The argument to eval.parent is evaluated before eval.parent
ever sees it. Try issuing this command before you run your
code:
debug(eval.parent)
and look at the value of the arguments as passed to eval.parent
in the debugger.
On Wed, Jan 28, 2009 at 2:29 AM, <markle...@verizon.net> wrote:
> I'm still going over old emails and trying to get my head around evaluation
> so I'm persistent if nothing else.
>
> A while back , an expert sent me below as an exercise in understanding and
> I only got around to it tonight. I understand some of the output but not all
> of it and I put "Why not Zero ?" next to the ones that I don't understand
> based on my reading of the various functions in the help pages. It's either
> my reading comprehension or the evaluation subtleties in R but I just can't
> understand some of them. If any of the expeRts has time to explain the ones
> that I marked with "WHY NOT ZERO ?", it would be much appreciated.
> Obviously, I don't expect a long explanation but I think my problem is that
> I keep thinking that eval.parent and eval(whatever, parent.frame) go back to
> the function that called with.options so f() and do the evaluation in there
> but that doesn't always seem to be the case. I'm also not so clear on the
> difference between print(x) and L[[len]]. Thanks a lot in advance to anyone
> who can be bothered with below.
>
> with.options <- function(...) {
> L <- as.list(match.call())[-1]
> len <- length(L)
> print(L)
>
> eval.parent(L[[len]]) # =0 MAKES SENSE
> eval(L[[len]]) # =1 MAKES SENSE
> eval(L[[len]],parent.frame()) # =0 MAKES SENSE
> eval.parent(print(x)) # =1 WHY NOT ZERO ? Somehow this is different
> from eval.parent(L[[len]])
> eval(print(x)) # =1 MAKES SENSE
> eval(print(x),parent.frame()) # =1 # WHY NOT ZERO ? Somehow this is
> different from eval(L[[len]],parent.frame)
> evalq(print(x)) # =1 MAKES SENSE
> evalq(print(x),parent.frame()) # =1 MAKES SENSE
> print("====================")
>
> x <- 2
>
> eval.parent(L[[len]]) # =0 MAKES SENSE
> eval(L[[len]]) # =2 MAKES SENSE
> eval(L[[len]],parent.frame()) # =0 MAKES SENSE
> eval.parent(print(x)) # =2 WHY NOT ZERO ? Somehow this is different from
> eval.parent(L[[len]])
> eval(print(x)) # 2 MAKES SENSE
> eval(print(x),parent.frame()) # 2 WHY NOT ZERO ? Somehow this is different
> from eval(L[[len]], parent.frame)
> evalq(print(x)) # 2 MAKES SENSE
> evalq(print(x),parent.frame()) # 1 WHY NOT ZERO ?
> print("====================")
>
> }
>
> x <- 1
>
> f <- function() {
> x <- 0
> with.options(width = 40, print(x))
> }
>
> f()
>
> ______________________________________________
> 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.
>
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