repeat;commands;until(false) - Looping control statement.

 repeat
   <commands>
 until(logical_expression)

This is a special looping structure for use in writing procedures.
At the end of each iteration of the loop, the logical argument of
the until command is evaluated.  If it is FALSE then the next
iteration proceeds and the commands within the loop are executed.
Otherwise execution will continue from the command following the
'until()' command.  This means that commands inside the loop will
be executed at least once - if this is not desirable, use the
alternative while(condition);...;end while structure.

There are also break and continue commands for breaking out of the
loop or starting the next iteration prematurely. See help looping
for more details.

Example:
0> i=0
0> repeat
1>   i=i+1
1>   print i
1> until(i>5)
1> print "Loop completed - i is now=",i

results in:
1.000000
2.000000
3.000000
4.000000
5.000000
6.000000
Loop completed - i is now= 6.000000