[Marxism] Human Origins
schaffer at optonline.net
Mon Aug 1 09:56:43 MDT 2005
Les Schaffer wrote:
> LISP and symbols
apologies, i hit the send key accidentally. this was a reminder to
myself to write something later to the list on symbols and (programming)
but briefly, i have been working a bit lately with two languages called
LISP and a dialect of LISP called Scheme:
in this language it is made explicit when one is creating symbols in
the language. and the ability to then manipulate these symbols within
the language allows one to do interesting things, like extend the
language, interpret the language, and so forth.
one of the earlier uses of LISP was symbolic computation.
say one defines a symbol, 'x [ (quote x) or 'x is the lisp way of
working with symbols]. at this point 'x does not even stand FOR
anything, does not map to anything.
what can one do with it?
well, one can compose these symbols with other symbols, for example 'x
'x (like x squared), and
3 x^2 + 2 x + 1
and so on. one can then manipulate these symbols according to rules --
one such set for example would be the rules of arithmetic polynomials.
after some work, voila, one has a scheme for doing calculus
symbolically. in fact there are several widely-used applications now on
the market that do this. no big deal for a quadratic polynomial. but i
know a physicist who used such a package for an astrophysical
computation, where the computer was left running all nite. that's NOT a
calculation one wants to do by hand!!!!!!
notice, however, that at NO POINT does the symbol 'x STAND FOR ANYTHING.
it COULD stand for #s of bananas, #'s of marxmail subscribers, or whatever.
there is a connection here to the discussion of Godel's work several
months ago. i'll leave that for later. but even that polynomial above,
we could follow all these rules without mentioning these are the
polynomials of our high school arithmetic. maybe its also a 'polyxnxnx,
where 'polyxnxnx is a ..............................................
(to be continued)
charles just wrote:
>Therefore "x" is being used symbolically when it is used to represent
hold this thought till we talk Godel again ;-)
one of the things you can read about on the Wiki page above is that
languages with symbols and symbol manipulation allow the language to be
self-reflective in an easy way. this is an amazing property for a
language, for a programming language that is, if you are brought up on C
or Fortran (or Cobol???).
one last thing. LISP/Scheme have a notion of delayed or lazy evaluation:
somehow i connect this loosely with the discussion on planning. we
intend to map sumbols, ideas, to *future* actions that may or may not
actually take place.
(sign-it '(Les Schaffer))
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