Drop instruction

drop variableList    where:   variableList is one or more symbol names separated by spaces. When a symbol name is enclosed in parentheses it is a special reference variable as described in the variable reference section below.

The drop instruction removes one or more variables. The value of these variables becomes unassigned.

Note: when the drop instruction removes variables that are exposed, in the current procedure context, the variables removed from a calling procedure context.

The variables being removed can be one of the following:

1. simple variable -- N, X, first_name

This removes a simple variable. The value of the symbol becomes its name in upper case.

2. compound variable -- color.favorite, array.N

This removes a compound variable, associated with its derived name. Assume N has a value 7, when array.N is dropped, then the variable that is removed is ARRAY.7. However, if N was not previously assigned then the variable that is removed is ARRAY.N. After a compound variable is dropped, its value is its derived name.

3. compound stem variable -- color., array.

When a compound stem variable is removed, that variable and all compound variables that begin with the stem are removed. The value of the removed stem symbol is its name in upper case. The values of the removed compound variables are their derived names.

Click here to review how Rexx variables are used.

Variable reference

Within the list of variables that are being dropped, one additional capability can be used. A variable name can be enclosed in parentheses. This removes the specific variable, and addition its value is used as a subsidiary list. The list consists of a series of variable names separated by spaces. Each of these are removed in sequence from left to right.

Note: the variable reference capability was added in language level 4.0 (TRL-2). Thus, this capability may be absent in some Rexx implementations.

Here is a simple example of the use of a variable reference in a drop instruction.

/* main procedure */ varlist = 'a b c' call getvalues say a b c drop (varlist) /* this removes varlist and the variables a, b, and c */ return 0 getvalues : procedure expose (varlist) parse value 'abra ca dabra' with a b c return