[OpenBIOS] Some thoughts on paflof.

[Stefan Reinauer]

* Klaus Seegebarth <kseege at t-online.de> [020613 12:52]:
> From my knowledge about OpenFirmware i remember, that OF is a 
> token threaded ANS-Forth with some extensions for the device-tree
> and a number of tokens (roundabout 300?) have a predefined value.

about 360 words are defined with existing fcode token. 

> So i would expect OpenBios to use token threading instead of 
> indirect threading. If OpenBios wants strict compatibility with 
> IEEE 1275, isn?t this necessary ?

There was a token threading approach that I wrote last year but it
showed up to be inflexible and it's a lot easier to have a sane forth
kernel with a seperated FCode evaluator written in Forth (Which is
similar to the normal interpreter, just reading tokens from a stream
instead of Forth source).
There are quite some words that dont have an FCode token, and those
cannot be supported without exceptions in a token threaded
implementation.

> The tokenizer/detokenizer for C-Code is a nice feature for all those, 
> who are frightened by Forth, but isn?t it just a convenient add-on, 
> while the token threaded Forth is the heart of the whole thing ?

It's actually just a Forth tokenizer/detokenizer _written_ in C. It does
not allow you to write C code which is translated to bytecode. There
have been some efforts in this area, but it probably does not make sense
to spend a lot of developers' resources while not having the base system
working. It's a non trivial problem generating effective Forth Code from
C source due to Forth's stack based nature. There are some papers
available on optimizing stack machines, but I am not into this..

Best regards,
  Stefan Reinauer
  
-- 
The x86 isn't all that complex - it just doesn't make a lot of
sense.          -- Mike Johnson, Leader of 80x86 Design at AMD
	                          Microprocessor Report (1994)
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