[racket] Why choose the 'let*' construct over the 'define' construct when both can have sequential scope?

I recommend a macro for these situations, it's almost always what you want: 

(thread-through x e_0 e ...)
==
(let ([x e_0])
  (set! x e)
  ...
  x)

(you can also use let* here). 

This brings across what you're really doing. 
  


On Feb 19, 2015, at 1:32 PM, Jens Axel Søgaard <jensaxel at soegaard.net> wrote:

> We have let and let*, but only define. I miss define* at times.
> 
> This is an error:
> 
>    (block
>      (define x 4)
>      (define x (+ x 1))
>      (+ x 2))
> 
> With a define* it becomes:
> 
>    (block
>      (define x 4)
>      (define* x (+ x 1))
>      (+ x 2))
> 
> which (should) expand to:
> 
>    (block
>      (define x 4)
>      (block
>        (define x (+ x 1))
>        (+ x 2)))
> 
> /Jens Axel
> 
> 2015-02-19 19:24 GMT+01:00 Laurent <laurent.orseau at gmail.com>:
>> But in such situations you can be vicious and abuse `let` to have your
>> `define`s:
>> (let ()
>>  (define x 3)
>>  (define y 4)
>>  (list x y))
>> 
>> It's even more vicious if you use `let*` instead of `let`, but quite less if
>> you use `begin` instead ;)
>> 
>> 
>> 
>> On Thu, Feb 19, 2015 at 5:49 PM, Matthias Felleisen <matthias at ccs.neu.edu>
>> wrote:
>>> 
>>> 
>>> In some places, you are allowed only one expression, and for that
>>> situation, you need let*.
>>> 
>>> 
>>> On Feb 19, 2015, at 12:40 PM, Don Green <infodeveloperdon at gmail.com>
>>> wrote:
>>> 
>>>> What is/are the reason(s) for choosing the 'let*' construct over the
>>>> 'define' construct?
>>>> 
>>>> (define (print-two f)
>>>>  (let* ([_ (print (first f))]
>>>>         [f (rest f)]
>>>>         [_ (print (first f))]
>>>>         [f (rest f)])
>>>>    f))
>>>> 
>>>> (define print-two
>>>>  (lambda (f)
>>>>   (print (first f))
>>>>   (set! f (rest f))
>>>>   (print (first f))
>>>>   (set! f (rest f))
>>>>   f))
>>>> 
>>>> (void (print-two '(1 2))) ;=> 12
>>>> 
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> 
> 
> 
> -- 
> --
> Jens Axel Søgaard