$ETRAP or $ZTRAP set to a DO command instructs GT.M to transfer execution temporarily to another line within this or another routine when it encounters an error. A QUIT command within the scope of the DO transfers control back to the code specified by the $ETRAP or $ZTRAP. When the code in the ISV terminates due to an explicit or implicit QUIT, the behavior of $ETRAP and $ZTRAP is different. When $ETRAP is in control, the level at which the error occurred is removed, and control returns to the invoking level. When $ZTRAP contains code, execution picks up at the beginning of the line with the error. A DO command within $ZTRAP is normally used for I/O errors that an operator may resolve, because a DO command permits re-execution of the line containing the error.

Example:

	GTM>ZPRINT ^EP6
	EP6WRITE !,"THIS IS "_$TEXT(+0)
	NEW
	NEW $ZTRAP SET $ZTRAP="DO ET"
	SET (CB,CE)=0
	BADSET CB=CB+1 WRITE A SET CE=CE+1
	WRITE !,"AFTER SUCCESSFUL EXECUTION OF BAD:",!
	ZWRITE
	SET 1="A IS NOT DEFINED"
	QUIT
	
	GTM>DO ^EP6
	
	THIS IS EP6
	CONTINUING WITH ERROR TRAP AFTER AN ERROR
	CB=1
	CE-0
	A IS NOT DEFINED
	AFTER SUCCESSFUL EXECUTION OF BAD:
	A="A IS NOW DEFINED"
	CB=2
	CE=1
	

This example sets $ZTRAP to a DO command. When the routine encounters an error in the middle of the line at label BAD, GT.M transfers control to label ET. After QUITting from routine ET, GT.M returns control to the beginning of the ine at label BAD.

Example:

		GTM>ZPRINT ^EP6A
		EP6AWRITE !,"THIS IS "_$TEXT(+0)
		NEW
		NEW $ETRAP SET $ETRAP="GOTO ET"
		SET (CB,CE)=0
		BADSET CB=CB+1 WRITE A SET CE=CE+1
		WRITE !,"AFTER SUCCESSFUL EXECUTION OF BAD:",!
		ZWRITE
		QUIT
		ETW !,"CONTINUING WITH ERROR TRAP AFTER AN ERROR",!
		ZWRITE
		SET A="A IS NOW DEFINED"
		SET RETRY=$STACK($STACK,"PLACE")
		SET $ECODE=""
		GOTO @RETRY
		
		GTM>DO EP6A
		
		THIS IS EP6A
		CONTINUING WITH ERROR TRAP AFTER AN ERROR
		CB=1
		CE=0
		A IS NOW DEFINED
		AFTER SUCCESSFUL EXECUTION OF BAD:
		A="A IS NOW DEFINED"
		CB=2
		CE=1
		RETRY="BAD^EP6A"
		
		GTM>	
	

This routine is an example of how $ETRAP handling can be coded to perform the same kind of resumtion of the original execution stream that occurs by default with $ZTRAP when there is no unconditional transfer of control.