bgerror man page on UnixWare

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bgerror(n)		     Tcl Built-In Commands		    bgerror(n)


       bgerror - Command invoked to process background errors

       bgerror message

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

       A background error is one that occurs in an event handler or some other
       command that didn't originate with the application.  For example, if an
       error  occurs  while  executing a command specified with the after com‐
       mand, 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 appli‐
       cation  can  report  the error in whatever way it wishes.  When a back‐
       ground error occurs, the unwinding ends in the Tcl library and there is
       no obvious way for Tcl to report the error.

       When  Tcl  detects  a  background error, it saves information about the
       error and invokes the bgerror command later as an idle  event  handler.
       Before invoking bgerror, Tcl restores the errorInfo and errorCode vari‐
       ables to their values at the time the error occurred, then  it  invokes
       bgerror	with the error message as its only argument.  Tcl assumes that
       the application has implemented the bgerror command, and that the  com‐
       mand  will  report the error in a way that makes sense for the applica‐
       tion.  Tcl will ignore any result returned by the  bgerror  command  as
       long as no error is generated.

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

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

       Tcl has no default implementation for bgerror.	However,  in  applica‐
       tions  using Tk there is a default bgerror procedure which posts a dia‐
       log box containing the error message and offers the user	 a  chance  to
       see a stack trace showing where the error occurred.

       background error, reporting

Tcl				      7.5			    bgerror(n)
                             _         _         _ 
                            | |       | |       | |     
                            | |       | |       | |     
                         __ | | __ __ | | __ __ | | __  
                         \ \| |/ / \ \| |/ / \ \| |/ /  
                          \ \ / /   \ \ / /   \ \ / /   
                           \   /     \   /     \   /    
                            \_/       \_/       \_/ 
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