[R] bug: Editing function formals deletes the environment

[Gabor Grothendieck]

If you are just modifying an S3 method in a package you may not need to reinsert
the method into the package since UseMethod first looks into the
caller environment
for methods anyways and only second does it look for methods in the
package.  Thus:

   HTML.data.frame <- R2HTML:::HTML.data.frame
   HTML.data.frame$Border <- 2
   HTML(BOD, file = file("clipboard", "w"), append = FALSE)

would be sufficient if you intend to call HTML.

There is one significant caveat.  If you intend to call a function in
R2HTML which in
turn calls HTML then the above would not be enough.  You would also
have to modify
the environment of the caller too.

Thus after running the above:

   HTML2clip(BOD)

would still get the old Border since we are calling HTML2clip which in
turn calls
HTML (as opposed to calling HTML directly).   In this case, we would
need to create
a new HTML2clip with a reset environment too:

   HTML2clip <- R2HTML:::HTML2clip
   environment(HTML2clip) <- environment()
   HTML2clip(BOD)

would get the Border=2 value.

On 10/13/06, Alex Brown <alex at transitive.com> wrote:
> First, here's the specific bug I have.  Later I'll say why I care.
>
>  > ls(zappo)
> Error in try(name) : object "zappo" not found
> # good.
>  > f = function(zappo) { function(y) zappo + y }
>  > g = f(1)
>  > g(1)
> [1] 2
>
>  > formals(g)
> $y
>
>  > formals(g)$y
>  > formals(g)$y = 2
>  > g
> function (y = 2)
> zappo + y
>  > g(1)
> Error in g(1) : object "zappo" not found
>
> # looks like formals strips the environment off stuff.
>
> anything I can do about this?
>
> -Alex
>
>
> Original question:
>
> I'm trying to change the behaviour of a package, to simplify the
> interface.
>
> I'd rather not change the package, although I could.
>
> There's a hidden function whose defaults I wish to change.
>
> I'm using R 2.3.1 for macosX.  Upgrading is not an option.
>
> This is what I do:
>
> library(R2HTML)
>
> # get the function to modify
> x = getFromNamespace("HTML.data.frame", "R2HTML")
> # change the default for an argument
> formals(x)["Border"]=list(NULL)
> # put the function back
> assignInNamespace("HTML.data.frame", x, "R2HTML")
>
> #test the function:
>
> HTML(data.frame(1:2), file=stdout())
>
> Error: could not find function "HTMLReplaceNA"
>
> # what seems to be happening is that the formals function is
> stripping the namespace off the variable x.  I can't tell why.
>
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