1.13. Assignments and Symbols

A variable is an object whose value can change during the running of a Rexx program. The process of changing the value of a variable is called assigning a new value to it. The value of a variable is a single object. Note that an object can be composed of other objects, such as an array or directory object.

You can assign a new value to a variable with the ARG, PARSE, PULL, or USE instructions, or the VALUE built-in function, but the most common way of changing the value of a variable is the assignment instruction itself. Any clause in the form

symbol= expression;

is taken to be an assignment. The result of expression becomes the new value of the variable named by the symbol to the left of the equal sign.

Example:

/* Next line gives FRED the value "Frederic" */
Fred="Frederic"

The symbol naming the variable cannot begin with a digit (0-9) or a period.

You can use a symbol in an expression even if you have not assigned a value to it, because a symbol has a defined value at all times. A variable to which you have not assigned a value is uninitialized. Its value is the characters of the symbol itself, translated to uppercase (that is, lowercase a-z to uppercase A-Z). However, if it is a compound symbol (described in Section 1.13.5, “Compound Symbols”), its value is the derived name of the symbol.

Example 1.20. Derived symbol names

/* If Freda has not yet been assigned a value,   */
/* then next line gives FRED the value "FREDA"   */
Fred=Freda

The meaning of a symbol in Rexx varies according to its context. As a term in an expression, a symbol belongs to one of the following groups: constant symbols, simple symbols, compound symbols, environment symbols, and stems. Constant symbols cannot be assigned new values. You can use simple symbols for variables where the name corresponds to a single value. You can use compound symbols and stems for more complex collections of variables although the collection classes might be preferable in many cases. See Section 5.3.2, “Collection Class”.

Notes:

When the ARG, PARSE, PULL, or USE instruction, the VALUE built-in function, or the variable pool interface changes a variable, the effect is identical to an assignment.
Any clause that starts with a symbol and whose second token is (or starts with) an equal sign (=) is an assignment, rather than an expression (or a keyword instruction). This is not a restriction, because you can ensure that the clause is processed as a command, such as by putting a null string before the first name, or by enclosing the expression in parentheses.
If you unintentionally use a Rexx keyword as the variable name in an assignment, this should not cause confusion. For example, the following clause is an assignment, not an ADDRESS instruction:
```
Address="10 Downing Street";
```
You can use the VAR function to test whether a symbol has been assigned a value. In addition, you can set NOVALUE to trap the use of any uninitialized variables (except when they are tails in compound variables or stem variables, which are always initialized with a Stem object when first used.)