

   IIss aann OObbjjeecctt AAttoommiicc oorr RReeccuurrssiivvee??

        is.atomic(x)
        is.recursive(x)

   DDeessccrriippttiioonn::

        `is.atomic' returns `TRUE' if `x' does not have a list
        structure and `FALSE' otherwise.

        `is.recursive' returns `TRUE' if `x' has a recursive
        (list-like) structure and `FALSE' otherwise.

   SSeeee AAllssoo::

        `is.list', `is.language', etc, and the
        `demo("is.things")'.

   EExxaammpplleess::

        is.a.r <- function(x) c(is.atomic(x), is.recursive(x))

        is.a.r(c(a=1,b=3))# TRUE FALSE
        is.a.r(list())    # FALSE TRUE ??
        is.a.r(list(2))   # FALSE TRUE
        is.a.r(lm)        #   "
        is.a.r(y ~ x)     #   "
        is.a.r(expression(x+1))# should be F-T (not in 0.62.3!)

