R devel - Aug 2010 - accessing tcl variables within R and tcl

Dear R users,

I have some troubles with dealing with tclObj objects. I try to explain
it with a toy example:

Say I define the following tcl procedure which just prints out each list
element

library(tcltk)
.Tcl('proc test {myList} {
    foreach i $myList {
      puts stdout  $i
    }
}')

and I call it with:
> tcl('test',letters[1:5])    # Works as expected
Now say I define a tcl variable first:
> a <- tclVar("")
> tclObj(a) <- as.tclObj(letters[1:5])
> tcl('set',a)  # output list
However
> tcl('test',a) # does not work as expected, returns the variable
name
Why not? In fact, how do get the name of the "a" list in tcl
(something
like RTcl...) so I could use it as follows
> .Tcl('test $RTcl1') #works
Loops are much quicker in tcl than in R, hence I try to do some
computations in tcl and not via wrapper function in R. I therefore need
a way to easily access tcl variables from within R and tcl.

Thanks for any help,

Adrian Waddell

On Thu, Aug 12, 2010 at 2:14 PM, Adrian Waddell <ml_a at waddell.ch>
wrote:
> Dear R users,
>
> I have some troubles with dealing with tclObj objects. I try to explain
> it with a toy example:
>
> Say I define the following tcl procedure which just prints out each list
> element
>
> library(tcltk)
> .Tcl('proc test {myList} {
> ? ?foreach i $myList {
> ? ? ?puts stdout ?$i
> ? ?}
> }')
>
> and I call it with:
>
>> tcl('test',letters[1:5]) ? ?# Works as expected
>
> Now say I define a tcl variable first:
>
>> a <- tclVar("")
>> tclObj(a) <- as.tclObj(letters[1:5])
>
>> tcl('set',a) ?# output list
>
> However
>
>> tcl('test',a) # does not work as expected, returns the variable
name
>
> Why not? In fact, how do get the name of the "a" list in tcl
(something
> like RTcl...) so I could use it as follows
>> .Tcl('test $RTcl1') #works
>
> Loops are much quicker in tcl than in R, hence I try to do some
> computations in tcl and not via wrapper function in R. I therefore need
> a way to easily access tcl variables from within R and tcl.
>
Try this:

tcl("test", tclvalue(a))

Adrian Waddell wrote:
> Dear R users,
> 
> I have some troubles with dealing with tclObj objects. I try to explain
> it with a toy example:
> 
> Say I define the following tcl procedure which just prints out each list
> element
> 
> library(tcltk)
> .Tcl('proc test {myList} {
>     foreach i $myList {
>       puts stdout  $i
>     }
> }')
> 
> and I call it with:
> 
>> tcl('test',letters[1:5])    # Works as expected
> 
> Now say I define a tcl variable first:
> 
>> a <- tclVar("")
>> tclObj(a) <- as.tclObj(letters[1:5])
> 
>> tcl('set',a)  # output list
> 
> However
> 
>> tcl('test',a) # does not work as expected, returns the variable
name
> 
> Why not? In fact, how do get the name of the "a" list in tcl
(something
> like RTcl...) so I could use it as follows
>> .Tcl('test $RTcl1') #works
> 
> Loops are much quicker in tcl than in R, hence I try to do some
> computations in tcl and not via wrapper function in R. I therefore need
> a way to easily access tcl variables from within R and tcl.
> 
> Thanks for any help,
Ow, that's been a while... However

tcl('test', tclvalue(a))

seems to do the trick, as does

tcl('test', tclObj(a))

The latter presumably being preferable, since it avoids conversion to
and from an R object.

If I remember these matters correctly, you are seeing the difference
between "set RTcl1" and "test $RTcl1".

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com