> The thing is it only create many bugs when you throw closures into the mix. So historically languages did it because it was easy to implement (create a counter, increment the counter, run the loop body).

It's a problem with references in general as this shows.

I also don't feel it's easier to implement at all.

One can either rewrite:

   for $id:var in $exp:iter { $code:body }

to:

   { let $id:var;
     while(True) {
       let result = $exp:iter.next();
       if(result.is_none()) break;
       $id:Var <- result.extract();
       $code:body
     }
   }

Or

   while(True) {
     let result = $exp:iter.next();
     if(result.is_none()) break;
     let $id:var = result.extract();
     $code:body
   }

The latter implementation is as far as I see easier, not more complex. Obviously all the code to create scoping already exists in the compiler and for-loops over an iterator work with a syntactic rewrite to an infinite loop with a break.