$ZL[EVEL] contains an integer value indicating the "level of nesting" caused by DO commands, XECUTE commands, and extrinsic functions in the M invocation stack.

$ZLEVEL has an initial value of one (1) and increments by one with each DO, XECUTE or extrinsic function. Any QUIT that does not terminate a FOR loop decrements $ZLEVEL. ZGOTO may also reduce $ZLEVEL. In accordance with the M standard, a FOR command does not increase $ZLEVEL. M routines cannot modify $ZLEVEL with the SET or NEW commands.

Use $ZLEVEL in debugging or in an error-handling mechanism to capture a level for later use in a ZGOTO argument.

Example:

GTM>zprint ^zleve
zleve;
 do B
 write X,!
 quit
B
 goto C
 quit
C
 do D
 quit
D
 set X=$ZLEVEL
 quit
GTM>do ^zleve
4
GTM>

This program, executed from Direct Mode, produces a value of 4 for $ZLEVEL. If you run this program from the shell, the value of $ZLEVEL is three (3).