On Sat, Mar 4, 2017 at 12:36 PM, Da Zheng <zhengda1...@gmail.com> wrote:
> In my case, I create a new type of matrices and override matrix > operations in R for these matrices. > My goal is to make the system as transparent as possible, which means > my system should execute the existing R code without modification. > The problem is that when data is in my own vectors or matrices, "if" > or "while" can't access their values unless we explicitly convert them > into R objects. But this means users need to modify the existing code. > So I hope I can override "if", "while", etc to access data in my own > vectors and matrices directly. > Does this sound reasonable? > > Would you really need the alternate representation for scalar logicals? I can see a case in the deferred evaluation context, although it would be problematic wrt side effects unless the deferral is complete. > Best, > Da > > On Sat, Mar 4, 2017 at 3:22 PM, Michael Lawrence > <lawrence.mich...@gene.com> wrote: > > I'm curious as to precisely why someone would want to do this. > > > > On Sat, Mar 4, 2017 at 11:49 AM, Da Zheng <zhengda1...@gmail.com> wrote: > >> > >> I'm just curious. Why making "if" generic is even more dangerous? > >> > >> Best, > >> Da > >> > >> On Sat, Mar 4, 2017 at 1:22 PM, Gábor Csárdi <csardi.ga...@gmail.com> > >> wrote: > >> > `!` is a generic, `if` is not. You can define an `if` that is generic, > >> > but this might be even more dangerous.... > >> > > >> > ❯ `if` <- function(a, b, c) UseMethod("if") > >> > ❯ `if.default` <- function(a,b,c) base::`if`(a, b, c) > >> > ❯ `if.foo` <- function(a, b, c) FALSE > >> > ❯ a <- structure(42, class = "foo") > >> > > >> > ❯ if (a) TRUE else FALSE > >> > [1] FALSE > >> > > >> > ❯ if (1) TRUE else FALSE > >> > [1] TRUE > >> > > >> > Gabor > >> > > >> > On Sat, Mar 4, 2017 at 5:47 PM, Da Zheng <zhengda1...@gmail.com> > wrote: > >> >> Thanks. > >> >> Can I override it for a specific class? > >> >> I can do that for operators such as "!". For example, "!.fm" works > for > >> >> objects of the class "fm". > >> >> It seems I can't do the same for "if". > >> >> > >> >> Best, > >> >> Da > >> >> > >> >> On Sat, Mar 4, 2017 at 12:41 PM, Gábor Csárdi < > csardi.ga...@gmail.com> > >> >> wrote: > >> >>> You can. Perhaps needless to say, be careful with this. > >> >>> > >> >>> ❯ `if` <- function(...) FALSE > >> >>> ❯ if (TRUE) TRUE else FALSE > >> >>> [1] FALSE > >> >>> > >> >>> G. > >> >>> > >> >>> On Sat, Mar 4, 2017 at 5:36 PM, Da Zheng <zhengda1...@gmail.com> > >> >>> wrote: > >> >>>> Hello, > >> >>>> > >> >>>> I heard we can override almost everything in R. Is it possible to > >> >>>> override "if" keyword in R to evaluate my own object instead of a > >> >>>> logical value? > >> >>>> > >> >>>> Thanks, > >> >>>> Da > >> >>>> > >> >>>> ______________________________________________ > >> >>>> R-devel@r-project.org mailing list > >> >>>> https://stat.ethz.ch/mailman/listinfo/r-devel > >> > >> ______________________________________________ > >> R-devel@r-project.org mailing list > >> https://stat.ethz.ch/mailman/listinfo/r-devel > > > > > [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel