R: Function Definition

function {base} | R Documentation

## Function Definition

### Description

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

### Usage

    function( 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.

### 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 it indicated when functions are printed.

### 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)

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