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


       after - Execute a command after a time delay

       after ms

       after ms ?script script script ...?

       after cancel id

       after cancel script script script ...

       after idle ?script script script ...?

       after info ?id?

       This  command is used to delay execution of the program or to execute a
       command in background sometime in the future.  It  has  several	forms,
       depending on the first argument to the command:

       after ms
	      Ms  must	be an integer giving a time in milliseconds.  The com‐
	      mand sleeps for ms milliseconds and  then	 returns.   While  the
	      command is sleeping the application does not respond to events.

       after ms ?script script script ...?
	      In  this	form  the command returns immediately, but it arranges
	      for a Tcl command to be executed ms  milliseconds	 later	as  an
	      event  handler.	The  command will be executed exactly once, at
	      the given time.  The delayed command is formed by	 concatenating
	      all  the script arguments in the same fashion as the concat com‐
	      mand.  The command will be executed at global level (outside the
	      context of any Tcl procedure).  If an error occurs while execut‐
	      ing the delayed command then the bgerror mechanism  is  used  to
	      report  the error.  The after command returns an identifier that
	      can be used to cancel the delayed command using after cancel.

       after cancel id
	      Cancels the execution of a delayed command that  was  previously
	      scheduled.   Id  indicates which command should be canceled;  it
	      must have been the return value from a previous  after  command.
	      If  the  command	given by id has already been executed then the
	      after cancel command has no effect.

       after cancel script script ...
	      This command also cancels the execution of  a  delayed  command.
	      The  script arguments are concatenated together with space sepa‐
	      rators (just as in the concat command).  If there is  a  pending
	      command  that matches the string, it is cancelled and will never
	      be executed;  if no such command is currently pending  then  the
	      after cancel command has no effect.

       after idle script ?script script ...?
	      Concatenates the script arguments together with space separators
	      (just as in the concat command), and arranges for the  resulting
	      script  to  be  evaluated later as an idle callback.  The script
	      will be run exactly once,	 the  next  time  the  event  loop  is
	      entered and there are no events to process.  The command returns
	      an identifier that can be used to	 cancel	 the  delayed  command
	      using  after  cancel.   If  an  error occurs while executing the
	      script then the bgerror mechanism is used to report the error.

       after info ?id?
	      This command returns information about existing event  handlers.
	      If no id argument is supplied, the command returns a list of the
	      identifiers for all existing event handlers created by the after
	      command  for  this interpreter.  If id is supplied, it specifies
	      an existing handler; id must have been  the  return  value  from
	      some  previous  call to after and it must not have triggered yet
	      or been cancelled.  In this case the command returns a list with
	      two elements.  The first element of the list is the script asso‐
	      ciated with id, and the second element is either idle  or	 timer
	      to indicate what kind of event handler it is.

       The after ms and after idle forms of the command assume that the appli‐
       cation is event driven:	the delayed  commands  will  not  be  executed
       unless the application enters the event loop.  In applications that are
       not normally event-driven, such as tclsh, the event loop can be entered
       with the vwait and update commands.

       This defines a command to make Tcl do nothing at all for N seconds:
	      proc sleep {N} {
		 after [expr {int($N * 1000)}]

       This arranges for the command wake_up to be run in eight hours (provid‐
       ing the event loop is active at that time):
	      after [expr {1000 * 60 * 60 * 8}] wake_up

       The following command can be used to do long-running  calculations  (as
       represented  here  by ::my_calc::one_step, which is assumed to return a
       boolean indicating whether another step should be performed) in a step-
       by-step	fashion, though the calculation itself needs to be arranged so
       it can work step-wise.  This technique is extra careful to ensure  that
       the  event  loop is not starved by the rescheduling of processing steps
       (arranging for the next step to	be  done  using	 an  already-triggered
       timer  event  only when the event queue has been drained) and is useful
       when you want to ensure that a Tk GUI remains responsive during a  slow
	      proc doOneStep {} {
		 if {[::my_calc::one_step]} {
		    after idle [list after 0 doOneStep]

       bgerror(n), concat(n), update(n), vwait(n)

       cancel, delay, idle callback, sleep, time

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