uplevel(n) Tcl Built-In Commands uplevel(n)_________________________________________________________________NAMEuplevel - Execute a script in a different stack frame
SYNOPSISuplevel ?level? arg ?arg ...?
_________________________________________________________________DESCRIPTION
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 com-
mand. 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 dis-
appear 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
procedure.
Uplevel makes it possible to implement new control con-
structs as Tcl procedures (for example, uplevel could be
used to implement the while construct as a Tcl procedure).
Tcl 1
uplevel(n) Tcl Built-In Commands uplevel(n)KEYWORDS
context, stack frame, variables
Tcl 2
