[R] Question about expression parser for "return" statement
Duncan Murdoch
murdoch.duncan at gmail.com
Sun Nov 13 19:35:57 CET 2016
On 13/11/2016 7:58 AM, Duncan Murdoch wrote:
> On 13/11/2016 6:47 AM, Duncan Murdoch wrote:
>> On 13/11/2016 12:50 AM, Dave DeBarr wrote:
>>> I've noticed that if I don't include parentheses around the intended return
>>> value for the "return" statement, R will assume the first parenthetical
>>> expression is the intended return value ... even if that parenthetical
>>> expression is only part of a larger expression.
>>>
>>> Is this intentional?
>>
>> Yes, return is just a function call that has side effects. As far as
>> the parser is concerned,
>>
>> return ((1/sqrt(2*pi*Variance))*exp(-(1/2)*((x - Mean)^2)/Variance))
>>
>> is basically the same as
>>
>> f((1/sqrt(2*pi*Variance))*exp(-(1/2)*((x - Mean)^2)/Variance))
>
> By the way, out of curiosity I took a look at the source of CRAN
> packages to see if this actually occurs. It turns out that "return" is
> used as a variable name often enough to make automatic tests tricky, so
> I don't know the answer to my question. However, I did turn up a number
> of cases where people have code like this:
>
> if (name == "") return;
>
> (from the bio.infer package), which never calls return(), so doesn't
> actually do what the author likely intended
I searched the R sources and the sources of CRAN packages, and found
this is a reasonably common problem: it's in 111 packages, including
one in base R. I'll be emailing the maintainers to let them know.
I'll see about putting a check for this into R CMD check.
Duncan Murdoch
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