[Rd] External special functions (SPECIALSXP)
Is it possible to define an external special function (SPECIALSXP)? I'm trying to do some language-level work, and don't want my arguments evaluated before they hit C. It looks like the only way to define a SPECIALSXP is by using XX0 in the `eval' field of R_FunTab; is there any way to make this applicable to externally defined functions? __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] External special functions (SPECIALSXP)
On 25/05/2011 1:10 PM, Peter Danenberg wrote:
Is it possible to define an external special function (SPECIALSXP)?
I'm trying to do some language-level work, and don't want my arguments
evaluated before they hit C.
It looks like the only way to define a SPECIALSXP is by using XX0 in
the `eval' field of R_FunTab; is there any way to make this applicable
to externally defined functions?
I don't think so. However, if you don't want to evaluate the arguments,
just pass substitute(arg) to your function instead of arg. For example,
f <- function(a, b) {
print(substitute(b))
print(substitute(a))
}
f( x <- 1, y <- 2 )
will print but never evaluate the assignments.
Duncan Murdoch
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Re: [Rd] External special functions (SPECIALSXP)
> However, if you don't want to evaluate the arguments, just pass
> substitute(arg) to your function instead of arg.
Thanks, Duncan; the problem is, I'm trying to substitute on `...' and
I don't think I can access `...' without inadvertently evaluating it.
I'm trying to write a debugging function which, given any number of
expressions, prints the expression next to its evaluation.
This is trivial to do in the single arity case:
debug <- function(expression) {
cat(substitute(expression), expression, "\n")
}
a <- 2
debug(a)
a 2
but I'm not sure how to make it work with variable arity without
resorting to SPECIALSXP.
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Re: [Rd] External special functions (SPECIALSXP)
> f <- function(...) {
+ dotArgList <- substitute(list(...))
+ dotArgList
+ }
> f(cat("foo\n"), stop("Oops"), warning("Hmm"))
list(cat("foo\n"), stop("Oops"), warning("Hmm"))
> # i.e., no argument was evaluated
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -Original Message-
> From: r-devel-boun...@r-project.org
> [mailto:r-devel-boun...@r-project.org] On Behalf Of Peter Danenberg
> Sent: Wednesday, May 25, 2011 11:06 AM
> To: Duncan Murdoch
> Cc: r-devel@r-project.org
> Subject: Re: [Rd] External special functions (SPECIALSXP)
>
> > However, if you don't want to evaluate the arguments, just pass
> > substitute(arg) to your function instead of arg.
>
> Thanks, Duncan; the problem is, I'm trying to substitute on `...' and
> I don't think I can access `...' without inadvertently evaluating it.
>
> I'm trying to write a debugging function which, given any number of
> expressions, prints the expression next to its evaluation.
>
> This is trivial to do in the single arity case:
>
> debug <- function(expression) {
> cat(substitute(expression), expression, "\n")
> }
>
> a <- 2
> debug(a)
>
> a 2
>
> but I'm not sure how to make it work with variable arity without
> resorting to SPECIALSXP.
>
> __
> R-devel@r-project.org mailing list
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>
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Re: [Rd] External special functions (SPECIALSXP)
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -Original Message-
> From: William Dunlap
> Sent: Wednesday, May 25, 2011 11:20 AM
> To: 'Peter Danenberg'
> Cc: r-devel@r-project.org
> Subject: RE: [Rd] External special functions (SPECIALSXP)
>
> > f <- function(...) {
> + dotArgList <- substitute(list(...))
> + dotArgList
> + }
> > f(cat("foo\n"), stop("Oops"), warning("Hmm"))
> list(cat("foo\n"), stop("Oops"), warning("Hmm"))
> > # i.e., no argument was evaluated
Or, if you'd prefer a pairlist over a call to list:
> fp <- function(...) {
+ dotArgList <- substitute(...())
+ dotArgList
+ }
> fp(message=cat("foo\n"), error=stop("Oops"),
possibleProblem=warning("Hmm"))
$message
cat("foo\n")
$error
stop("Oops")
$possibleProblem
warning("Hmm")
> class(.Last.value)
[1] "pairlist"
I would not have thought of this syntax myself but have
seen it in other folks' code.
