The schema doesn't seem to match the structure of the message you've supplied; the OBRuniongrp group should be a repeating group and indicate such with parentheses (i.e. OBRuiniongrp()). Assuming that's fixed in the schema, you should be able to get at the fields in question in repeating OBR segments with something like:

Set tStudy = 0
// Get count of OBR segments
Set tOBRCnt = request.GetValueAt("ORCgrp(1).OBRuniongrp(*)")
// Loop through OBRs and evaluate field contents
For tIter = 1:1:tOBRCnt
{
   If request.GetValueAt("ORCgrp(1).OBRuniongrp("_tIter_").OBRunion.OBR:UniversalServiceIdentifier.Identifier") = "match_value"
   {
      Set tStudy = 1
   }
}
If tStudy
{
   ...insert action to take here...
}

The above may need to be modified to use context variables if it's being used in a BPL.

Rather than:

s target.{ORCgrp(k1).OBRgrp(k2).OBXgrp(k3).NTE(iNteCnt)} sTmp

Try:

d target.SetValueAt(iNteCnt, "ORCgrp("_k1_").OBRgrp("_k2_").OBXgrp("_k3_").NTE("_iNteCnt_"):1")
d target.SetValueAt(sTmp, "ORCgrp("_k1_").OBRgrp("_k2_").OBXgrp("_k3_").NTE("_iNteCnt_"):3")

Assuming you want the value in the 3rd field of the NTE. You should also change the value stored in sNTE to:

source.{ORCgrp(k1).OBRgrp(k2).OBXgrp(k3).NTE(1):3}

If there's only one NTE segment in each OBXgrp of the the inbound message.

Building an interface in Ensemble would require essentially emulating the printing protocol used by Meditech (lpr/lpd?). While that might be fun, I don't know that it's the best use of your time

Depending on your OS platform, it might be possible to route Meditech's printer output to files. This would be done by configuring a custom printer definition on either the Ensemble host or a host that Ensemble has file (ftp/sftp/cifs/etc.) access to. For Unix/Linux, this isn't terribly hard to do with lpd, and I imagine it can be done with CUPS as well.

I know Windows can function as an lpd server, but I'm not sure how you would get its output routed to a file.

Once the printed output is in file form, you could then create a file service in Ensemble to pick up and process it.

The documentation is available both in the DTL editor when you use the Exists() method in the Expression Editor for a rule:

And in the Class Reference for Ens.Rule.FunctionSet -- the Exists() Method:

The Class reference is clearer about the table argument being a quoted string.

Did you get an actual compilation error, or just an error indicator in the expression editor?

In my case, the dialog box shows the expression indicated an error, but it doesn't cause a compilation problem.

I don't have any sample messages to test with at the moment, so I'm not sure it will actually work ...

I set up a test scenario based on your criteria. I created a service, HL7 router process and 3 operations:

Service: HL7 MLLP, target HL7 Router, AckMode=Application

Process: HL7 Router, ForceSyncSend: True, ReplyCodeActions: E=F

Target Operation 1: HL7 File Out

Target Operation 2: Custom Operation that returns an HL7 NAK, sets IsError to 1, logs an error code of 5001 with text "Forced NAK", ReplyCodeActions: E=F

Target Operation 3: HL7 File Out

Observations:

1. Message arrives in router process
2. Routes to Operation 1, completes successfully
3. Routes to Operation 2, receives error
4. Router responds to Service with Error; shuts down ... no message delivered to Operation 3
5. Service returns NAK to sending application
6. Message remains queued for Router

Isn't this what you would want to happen?

Seems to work fine if you route the ACK to another Business Process. For the router handling messages from an inbound service:

Response comes in from TestTCPOut; the received ACK is sent to the original service and forwarded to a BP called AckWrangler. That BP runs a routing rule that optionally transforms the ACK and passes it off to another operation called AckTarget: