[racket] Definitions in cond-bodies

Ah silly me, another senior moment :-) 


On Jun 8, 2012, at 12:06 PM, Robby Findler wrote:

> Yes, of course it is and that first branch executes and thus the error
> in the second branch (now a runtime error, thanks to the repl), is not
> signaled.
> 
> Robby
> 
> On Fri, Jun 8, 2012 at 11:01 AM, Matthias Felleisen
> <matthias at ccs.neu.edu> wrote:
>> 
>> With all due respect, I disagree. Like Jens, I consider the (define u ..) nested and scoped inside the first cond branch.
>> 
>> 
>> On Jun 8, 2012, at 11:56 AM, Sam Tobin-Hochstadt wrote:
>> 
>>> On Fri, Jun 8, 2012 at 11:42 AM, Jens Axel Søgaard
>>> <jensaxel at soegaard.net> wrote:
>>>> 
>>>> When
>>>> 
>>>> (let ([x 1])
>>>>  (cond
>>>>    [(= x 1)
>>>>     (define u 2)
>>>>     (+ u 1)]
>>>>    [else u]))
>>>> 
>>>> is pasted into the interaction window, I get 3  !
>>>> 
>>>> I was expecting an error.
>>> 
>>> This is the same behavior as:
>>> 
>>> -> (if #f x 1)
>>> 1
>>> 
>>> What's happening is that `#%top` behaves differently at the REPL than
>>> in a module.  This enables you to write:
>>> 
>>> -> (define (even? x) (or (zero? x) (odd? (sub1 x))))
>>> -> (define (odd? x) (or (= x 1) (even? (sub1 x))))
>>> 
>>> without getting an error when entering the first line.
>>> --
>>> sam th
>>> samth at ccs.neu.edu
>>> 
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>> 
>> 
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