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% File src/library/base/man/function.Rd
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% File src/library/base/man/function.Rd
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% Part of the R package, http://www.R-project.org
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% Part of the R package, http://www.R-project.org
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% Copyright 1995-2007 R Core Development Team
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% Copyright 1995-2012 R Core Development Team
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% Distributed under GPL 2 or later
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% Distributed under GPL 2 or later
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\name{function}
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\name{function}
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\alias{function}
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\alias{return}
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\alias{closure}
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\title{Function Definition}
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\title{Function Definition}
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\usage{
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\usage{
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\special{function( arglist ) expr}
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\special{function( arglist ) expr}
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\special{return(value)}
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\special{return(value)}
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}
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}
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\alias{function}
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\alias{return}
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\description{
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\description{
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  These functions provide the base mechanisms for defining
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  These functions provide the base mechanisms for defining
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  new functions in the \R language.
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  new functions in the \R language.
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}
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}
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\arguments{
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\arguments{
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    \item{arglist}{Empty or one or more name or name=expression terms.}
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    \item{arglist}{Empty or one or more name or name=expression terms.}
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    \item{expr}{An expression.}
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    \item{value}{An expression.}
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    \item{value}{An expression.}
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}
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}
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\details{
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\details{
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  The names in an argument list can be back-quoted non-standard names
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  The names in an argument list can be back-quoted non-standard names
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  (see \sQuote{\link{backquote}}).
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  (see \sQuote{\link{backquote}}).
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  \code{\link{on.exit}} expression is evaluated.)
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  \code{\link{on.exit}} expression is evaluated.)
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  If the end of a function is reached without calling \code{return}, the
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  If the end of a function is reached without calling \code{return}, the
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  value of the last evaluated expression is returned.
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  value of the last evaluated expression is returned.
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}
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}
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\section{Warning}{
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\section{Technical details}{
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  Prior to \R 1.8.0, \code{value} could be a series of non-empty
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  This type of function is not the only type in \R: they are called
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  expressions separated by commas.  In that case the value
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  \emph{closures} (a name with origins in LISP) to distinguish them from
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  \link{primitive} functions.
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  returned is a list of the evaluated expressions, with names set to
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  A closure has three components, its \code{\link{formals}} (its argument
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  the expressions where these are the names of \R objects.  That is,
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  list), its \code{\link{body}} (\code{expr} in the \sQuote{Usage}
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  \code{a=foo()} names the list component \code{a} and gives it the value
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  section) and its \code{\link{environment}} which provides the
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  which results from evaluating \code{foo()}.
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  enclosure of the evaluation frame when the closure is used.
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  This has been deprecated (and a warning is given), as it was never
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  There is an optional further component if the closure has been
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  documented in S, and whether or not the list is named differs by S
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  byte-compiled.  This is not normally user-visible, but it indicated
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  versions.  Supply a (named) list \code{value} instead.
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  when functions are printed.
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}
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}
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\seealso{
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\seealso{
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  \code{\link{args}}.
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  \code{\link{args}} and \code{\link{body}} for accessing the arguments
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  \code{\link{formals}}, \code{\link{body}} and
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  \code{\link{environment}} for accessing the component parts of a
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  and body of a function.
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  function.
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  \code{\link{debug}} for debugging; using \code{\link{invisible}} inside
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  \code{\link{debug}} for debugging; using \code{\link{invisible}} inside
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  \code{return(.)} for returning \emph{invisibly}.
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  \code{return(.)} for returning \emph{invisibly}.
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}
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}
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\references{
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\references{