function Function Definition

Description

These functions provide the base mechanisms for defining new functions in the R language.

Usage

function( arglist ) expr
\( arglist ) expr
return(value)

Arguments

arglist	Empty or one or more name or name=expression terms.
expr	An expression.
value	An expression.

Details

The names in an argument list can be back-quoted non-standard names (see ‘backquote’).

If value is missing, NULL is returned. If it is a single expression, the value of the evaluated expression is returned. (The expression is evaluated as soon as return is called, in the evaluation frame of the function and before any on.exit expression is evaluated.)

If the end of a function is reached without calling return, the value of the last evaluated expression is returned.

The shorthand form \(x) x + 1 is parsed as function(x) x + 1. It may be helpful in making code containing simple function expressions more readable.

Technical details

This type of function is not the only type in R: they are called closures (a name with origins in LISP) to distinguish them from primitive functions.

A closure has three components, its formals (its argument list), its body (expr in the ‘Usage’ section) and its environment which provides the enclosure of the evaluation frame when the closure is used.

There is an optional further component if the closure has been byte-compiled. This is not normally user-visible, but is indicated when functions are printed.

Note

The shorthand function notation is experimental and may change prior to release.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

args.

formals, body and environment for accessing the component parts of a function.

debug for debugging; using invisible inside return(.) for returning invisibly.

Examples

norm <- function(x) sqrt(x%*%x)
norm(1:4)

## An anonymous function:
(function(x, y){ z <- x^2 + y^2; x+y+z })(0:7, 1)