Thanks for the pointer to substitute(), William. This seems to work and is a little shorter than yours:
a <- 1; foo <- eval(substitute(function () print(a), env=list(a=a))) a <- 2; foo() # [1] 1 Not the clearest code I have ever seen, especially as 'foo' still shows 'a': print(foo) # function () a Allan On 02/07/09 18:28, William Dunlap wrote: >> From: r-help-boun...@r-project.org >> [mailto:r-help-boun...@r-project.org] On Behalf Of Allan Engelhardt >> Sent: Thursday, July 02, 2009 9:47 AM >> To: r-help@r-project.org >> Subject: [R] How to use current value of variable in function >> definition? >> >> Must be the heat or something but I can't get my brain into gear and >> figure out how to get something like >> >> if (1) { c<- 1; foo<- function () print(c); } >> c<- 2 >> foo() >> >> to print 1, not 2. (The real life example is a little more >> complex, but >> you get the idea. I don't want the variable c in the function >> definition, I want its value at that time.) >> >> The only thing I have been able to come up with is something like >> >> if (1) foo<- (function () { c<- 1; return(function () print(c)) })() >> c<- 2 >> foo() >> # [1] 1 >> > You might try local(), as in > > c<-1 ; foo.local<-local({orig.c<- c ; function()orig.c}) > > foo.local() > [1] 1 > > c<-3 > > foo.local() > [1] 1 > It is possible for someone to alter the orig.c after you create > foo.local, as in > > assign("orig.c", 17, env=environment(foo.local)) > > foo.local() > [1] 17 > Looking at the function's code will not make it clear where > orig.c is coming from. The clue is that its environment is not > one of the standard named ones, but it given by a hex number. > > foo.local > function()orig.c > <environment: 0x02108c54> > > You could also use substitute() to change the code in the function. > It can be messy to do but the resulting code may be clearer (although > it won't give a hint as to where that constant came from). E.g., > > foo.substitute<-function()orig.c > > c<-1 ; functionBody(foo.substitute)<-do.call(substitute, > list(functionBody(foo.substitute), list(orig.c=c))) > > foo.substitute() > [1] 1 > > foo.substitute > function () > 1 > > Bill Dunlap > TIBCO Software Inc - Spotfire Division > wdunlap tibco.com > > >> but that just hurts. Please make the pain go away. >> >> Can someone wake up my brain? >> >> Allan. >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> >> [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
