CM_MATCHES_BITS_IN_COMMON in scm.h for more information.
 *
 * scm_is_lisp_false(x) returns 1 if and only if x is one of the
 * following: SCM_BOOL_F, SCM_ELISP_NIL, SCM_EOL or
 * SCM_XXX_ANOTHER_LISP_FALSE_DONT_USE.  Otherwise, it returns 0.
 */
#define scm_is_lisp_false(x)  \
  (SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_F, SCM_EOL))