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uplevel(3Tcl)							 uplevel(3Tcl)

NAME    [Toc]    [Back]

     uplevel - Execute a script	in a different stack frame

SYNOPSIS    [Toc]    [Back]

     uplevel ?level? arg ?arg ...?

DESCRIPTION    [Toc]    [Back]

     All of the	arg arguments are concatenated as if they had been passed to
     concat; the result	is then	evaluated in the variable context indicated by
     level.  Uplevel returns the result	of that	evaluation.

     If	level is an integer then it gives a distance (up the procedure calling
     stack) to move before executing the command.  If level consists of	#
     followed by a number then the number gives	an absolute level number.  If
     level is omitted then it defaults to 1.  Level cannot be defaulted	if the
     first command argument starts with	a digit	or #.

     For example, suppose that procedure a was invoked from top-level, and
     that it called b, and that	b called c.  Suppose that c invokes the
     uplevel command.  If level	is 1 or	#2  or omitted,	then the command will
     be	executed in the	variable context of b.	If level is 2 or #1 then the
     command will be executed in the variable context of a.  If	level is 3 or
     #0	then the command will be executed at top-level (only global variables
     will be visible).

     The uplevel command causes	the invoking procedure to disappear from the
     procedure calling stack while the command is being	executed.  In the
     above example, suppose c invokes the command

	  uplevel 1 {set x 43; d}

     where d is	another	Tcl procedure.	The set	command	will modify the
     variable x	in b's context,	and d will execute at level 3, as if called
     from b.  If it in turn executes the command

	  uplevel {set x 42}

     then the set command will modify the same variable	x in b's context:  the
     procedure c does not appear to be on the call stack when d	is executing.
     The command ``info	level''	may be used to obtain the level	of the current

     Uplevel makes it possible to implement new	control	constructs as Tcl
     procedures	(for example, uplevel could be used to implement the while
     construct as a Tcl	procedure).

KEYWORDS    [Toc]    [Back]

     context, stack frame, variables

									PPPPaaaaggggeeee 1111
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