These functions provide the base mechanisms for defining new functions in the R language.
function( arglist ) expr
Empty or one or more name or name=expression terms.
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
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.
The names in an argument list can be back-quoted non-standard names (see ‘backquote’).
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
value of the last evaluated expression is returned.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.