14.2.10 Macro Variable Assignment

The !LET construct evaluates an expression and assigns the result to a macro variable. It may create a new macro variable or change the value of one created by a previous !LET or !DO, but it may not change the value of a macro argument. !LET has the following form:

!LET !var = expression

If expression is more than one token, it must be enclosed in parentheses.