expression(expr) expression(expr, ...) is.expression(expr) as.expression(expr)
expression
returns a symbolic (unevaluated) version of that argument.
If passed multiple arguments,
expression returns a symbolic compound expression, consisting
of the symbolic form of the arguments
grouped with \{ and \}.
is.expression returns true if expr is an object of mode language
and false otherwise.
as.expression is unused. It doesn''t make sense to assign mode expression
to an arbitrary object.