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From: Don Geddis on 4 May 2010 13:58
His kennyness <kentilton(a)gmail.com> wrote on Sat, 01 May 2010:
> RG wrote:
>> So when I met McCarthy for the first time a few years back [...]
> When John asked to use my laptop at the same conference [...]

Oh! Is this a game of "personal encounters with Saint John McCarthy"?
Can I play?

"When I was giving my thesis defense and Johnny Boy was on my committee,
he fell asleep during my presentation. Later, during the private
question section, he gave a long anecdote about some other work he had
recently encountered, and asked whether that related to my own work. I
replied 'no'. McCarthy had no further questions."

(Just to be clear: the previous story in no way reflects on my great
respect for McCarthy's enormous contributions to computer science and AI.)
_______________________________________________________________________________
Don Geddis http://don.geddis.org/ don(a)geddis.org
From: RG on 4 May 2010 15:04
In article <87vdb3mtun.fsf(a)mail.geddis.org>,
Don Geddis <don(a)geddis.org> wrote:

> His kennyness <kentilton(a)gmail.com> wrote on Sat, 01 May 2010:
> > RG wrote:
> >> So when I met McCarthy for the first time a few years back [...]
> > When John asked to use my laptop at the same conference [...]
>
> Oh! Is this a game of "personal encounters with Saint John McCarthy"?

Actually, my intention was for it to be a game of "let's mess with
Kazimir Majornic's head." But it seems to be mutating rapidly into a
game of "how outrageously improbable can a story be without people on
c.l.l. realizing that it's a joke."

> Can I play?

Apparently.

rg
From: Scott L. Burson on 4 May 2010 17:28
In a Herbrand universe, no one can hear you scream.

-- Scott

From: Captain Obvious on 5 May 2010 04:13
??>> Once again, McCarthy _defines_ what symbolic expressions are, in his
??>> own way. If he would take some widely used term and hijack it defining
??>> it in its own way, that would be really stupid. Do you think that
??>> McCarthy is stupid?
??>>
KM> You are too emotional.

Huh? That was logical reasoning.. Syllogism.

(1) McCarthy creates new definition for symbolic expression.
(2) One who creates new definition for something which is already defined
in other way is dumb.
(3) Symbolic expressions were already defined.
=> (4) McCarthy is dumb.

Either that, or symbolic expressions were not already defined.

KM> It is impossible to productively discuss in terms like "computer
KM> scientist X was stupid" and similar.

Well, change it to "was mistaken" if you're so serious.
But I think no sane person would make mistake like that.
Don't let your emotions to interfere with your reasoning.

