[Rd] [EXTERNAL] Re: NOTE: multiple local function definitions for ?fun? with different formal arguments
Martin Morgan
mtmorg@n@xyz @end|ng |rom gm@||@com
Wed Feb 7 00:17:03 CET 2024
I went looking and found this in codetools, where it's been for 20 years
https://gitlab.com/luke-tierney/codetools/-/blame/master/R/codetools.R?ref_type=heads#L951
I think the call stack in codetools is checkUsagePackage -> checkUsageEnv -> checkUsage, and these are similarly established. The call from the tools package https://github.com/wch/r-source/blame/95146f0f366a36899e4277a6a722964a51b93603/src/library/tools/R/QC.R#L4585 is also quite old.
I'm not sure this had been said explicitly, but perhaps the original intent was to protect against accidentally redefining a local function. Obviously one could do this with a local variable too, though that might less often be an error…
toto <- function(mode) {
tata <- function(a, b) a * b # intended
tata <- function(a, b) a / b # oops
…
}
Another workaround is to actually name the local functions
toto <- function(mode) {
tata <- function(a, b) a * b
titi <- function(u, v, w) (u + v) / w
if (mode == 1)
tata
else
titi
}
… or to use a switch statement
toto <- function(mode) {
## fun <- switch(…) for use of `fun()` in toto
switch(
mode,
tata = function(a, b) a * b,
titi = function(u, v, w) (u + v) / w,
stop("unknown `mode = '", mode, "'`")
)
}
… or similarly to write `fun <- if … else …`, assigning the result of the `if` to `fun`. I guess this last formulation points to the fact that a more careful analysis of Hervé's original code means that `fun` can only take one value (only one branch of the `if` can be taken) so there can only be one version of `fun` in any invocation of `toto()`.
Perhaps the local names (and string-valued 'mode') are suggestive of special case, so serve as implicit documentation?
Adding `…` to `tata` doesn't seem like a good idea; toto(1)(3, 5, 7) no longer signals an error.
There seems to be a lot in common with S3 and S4 methods, where `toto` corresponds to the generic, `tata` and `titi` to methods. This 'dispatch' is brought out by using `switch()`. There is plenty of opportunity for thinking that you're invoking one method but actually you're invoking the other. For instance with dplyr, I like that I can tbl |> print(n = 2) so much that I find myself doing this with data.frame df |> print(n = 2), which is an error (`n` partially matches `na.print`, and 2 is not a valid value); both methods silently ignore the typo print(m = 2).
Martin Morgan
From: R-devel <r-devel-bounces using r-project.org> on behalf of Henrik Bengtsson <henrik.bengtsson using gmail.com>
Date: Tuesday, February 6, 2024 at 4:34 PM
To: Izmirlian, Grant (NIH/NCI) [E] <izmirlig using mail.nih.gov>
Cc: r-devel using r-project.org <r-devel using r-project.org>
Subject: Re: [Rd] [EXTERNAL] Re: NOTE: multiple local function definitions for ?fun? with different formal arguments
Here's a dummy example that I think illustrates the problem:
toto <- function() {
if (runif(1) < 0.5)
function(a) a
else
function(a,b) a+b
}
> fcn <- toto()
> fcn(1,2)
[1] 3
> fcn <- toto()
> fcn(1,2)
[1] 3
> fcn <- toto()
> fcn(1,2)
Error in fcn(1, 2) : unused argument (2)
How can you use the returned function, if you get different arguments?
In your example, you cannot use the returned function without knowing
'mode', or by inspecting the returned function. So, the warning is
there to alert you to a potential bug. Anecdotally, I'm pretty sure
this R CMD check NOTE has caught at least one such bug in one of
my/our packages.
If you want to keep the current design pattern, one approach could be
to add ... to your function definitions:
toto <- function(mode)
{
if (mode == 1)
fun <- function(a, b, ...) a*b
else
fun <- function(u, v, w) (u + v) / w
fun
}
to make sure that toto() returns functions that accept the same
minimal number of arguments.
/Henrik
On Tue, Feb 6, 2024 at 1:15 PM Izmirlian, Grant (NIH/NCI) [E] via
R-devel <r-devel using r-project.org> wrote:
>
> Because functions get called and therefore, the calling sequence matters. It’s just protecting you from yourself, but as someone pointed out, there’s a way to silence such notes.
