⟨Datum⟩ is what the read procedure (see Input)
successfully parses. Note that any string that parses as an
⟨expression⟩ will also parse as a ⟨datum⟩.
⟨datum⟩ ⟶ ⟨simple datum⟩ | ⟨compound datum⟩ | ⟨label⟩=⟨datum⟩ | ⟨label⟩# ⟨simple datum⟩ ⟶ ⟨boolean⟩ | ⟨number⟩ | ⟨character⟩ | ⟨string⟩ | ⟨symbol⟩ | ⟨bytevector⟩ ⟨symbol⟩ ⟶ ⟨identifier⟩ ⟨compound datum⟩ ⟶ ⟨list⟩ | ⟨vector⟩ | ⟨abbreviation⟩ ⟨list⟩ ⟶ (⟨datum⟩*) | (⟨datum⟩+ . ⟨datum⟩) ⟨abbreviation⟩ ⟶ ⟨abbrev prefix⟩ ⟨datum⟩ ⟨abbrev prefix⟩ ⟶ ' | ` | , | ,@ ⟨vector⟩ ⟶ #(⟨datum⟩*) ⟨label⟩ ⟶ #⟨uinteger 10⟩