[r6rs-discuss] Names in let* bindings

From: Jason Orendorff <jason.orendorff>
Date: Wed Oct 25 06:53:11 2006

Section 5.7 of R5.91RS says implementations must detect syntax
violations. In the definition of (let), section 9.5.6 says, "It is a
syntax violation for a <variable> to appear more than once in the list
of variables being bound." Section 9.5.6 then defines (let*) as

  similar to let, but the bindings
  are performed sequentially from left to right, and the
  region of a binding indicated by (<variable> <init>) is that
  part of the let* expression to the right of the binding.

I can't tell if the restriction on variable names in (let) is meant to
apply to (let*). Is the following allowed?

  (let* ((foo (make-foo))
         (foo (decorate foo)))
    ...)

If so, the spec could be clearer. If not, the example implementation
of (let*) using syntax-rules would appear to be incorrect. It doesn't
detect the error.

-j
Received on Wed Oct 25 2006 - 06:53:04 UTC