The procedure until is not in the core, but you can define it yourself as follows:
proc until {cond code} { uplevel 1 [list while !($cond) $code] }
See also control::do (in tcllib).
PL: The original rewriting of the command was like this:
list while !$cond $code
but that doesn't work since a cond value of, say, $i > 5 is rewritten as the condition argument !$i > 5 which will always evaluate to false (the ! operator has priority, and the result of evaluating it is either 1 or 0, which is never greater than 5). Other condition strings are likely to lead to other interesting errors.
Rewriting the command as
list while !($cond) $code
ensures that all of $cond is evaluated before negating the result.
This doesn't implement the usual meaning of until, which executes the code and then tests cond after.
Larry Smith I use:
# an unbounded loop or one with a terminating condition of while or until. # always executes at least once. If no while or until conditions is attached, # loops forever until <break>. proc repeat {args} { > script whenexit test if {[catch {^^ $script} err]} ^ case $whenexit { "" {^^ "while 1 \{$script\}"} "while" {^^ "while \{$test\} \{$script\}"} "until" {^^ "while \{!($test)\} \{$script\}"} } }
The advantage of the above is you can leave out the while or until entirely and just use break to exit from anywhere in the loop.
DKF: The usual definition is typically expressed as a do-while loop, which is a form that puts the test last. When expressed condition-first, it is natural to expect the condition to be checked first...
RLH Someone else was thinking about this too: until