.BG
.FN expression
.FN as.expression
.FN is.expression
.TL
Expression Objects
.CS
expression(...)
as.expression(x)
is.expression(x)
.AG ...
any valid S expressions.  They will
.I not
be evaluated by the call to
`expression'.
.AG x
an S object.
.RT
an expression, that is, an object of mode `"expression"'.
Its elements are the arguments, unsubstituted and unevaluated.
.PP
`as.expression' merely changes the mode of `x' to `"expression"'.
`is.expression' tests whether `x' is a expression.
.SA
`eval', `parse', `substitute'.
.EX
methods \(<- expression(lsfit(x,y),l1fit(x,y))
eval(methods[[which]])
.KW programming
.WR
