Conceptually, the task of generating an ACK message is a different task from complete message parsing and executing business logic.

For this reason a well-designed HL7 interface will keep the functionality required to implement ACK messages separate from the general message parsing logic.

It is recommended that you take advantage of the auto acknowledgement technique. This means that you will end up with at least two instances of the Chameleon engine. One should just be used to implement the generation of ACKs, while the other should be used to do the actual parsing of messages.