# Constant Expressions

Constant expressions are a subset of the general class of expressions, restricted by the requirement that it be possible to evaluate the expression statically. All operations are legal in constant expressions except for `ADR`, `LOOPHOLE`, `TYPECODE`, `NARROW`, `ISTYPE`, `SUBARRAY`, `NEW`, dereferencing (explicit or implicit), and the only procedures that can be applied are the functions in the `Word` interface.

A variable can appear in a constant expression only as an argument to `FIRST`, `LAST`, `NUMBER`, `BITSIZE`, `BYTESIZE`, or `ADRSIZE`, and such a variable must not have an open array type. Literals and top-level procedure constants are legal in constant expressions.

    Last modified on Wed Apr  3 09:39:10 PST 1996 by heydon
         modified on Mon Apr 18 13:46:48 PDT 1994 by kalsow