$ZPOS[ITION] contains a string value specifying the current entryref, where entryref is [label][+offset]^routine, and the offset is evaluated from the closest preceding label.
GT.M does not permit the SET or NEW commands to modify $ZPOSITION.
GTM>WRITE !,$ZPOS,! ZPRINT @$ZPOS
This example displays the current location followed by the source code for that line.