On Sun, Mar 5, 2017 at 2:50 PM, Michael Lawrence <lawrence.mich...@gene.com> wrote: > > > 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. This is exactly why I want to use my own matrix objects and redefine "if" for the matrices. In my framework, all matrices are read-only, so there isn't side effect.
Best, Da > > > >> >> 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 >> > >> > > > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel