On 05/07/2014 02:01 PM, peter dalgaard wrote:
On 07 May 2014, at 21:52 , Simon Urbanek <simon.urba...@r-project.org> wrote:
On May 7, 2014, at 3:37 PM, Hervé Pagès <hpa...@fhcrc.org> wrote:
No big deal. These things can be tricky:
https://stat.ethz.ch/pipermail/r-devel/2006-January/036022.html
Sorry I couldn't resist ;-)
Yeah, but that's just yet another trip down the rabbit hole - why is -2 parsed
as `-`(2) and not a single constant? Is there a way to express a negative
constant in R? Hmm…
It's painful, but
bquote(.(-2)^2)
-2^2
eval(bquote(.(-2)^2))
[1] 4
bquote(.(-2)^2)[[2]]
[1] -2
mode(bquote(.(-2)^2)[[2]])
[1] "numeric"
The difficulty is that the tokenizer, which recognizes language elements before the parser goes to
work on the grammatical structure, is unable to distinguish the -2 in "-2 + 2" from the
one in "-2 ^ y".
Are you saying that the tokenizer could be made smarter and recognize
"-2" as a token in "-2 ^ y", just because you didn't put a space between
"-" and "2"? So in "-2 ^ y" it would be token, but not in "- 2^y".
An therefore precedence would now depend on whether there is a space
after the minus or not, or something like that? I'm confused.
H.
And since constants are generated by the tokenizer, negative ones are not generated. I
don't think it is completely out of reach for the parser to recognize the pattern
"unary minus a numeric constant" and fold it into a constant of the opposite
sign, but I'm not volunteering... (and anyways, it is part of the bigger issue of general
constant folding --- I suppose that Luke has a handle on that.)
On 05/07/2014 09:16 AM, John Chambers wrote:
On 5/7/14, 5:21 AM, Therneau, Terry M., Ph.D. wrote:
Hadley asked about the Blue book; my shelf still has the earlier brown
book
Becker and Chambers, 1984, S: An interactive environment for data
analysis and graphics.
Historically interesting, but there was never a guarantee that Version 3
of S (the "blue book") was back-compatible with earlier versions. We
gave users some help in "getting on the road" to converting, that was
all (see Appendix 4 to the blue book).
For that one brief moment, we felt free to innovate.
John
The manual page for precedence is
$ component select
%x special operator
- unary minus
: sequence operator
^ ** exponentiation
* / mult/div
+ - add/sub
< > <= >= == != logical
! not
& | and/or
<- -> assignment
Terry Therneau
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--
Hervé Pagès
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024
E-mail: hpa...@fhcrc.org
Phone: (206) 667-5791
Fax: (206) 667-1319
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______________________________________________
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https://stat.ethz.ch/mailman/listinfo/r-devel
--
Hervé Pagès
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024
E-mail: hpa...@fhcrc.org
Phone: (206) 667-5791
Fax: (206) 667-1319
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