> Hi, I'm just starting out with Scheme (and Lisp) and am going through The
> Little Schemer.

> I'm confused, right at the beginning and wanted to ask, since this seems
> important (cf. The First Commandment)...

> lat? is defined in the book as

> (define lat?
>   (lambda (l)
>     (cond
>       ((null? l) #t)
>       ((atom? (car l)) (lat? (cdr l)))
>       (else #f))))

> This terminates with #t when l has become the empty list (and all its
> elements were atoms).

> However, it also evaluates to #t if given the empty list to start with.

> But atom? is defined as

> (define atom?
>   (lambda (x)
>     (and
>       (not (pair? x))
>       (not (null? x)))))

> which says that x must not be null.

> My attempt at lat? was

> (define lat?
>   (lambda (l)
>     (and
>       ((atom? (car l))
>       (or
>         (null? (cdr l))
>         (lat? (cdr l))))))

> which reads as "the first element is an atom and the rest is null, or a list
> of atoms". That works, except when given the empty list, where (car l) batfs.
> Which isn't much better than returning #t :-)

> [I've done a couple of days of Lisp where (car ()) => nil. In Scheme I don't
> even know how to *type* an empty list yet, so I'm using (cdr '(a)) or (lambda
> () ())]

> So. If you've got this far, I suppose the question is should lat? return #t
> for an empty list?