> G
>
>
> From: Hervé Pagès <hpages.on.github using gmail.com>
> Sent: Tuesday, February 6, 2024 2:40 PM
> To: Izmirlian, Grant (NIH/NCI) [E] <izmirlig using mail.nih.gov>; Duncan Murdoch <murdoch.duncan using gmail.com>; r-devel using r-project.org
> Subject: Re: [EXTERNAL] Re: [Rd] NOTE: multiple local function definitions for ?fun? with different formal arguments
>
>
> On 2/6/24 11:19, Izmirlian, Grant (NIH/NCI) [E] wrote:
> The note refers to the fact that the function named ‘fun’ appears to be defined in two different ways.
>
> Sure I get that. But how is that any different from a variable being defined in two different ways like in
>
> if (mode == 1)
> x <- -8
> else
> x <- 55
>
> This is such a common and perfectly fine pattern. Why would this be considered a potential hazard when the variable is a function?
>
> H.
>
> From: Hervé Pagès <hpages.on.github using gmail.com><mailto:hpages.on.github using gmail.com>
> Sent: Tuesday, February 6, 2024 2:17 PM
> To: Duncan Murdoch <murdoch.duncan using gmail.com><mailto:murdoch.duncan using gmail.com>; Izmirlian, Grant (NIH/NCI) [E] <izmirlig using mail.nih.gov><mailto:izmirlig using mail.nih.gov>; r-devel using r-project.org<mailto:r-devel using r-project.org>
> Subject: [EXTERNAL] Re: [Rd] NOTE: multiple local function definitions for ?fun? with different formal arguments
>
>
> Thanks. Workarounds are interesting but... what's the point of the NOTE in the first place?
>
> H.
> On 2/4/24 09:07, Duncan Murdoch wrote:
> On 04/02/2024 10:55 a.m., Izmirlian, Grant (NIH/NCI) [E] via R-devel wrote:
>
>
> Well you can see that yeast is exactly weekday you have. The way out is to just not name the result
>
> I think something happened to your explanation...
>
>
>
>
> toto <- function(mode)
> {
> ifelse(mode == 1,
> function(a,b) a*b,
> function(u, v, w) (u + v) / w)
> }
>
> It's a bad idea to use ifelse() when you really want if() ... else ... . In this case it works, but it doesn't always. So the workaround should be
>
>
> toto <- function(mode)
> {
> if(mode == 1)
> function(a,b) a*b
> else
> function(u, v, w) (u + v) / w
> }
>
>
>
>
>
>
> ________________________________
> From: Grant Izmirlian <izmirlidroid using gmail.com><mailto:izmirlidroid using gmail.com>
> Date: Sun, Feb 4, 2024, 10:44 AM
> To: "Izmirlian, Grant (NIH/NCI) [E]" <izmirlig using mail.nih.gov><mailto:izmirlig using mail.nih.gov>
> Subject: Fwd: [EXTERNAL] R-devel Digest, Vol 252, Issue 2
>
> Hi,
>
> I just ran into this 'R CMD check' NOTE for the first time:
>
> * checking R code for possible problems ... NOTE
> toto: multiple local function definitions for �fun� with different
> formal arguments
>
> The "offending" code is something like this (simplified from the real code):
>
> toto <- function(mode)
> {
> if (mode == 1)
> fun <- function(a, b) a*b
> else
> fun <- function(u, v, w) (u + v) / w
> fun
> }
>
> Is that NOTE really intended? Hard to see why this code would be
> considered "wrong".
>
> I know it's just a NOTE but still...
>
> I agree it's a false positive, but the issue is that you have a function object in your function which can't be called unconditionally. The workaround doesn't create such an object.
>
> Recognizing that your function never tries to call fun requires global inspection of toto(), and most of the checks are based on local inspection.
>
> Duncan Murdoch
>
> ______________________________________________
> R-devel using r-project.org<mailto:R-devel using r-project.org> mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> --
>
> Hervé Pagès
>
>
>
> Bioconductor Core Team
>
> hpages.on.github using gmail.com<mailto:hpages.on.github using gmail.com>
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and are confident the content is safe.
>
>
> --
>
> Hervé Pagès
>
>
>
> Bioconductor Core Team
>
> hpages.on.github using gmail.com<mailto:hpages.on.github using gmail.com>
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and are confident the content is safe.
>
>
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>
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