

   IIss aann OObbjjeecctt aa LLaanngguuaaggee OObbjjeecctt??

        is.language(x)

   DDeessccrriippttiioonn::

        `is.language' returns `TRUE' if `x' is either a vari-
        able `name', a `call', or an `expression'.

   EExxaammpplleess::

        ll <- list(a=expression(x^2 - 2*x + 1), b= as.name("Jim"),
                c=as.expression(exp(1)), d=call("sin",pi))
        sapply(ll, typeof)
        sapply(ll, mode)
        sapply(ll, is.language)# all TRUE

