From: Bob Hutchison <hutch@...>
Date: 2005-09-29T20:20:51+09:00
Subject: Re: Lisp macros


On Sep 29, 2005, at 3:46 AM, Robert Klemme wrote:

> Well, I think my point focused around the fact whether a language  
> allows
> for code modification at runtime (regardless of whether you use it  
> or not;
> I'm rather trying to grasp the nature of the language if you  
> will).  You
> can do that with Lisp and as far as I understood it's a core  
> feature of
> the language.  You can't do that with standard C (well, you *can*  
> but that
> typically involves features not part of the language like shared  
> objects).

You are right about run-time changes to lisp being an important  
capability. The fun thing is that you don't actually need to eval or  
compile anything inside the program being modified. You have to  
compile for sure, but that can be done outside by the developer then  
loaded into the running image -- no eval happens. There are also very  
interesting things you can do with returning functions from functions  
that don't require eval (this can be a bit astonishing the first time  
you see it, and every now and again after the first time :-) Here is  
a quick example:

(defun make-a-function (n)
   (lambda (m) (* n m)))

is returning a compiled run-time generated function (with no eval,  
not even a hidden one :-)

>
> (A funny consequence seems to be that you can view machine code as a
> dynamic language...)

Very dynamic. Every now and again when I was working in assembler (a  
while ago now :-) we made use of that (in fact, one computer I worked  
on had instructions built into it that explicitly supported changing  
the code). These days machine code as a dynamic language comes up  
every now and again as a 'buffer overrun attack' :-)

Cheers,
Bob

>
> Kind regards
>
>     robert
>

----
Bob Hutchison          -- blogs at <http://www.recursive.ca/hutch/>
Recursive Design Inc.  -- <http://www.recursive.ca/>
Raconteur              -- <http://www.raconteur.info/>