ANSI Common Lisp 14 Conses 14.2 Dictionary of Conses
- Arguments and Values:
list - a list,
which might be a dotted list or a circular list.
generalized-boolean - a generalized boolean.
Returns true if list is the empty list.
Returns false if list is a cons.
(endp nil) true
(endp '(1 2)) false
(endp (cddr '(1 2))) true
- Exceptional Situations:
Should signal an error of type type-error if list is not a list.
The purpose of endp is to test for the end of proper list.
Since endp does not descend into a cons,
it is well-defined to pass it a dotted list.
However, if shorter "lists" are iteratively produced
by calling cdr on such a dotted list
and those "lists" are tested with endp,
a situation that has undefined consequences will eventually result
when the non-nil atom (which is not in fact a list)
finally becomes the argument to endp.
Since this is the usual way in which endp is used,
it is conservative programming style
and consistent with the intent of endp
to treat endp as simply a function on proper lists
which happens not to enforce an argument type of proper list except
when the argument is atomic.
- Allegro CL Implementation Details: