Comment by GregBuchholz

It looks like Racket nerfed the shared-structure / "Datum Labels" for circular lists and the like (I see it is still in section 2.4 of r7rs):

  '#0=(0 . #0#)

...and I should have included `#|block comments|#`, datum `#;comments`, and probably `|symbols with spaces|`.

  (let ((|1 + 2| (+ 1 2)))
    (display |1 + 2|))