I am not 100% sure what's going on, but you can use `read` mode this way:

    #lang racket
    (let ((a (read (open-input-string "#0=(0 . #0#)"))))
      (display (car a)))

I think the problem is that `read` / `write` support shared data constructed using `shared`. But programs (read by `read-syntax` are not allow to have cycles.