Thank you. I am looking into it. On Thu, Jan 27, 2011 at 5:05 PM, wrote:

It seems that the problem is to follow a protocol, reporting protocol errors (unexpected responses) and permitting recovery if the `supervisor' decided that the error can be fixed by re-reading from the server.

This problem -- specifically, communicating with a supervisor `out-of-band' and recovery -- is a good use case for delimited continuations.

The following code implements the scenario in Magicloud's message.   http://okmij.org/ftp/continuations/CCmonad/ProtocolRecovery.hs

Actually, the code is interactive, letting the use play a good or a bad server. One can see for themselves the effect of expected or unexpected responses. The title comments show the examples of good or bad interactions. Here is a sample transcript of several interactions.

ProtocolRecovery> main Client Connected sending: Req_hello Enter response, as a number 1..4 1 sending: Req_who_are_you Enter response, as a number 1..4 2 Client Dis-connected

ProtocolRecovery> main Client Connected sending: Req_hello Enter response, as a number 1..4 1 sending: Req_who_are_you Enter response, as a number 1..4 3 Exception: Err_bad_resp Res_debug DEBUG Enter response, as a number 1..4 3 Exception: Err_bad_resp Res_debug DEBUG Enter response, as a number 1..4 2 Client Dis-connected

*ProtocolRecovery> main Client Connected sending: Req_hello Enter response, as a number 1..4 1 sending: Req_who_are_you Enter response, as a number 1..4 4 Exception: Err_bad_resp Res_disconnect Aborting Client Dis-connected

*ProtocolRecovery> main Client Connected sending: Req_hello Enter response, as a number 1..4 1 sending: Req_who_are_you Enter response, as a number 1..4 1 Exception: Err_bad_resp Res_hello Really bad response! Client Dis-connected

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