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[REBOL] Fwd: Re: Re: On mutability and sameness

From: robbo1mark:aol at: 20-Jun-2001 5:34

D'oh!!!!! stupid stupid stupid Mark! Of course defining '+ should read
>> set '+ func [x y] [add x y]
That way it works as I Intended. Sorry again! folks. Mark -- Attached file included as plaintext by Listar -- Return-Path: <[Robbo1Mark--aol--com]> Received: from ( []) by (v79.20) with ESMTP id MAILINID75-0620052012; Wed, 20 Jun 2001 05:20:12 -0400 Date: Wed, 20 Jun 2001 05:20:10 EDT From: [Robbo1Mark--aol--com] Subject:Re: [REBOL] Re: On mutability and sameness To: <[rebol-list--rebol--com]> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Mailer: Unknown (No Version) Message-ID: <[43--16dad16d--2861c4cc--aol--com]> REBOL AS IT'S OWN META-LANGUAGE I've read recently from Jeff & Joel, and other's in the previously, that REBOL is it's own meta-language. This is bunk! or at least only partially true. Yes for any particular instance or behaviour you can generally write a rebol function or object to model it's behaviour but you cannot do this for the "entirety" REBOL, sooner or later you run into irreducibility. Consider this model of REBOL addition...
>> add: func [ x y ] [ + x y ] >> add 1 2
== 3 Fine so far, however how do you define the '+ in the function body? If you say
>> set 'x func [ x y ] [ add x y ]
On the surface it looks okay, but try....
>> add 4 5
** Internal Error: Stack overflow ** Near: add x y
>> + 4 5
** Internal Error: Stack overflow ** Near: add x y
Your into infinite recursion here, so REBOL as a complete meta-language is "insufficient". However this is NOT a slight on REBOL just a fact about the notion of meta-languages, you CAN'T have a complete & self contained descriptive system. Here's a quote from Chuck Moore about Forth which equally applies to REBOL I like to quote Goedel on this, it goes back to 1930. he proved that a self contained formal system cannot be contained. horribly non- sequator but, all right within a system you can't describe itself. Within forth you can't describe Forth. Well, our systems are not so esoteric as Goedel's but I think you can say that within a system you cannot describe it simply. Now yes it is "preferable" to use REBOL to describe REBOL whenever possible as this should lead to "less" confusion however you simply "cannot" completely model REBOL in REBOL as a whole entity. If this was the case there would be no need for RT Inc. to write any more interpreters, we could simply write and extend REBOL in and from REBOL and we'd all live happily ever after. Unfortunitely there are these "irreducibles" or "primitives" that you simply MUST have to get the system up and running. It is for this reason that you sometimes have to use C or Java or something else to "explain" or implement REBOL. You can however devise a way to construct these "primitives" from within REBOL / your "meta-language" then you get into the realms and possibilities of META-COMPILATION which is a system written in itself, however you still have to bootstrap the whole process from something else first whether this be Assembler or C or Java or whatever. Forth proves this is possible and has had this capability for nearly thirty years now, maybe someday REBOL will catch up & we'll be dispensed with the need for RT to write our REBOL interpreters for us, if we so choose of course. 8-) Oh Dear, why am I always so contrary? I don't know about painting that fence Jeff, maybe I should come round from the wrong side of it and you can break the fence apart & hit me over the head with it! ; see I can be "light hearted" sometimes! Cheers my REBOL friends. Mark Dickson In a message dated Tue, 19 Jun 2001 2:16:27 PM Eastern Daylight Time, Jeff Kreis <[jeff--rebol--net]> writes: << Hello, Robbo:
> JEFF, > > I essence you are correct, but how easier can you more > properly explain these examples..... > > >> a: "123" > == "123" > >> b: a > == "123" > >> c: "123" > == "123" > > 'a & 'b are the "SAME" string! and refer to the same memory > location. 'c has the same value on the surface but is a > separate instance of a string! value and is stored at a > separate memory location.
I think explaining the above in C is vastly more complex than explaining it in terms REBOL has already established. You may very well wreak havoc on the understanding people DO have of the above by trying to explain it using C. 'A and 'B are both different words. They are NOT strings. Both words refer to (have the value of) the same string. 'C is also a different word than 'A and 'B. It refers to a different value (a different string). These particular notions of WORDS and VALUES are a distinct aspect of REBOL and they are not an aspect of C. WORDS and VALUES are within in the vocabulary of REBOL, but they are not to be found in the vocabulary of C. C's typed variables are an especially poor analogy to REBOL WORDS, for example please describe the following in C: word: 1 word: make object! [word: func [][print "I am a function"]] word: word/word word: 'word I can easily explain the above in terms of WORDS and VALUES, but I would find it very difficult to explain in terms of C's typed variables and pointers. That's like explaining calculus using Lincoln Logs. REBOL is first class and EVERYTHING is data. This concept is utterly absent from C. Please provide an example of how one may understand the nature of REBOL's first class code/data duality with C code.
> That is why this.... > > >> insert b "abc" > == "123" > >> b > == "abc123" > >> a > == "abc123" > >> c > == "123" > > The value of 'A & 'B both change but 'C remains unaltered. You can show this in 'C ( or some other language ) by use of pointers and references as Joel > did.
.."or some other language".. hmmm.. what would be a good language for describing REBOL... hmmm... maybe REBOL? It's its own metalanguage, afterall! :-)
> Similarly.... > > >> a: <abc> > == <abc> > >> parse a [b:] > == false > >> b > == "123" > > How do you explain that unless you drop down to C or > something else and show your any-string! or any-block! > models with pointers to memory storage for the actual "data" values. > In the above example both reference the "Same" string! > data but 'a has the datatype! value tag! whilst 'b is > a normal string! datatype!
Well, you might start by understanding that in REBOL there are WORDS and WORDS can refer to VALUES. (Words are VALUES themselves, by the way.) Once you have those concepts firmly in hand, move onto understanding how PARSE treats set-words in a rule. Would you explain the movement of the knight in chess in terms of the way you play checkers?
> Also what is wrong with helping your neighbour to paint > his fence is you neighbour is your friend?
It depends on the informed consent of the fence painter, and who claims credit for the fence being painted. :-) -jeff