function
Function Definition
These functions provide the base mechanisms for defining new functions in the R language.
- Keywords
- programming
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 is 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
library(base)
# NOT RUN {
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)
# }