And this is where I really miss Sather:

  loop
    while!(condition);
    ...
  end;

for while, versus

  loop
    ...
    while!(condition);
  end;

for do-while, and

  loop
    ...
    while!(condition);
    ...
  end;

in place of:

  while True:
    ...
    if not condition:
      break
    ...

Alas, it never really took off.