Classic BASIC Names

Early versions of BASIC supported only a very limited namespace for
program objects. Some versions (e.g. Dartmouth BASIC) impose the
additional restriction of using the same namespace for variables and
arrays, i.e. a given name can be used for a variable or an array but
not both.

* Numeric Variables

- [A-Z]         (26)
- [A-Z][0-9]    (260)

* String Variables

- [A-Z]$        (26)

* Numeric Arrays

- [A-Z]()       (26)
- [A-Z][0-9]()  (260)

* String Arrays

- [A-Z]$()      (26)

* Numeric Functions

- FN[A-Z]()     (26)

* String Functions

- FN[A-Z]$()    (26)