[plt-scheme] Comments on an alternate syntax for let?

On 07/04/2008, Majorinc, Kazimir <kazimir at chem.pmf.hr> wrote:
>  What is the the advantage of
>
>  (let ((x 0)(y 1)(z 2)) ...)
>
>  over
>
>  (let ()
>    (define x 0)
>    (define y 1)
>    (define z 2)
>    ...)
>
>  except that simultaneus evaluation in the first case? What we can not do
> with second and we can with first?

The second is equivalent to a letrec. The first example which pops to mind is

>
(let ((x 1)
      (y 6))
  (let ((x (add1 x))
        (y (sub1 y)))
    (+ x y)))
7
>
(let ()
  (define x 1)
  (define y 6)
  (let ()
    (define x (add1 x))
    (define y (sub1 y))
    (+ x y)))
add1: expects argument of type <number>; given #<undefined>

    Henk Boom