\HeaderA{environment}{Environment Access}{environment}
\aliasA{.BaseNamespaceEnv}{environment}{.BaseNamespaceEnv}
\aliasA{.GlobalEnv}{environment}{.GlobalEnv}
\aliasA{baseenv}{environment}{baseenv}
\aliasA{emptyenv}{environment}{emptyenv}
\aliasA{environment<\Rdash}{environment}{environment<.Rdash.}
\aliasA{globalenv}{environment}{globalenv}
\aliasA{is.environment}{environment}{is.environment}
\aliasA{new.env}{environment}{new.env}
\aliasA{parent.env}{environment}{parent.env}
\aliasA{parent.env<\Rdash}{environment}{parent.env<.Rdash.}
\keyword{data}{environment}
\keyword{programming}{environment}
\begin{Description}\relax
Get, set, test for and create environments.
\end{Description}
\begin{Usage}
\begin{verbatim}
environment(fun = NULL)
environment(fun) <- value

is.environment(obj)

.GlobalEnv
globalenv()
.BaseNamespaceEnv

emptyenv()
baseenv()

new.env(hash = FALSE, parent = parent.frame())

parent.env(env)
parent.env(env) <- value
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{fun}] a \code{\LinkA{function}{function}}, a \code{\LinkA{formula}{formula}}, or
\code{NULL}, which is the default.
\item[\code{value}] an environment to associate with the function
\item[\code{obj}] an arbitrary \R{} object.
\item[\code{hash}] a logical, if \code{TRUE} the environment will be hashed
\item[\code{parent}] an environment to be used as the enclosure of the
environment created.
\item[\code{env}] an environment
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
Environments consist of a \emph{frame}, or collection of named
objects, and a pointer to an \emph{enclosing environment}.  The most
common example is the frame of variables local to a function call;
its enclosure is the environment where the function was
defined.  The enclosing environment is distinguished from the
\emph{parent frame}:  the latter (returned by
\code{\LinkA{parent.frame}{parent.frame}}) refers to the environment of the caller
of a function.

When \code{\LinkA{get}{get}} or \code{\LinkA{exists}{exists}} search an environment
with the default \code{inherits = TRUE}, they look for the variable
in the frame, then in the enclosing frame, and so on.

The global environment \code{.GlobalEnv}, more often known as the
user's workspace, is the first item on the search path.  It can also
be accessed by \code{globalenv()}.  On the search path, each item's
enclosure is the next item.

The object \code{.BaseNamespaceEnv} is the namespace environment for
the base package.  The environment of the base package itself is
available as \code{baseenv()}.  The ultimate enclosure of any environment
is the empty environment \code{emptyenv()}, to which nothing may
be assigned.
If one follows the \code{parent.env()} chain of enclosures back far
enough from any environment, eventually one reaches the empty
environment.

The replacement function \code{parent.env<-} is extremely dangerous as
it can be used to destructively change environments in ways that
violate assumptions made by the internal C code.  It may be removed
in the near future.

\code{is.environment} is generic: you can write methods to handle
specific classes of objects, see \LinkA{InternalMethods}{InternalMethods}.
\end{Details}
\begin{Value}
If \code{fun} is a function or a formula then \code{environment(fun)}
returns the environment associated with that function or formula.
If \code{fun} is \code{NULL} then the current evaluation environment is
returned.

The replacement form sets the environment of the function or formula
\code{fun} to the \code{value} given.

\code{is.environment(obj)} returns \code{TRUE} iff \code{obj} is an
\code{environment}.

\code{new.env} returns a new (empty) environment enclosed in the
parent's environment, by default.

\code{parent.env} returns the parent environment of its argument.

\code{parent.env<-} sets the enclosing environment of its first
argument.
\end{Value}
\begin{SeeAlso}\relax
The \code{envir} argument of \code{\LinkA{eval}{eval}}, \code{\LinkA{get}{get}},
and \code{\LinkA{exists}{exists}}.

\code{\LinkA{ls}{ls}} may be used to view the objects in an environment.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
f <- function() "top level function"

##-- all three give the same:
environment()
environment(f)
.GlobalEnv

ls(envir=environment(approxfun(1:2,1:2, method="const")))

is.environment(.GlobalEnv) # TRUE

e1 <- new.env(parent = baseenv())  # this one has enclosure package:base.
e2 <- new.env(parent = e1)
assign("a", 3, env=e1)
ls(e1)
ls(e2)
exists("a", env=e2)     # this succeeds by inheritance     
exists("a", env=e2, inherits = FALSE)
exists("+", env=e2)     # this succeeds by inheritance
\end{ExampleCode}
\end{Examples}

