program = empty list | proper list.
empty list = {white space}.
proper list = datum, [";", proper list].
datum = form | expression.
form = operator, (form | expressions)
     | (form | expressions), operator, [(form | expressions)].
operator = identifier.
identifier = <any unicode non-digit, non-separator character>
             {<any unicode non-separator character>}.
expressions = (expression | block), [expressions].
block = "(", proper list ")".
expression = variable | literal | compound expression.
variable = identifier.
literal = atom | number | string.
atom = "#" (identifier | string).
number = [sign] digits ["." digits].
digits = digit {digit}.
digit = "0" | ... | "9".
compound expression = list | vector | function call | method call.
list = "{", (empty list | (proper list, [".", datum])), "}".
vector = "#{", (empty list | proper list), "}".
function call = expression, "[", (empty list | proper list), "]".
method call = expression, atom, "[", (empty list | proper list), "]".