tkerror(3Tk)

NAME
     tkerror - Command invoked to process background errors

SYNOPSIS
     tkerror message


DESCRIPTION
     The tkerror command doesn't exist as built-in part of Tk.  Instead,
     individual applications or users can define a tkerror command (e.g. as a
     Tcl procedure) if they wish to handle background errors.

     A background error is one that occurs in a command that didn't originate
     with the application.  For example, if an error occurs while executing a
     command specified with a bind of after command, then it is a background
     error.  For a non-background error, the error can simply be returned up
     through nested Tcl command evaluations until it reaches the top-level
     code in the application; then the application can report the error in
     whatever way it wishes.  When a background error occurs, the unwinding
     ends in the Tk library and there is no obvious way for Tk to report the
     error.

     When Tk detects a background error, it saves information about the error |
     and invokes the tkerror command later when Tk is idle.  Before invoking  |
     tkerror, Tk restores the errorInfo and errorCode variables to their      |
     values at the time the error occurred, then it invokes tkerror with the
     error message as its only argument.  Tk assumes that the application has
     implemented the tkerror command, and that the command will report the
     error in a way that makes sense for the application.  Tk will ignore any
     result returned by the tkerror command.

     If another Tcl error occurs within the tkerror command (for example,
     because no tkerror command has been defined) then Tk reports the error
     itself by writing a message to stderr.

     If several background errors accumulate before tkerror is invoked to     |
     process them, tkerror will be invoked once for each error, in the order  |
     they occurred.  However, if tkerror returns with a break exception, then |
     any remaining errors are skipped without calling tkerror.

     The Tk script library includes a default tkerror procedure that posts a
     dialog box containing the error message and offers the user a chance to
     see a stack trace showing where the error occurred.


KEYWORDS
     background error, reporting