

   CChhaannggee tthhee PPrriinntt MMooddee ttoo IInnvviissiibbllee

        invisible(expr)

   VVaalluuee::

        This function returns a (temporarily) invisible copy of
        its argument.  This can be useful when it is desired to
        have functions return values which can be assigned, but
        which do not print when they are not assigned.

   EExxaammpplleess::

        # These functions both return their argument
        # The value returned by the second does not print
        f1 <- function(x) x
        f2 <- function(x) invisible(x)