From: His kennyness on 5 May 2010 08:05
Captain Obvious wrote:
> KM> The term "formula" is usual for such, purely syntactic objects. For
> KM> example, in propositional logic theories, one will speak about
> KM> "formulas", and if context is needed, "formulas of propositional
> KM> calculus." "Expression" has a connotation of expressing something that
> KM> existed prior to, well, its "expression."
>
> Let's look up wikipedia on difference between expression and formula:
>
> http://en.wikipedia.org/wiki/Expression_(mathematics)
> ----
> In mathematics, an expression is a finite combination of symbols that are
> well-formed according to the rules applicable in the context at hand.
> Symbols can designate values (constants), variables, operations, relations,
> or can constitute punctuation or other syntactic entities.
> ----
>
> http://en.wikipedia.org/wiki/Formula
> -----
> In mathematics, a formula (plural: formulas or formulae) is an entity
> constructed using the symbols and formation rules of a given logical
> language.
>
> In science, a formula is a concise way of expressing information
> symbolically (as in a mathematical or chemical formula), or a general
> relationship between quantities. Colloquial use of the term in mathematics
> often refers to a similar construct.
> ...
> Expressions are distinct from formulas in that they cannot contain an
> equals
> sign; whereas formulas are comparable to sentences, expressions are more
> like phrases.
> -----
>
> So, if you have a thing like `3x+2`, it is an expression. (And it very
> well coresponds to a Lisp "form", by the way.)
> If you have `3x+2=y-5`, then it is an equation.
>
> And where is formula then? Technically, both are, but expression and
> equation are more specific and useful terms to describe objects so you
> can work with them (simplify an expression, solve an equation).
>
> So term 'formula' is not that widely used in math. I think it is mostly
> used in context of theorems and laws, e.g. `v = s/t` is a formula for
> calculating speed.
>
> I dunno about logic, maybe you use formulas more widely there, but I
> don't think it is relevant here.
>
> I believe that expression is the right term, as it matches what Lisp does.
>
> KM> Lisp is introduced on very formal way. "S-expressions" are defined
> KM> syntactically, without "model" - and one possible "representation" is
> KM> introduced later.
>
> Are you sure we're reading same paper? I think textual representation
> and semantical representation are defined in parallel. Perhaps it's just
> a bit easier to speak about semantics when you've already explained how
> to denote the damn thing.
>
> But note what is the first sentence of the section "Recursive Functions
> of Symbolic Expressions":
> http://www-formal.stanford.edu/jmc/recursive/node3.html
>
> "We shall first define a class of symbolic expressions in terms of
> ordered pairs and lists."
>
> Ordered pairs and lists, not parentheses and dots!
> I think it's sends us a clear message that McCarthy considers semantics
> more important than textual representation. (Duh.)
>
> KM> But OK, my guess is that McCarthy wasn't that pedantic, and he used
> KM> "expression" because he followed tradition of lambda calculus.
>
> Is it a bad thing? Probably it is better to follow traditional
> terminology than some "connotations" which Kazimir Majorinc have just
> made up.
>
> KM> But, why "symbolic expressions"?
>
> Because those are expressions consisting of symbols, duh.
>
> "A Class of Symbolic Expressions. We shall now define the S-expressions (S
> stands for symbolic). They are formed by using the special characters . ( )
> and and an infinite set of distinguishable atomic symbols."
>
> SYMBOLS.
> DISTINGUISHABLE ATOMIC SYMBOLS.
>
> This is a huge thing, actually. There are some programming languages
> which try to implement macros on text level and it doesn't really work.
> Using atomic symbols allowed to skip all non-essential bullshit and
> concentrate on important.
>
> Actually it is explained in the paper:
>
> "There is a twofold reason for departing from the usual mathematical
> practice of using single letters for atomic symbols. First, computer
> programs frequently require hundreds of distinguishable symbols that
> must be formed from the 47 characters that are printable by the IBM 704
> computer. Second, it is convenient to allow English words and phrases to
> stand for atomic entities for mnemonic reasons. The symbols are atomic
> in the sense that any substructure they may have as sequences of
> characters is ignored."
>
> KM> My guess is - only to distinguish from M-expressions introduced in
> KM> same article. As term "M-expression" is somehow abandoned, the term
> KM> "S-expression" left "hanging".
>
> I really do not understand how M-expressions can justify S-expressions.
>
> S-expression is just a name. It is not meant to describe what it is.
> But I think it fits very well, because expressions made of symbols are
> really symbolic expressions.
>
> KM> But, there is another possibility - that term "symbolic expression" was
> KM> already in use in some jargon of mathematics, logic or computer
> KM> science. For example, Bertrand Russell in Principia Mathematica uses
> KM> term "symbolic expression." Maybe there was some other, more actual
> KM> book. I believe that McCarthy's use is independent of all these - but I
> KM> don't know that.
>
> Once again, McCarthy _defines_ what symbolic expressions are, in his own
> way. If he would take some widely used term and hijack it defining it in
> its own way, that would be really stupid. Do you think that McCarthy is
> stupid?
>

ISTR Lisp was shaped fundamentally by what even McCarthy concedes was a
misreading of Church. But that does not mean he is stupid, that means he
is a hacker at heart more interested in solving problems (AI) than
studying dead trees.

kzo


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