

   FFuunnccttiioonnss ttoo aacccceessss tthhee ffuunnccttiioonn ccaallll ssttaacckk..

        sys.call(which=<<see below>>)
        sys.frame(which=<<see below>>)
        sys.nframe()
        sys.function(n=<<see below>>)
        sys.parent(n=1)

        sys.calls()
        sys.frames()
        sys.parents()
        sys.on.exit()
        sys.status()

   AArrgguummeennttss::

      which: the frame number.

          n: the number of frame generations to go back.

   DDeessccrriippttiioonn::

        These functions provide access to `environment's
        (``frames'' in S-speak) associated with functions fur-
        ther up the calling stack.

   SSeeee AAllssoo::

        `eval' for the usage of `sys.frame'.

   EExxaammpplleess::

        ff <- function(x) gg(x)
        gg <- function(y) sys.status()
        str(ff(1))

