is true.
• 5 is not guaranteed.

In general you should write your code to not rely on the order of packets coming from the kernel. The evaluation should be considered "active" until you receive a new InputNamePacket. OutputNamePacket should update some variable. ReturnExpressionPacket should use the current output name from that variable. If you receive an unknown packet simply ignore it and move on to the next packet.