tkerror(n)		     Ck Built-In Commands		    tkerror(n)



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NAME
       tkerror - Command invoked to process background errors

SYNOPSIS
       tkerror message
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DESCRIPTION
       The tkerror command doesn't exist as built-in part of Ck.  Instead, in-
       dividual 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 origi-
       nate with the application.  For example, if an error occurs while  exe-
       cuting  a  command specified with a bind or 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 Ck library and there is no obvious way for Ck  to
       report the error.

       When  Ck detects a background error, it saves information about the er-
       ror and invokes the tkerror command later when Ck is idle.  Before  in-
       voking  tkerror,	 Ck  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.  Ck assumes that the ap-
       plication has implemented the tkerror command,  and  that  the  command
       will  report  the  error in a way that makes sense for the application.
       Ck 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 Ck 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 Ck 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



Ck				      8.0			    tkerror(n)
