 into <dfn>atomic constructors</dfn> and <dfn>aggregate constructors</dfn>; <dfn>aggregate initializers</dfn>; and <dfn>member handlers</dfn>.  An atomic constructor is invoked when the parser encounters an atomic datum (<code class="json">Number</code> or <code class="json">Boolean</code>), is passed the token which constitutes the datum, and is supposed to return the Lisp value that corresponds to the datum.  An aggregate initializer is invoked when the parser encounters the beginning of an aggregate datu