Dear Brian, > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Prof Brian Ripley > Sent: Friday, June 28, 2013 11:16 AM > To: r-help@r-project.org > Subject: Re: [R] Lexical scoping is not what I expect > > On 28/06/2013 15:54, John Fox wrote: > > Dear Duncan and Steve, > > > > Since Steve's example raises it, I've never understood why it's legal > to > > change the built-in global "constants" in R, including T and F. That > just > > seems to me to set a trap for users. Why not treat these as reserved > > symbols, like TRUE, Inf, etc.? > > Because people wanted to use them as names of things. Maybe a T (not > t) > statistic. > > And BTW, you can change the value of T for yourself, but you will not > change it for any package code, including R itself, since the base > namespace is ahead of the workspace in namespace scoping. Because of > that, it is years since I have seen anyone actually trip themselves up > over this.
I was unaware that the base namespace is ahead of the workspace in this context, and that effectively answers my objection. Thanks, John > > > > > Best, > > John > > > >> -----Original Message----- > >> From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > >> project.org] On Behalf Of Duncan Murdoch > >> Sent: Friday, June 28, 2013 9:40 AM > >> To: S Ellison > >> Cc: r-help@r-project.org > >> Subject: Re: [R] Lexical scoping is not what I expect > >> > >> On 28/06/2013 9:28 AM, S Ellison wrote: > >>> > >>>>> I too find R's lexical scoping rules straightforward. > >>>>> However, I'd say that if your code relies on lexical > >>>>> scoping to find something, you should probably rewrite your code. > >>>> > >>>> Except of course that almost every function relies on lexical > >>>> scoping to some extent! > >>> > >>> This could get messy, because a) that's true and b) it actually > leads > >> to some genuine risks when 'globals' get redefined or masked*. > >>> > >>> How about I amend the assertion to "if your code relies on lexical > >> scoping to find a variable you defined, you should probably rewrite > >> your code." > >>> and leave it at that, subject to some common sense about whether > you > >> know what you're doing? > >> > >> That still isn't right, because users should feel free to define > >> functions and call them from their other functions. > >> > >> I think who defined it isn't the issue, the issue is whether it > might > >> change unexpectedly. The user owns globalenv(). The package author > >> owns the package namespace. So packages should almost never read or > >> write things directly from/to globalenv() (the user might change > them), > >> but they can create their own private environments and write there. > >> > >> Where it gets a little less clear is when the user writes a > function. > >> I > >> would say functions should never write directly to globalenv(), but > >> it's > >> perfectly fine to reference constants there (like other functions > >> written by the user). Referencing things there that change is the > >> risky > >> thing. > >> > >> Duncan Murdoch > >> > >> > >>> > >>> Steve E > >>> > >>> > >>> *Example > >>>> sin.deg <- function(deg) sin(deg * pi/180) > >>>> sin.deg(45) > >>> [1] 0.7071068 > >>> #looks about right > >>> > >>>> pi <- 3.2 #Indiana General Assembly bill #247, 1897. > >>>> sin.deg(45) > >>> [1] 0.7173561 > >>> #oops ... > >>> > >>> > >>> > >>> > >>> ******************************************************************* > >>> This email and any attachments are confidential. Any > >> use...{{dropped:8}} > >>> > >>> ______________________________________________ > >>> 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. > >> > >> ______________________________________________ > >> 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. > > > > ______________________________________________ > > 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. > > > > > -- > Brian D. Ripley, rip...@stats.ox.ac.uk > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UK Fax: +44 1865 272595 > > ______________________________________________ > 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. ______________________________________________ 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.
