Major Section: ACL2-BUILT-INS
Len returns the length of a list.
A Common Lisp function that is appropriate for both strings and
proper lists is
length; see length. The guard for
(Low-level implementation note. ACL2 provides a highly-optimized
len, which is tail-recursive and fixnum-aware, that
differs from its simple ACL2 definition.)
To see the ACL2 definition of this function, see pf.