From: "Jürgen Strobel" <strobel@...>
Date: 2006-08-09T23:57:36+09:00
Subject: Re: does ":" have an anolog in another language?

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On Sat, Jul 29, 2006 at 04:53:25AM +0900, nothinghappens@mchsi.com wrote:
> Sorry if anyone's beat me to this, I find it hard to keep up with such a =
busy list...
>=20
> : is used to denote a symbol.  The idea of a symbol has a rather broad in=
terpretation, but I think that technically any identifier you make in a pro=
gram -- a variable name or function name, for instance -- is a symbol.
>=20
> Lisp languages have symbols in a similar sense that Ruby does, and they a=
re usually used in much the same capacity as variable names -- they get eva=
luated into any binding they currently have to a function or piece of data.=
  However, if quoted with a single quote (like 'this) they are left unevaul=
ated and treated as the symbols themselves.
>=20
> Lisp symbols don't have to start with :, but certain uses of them where t=
hey have semantic significance use that convention, which might be where Ru=
by borrows the syntax from.  For example, a common idiom in Common Lisp is =
the associative list, where elements are alternated with symbols that must =
start with : and elements can be referenced by the :-symbol right before th=
em.  So you might have a list like (:a 1 :b 2 :c 3) called mylist, and (get=
f mylist :b) will return the 2.  Similarly, :-symbols are used a lot in arg=
ument lists for many Common Lisp functions, to denote values meant to be pa=
ssed to named parameters (aka keyword parameters).
>=20

In (Common) Lisp, every new word (loosely) the reader sees is interned
as a new symbol into the current package. But every word that begins
with a : is interned into a special package named "keyword", so
those are available as distinct, immediate, immutable identifiers
everywhere. They are usually called keyword symbols.

I heartily reccomend reading "Practical Common Lisp" (online at
http://www.gigamonkeys.com/book/). Even if you don't plan on
programming in Lisp yourself, it will help you to understand a lot
about Ruby and programming in general too.

As Ruby started out as a simple Lisp dialect, that's certainly where
:symbols come from.

J=FCrgen

--=20
 The box said it requires Windows 95 or better so I installed Linux

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