WHILE _ _ _ _ _ _ _ _ _ _ _ _ command
The while command causes a statement to be repeatedly executed until a given condition is true. If the condition is initially false, the statement is not executed at all.
while<condition> do <statement>
<condition> is given by a logical operator, <statement> must be a single REDUCE statement, or a group (<<...>>) or begin...end block.
a := 10; A := 10 while a <= 12 do <<write a; a := a + 1>>; 10 11 12 while a < 5 do <<write a; a := a + 1>>; nothing is printed