loop ::= ['while' expression ] 'loop' block 'end' .
Example: loop i := 1.upto!(10) ...end 
A loop statement while e loop S end is processed by repeating the evaluation of e and the execution of the block S, the body of the loop, as long as the expression e evaluates to true or until a statement terminating the loop is executed. e must be of type BOOL. loop S end has the same meaning as while true loop S end.
The statement break terminates the innermost loop containing it. It must be syntactically contained within a loop.
A loop body may contain one or more stream calls like until! or upto! which may influence the termination of the loop, cf. 6.7.2.