Editing Sather (section)

== Example of iterators ==

This program prints numbers from 1 to 10.

<syntaxhighlight lang="eiffel" line>
 class MAIN is
   main is
     loop
      i := 1.upto!(10);
      #OUT + i + "\n";
     end;
   end;
 end;
</syntaxhighlight>

The <code>loop</code> ... <code>end</code> construct is the preferred means of defining loops, although <code>while</code> and <code>repeat</code>-<code>until</code> are also available. Within the construct, one or more iterators may be used. Iterator names always end with an exclamation mark. (This convention is enforced by the compiler.) <code>upto!</code> is a method of the <code>INT</code> class accepting one <code>once</code> argument, meaning its value won't change as the iterator yields. <code>upto!</code> could be implemented in the <code>INT</code> class with code similar to the following one.

<syntaxhighlight lang="eiffel">
  upto!(once m:INT):SAME is
    i: INT := self; -- initialise i to the value of self, 
                    -- that is the integer of which this method is called
    loop
      if i>m then 
        quit;  -- leave the loop when i goes beyond m
      end;
      yield i; -- else use i as return value and stay in the loop
      i := i + 1; -- and increment
    end;
  end;
</syntaxhighlight>

Type information for variables is denoted by the postfix syntax <code>variable:CLASS</code>. The type can often be inferred and thus the typing information is optional, as in <code>anInteger::=1</code>. <code>SAME</code> is a pseudo-class referring to the current class.