[R-SIG-Mac] Starting tcltk without Tk

[Prof Brian Ripley]

Returned to just R-sig-mac.

On Tue, 6 May 2008, Philippe Grosjean wrote:

> Simon Urbanek wrote:
>> It turns out that the behavior of starting just Tcl was actually a bug. 
>
> Not completely. At least, loading of tcltk was correct when the "bug" was 
> there, but I totally agree that the mechanism used (according to the presence 
> or not of the DISPLAY variable is not the best one). It is not true that 
> there was no intention to allow loading tcltk without Tk. Otherwise, why 
> would you have this (tcltk.c, tcltk_init(), line 643 in the R 2.7.0 source):
>
> warning(_("no DISPLAY variable so Tk is not available"));
>
> This message strongly suggests that starting tcltk without Tk is allowed, and

'Tolerated' would be more accurate.  It is there to cope with packages 
that loaded tcltk during installation, which is often done headless.
The intention is that the package would load, not that it would do usefule 
things.

The 'bug' was that this worked at all on MacOS --with-aqua builds.  That 
line was not intended to be used in that case.  Simon did state that 
clearly in his next para.

> it also suggests the mechanism: by eliminating the DISPLAY environment 
> variable before starting tcltk. It is certainly undocumented, most probably 
> underused, and certainly requires a better way to specify that the user does 
> want to load Tk,... but at least, it worked for me up to now.
>
>> Apparently the intention was to attempt to start Tk regardless of the 
>> DISPLAY variable, because some TclTk implementation such as Aqua Tcl/Tk 
>> don't require DISPLAY and thus would not be loaded. Due to a bug (HAVE_AQUA 
>> was not included in Rconfig.h before R 2.7.0), though, this was not the 
>> case. I'll leave it to tcltk users/maintainers to decide the right way 
>> forward. Essentially I see two options:
>> 
>> 1) status quo: tcltk always attempts to load Tk and fails on an error
>> 2) allow some (possibly cross-platform) way of specifying that it is ok to 
>> not load Tk - essentially make failure to load Tk non-fatal.
>
> I vote for the second option.

Only those who do the work have votes.  There is another possibility, that 
tcltk on MacOS always attempts to load Tk and warns on error.

> Many thanks,
>
> Philippe
>
>> Right now there is no (semantically correct) way to inhibit the loading of 
>> Tk (DISPLAY is a sort of abuse and not a solution).
>> 
>> Cheers,
>> Simon
>> 
>> (CC to R-devel where this started...)
>> 
>> On May 5, 2008, at 9:12 AM, Simon Urbanek wrote:
>> 
>>> Philippe,
>>> 
>>> I'm not quite sure why you are asking on a Mac list, but the error comes 
>>> from Tcl/Tk. I'd suggest asking on R-devel, the Tcl/Tk used in the R 
>>> binary is the same for R 2.6.x and 2.7.0 so it must be a change in tcltk.
>>> 
>>> Cheers,
>>> Simon
>>> 
>>> 
>>> On May 4, 2008, at 7:01 AM, Philippe Grosjean wrote:
>>> 
>>>> Hello,
>>>> 
>>>> Up to R 2.6.2, I used to start Tcl *without Tk* (I need only Tcl for some 
>>>> part of my work, like a socket server written in Tcl only, for instance) 
>>>> with this code under Mac OS X (particularly on this system, because I 
>>>> don't want to start X11 just to use Tcl code, which is required for Tk!):
>>>> 
>>>> > Sys.unsetenv("DISPLAY")
>>>> > library(tcltk)
>>>> 
>>>> I got then the message "no DISPLAY variable so Tk is not available", but 
>>>> could work with Tcl without problems.
>>>> 
>>>> Now, with R 2.7.0, I got the following and Tcl failed to load:
>>>> Loading Tcl/Tk interface ... Error in fun(...) : no display name and no 
>>>> $DISPLAY environment variable
>>>> Error : .onLoad failed in 'loadNamespace' for 'tcltk'
>>>> Error: package/namespace load failed for 'tcltk'
>>>> 
>>>> I try to locate the message "no display name and no $DISPLAY environment 
>>>> variable" in the code but I cannot find it. Could someone help me please?
>>>> 
>>>> I understand that starting Tcl without Tk from R is not an intended 
>>>> behaviour, but would it be possible to include an option to do so?
>>>> 
>>>> > sessionInfo()
>>>> R version 2.7.0 Patched (2008-04-22 r45460)
>>>> i386-apple-darwin8.10.1
>>>> 
>>>> locale:
>>>> en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8
>>>> 
>>>> attached base packages:
>>>> [1] stats     graphics  grDevices utils     datasets  methods   base
>>>> 
>>>> Many thanks,
>>>> 
>>>> Philippe Grosjean
>>>> -- 
>>>> ..............................................<°}))><........
>>>> ) ) ) ) )
>>>> ( ( ( ( (    Prof. Philippe Grosjean
>>>> ) ) ) ) )
>>>> ( ( ( ( (    Numerical Ecology of Aquatic Systems
>>>> ) ) ) ) )   Mons-Hainaut University, Belgium
>>>> ( ( ( ( (
>>>> ..............................................................
>>>> 
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>>> 
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>> 
>> 
>
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-- 
Brian D. Ripley,                  ripley at 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