Define "local" function

I discovered a bug in a program I am writing which was due to the
program using a global variable within a function.

For example,

myfunc <- function(x) { y}

That is, I made a mistake when defining the function and wrote "y"
when I should have written "x".

However, there was a variable y in the global environment and the
function "worked" but gave the wrong answer.

I would like to avoid this problem by defining a "local" function.
That would mean a function that only accepts as variables those that
were defined within its body or were passed as parameters, and would
generate an error when I try to define it if I am using an "external"
variable. Something like:

myfunc <- function(x, type = 'local') { y}

Error: using external variable
 
I read the documentation about environments (I still do not understand
a lot of it, have been working with R for four days now), and searched
the newsgroups, but I could not find the way to do this.

Thanks for any suggestions.

FS

I discovered a bug in a program I am writing which was due to the
program using a global variable within a function.

For example,

myfunc <- function(x) { y}

That is, I made a mistake when defining the function and wrote "y"
when I should have written "x".

However, there was a variable y in the global environment and the
function "worked" but gave the wrong answer.

I would like to avoid this problem by defining a "local" function.
That would mean a function that only accepts as variables those that
were defined within its body or were passed as parameters, and would
generate an error when I try to define it if I am using an "external"
variable. Something like:

myfunc <- function(x, type = 'local') { y}

Error: using external variable

I read the documentation about environments (I still do not understand
a lot of it, have been working with R for four days now), and searched
the newsgroups, but I could not find the way to do this.

Thanks for any suggestions.

y <- 3
f <- function(x) y
environment(f) <- NULL
f(1)

On 4/15/05, Fernando Saldanha <fsaldan1 at gmail.com> wrote:

I discovered a bug in a program I am writing which was due to the
program using a global variable within a function.

For example,

myfunc <- function(x) { y}

That is, I made a mistake when defining the function and wrote "y"
when I should have written "x".

However, there was a variable y in the global environment and the
function "worked" but gave the wrong answer.

I would like to avoid this problem by defining a "local" function.
That would mean a function that only accepts as variables those that
were defined within its body or were passed as parameters, and would
generate an error when I try to define it if I am using an "external"
variable. Something like:

myfunc <- function(x, type = 'local') { y}

Error: using external variable

I read the documentation about environments (I still do not understand
a lot of it, have been working with R for four days now), and searched
the newsgroups, but I could not find the way to do this.

Thanks for any suggestions.

Try this:

y <- 3
f <- function(x) y
environment(f) <- NULL
f(1)

Error in f(1) : Object "y" not found

I am also very interested how this could be done, possibly in such a way
that this would be incorporated in the function itself and there wouldn't be
a need to write "environment(f) <- NULL" before calling a function, as is
proposed in the reply below and in a thread a few days ago!

Thanks for any suggestions,
Ales Ziberna

----- Original Message -----
From: "Gabor Grothendieck" <ggrothendieck at gmail.com>
To: <fsaldanha at alum.mit.edu>
Cc: "Submissions to R help" <r-help at stat.math.ethz.ch>
Sent: Friday, April 15, 2005 5:05 PM
Subject: Re: [R] Define "local" function

On 4/15/05, Fernando Saldanha <fsaldan1 at gmail.com> wrote:

I discovered a bug in a program I am writing which was due to the
program using a global variable within a function.

For example,

myfunc <- function(x) { y}

That is, I made a mistake when defining the function and wrote "y"
when I should have written "x".

However, there was a variable y in the global environment and the
function "worked" but gave the wrong answer.

I would like to avoid this problem by defining a "local" function.
That would mean a function that only accepts as variables those that
were defined within its body or were passed as parameters, and would
generate an error when I try to define it if I am using an "external"
variable. Something like:

myfunc <- function(x, type = 'local') { y}

Error: using external variable

I read the documentation about environments (I still do not understand
a lot of it, have been working with R for four days now), and searched
the newsgroups, but I could not find the way to do this.

Thanks for any suggestions.

Try this:

y <- 3
f <- function(x) y
environment(f) <- NULL
f(1)

Error in f(1) : Object "y" not found

I am also very interested how this could be done, possibly in such a
way that this would be incorporated in the function itself and there
wouldn't be a need to write "environment(f) <- NULL" before calling a
function, as is proposed in the reply below and in a thread a few days
ago!

f <- function(){mean(rnorm(10))}
environment(f)<-NULL
f()

Ales Ziberna <ales.ziberna at guest.arnes.si> writes:

I am also very interested how this could be done, possibly in such a
way that this would be incorporated in the function itself and there
wouldn't be a need to write "environment(f) <- NULL" before calling a
function, as is proposed in the reply below and in a thread a few days
ago!

Notice BTW, that environment(f) <- NULL may have unexpected
consequences. What it really means is that the lexical scope of f
becomes the base package. This interpretation of NULL may change in
the future, since it is somewhat illogical and it has a couple of
undesirable consequences that there's no way to specify a truly empty
environment. So

a) if you're calling a function outside of the base package, you get
the effect of

f <- function(){mean(rnorm(10))}
environment(f)<-NULL
f()

Error in mean(rnorm(10)) : couldn't find function "rnorm"

b) even if it does work now, it may be broken by a future change to R.
Notice that *all* functions contain unbound variables in the form of
functions so if we get an empty NULL environment, even "<-" may stop
working.