loop var first limit ?increment? body
Loop is a looping command, similar in behavior to
the Tcl for statement, except that the loop state-
ment achieves substantially higher performance and
is easier to code when the beginning and ending
values of a loop are known, and the loop variable
is to be incremented by a known, fixed amount every
time through the loop.
The var argument is the name of a Tcl variable
that will contain the loop index. The loop index
is set to the value specified by first. The Tcl
interpreter is invoked upon body zero or more
times, where var is incremented by increment every
time through the loop, or by one if increment is
not specified. Increment can be negative in which
case the loop will count downwards.
When var reaches limit, the loop terminates without
a subsequent execution of body. For instance, if
the original loop parameters would cause loop to
terminate, say first was one, limit was zero and
increment was not specified or was non-negative,
body is not executed at all and loop returns.
The first, limit and increment are integer expres-
sions. They are only evaluated once at the begin-
ning of the loop.
If a continue command is invoked within body then
any remaining commands in the current execution of
body are skipped, as in the for command. If a
break command is invoked within body then the loop
command will return immediately. Loop returns an
empty string.
This command is provided by Extended Tcl.