HELP ISASSIGNABLE                           Jonathan Laventhol, August 1984.

    isassignable(<word>) -> <boolean>

The POP system won't let you assign to system identifers or initialised
constants (You'll get a 'COMPILING ILLEGAL ASSIGNMENT TO SYSTEM IDENTIFIER' or
'ILLEGAL ASSIGNMENT TO CONSTANT' mishap.)

If you want to find out if you can assign to an identifier, try this procedure
on its name:

        isassignable("if") =>
        ** <false>                  ;;; because it is protected

        vars x;
        isassignable("x") =>
        ** <true>                   ;;; ordinary variable

        constant c; 3 -> c;
        isassignable("c") =>
        ** <false>                  ;;; because it is initialised constant

See HELP * ISPROTECTED, *ISCONSTANT, *VARS