\Header{expression}{Unevaluated Expressions}
\alias{is.expression}{expression}
\alias{as.expression}{expression}
\alias{as.expression.default}{expression}
\keyword{programming}{expression}
\keyword{dplot}{expression}
\begin{Usage}
\begin{verbatim}
expression(...)

is.expression(expr)
as.expression(expr)
\end{verbatim}
\end{Usage}
\begin{Value}
\texttt{expression} returns a vector of mode \texttt{"expression"}
containing its arguments as unevaluated ``\link{call}s''.

\texttt{is.expression} returns \texttt{TRUE} if \texttt{expr} is
an expression object and \texttt{FALSE} otherwise.

\texttt{as.expression} attempts to coerce its argument
into an expression object.\end{Value}
\begin{SeeAlso}
\texttt{\Link{call}}, \texttt{\Link{eval}}, \texttt{\Link{function}}.
Further, \texttt{\Link{text}} and \texttt{\Link{legend}} for plotting math
expressions.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
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)
\end{ExampleCode}
\end{Examples}

