R help - Nov 2008 - breaking out of a loop from within a function

Hello useRs,

I would like to break out of a for loop from within a function upon
some user input. For example, a user hits "Cancel" from a tcl widget 
called iteratively within a for loop. The for loop then breaks at the 
current iteration.

I can only seem to get break and stop to work at the top-level.

The following example would make this more clear:


#start tcltk
require(tcltk)

#Define a R+tlk/tk environment from which to obtain user input   
   checktext<-function(event,anchor,text1,text2){   
      fun.env<-environment()
      hdr<-paste("You are coding disputed event:",event,
"\n\t","located
at anchor:",anchor,sep=" ")
      a<-0
      OnAdvance <- function()
      {
         assign("a",tclvalue(tt.acceptval),envir=fun.env)
         tkdestroy(tt)
      }
      OnStop <- function()
      {
  #Here is where the break function is defined for tcl
       break
       tkdestroy(tt)
      }
      tt <- tktoplevel()
      tt.header<-
tktext(tt,bg="lightpink",fg="black",width=50,height=5)
      tt.text1 <- 
tktext(tt,bg=gray(.05),font="courier",fg="lightblue",width=50,height=25)
      tt.text2 <- 
tktext(tt,bg=gray(.05),font="courier",fg="lightgreen",width=50,height=25)
      tt.accept<-tkcheckbutton(tt,text="Accept Code",width=10)
      tt.acceptval<-tclVar("0")
      tkconfigure(tt.accept,variable=tt.acceptval)
      tt.advance<-tkbutton(tt,text="Advance 
Recon",command=OnAdvance,bg="green")
      tt.stop<-tkbutton(tt,text="Stop
Recon",command=OnStop,bg="red")
      tkinsert(tt.header,"end",hdr)
      tkinsert(tt.text1,"end",text1)
      tkinsert(tt.text2,"end",text2)
      tkgrid(tt.header,column=1,row=1,columnspan=3)
      tkgrid(tt.text1,column=2,row=2)
      tkgrid(tt.text2,column=3,row=2)
      tkgrid(tt.accept,column=2,row=4,rowspan=3)
      tkgrid(tt.advance,column=3,row=4,rowspan=3,sticky="w")
      tkgrid(tt.stop,column=3,row=4,sticky="e")
      tkfocus(tt)
      tkwait.window(tt)
      a
   }

#Some arbitrary text to code
event<-"blup"
anchor<-"1234"
text1<-"Batman struck the Riddler with his gauntlet.
KAPOW!<anchor=1234>"
text2<-"Batman struck the Riddler with his gauntlet. KAPOW!"

#Ideally, if the user hits "Cancel" the loop would end on the current 
ith iteration and return to the console
output<-NULL
for(i in 1:3){
output[i]<-checktext(rep(event,3)[i],rep(anchor,3)[i],text1,text2)
}


Regards,
Christopher Marcum
Department of Sociology / Cal(it)^2
University of California - Irvine