[R] Open directory within a menu in tcltk

[Peter Dalgaard]

Judith Flores wrote:
> Hello,
>
>     I am trying to setup a menu to open files and directories. I have the following code:
>
>
>
>
> opendir<-function() {
>   dirname<<-tclvalue(tkchooseDirectory())
> }
>
> openfile<-function() {
>   filename<<-tclvalue(tkgetOpenFile())
> }
>
> require(tcltk)
> t1<-tktoplevel()
> topMenu<-tkmenu(t1)
> tkconfigure(t1,menu=topMenu)
>
> plotMenu<-tkmenu(topMenu, tearoff=FALSE)
>
> tkadd(plotMenu,"command",label="Open file", command=openfile)
> tkadd(plotMenu, "command",label="Select directory",command=opendir)
> tkadd(plotMenu,"command",label="Quit", command=function() tkdestroy(t1))
> tkadd(topMenu, "cascade", label="Menu",menu=plotMenu) 
>
> tkfocus(t1)
>
>   I can extract a file, but not a directory, I obtain the following error message:
>
> Error in function ():
> cannot change value of locked binding for 'dirname'.
>
>   I would appreciate very much any help or explanation on this.
>   

This is mainly the effect of an unfortunate choice of variable name. 
Beware the semantics of "<<-". You need to ensure that you have control 
of where the assignment goes to.

It is in general unfortunate to make such assignments to the global 
environment, where they can mask and clobber other objects. I'd consider 
a redesign along the lines of

myGui <- function(....) {
    opendir<-function() {
        dirname<<-tclvalue(tkchooseDirectory())
   }
    dirname <- NA
    tl <- tktoplevel()
   ......
}


> As always, thank you,
>
> Judith
>
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> and provide commented, minimal, self-contained, reproducible code.
>   


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