

   UUnneevvaalluuaatteedd EExxpprreessssiioonnss

        expression(...)

        is.expression(expr)
        as.expression(expr)

   VVaalluuee::

        `expression' returns a vector of mode `"expression"'
        containing its arguments as unevaluated ``calls''.

        `is.expression' returns `TRUE' if `expr' is an expres-
        sion object and `FALSE' otherwise.

        `as.expression' attempts to coerce its argument into an
        expression object.

   SSeeee AAllssoo::

        `call', `eval', `function'.  Further, `text' and `leg-
        end' for plotting math expressions.

   EExxaammpplleess::

        length(ex1 <- expression(1+ 0:9))# 1
        ex1
        eval(ex1)# 1:10

        length(ex3 <- expression(u,v, 1+ 0:9))# 3
        mode(ex3 [3]) # expression
        mode(ex3[[3]])# call
        rm(ex3)

