[Rd] anonymous function parsing bug?

luke-tierney at uiowa.edu
Fri, 21 Oct 2016 21:59:58 -0000

On Fri, 21 Oct 2016, William Dunlap via R-devel wrote:

> Am 21.10.2016 um 18:10 schrieb William Dunlap:
>>
>> Are you saying that
>
>    f1 <- function(x) log(x)
>
>    f2 <- function(x) { log } (x)
>
> should act differently?
>
> yes.
>
>
> But that would mean that {log} would act differently than log.
> I suppose it is a matter of taste, but I say yuck.
>
> As for 'return', don't use it if you want readable code.  It is
> like a goto but worse.  It is never necessary.

As a rule I agree, but one case where return is clearer than the alternative is

repeat {
    ....
    if (...)
       return(...)
}

Complicated nested if expressions are also sometimes clearer using
return as an early breakout.

Best,

luke

>
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
> On Fri, Oct 21, 2016 at 10:17 AM, Wilm Schumacher <wilm.schumacher at
gmail.com
>> wrote:
>
>> Hi,
>>
>>
>> Am 21.10.2016 um 18:10 schrieb William Dunlap:
>>
>>> Are you saying that
>>>     f1 <- function(x) log(x)
>>>     f2 <- function(x) { log } (x)
>>> should act differently?
>>>
>> yes. Or more precisely: I would expect that. "Should"
implies, that I want
>> to change something. I just want to understand the behavior (or file a
bug,
>> if this would have been one).
>>
>> As I wrote, in e.g. node.js the pendents to the lines that you wrote
are
>> treated differently (the first is a function, the latter is a parsing
>> error).
>>
>> Let's use this example instead:
>> x <- 20
>> f1 <- function(x) { x<-x+1; log(x) }
>> f2 <- function(x) { x<-x+1; log } (x)
>> which act equally.
>>
>> But as the latter is a legal statement, I would read it as
>> f2 <- (function(x) { x<-x+1; log }) (x)
>>
>> thus, I would expect the first to be a function, the latter to be a
>> numeric ( log(20) in this case ).
>>
>>
>> Using 'return' complicates the matter, because it affects
evaluation, not
>>> parsing.
>>>
>>
>> But perhaps it illustrates my problem a little better:
>> x <- 20
>> f1 <- function(x) return(log(x))
>> f2 <- function(x) { return(log) } (x)
>>
>> f1(10) is a numeric, f2(10) is the log function. Again: as the latter
is a
>> legal statement, I would expect:
>> f2 <- (function(x) { x<-x+1; log }) (x)
>>
>> However, regarding the answers I will try to construct the AST
regarding
>> the grammar defined in gramm.y of that statement
>> f2 <- function(x) { x<-x+1; log } (x)
>> to understand what the R interpreter really does.
>>
>> Best wishes,
>>
>> Wilm
>>
>>
>>
>>
>>
>
> 	[[alternative HTML version deleted]]
>
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>

--
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
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