[Rd] return (x+1) * 1000

[Duncan Murdoch]

On 20/11/2020 5:36 p.m., Mateo Obregón wrote:
> I'm not thinking of complicated cases.
> 
> This happened to me in a function that returns 10 minute slots
> 
> slot <- function (seconds) {
>      return (seconds %/% 600) * 600
> }
> 
> Obviously I found the issue while debugging and corrected my code with
> surrounding parenthesis, but I was surprised that the R parser did not catch
> this syntactic error.
> 
> This is especially poignant when we have to switch between languages like
> python where the original line would produce the desired result.

That's legal code, so the parser can't catch it, it needs to be caught 
by some lint-like thing that looks for bad usage.  The package check 
code has lots of that kind of check (including this one, though not yet 
in released R).  So if you put this in a package and run the --as-cran 
checks in R-devel, you'll be notified about it.

The fact that Python is different is something that's always going to 
cause problems for people who are more familiar with Python.  I don't 
know Python well enough to list all the gotchas, but I'm sure there are 
lots of them.

Duncan Murdoch

> 
> Mateo.
> --
> Mateo Obregón.
> 
> On Friday, 20 November 2020 21:58:29 GMT Gabriel Becker wrote:
>> Hi all,
>>
>> I can confirm this occurs for me as well.
>>
>> The one thing that comes to mind is that there are certain larger
>> expressions that contain calls to return which we absolutely don't want to
>> be an error, e.g
>>
>> if(somestuff)
>>      return(TRUE)
>>
>>
>> That said, the actual expression Mateo pointed out certainly does look like
>> an error (it definitely isn't going to do what the developer intended).
>>
>> I haven't looked at the parser much, to be honest. I assume there is
>> perhaps enough differentiation of if/else that return() could be allowed
>> within that but not inside a larger expression without it?
>>
>> There would be things that are legal (though horrifying) now that would
>> stop working though, such as:
>>
>> f = function(a) {
>>
>>      ret = switch(a,
>>
>>                   "1"= return("haha got 1!"),
>>
>>                   "2" = "regular ole 2")
>>
>>      ret
>>
>> }
>>
>>
>> Whether it would be a problem or not that such insanity wouldn't work is
>> less clear. Are there valid non-if embedded return() cases that are
>> important to allow? If so (and if they're not differentiated by the parser,
>> which I somewhat doubt switch is, for example, though I'm not certain), I'm
>> skeptical we'd be able to do as he suggests.
>>
>> It does seem worth considering though. If it can't be a hard parse error
>> but we agree many/most cases are problematic, perhaps adding detecting this
>> to the static checks that R CMD CHECK performs is another way forward.
>>
>> Best,
>> ~G
>>
>> On Fri, Nov 20, 2020 at 1:34 PM Mateo Obregón <obregonmateo using gmail.com>
>>
>> wrote:
>>> Dear r-developers-
>>>
>>> After many years of using and coding in R and other languages, I came
>>> across
>>> something that I think should be flagged by the parser:
>>>
>>> bug <- function (x) {
>>>
>>>       return (x + 1) * 1000
>>>
>>> }
>>>
>>>> bug(1)
>>>
>>> [1] 2
>>>
>>> The return() call is not like any other function call that returns a value
>>> to
>>> the point where it was called from. I think this should straightforwardly
>>> be
>>> handled in the parser by flagging it as a syntactic error.
>>>
>>> Thoughts?
>>>
>>> Mateo.
>>> --
>>> Mateo Obregón.
>>>
>>> ______________________________________________
>>> R-devel using r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
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