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

[luke at stat.uiowa.edu]

Looks like an infinite recursion in R_isMissing, which I think may be
turned into an infinite loop if the C compiler is doing tail call
optimization.  I need to understand why this is written the way it is
and also why another case that I would expect to also have this
problem does not before identifying the appropriate fix.

luke

On Tue, 10 Mar 2009, Peter Dalgaard wrote:

> Stavros Macrakis wrote:
>> Tested in: R version 2.8.1 (2008-12-22) / Windows
>> 
>> Recursive default argument references normally give nice clear errors.
>>  In the first set of examples, you get the error:
>>
>>   Error in ... :
>>   promise already under evaluation: recursive default argument
>> reference or earlier problems?
>>
>>   (function(a = a) a      ) ()
>>   (function(a = a) c(a)   ) ()
>>   (function(a = a) a[1]   ) ()
>>   (function(a = a) a[[1]] ) ()
>>   (function(a = a) a$x    ) ()
>>   (function(a = a) mean(a) )   ()
>>   (function(a = a) sort(a) ) ()
>>   (function(a = a) as.list(a) ) ()
>> 
>> But in the following examples, R seems not to detect the 'promise
>> already under evaluation' condition and instead gets a stack overflow,
>> with the error message:
>>
>>   Error: C stack usage is too close to the limit
>>
>>   (function(a = a)  (a)    ) ()
>>   (function(a = a)  -a     ) ()
>>   (function(a = a) var(a) ) ()
>>   (function(a = a) sum(a) ) ()
>>   (function(a = a) is.vector(a) ) ()
>>   (function(a = a) as.numeric(a) ) ()
>> 
>> I don't understand why the two sets of examples behave differently.
>
> Ouch!!!
>
> This shouldn't happen, I'm pretty sure. In particular not the apparently 
> unstoppable loop under Linux. Thanks for pointing it out.
>
>
>

-- 
Luke Tierney
Chair, Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:      luke at stat.uiowa.edu
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