[R] About Tcl/Tk after command in R

[Peter Dalgaard]

Duncan Murdoch wrote:
> On 1/15/2009 10:18 AM, davide.massidda at unipd.it wrote:
>> Dear R-helpers,
>> I have a problem with the tcl "after" instruction. When I send:
>>
>>> library(tcltk)
>> Loading Tcl/Tk interface ... done
>>
>>> tcl("after",1000,cat("try tcl after\n"))
>> try tcl after
>> <Tcl>
>>
>> the tcl command works fine. Similarly, the tcl command:
>>
>>> tcl("after",1000,plot(rnorm(100)))
>> <Tcl>
>>
>> works fine. But, if I send the command:
>>
>>> tcl("after",1000,10^2)
>> <Tcl> after#0
>>
>> appears a popup window which reports:
>>
>> Error: invalid command name “100”
>>
>> Why?
> 
> The value of cat("something") is NULL, the value of plot(something) is
> NULL, but the value of 10^2 is 100.  You're trying to execute no Tcl
> command in the first two cases, but you're trying to execute the command
> "100" in the last, and that's not a legal Tcl command.

Yes. Notice also that the argument is intended to be something to do
*after* the period of time has elapsed, and as written, it happens
immediately. You can use an R expression there, but it needs to be an
unevaluated call, usually created by
quote() or expression().


> tcl("after",5000,quote(cat("try tcl after\n"))) ; for (i in
1:10){print(i);Sys.sleep(1)}
<Tcl> after#4
[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
try tcl after
[1] 6
[1] 7
[1] 8
[1] 9
[1] 10

-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907