The ZWITHDRAW command KILLs the data value for a variable name without affecting the nodes descended from that node.
The format of the ZWITHDRAW command is:
The optional truth-valued expression immediately following the command is a command postconditional that controls whether or not GT.M executes the command.
The global or local variable name identifies the variable for which ZWITHDRAW removes the data value.
An indirection operator and an expression atom evaluating to a list of one or more ZWITHDRAW arguments form a legal argument for a ZWITHDRAW.
ZWITHDRAW provides a tool to quickly restore a node to a state where it has descendants and no value-- that is, where $DATA for that node will have a value of 10 -- for the case where such a state has some control meaning. GT.M also provides the ZKILL command, with functionality identical to ZWITHDRAW.
Kill A Set A="A",A(1)=1,A(1,1)=1 WRite $Data(A(1)),! ZWIthdraw A(1) WRite $D(A(1)),! ZWRite A Quit
produces the result:
11 10 A="A" A(1,1)=1
This sets up local variables A and A(1) and A(1,1). It then deletes the data for A(1) with ZWITHDRAW. The ZWRITE command shows ZWITHDRAW KILLed A(1) but left A and A(1,1).