Network-Level self-checking scripts

Although the message-level IF statement is a fundamental part of self-checking scripts, you can code network-level IF statements to enhance the self-checking qualities of your scripts further and to reduce the size of the TEXT-IF-WAIT blocks in your message generation decks, as shown in the following example 
NET1  NTWRK
*                 Sample WSim Script
*   This script illustrates using network IF statements to reduce the
*   size of message generation decks.
*
*                                    Beginning of NET1.
SEND  IF   LOC=D+0,TEXT=(ANYTHING),
           THEN=WAIT,ELSE=WAIT,
           WHEN=OUT
RECV  IF   LOC=D+0,TEXT=RESP,
           SCAN=YES,THEN=CONT,
           ELSE=CERROR,WHEN=IN
       .
       .                             Network definition statements.
       .
DECK1 MSGTXT
*                                    Beginning of DECK1.
MSG1  TEXT  (MESSAGE 1),             Defines MSG1.
            RESP=(REPLY 1)
MSG2  TEXT  (MESSAGE 2),             Defines MSG2.
            RESP=(REPLY 2)
       .
       .                             Message generation statements.
       .
      ENDTXT                         End of DECK1.
ERROR MSGTXT
*                                    Beginning of ERROR deck.
      WTO   (EXPECTED RESPONSE ),
            (NOT RECEIVED. ),
            (PLEASE HELP!)           Message to operator.
WAIT1 WAIT
      ENDTXT                         End of ERROR deck.

WSim evaluates network-level IF statements SEND and RECV for every message sent and received by all terminals in the network. The following steps describe the sequence of events in message generation for the preceding example:

Steps:
  1. When WSim sends MSG1, IF statement SEND puts the terminal into a wait state. The RESP=(REPLY 1) operand on the TEXT statement indicates the expected response to this request.
  2. The terminal waits until WSim receives a message.
  3. IF statement RECV checks the message received and determines if the expected response REPLY 1 exists anywhere in the data stream. If so, THEN=CONT resets the WAIT indicator and enables the terminal to continue and send MSG2.
  4. If the expected response did not exist in the message received, IF statement RECV causes WSim to take the ELSE=CERROR action. CERROR specifies that WSim calls (C) the message generation deck named ERROR. This message generation deck notifies the operator that WSim did not receive the expected response. In fact, you could have set up this message generation deck to perform various error recovery actions, relieving the operator of manual intervention.
When you code IF statements along with message generation statements such as TEXT, WAIT and WTO, you can create many types of self-checking scripts. The type of self-checking script you decide to code may depend on the considerations discussed in the following sections.
Parent topic: Creating self-checking scripts