Theres only a case here where iterating over a parent/child relationship, and testing for nullability, its more clear with the c-style for than with a while loop:

// old

for x: Thing? = thing; x != nil; x = x.parent {

  ...

}

// and now

var x: Thing? = thing

while x != nil {

  ...

  x = x.parent

}

It was the only case i've really missed it.. unless theres a better way to do it that im not aware of..

But the for c-style loop for numbers is really not needed