[racket] TLS "atom?" definition for Scheme does not work in DrRacket

Well that’s weird.  And after it stopped working with the parens, then it worked without them?
It doesn’t do that for me:
(define atom? (lambda (arg1)
                and (not (pair? arg1))
                    (not (null? arg1))))
;. and: bad syntax in: and

Is there a specific way to reproduce it?


On Mar 3, 2015, at 3:50 PM, Rufus <rlaggren at mail.com> wrote:

> Alexander
> 
> Well, in fact, I thought it worked for me, too. And then it stopped
> working; DrR threw an  "application: not a procedure;" error saying it
> was given a null list instead of an application. Removing the parens got
> it working again.
> 
> Now that just doesn't make any sense at all but that's what I seem to
> have observed. Looking at some StackOverflow responses on similar errors
> I found that parens in certain positions are interpreted as invoking a
> function regardless of what may in fact be inside the parens. IOW, extra
> parens will trigger that error. I believe that initially it was working.
> Perhaps I had run it in the executable pane instead of loading and
> running the defs file? If I have more time somewhere along, I'll try to
> recreate things.
> 
> When I first defined atom? I was using a very small definitions file
> with the " #lang racket" spec; IIRC atom? worked. After trying BSL and
> then going back to using the #lang spec and adding some comments and the
> list of variable defs - it didn't work.
> 
> At the moment I don't have any good ideas, except to chg the code to get
> it to work and proceed.
> 
> Rufus
> 
> 
> 
> On 03/03/2015 02:21 PM, Alexander D. Knauth wrote:
>> This works for me:
>> (define atom? (lambda (arg1)
>>                (and (not (pair? arg1))
>>                     (not (null? arg1)))))
>> 
>> 
>> On Mar 3, 2015, at 3:16 PM, Rufus <rlaggren at mail.com> wrote:
>> 
>>> On page 10 of TLS there is a note defining the "atom?" function for the
>>> reader to use w/Lisp or Scheme. The definition for Scheme (which is the
>>> most likely one to use for DrR) does not work. To fix one must remove
>>> the parens that open at the "and". Apparently the DrR
>>> compiler/interpreter sees them as an attempt to invoke a function and
>>> that's not correct here. I don't know if other Lisp versions would find
>>> the code in the book correct.
>>> 
>>> In the text below XXX shows where I removed a set of parens to make the
>>> function work.
>>> 
>>> (define atom? (lambda (arg1)
>>>              XXX and (not (pair? arg1))
>>>                      (not (null? arg1))
>>>              XXX
>>>             )
>>> )
>>> 
>>> 
>>> Rufus
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>>> Racket Users list:
>>> http://lists.racket-lang.org/users
>> 
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