Re: [PATCH] Move ambitus print callback to scheme

[David Kastrup]

Carl Sorensen <address@hidden> writes:

> On 8/28/09 10:56 PM, "David Kastrup" <address@hidden> wrote:
>
>> Carl Sorensen <address@hidden> writes:
>> 
>>> On Aug 28, 2009, at 1:16 PM, "Nicolas Sceaux" <address@hidden>
>>> wrote:
>>> 
>>>> 
>>>> According to R5RS, it is an error to modify a literal list.
>>>> If a function returns '(), the caller won't be allowed to
>>>> apply a modifying function on the result (eg. append!)
>>>> 
>>> 
>>> IIUC, '() is not a literal list, but a constant that represents the
>>> empty list.
>> 
>> It is a literal list in my opinion, but one that happens to have no
>> unique and/or modifiable conses.  Append will work just fine on it.
>
> It is *not* a literal list.
>
> Here is the proof:
>
> guile> (define a '(4 5))
> guile> (define b '(4 5))
> guile> (eq? a b)
> #f
> guile> (define c '())
> guile> (define d '())
> guile> (eq? c d)
> #t
>
>
> '(4 5) is a literal list, and thus a is not eq? to b, although it is equal?
> to b

Huh?  What kind of argument is that supposed to be?

(define a 4)
(define b 4)
(eq? a b)

Would you claim that 4 is not a literal integer?

'() is literal (namely explicitly specified) and it is a list (namely a
cons or nil).

'() is not a literal _cons_, and it is not unique.  But it certainly is
literal (a spelled out value) and a list.


> On the other hand, c is eq? to d, because '() is a constant, and both c and
> d are set to the same constant.

I think you are just confused about the meaning of "literal".

-- 
David Kastrup