

Forms of cycle


    The permissible forms of cycle are these:

a)  %cycle      (endless cycle)
     :
    %repeat

b)  %while condition %cycle
     :
    %repeat

c)  %cycle
     :
    %repeat %until condition

d)  %for var = init, inc, final %cycle
     :
    %repeat


    The unconditional instructions  %continue  and  %exit  can  be  used
inside  a  cycle  of  any  type.   %continue causes a branch to the next
%repeat; %exit causes a branch  to  the  statement  following  the  next
%repeat.

    Notes on the cycle types:

b)  %while  cycles are executed zero or more times.  When the cycle body
    consists of a single statement, the form
    
          statement %while condition
    
    can be used.

    Example:
          SKIPSYMBOL %while NEXTSYMBOL=' '

    The IMP9 form %while condition %then statement is not allowed.


c)  %until cycles are executed one or more times.  The simple form is

          statement %until condition

    The IMP9 form %until condition %then statement is not allowed.


d)  %for cycles: the cycle variable must be of type %integer; it  should
    not  be  changed explicitly within the cycle body; the cycle body is
    executed (final-init) //inc + 1 times or zero  times,  whichever  is
    the  greater; if the cycle is not executed the cycle variable is set
    to be unassigned; (final-init) must be exactly divisible by  inc. It
    follows from this that a cycle starting

          %for I=10,1,8 %cycle

    will  not be executed, but will not be faulted either.  This differs
    from IMP9, where the equivalent form

          %cycle I=10,1,8

    would be faulted.

    The simple form of %for is

          statement %for var = init, inc, final

    Example:
          A(I)=0 %for I=20,-1,1

    [Going down in steps of -1 to 1 happens to be more efficient on EMAS
     2900 than the more usual 1,1,20.]