body {base}

R Documentation

Access to and Manipulation of the Body of a Function

Description

Get or set the body of a function which is basically all of the function definition but its formal arguments (formals), see the ‘Details’.

Usage

body(fun = sys.function(sys.parent()))
body(fun, envir = environment(fun)) <- value

Arguments

fun	a function object, or see ‘Details’.
envir	environment in which the function should be defined.
value	an object, usually a language object: see section ‘Value’.

Details

For the first form, fun can be a character string naming the function to be manipulated, which is searched for from the parent frame. If it is not specified, the function calling body is used.

The bodies of all but the simplest are braced expressions, that is calls to {: see the ‘Examples’ section for how to create such a call.

Value

body returns the body of the function specified. This is normally a language object, most often a call to {, but it can also be a symbol such as pi or a constant (e.g., 3 or "R") to be the return value of the function.

The replacement form sets the body of a function to the object on the right hand side, and (potentially) resets the environment of the function, and drops attributes. If value is of class "expression" the first element is used as the body: any additional elements are ignored, with a warning.

See Also

The three parts of a (non-primitive) function are its formals, body, and environment.

Further, see alist, args, function.

Examples

body(body)
f <- function(x) x^5
body(f) <- quote(5^x)
## or equivalently  body(f) <- expression(5^x)
f(3) # = 125
body(f)

## creating a multi-expression body
e <- expression(y <- x^2, return(y)) # or a list
body(f) <- as.call(c(as.name("{"), e))
f
f(8)

## Using substitute() may be simpler than 'as.call(c(as.name("{",..)))':
stopifnot(identical(body(f), substitute({ y <- x^2; return(y) })))

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