Model

[BRIAN SPILSBURY]

> I hesitated to bring this up here.  I feel it will probably get shot down
> pretty thoroughly.  How about ANSI Forth (with much extension) as the low
> level core (and ultimately the implementation language for whatever Lisp
> is chosen, until the Lisp compiles itself and we can throw away that 
> compiler).

I'm not familiar with forth, but from what I've heard it is a
good choice for extremely low level code, and from memory it probably
has the reflective properties we need, without lots of overhead.
 
> Advantages:
> 
>   - Many of today's machines (Sparcs, PowerPCs, some PCI-bus machines)
>     come with a full ANSI Forth core in the OpenBoot Firmware.  There
>     will be for these machines complete low level diagnostics and some
>     primitive kind of device driver available for all supported 
>     devices.  Those machines without OpenBoot Firmware could be made
>     to quickly load an ANSI Forth core.   

This is an excellent point. :) Device drivers are a bastard to write.

>   - Forth is well known to port very easily and runs in all kinds of
>     environments.  If the LispVM were implemented in Forth then we
>     could quickly bring it up under various OS's, standalone, have
>     real-time subset implementations for embedded distributed 
>     applications, etc. etc.  A portable Forth like GForth (GNU)
>     could be used for initial ports.  One report I read recently was that
>     2 guys brought up GForth in a new embedded environment on a
>     new machine architecture in a weekend.  Now, they feel with the
>     work they did to simplify the porting, it could be done in an
>     >afternoon<.
> 
>   - Mop systems have been implemented in Forth and seem to work quite well.
>     Reflection seems possible, but I don't know of any practice along these
>     lines.

This could be the only real sticking point.
 
> Disadvantages:
> 
>   - Including threading support might be tricky in any portable way.

I can't think of any portable threading systems, but it should be
relatively easy, this is where people want to think if they want
a continuation passing style system, or one with chunky stacks.

>   - Forth scales poorly, but I do propose getting to a Lisp language
>     fairly quickly.

Yeah, it would be interesting to see a toy lisp-over-forth system.
There may be one already around, I'll have a look over the web.

but I think its a great idea, and if you haven't hit the nail on the head
you're not far off.

Brian