These statements have the syntax
⟨assignment statement⟩ ::= ⟨expression⟩:=⟨expression⟩
The ⟨expression⟩ on the left side is normally the name of a variable, an operator symbol with its list of arguments filled in, or an array name with the proper number of integer subscript values within the array bounds. For example:
|a1 := b + c|
|h(l,m) := x-2*y||(where h is an operator)|
|k(3,5) := x-2*y||(where k is a 2-dim. array)|
More general assignments such as a+b := c are also allowed. The effect of these is explained in Section 11.2.5.
An assignment statement causes the expression on the right-hand-side to be evaluated. If the left-hand-side is a variable, the value of the right-hand-side is assigned to that unevaluated variable. If the left-hand-side is an operator or array expression, the arguments of that operator or array are evaluated, but no other simplification done. The evaluated right-hand-side is then assigned to the resulting expression. For example, if a is a single-dimensional array, a(1+1) := b assigns the value b to the array element a(2).
If a semicolon is used as the terminator when an assignment is issued as a command (i.e. not as a part of a group statement or procedure or other similar construct), the left-hand side symbol of the assignment statement is printed out, followed by a “:=”, followed by the value of the expression on the right.
It is also possible to write a multiple assignment statement:
In this form, each ⟨expression⟩ but the last is set to the value of the last ⟨expression⟩. If a semicolon is used as a terminator, each expression except the last is printed followed by a “:=” ending with the value of the last expression.
In some cases, it is desirable to perform an assignment in which both the left- and right-hand sides of an assignment are evaluated. In this case, the SET statement can be used with the syntax:
For example, the statements
assigns the value X to A23.
To remove a value from such a variable, the UNSET statement can be used with the syntax:
For example, the statement
clears the value of A23.