Something goes wrong with a 'for' in a 'let'

[masak]

This works, as it should:

$ bel
Language::Bel 0.63 -- msys.
> (let x 0 (for i 1 1))
nil
>

But then this doesn't:

$ cat golf.bel
(let (x 0)
  (for i 1 1))

$ bel golf.bel
Error: bad-clo

Very weird. No idea why this happens; also no idea why it only happens in a file, not in the REPL.