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
> > -Original Message-
> > From: r-devel-boun...@r-project.org
> > [mailto:r-devel-boun...@r-project.org] On Behalf Of Peter Danenberg
> > Sent: Wednesday, May 25, 2011 11:06 AM
> > To: Duncan Murdoch
> > Cc: r-devel@r-project.org
> > Subject: Re: [Rd] External special functions (SPECIALSXP)
> >
> > > However, if you don't want to evaluate the arguments, just pass
> > > substitute(arg) to your function instead of arg.
> >
> > Thanks, Duncan; the problem is, I'm trying to substitute on
> `...' and
> > I don't think I can access `...' without inadvertently
> evaluating it.
> >
> > I'm trying to write a debugging function which, given any number of
> > expressions, prints the expression next to its evaluation.
> >
> > This is trivial to do in the single arity case:
> >
> > debug <- function(expression) {
> > cat(substitute(expression), expression, "\n")
> > }
> >
> > a <- 2
> > debug(a)
> >
> > a 2
> >
> > but I'm not sure how to make it work with variable arity without
> > resorting to SPECIALSXP.
> >
> > __
> > R-devel@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
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Re: [Rd] External special functions (SPECIALSXP)
On 25/05/2011 2:05 PM, Peter Danenberg wrote:
> However, if you don't want to evaluate the arguments, just pass
> substitute(arg) to your function instead of arg.
Thanks, Duncan; the problem is, I'm trying to substitute on `...' and
I don't think I can access `...' without inadvertently evaluating it.
I'm trying to write a debugging function which, given any number of
expressions, prints the expression next to its evaluation.
This is trivial to do in the single arity case:
debug<- function(expression) {
cat(substitute(expression), expression, "\n")
}
a<- 2
debug(a)
a 2
but I'm not sure how to make it work with variable arity without
resorting to SPECIALSXP.
I suppose you can do a clunky workaround like this:
debug <- function(e1, e2, sentinel) {
e1 <- if(!missing(e1)) substitute(e1)
e2 <- if(!missing(e2)) substitute(e2)
if (!missing(sentinel)) stop("this function only handles 2
expressions")
print(e1)
print(e2)
}
(but use some finite limit that's more than 2).
Duncan Murdoch
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Re: [Rd] External special functions (SPECIALSXP)
Quoth William Dunlap on Setting Orange, the 72nd of Discord:
> > f <- function(...) {
> + dotArgList <- substitute(list(...))
> + dotArgList
> + }
> > f(cat("foo\n"), stop("Oops"), warning("Hmm"))
> list(cat("foo\n"), stop("Oops"), warning("Hmm"))
> > # i.e., no argument was evaluated
Thanks, William! Something like this works perfectly:
> debug <- function(...) {
+ promises <- as.list(substitute(list(...)))[-1]
+ str(structure(Map(eval, promises),
+ names=Map(deparse, promises)))
+ }
>
> a <- 2
> debug(a, a + a)
List of 2
$ a: num 2
$ a + a: num 4
>
For some reason, I had tried every permutation of `substitute', `list'
and `...' except that one; coming to the erroneous conclusion that I
couldn't avoid eval-ing `...'.
I may have to screw around with the evaluation environment; but,
otherwise, this is fantastic!
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Re: [Rd] Curry: proposed new functional programming, er, function.
Sharpie wrote: > Currently, the only Curry implementation I know of is in the roxygen > package which is kind of a weird dependency to install just for this > one function. I end up using Curry so much outside of Roxygen that I spun it off into the `functional' package: https://r-forge.r-project.org/projects/functional/ Compose is there, too, and a couple other superfluous things. __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
