

   IIss aa VVaarriiaabbllee DDeeffiinneedd??

        exists(x, where =NULL, envir=sys.frame(sys.parent()), frame =NULL,
               mode = "any", inherits = TRUE)

   AArrgguummeennttss::

          x: a variable name (given as a quoted string).

   where, envir, frame: an environment to be searched.  By
             default this is the environment where the call to
             `envir' takes place.

       mode: the type of interest for the object.

   inherits: should the enclosing frames of the environment be
             inspected.

   DDeessccrriippttiioonn::

        This function looks to see if the name `x' has a value
        bound to it.  If `inherits' is `TRUE' and a value is
        not found for `x', then the parent frames of `envir'
        are searched until the name `x' is encountered. Warn-
        ing: This is the default behaviour for R but not for S.

        If `mode' is specified then only objects of that mode
        are sought.  The function returns `TRUE' if the vari-
        able is encountered and `FALSE' if not.

   SSeeee AAllssoo::

        `get'.

   EExxaammpplleess::

        ##  Define a substitute function if necessary:
        if(!exists("some.fun", mode="function"))
         some.fun <- function(x) { cat("some.fun(x)\n"); x }
        search()
        exists("ls", 2) # true even though ls is in pos=3
        exists("ls", 2, inherits=F) # false

