From: Ike <rxv@...>
Date: 2006-07-29T10:15:09+09:00
Subject: Re: does ":" have an anolog in another language?


<nothinghappens@mchsi.com> wrote in message 
news:072820061953.19665.44CA6B2700073D1500004CD1219791280203010CD2079C080C03BF9C020A9F9F0E08090207089B0102@mchsi.com...
> Sorry if anyone's beat me to this, I find it hard to keep up with such a 
> busy list...
>
> : is used to denote a symbol.  The idea of a symbol has a rather broad 
> interpretation, but I think that technically any identifier you make in a 
> program -- a variable name or function name, for instance -- is a symbol.
>
> Lisp languages have symbols in a similar sense that Ruby does, and they 
> are usually used in much the same capacity as variable names -- they get 
> evaluated 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 
> unevaulated and treated as the symbols themselves.
>
> Lisp symbols don't have to start with :, but certain uses of them where 
> they have semantic significance use that convention, which might be where 
> Ruby 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 them.  So you might have a list like (:a 1 :b 2 :c 3) called 
> mylist, and (getf mylist :b) will return the 2.  Similarly, :-symbols are 
> used a lot in argument lists for many Common Lisp functions, to denote 
> values meant to be passed to named parameters (aka keyword parameters).
>
> I think there's also something like it in Smalltalk but I'm not sure.
>
> So basically, a symbol is this little constant singleton identifier thing, 
> that you can use to mean whatever ;)
>
> --ch--
>

Doesn;t that therefore make it the same thing as a reference in c++ ? -Ike