- | "array" -> Some ARRAY
- | "break" -> Some BREAK
- | "do" -> Some DO
- | "else" -> Some ELSE
- | "end" -> Some END
- | "for" -> Some FOR
- | "function" -> Some FUNCTION
- | "if" -> Some IF
- | "in" -> Some IN
- | "let" -> Some LET
- | "nil" -> Some NIL
- | "of" -> Some OF
- | "then" -> Some THEN
- | "to" -> Some TO
- | "type" -> Some TYPE
- | "var" -> Some VAR
- | "while" -> Some WHILE
- | _ -> Some (ID id)