----- Original Message ----- 
From: Conrad Schneiker/Austin/Contr/IBM <schneik / us.ibm.com>
To: ruby-talk ML <ruby-talk / netlab.co.jp>
Sent: Wednesday, October 25, 2000 10:05 PM
Subject: [ruby-talk:5863] Re: Symbolic evaluation without quoting trick.


> Hal wrote:
> 
> # What are s-expressions? Is this symbolic math, as in symbolic
> # differentiation and so on?
> 
> Once a pun a time, it was an ancient Lisp expressions, parenthetically 
> speaking.

Never used Lisp, though I've heard the legends. (It stands for Lots of
InSignificant Parenthese, you know.)

> Simplistically speaking, think of using something like 
> 
>     s-exp = (a (b c) (d (e f (g)))) 

Yes, I wrote some binary tree code the other day and gave something
like this as a print option.

> 
> to represent a tree structure. This can be generalized to arbitrary 
> directed graphs.

Now that's neat. It's obvious how a multiway tree could be represented, but
it's not obvious to me how a directed graph with loops could be represented
this way.

> Here is an interesting application 
> (http://www.toc.lcs.mit.edu/~rivest/sexp.html):
> 

That really is interesting. But the link doesn't seem to have been 
touched in three and a half years. Maybe it's sort of abandoned?

Hal