Luke Tierney wrote: > On Thu, 21 Dec 2006, [EMAIL PROTECTED] wrote: > > >> Prof Brian Ripley wrote: >> >>> On Thu, 21 Dec 2006, Peter Dalgaard wrote: >>> >>> [...] >>> >>> >>> >>>> This seems reproducible on Linux, except that it goes into an infinite >>>> loop. The lm call seems to be the real culprit: >>>> >>>> >>>> >>>>> testfun <- function(aa=aa) return(aa) >>>>> testfun() >>>>> >>>>> >>>> Error in testfun() : recursive default argument reference >>>> >>>> >>>>> testfun <- function(aa=aa) lm(x~y,data=aa) >>>>> testfun() >>>>> >>>>> >>>> (*poof*) >>>> >>>> >>> The difference is in argument evaluation between closures and internal >>> functions (c() in my example, return() in yours). >>> >>> >> Er? I'd rather say that the issue is in the semantics of missing(): >> >> >>> f <- function(x) missing(x) >>> testfun <- function(aa=aa) f(aa) >>> testfun() >>> >> Error: segfault from C stack overflow >> >> which is a bit nasty. AFAICS the thing is that the logic for detection >> of recursive arguments works by forcing promises (if you at some point >> need the result of the same promise you are forcing, you know that >> something is wrong), but missing() tries hard not to force promises. We >> already have the following anomaly, >> >> >>> g <- function(v) missing(v) >>> f <- function(v) g(v) >>> f() >>> >> [1] TRUE >> >>> f <- function(v=!h, h=!v) g(v) >>> f() >>> >> [1] FALSE >> >>> f <- function(v=!h, h) g(v) >>> f() >>> >> [1] FALSE >> >> so the fix could be to realize that we cannot detect missingness in a >> perfectly reliable way and just pretend that arguments are always >> non-missing when they have a default. >> > > We could also mark the promise created for default arguments so it can > be identified as such and use that info in missing(). Probably worth > deciding what the intended semantics are here and then figuring out > the implementation. > > Yes, always a good idea...
Just to be precise: The current semantics seems to be that we stop and declare missingness to be FALSE if any sort of computation is involved in the default: > f <- function(v=h,h=v) g(v) > f() Error: segfault from C stack overflow but > f <- function(v=(v)) g(v) > f() [1] FALSE -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
