expression
Expression Objects

### Description

Creates or tests for objects of mode expression.

### Usage

    expression(...)
    is.expression(x)
    as.expression(x)
    ## Default S3 method:
    as.expression(x)

### Arguments

... | any valid expression. Not evaluated by the call to expression.
x | any object.

### Details

as.expression is a generic function, but currently there is only the default method.
Value

expression | returns an expression; that is, a list-like object of mode "expression". Its elements are the arguments, unsubstituted and unevaluated.
is.expression | returns TRUE if x has mode "expression". Otherwise it returns FALSE.
as.expression | changes the mode of x to "expression".

Background
The output from parse is of mode "expression".
References
Becker, R. A., Chambers, J. M., and Wilks, A. R. 1988. The New S Language. Pacific Grove, CA: Wadsworth & Brooks/Cole Advanced Books and Software.
See Also
eval, parse, substitute.
Examples

    x<-c(1,2,3)
    y<-c(2,4,6)
    mymethod <- expression(lsfit(x,y), rexp(1))
    eval(mymethod[[which(x == 1)]])
    rand.choice <- expression("Gaussian"=rnorm(1),"exp"=rexp(1),
       "uniform"=runif(1))
    eval(rand.choice[["exp"]])

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