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

[Peter Dalgaard]

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.


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