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From: Tim Bradshaw on 2 May 2010 04:33
On 2010-05-01 18:53:01 +0100, RG said:

> Lisp doesn't distinguish between statements and expressions. Instead,
> Lisp conflates those two concepts into one, called a FORM. What I said
> was that MOST FORMS return a value, and that this is true for most
> languages.

And, in Lisp, ALL forms can be used in a place which syntactially
expects a value or values (possibly creating a run-time error if there
is a mismatch in value count, which may in turn be elevated to
compile-time in some cases with a sufficiently smart compiler). This
is not true in languages which have several kinds of form.

From: Tim Bradshaw on 2 May 2010 04:35
On 2010-05-01 19:23:58 +0100, Espen Vestre said:

> But is the space of lisp return values a Hilbert space?

No, there's no norm, and I think Hilbert spaces need one

From: Espen Vestre on 2 May 2010 16:00
Tim Bradshaw <tfb(a)tfeb.org> writes:

>> But is the space of lisp return values a Hilbert space?
>
> No, there's no norm, and I think Hilbert spaces need one

:-)

--
(espen)
From: Rob Warnock on 3 May 2010 04:00
Tim Bradshaw <tfb(a)tfeb.org> wrote:
+---------------
| Espen Vestre said:
| > But is the space of lisp return values a Hilbert space?
|
| No, there's no norm, and I think Hilbert spaces need one
+---------------

Is Cheers a Hilbert space?

http://en.wikipedia.org/wiki/Norm_Peterson


-Rob

-----
Rob Warnock <rpw3(a)rpw3.org>
627 26th Avenue <URL:http://rpw3.org/>
San Mateo, CA 94403 (650)572-2607

From: Johan Ur Riise on 3 May 2010 05:37
Espen Vestre <espen(a)vestre.net> writes:

> His kennyness <kentilton(a)gmail.com> writes:
>
>> meanwhile, here, I'll ask floor for its third value and see what it says:
>>
>> (nth-value 3 (floor 42 10)) -> nil
>
> I can "ask" nth-value for it googolth value, and it still returns nil:
>
> CL-USER 9 > (defparameter *googol* (expt 10 100))
> *GOOGOL*
>
> CL-USER 10 > (nth-value *googol* (floor 42 10))
> NIL
>
> But the definition of nth-value actually says the following: "Evaluates
> n and then form, returning as its only value the nth value yielded by
> form, or nil if n is greater than or equal to the number of values
> returned by form. (The first returned value is numbered 0.)".

We obviously need a new nth-value, free of this defect.
Here nth-value-x returns two values, the second is T if
the nth value in fact exists, nil else.

(defmacro nth-value-x (n form)
`(let ((reslist (multiple-value-list ,form)))
(if (> ,n (length reslist))
(values nil nil)
(values (nth ,n reslist) t))))

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