lows.  Below, body, expression,
and identifier are free.  Each instantiation of binding-name must be
unique.
</p>

<p>
<pre>
            let = "(" "let" let-bindings body ")"
    expressions = nothing | expression expressions
   let-bindings = let-name bindings
                | "(" let-name "." bindings ")"
       let-name = identifier
       bindings = "(" ")"
                | rest-binding
                | "(" normal-bindings ["." rest-binding] ")"
normal-bindings = nothi