In article <··········@urmel.informatik.rwth-aachen.de>,
<·······@abmx.rz.rwth-aachen.de> wrote:
>
>
>my previous posting:
>
>
>
>> I read the answers to the NIL Question with interest, but back to the
>o> riginal posting.
>>
>> > While is NIL an Atom, and why do first rest and second applied to it
>>> return Nil instead of some sort of error ?
>>
>>
>> It leads me to the question, why is it not logical to say the CAR of nothing
>i> s nothing ?
>
>
>Indeed, thats's a dilemma. Based on the different meanings of NIL as already
>mentioned by some others.
>I gave it some thoughts:
>
>1. NIL stands for an empty list. But it IS a list ( (LISTP NIL) returns T,
> that's the supposition for applying CAR ),
> so (CAR NIL) should be appliable.
>
>2. NIL stands for Boolean false. (CAR NIL) returns NIL. So the returned
> value can also be interpreted as FALSE, there is no CAR. Seems to be
> logical too.
>
>3. But 1. and 2. leads to the dilemma
> (EQUAL (CONS (CAR x) (CDR x)) x) returns NIL if x is bound to NIL.
> *( thanks to Tim )*
>
>Think this puzzles some other guys already
>CLtL2 says: * By DEFINITION, the car of () is () * .
>
This thread has interested me greatly, since I had to learn about NIL
the hard way whilst implementing an interpreter. I would like to add
my $.02 worth:
I used to have CAR and CDR and similar functions return errors when
given NIL, but had to change when I ported som CL source. In the
process I have reasoned that the CL way of doing things is the result
of many years of evolution. It may be that the _reason_ behind many
things in CL has become lost, you might say, in the mists of
time. Things that evolve over time often defy cause-and-effect
identification of why they are as they are.
For example, people who make carriages use certain types of wood for
certain parts, possibly learned by word of mouth. They may not know
"why" they do it that way though.
This is one of the attractions of CL for me. Many of the protruding
gotchas you find in new languages have been worm smooth in CL. For
example, this NIL business. Most things in CL just fit together so
well, programming is much less frustrating than in say, C++.
Bill
--
····@zikzak.apana.org.au Bill Birch on ZikZak (Melbourne, Australia)
{:-) A bas la loi Toubon! {:-)
In article <··········@zikzak.apana.org.au>
····@zikzak.apana.org.au "Bill Birch" writes:
> This is one of the attractions of CL for me. Many of the protruding
> gotchas you find in new languages have been worm smooth in CL. For
> example, this NIL business. Most things in CL just fit together so
> well, programming is much less frustrating than in say, C++.
This was my feeling even when I could only read about it. I went
as far as writing my own interpreter (a small subset) of CL so
I could code in it. I now use CLISP, in spite the of the problems
I have running it on my machine.
C++ is still worse, in my opinion, tho that at least allows me to
write graphical apps. Still, some sacrifices must be made from time
to time, and this may be one of them, at least until I can get a
machine that can run Linux and X-Windows.
Perhaps MIT Scheme for MS Windows will keep me happy, but I'd prefer
CLISP. My present circumstances (a C compiler *full* of bugs, a
machine too old to run Linux) make that a distant possiblity.
--
Martin Rodgers, WKBBG, London UK AKA "Cyber Surfer"
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············@wildcard.demon.co.uk (Martin Rodgers) writes:
>I now use CLISP, in spite the of the problems
>I have running it on my machine.
>Perhaps MIT Scheme for MS Windows will keep me happy, but I'd prefer
>CLISP. My present circumstances (a C compiler *full* of bugs, a
>machine too old to run Linux) make that a distant possiblity.
Ouch, a 386 is distant possibility? Life must be rough in the UK.
In article <··········@ursula.ee.pdx.edu>
······@ee.pdx.edu "Marcus Daniels" writes:
> Ouch, a 386 is distant possibility? Life must be rough in the UK.
Oh, I have a 386 alright, but that's not enough if you want to run
X-Windows, so I'm told. That's a matter for another newsgroup...
--
Martin Rodgers, WKBBG, London UK AKA "Cyber Surfer"
If "One likes to believe in the freedom of email", email
················@cpsr.org and tell them you oppose Clipper.
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