[Rd] E`<`<rrors in recursive default argument references

[Wacek Kusnierczyk]

Stavros Macrakis wrote:
> On Mon, Mar 9, 2009 at 5:40 PM, Wacek Kusnierczyk
> <Waclaw.Marcin.Kusnierczyk at idi.ntnu.no> wrote:
>   
>> Stavros Macrakis wrote:
>>     
>>> Tested in: R version 2.8.1 (2008-12-22) / Windows
>>>       
>
>   
>> when i run these examples, the execution seems to get into an endless
>> loop with no error messages whatsoever.  how much time does it take
>> before you get the error?  (using r 2.8.0 and also the latest r-devel).
>>     
>
> In 2.8.1/Windows (32 bit), they return immediately, though the
> stack-overflow case is about 13x slower.
>
>   
>> system.time(for (i in 1:100) {trySilent((function(a=a)(a))())})
>>     
>    user  system elapsed
>    0.67    0.00    0.67
>   

this won't stop within a minute, running at 100% cpu, have to kill the
process.

>> system.time(for (i in 1:100) {trySilent((function(a=a)as.POSIXct(a))())})
>>     
>    user  system elapsed
>    0.05    0.00    0.05
>   
   user  system elapsed
  0.064   0.000   0.067


> Are you running under 64 bits?  How long does a vanilla infinite
> recursion take to fail on your machine?  I get:
>   

32 bits ubuntu 8.04

>   
>> system.time(for (i in 1:100) trySilent({fff <- function()fff(); fff()}))
>>     
>    user  system elapsed
>    0.27    0.00    0.26
>   

   user  system elapsed
  0.204   0.008   0.212


vQ

PS i'm looking into the sources; in src/main/eval.c:317 there is a check
for whether the promise has been seen:

    if(PRSEEN(e))

it appears that when i evaluate

    (function(a=a) -a)()

the check is not passed (the condition is false -- promise not seen). 
seems like the evaluation goes into a loop before the promise is marked
as seen.  (or i misunderstand the code, likely.)

vQ