R devel - Feb 2001 - tk non-widget commands (esp. update and winfo)

Hi,

I've been playing with the tcltk package.  It's very nice to have
access to buttons, menus etc. now.  Thank you!

Alas, I also have questions: In Tcl everything is a string [*].  This
is not the case in R, of course.  So why are return values of tk
commands still strings?  (Is there any other reason than speed or
"package is work in progress"?)

Example:

   > tt <- tktoplevel ()
   > tkwinfo ("width", tt)
  [1] "200"

Could (Should?) be:

   > tt <- tktoplevel ()
   > tkwinfo ("width", tt)
  [1] 200

with 
   > tkwidth <- function (widget) as.numeric (tkcmd ("winfo",
"width", widget))

Maybe a better example is the use of logical results:

  > if (tkwinfo ("exists", tt)) cat ("exists\n")
  Error in if (tkwinfo("exists", tt)) cat("exists\n") : 
          argument of if(*) is not interpretable as logical

Huh? Here you might have expected:

  > if (tkexists (tt)) cat ("exists\n")
  exists

with
  > tkexists <- function (widget) (tkcmd ("winfo",
"exists", widget) == "1")

One problem is that the number of functions just explodes, so it might
be better to wrap them into one enchillada?

  >  tkwinfo <- function (widget, what="exists", ...) 
     switch (what,
             exists=tkcmd("winfo", "exists",
widget)=="1",
             ismapped=tkcmd("winfo", "ismapped",
widget)=="1",
             width=as.numeric (tkcmd("winfo", "width",
widget)),
             height=as.numeric (tkcmd("winfo", "height",
widget)),
             tkcmd ("winfo", what, widget, ...))

(The other problem is that tkcmd("winfo",...) may fail.)

Oh, while I'm at it:  There is no tkupdate:
  >  tkupdate <- function (idletasks=FALSE)
     if (idletasks) tkcmd ("update", "idletasks") else tkcmd
("update")

(which is essential to making sure that a window is mapped before its
width or height is queried.)  That's trivial if you have hacked Tcl/Tk
before -- so who is the package tlctk aimed at?

Regards,
  -tom


[*] Nowadays, they have glorified strings into objects.  Anywho...

-- 
mailto:tov@ece.cmu.edu (Tom Vogels)   Tel: (412) 268-6638   FAX: -3204

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Thomas Vogels <tov@ece.cmu.edu> writes:
> Hi,
> 
> I've been playing with the tcltk package.  It's very nice to have
> access to buttons, menus etc. now.  Thank you!
> 
> Alas, I also have questions: In Tcl everything is a string [*].  This
> is not the case in R, of course.  So why are return values of tk
> commands still strings?  (Is there any other reason than speed or
> "package is work in progress"?)
The latter. Also to some extent the fact that it requires more
knowledge about the content of the return value. The argument passing
scheme is as you can see quite general and essentially ignorant of the
routines that are called. In essence the issue is that it is fairly
easy to convert whatever to strings, but harder the other way around.
So for the first iteration of the package, the idea would be to have
the user do the necessary as.xxx conversions of return values.
> One problem is that the number of functions just explodes, so it might
> be better to wrap them into one enchillada?
> 
>   >  tkwinfo <- function (widget, what="exists", ...) 
>      switch (what,
>              exists=tkcmd("winfo", "exists",
widget)=="1",
>              ismapped=tkcmd("winfo", "ismapped",
widget)=="1",
>              width=as.numeric (tkcmd("winfo", "width",
widget)),
>              height=as.numeric (tkcmd("winfo",
"height", widget)),
>              tkcmd ("winfo", what, widget, ...))
> 
> (The other problem is that tkcmd("winfo",...) may fail.)
> 
> Oh, while I'm at it:  There is no tkupdate:
>   >  tkupdate <- function (idletasks=FALSE)
>      if (idletasks) tkcmd ("update", "idletasks") else
tkcmd ("update")
> 
> (which is essential to making sure that a window is mapped before its
> width or height is queried.)  That's trivial if you have hacked Tcl/Tk
> before -- so who is the package tlctk aimed at?
Tcl/Tk hackers of course, the author of the package not being one...

Basically, the plan is to add stuff as it becomes necessary to do
useful things, so feedback and suggestions from developers are always
welcome.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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