[self-interest] prototypes, "meta" and reflective programming

[Jecel Assumpcao Jr]

On Fri, 12 Jan 2001, Dru Nelson wrote:
> C. Ramakrishnan wrote:
> >   (|slot1 = foo. slot2 = bar| code)
> > 
> > is a form of lightweight meta-programming?

I would call that "plain programming".

> what is meta-programming?

Well, my explanation in a previous message seems to have been too brief
so I'll try to be more detailed here.

"Meta" means "beyond", as in these three examples:

----

"Physics" is the study of the laws of the universe. It asks questions
like "if I let this object go, will it fall down or fly away?".

"Meta-physics" is the study of physics. It asks questions like "are the
laws we see in the universe the only possible ones? Are they random or
the product of an intelligent design?".

----

This list is for the discussion of the Self programming language. If we
start talking about the list itself, asking questions like "should a
simple reply go to the list or just to the author? Should we just
discuss Self or are Self-like languages ok?" then we can say that we
are having a "meta discussion".

----

Here is a bit of programming in Self:

     failed: students copyFilteredBy: [ |:s| s grade < 5.0 ]

This program is *about* students and their grades. Now here is a bit of
meta-programming in Self:

    enumerating all enumerate asList copyFilteredBy:
       [ |:m| m isReflecteeMethod &&
                     [m sourceString asTextLines size == 10]]

This program is *about* a program - it finds the list of all methods in
the system that are exactly 10 lines long. Though this code looks very
much like the previous one, there is a subtle difference in that 's'
was an object and 'm' is a meta-object (a mirror). But there is
sometimes no difference at all in the tools used by programmers and
meta-programmers. In the example of a discussion and a meta-discussion
both used exactly the same tool: English.

-- Jecel