[EXTERNAL] Re: NOTE: multiple local function definitions for ?fun? with different formal arguments

Tue, Feb 6, 2024 5:09 PM

Hopefully to too much of a tangent: A related problem this check doesn?t catch is accidental top-level redefinitions in package code, such as

## a.R:
helper <- function() 1

f <- function() {
helper()
}
# ?cool, f() must return 1"

## b.R:
helper <- function(x) 2

g <- function() {
helper()
}
# ?cool, g() must return 2"

## Runtime: 
# > c(pkg::f(), pkg::g())
# [1] 2 2
# ?oh right, only the last definition of helper() is used?
 
I?ve seen several variants of this issue in code from folks who are new to package development, especially if they're naively refactoring something that started out as an interactively-run analysis. Collaborators who are puzzled by it get my ?packages are collections of objects not sequences of expressions, yes that needs to be in your mental model, here?s the link to RWE again? talk, but I would be happy to be able to point them to a check result to go along with it.

I don?t think this is grounds on its own to change a 20-year precedent, but in case anyone is collecting wishlist reasons to make the check look harder...

Thanks,
Chris

On Feb 6, 2024, at 3:17 PM, Martin Morgan <mtmorgan.xyz at gmail.com> wrote:

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 Herv?'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 at r-project.org> on behalf of Henrik Bengtsson <henrik.bengtsson at gmail.com>
Date: Tuesday, February 6, 2024 at 4:34?PM
To: Izmirlian, Grant (NIH/NCI) [E] <izmirlig at mail.nih.gov>
Cc: r-devel at r-project.org <r-devel at 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 at 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: Herv? Pag?s <hpages.on.github at gmail.com>
Sent: Tuesday, February 6, 2024 2:40 PM
To: Izmirlian, Grant (NIH/NCI) [E] <izmirlig at mail.nih.gov>; Duncan Murdoch <murdoch.duncan at gmail.com>; r-devel at 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: Herv? Pag?s <hpages.on.github at gmail.com><mailto:hpages.on.github at gmail.com>
Sent: Tuesday, February 6, 2024 2:17 PM
To: Duncan Murdoch <murdoch.duncan at gmail.com><mailto:murdoch.duncan at gmail.com>; Izmirlian, Grant (NIH/NCI) [E] <izmirlig at mail.nih.gov><mailto:izmirlig at mail.nih.gov>; r-devel at r-project.org<mailto:r-devel at 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 at gmail.com><mailto:izmirlidroid at gmail.com>
Date: Sun, Feb 4, 2024, 10:44 AM
To: "Izmirlian, Grant (NIH/NCI) [E]" <izmirlig at mail.nih.gov><mailto:izmirlig at 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

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[EXTERNAL] Re: NOTE: multiple local function definitions for ?fun? with different formal arguments

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