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Re: Lightning Bindings


From: Noah Lavine
Subject: Re: Lightning Bindings
Date: Mon, 31 May 2010 18:49:42 -0400

Hi Ludo,

I didn't realize guile-lightning existed! It looks like that project already 
has most of the code for Lightning bindings, so it might be better to try to 
update it to work with Guile 2.0. I also saw your idea for JIT, which I could 
work on as well. However, all three projects use different ideas of how 
Lightning should connect to Guile, so before I code more I would like to talk 
about which would be better.

Here is my understanding of the three approaches:

The approach in my project was to make machine code a Guile datatype, which you 
could allocate with a special init function and write to with writing functions 
which are just Guile versions of the Lightning macros. It could be called as a 
function through the dynamic FFI.

The approach in the other guile-lightning project is to represent the Lightning 
code as a Guile list which mirrors the Lightning virtual instruction set. When 
a list is completely built, it would then be passed to a special function 
(written in C) to assemble it. It also has some infrastructure for labels and a 
special method of calling these functions, neither of which I understand yet.

The approach in your plan for JIT, as I understand it, is to implement this 
completely in the C layer. The machine code would be stored as part of the 
representation of a procedure, and would be invisible from the Scheme side.

(I should also point out that my plan for compilation was to first start 
generating machine code with as few inlined instructions as possible, which 
would just call VM functions to do its work. This was also your plan, and I 
believe also the plan of the earlier guile-lightning project.)

It is not clear to me which one of these is the best way, or even if there is a 
best way.

The reason I did not use the approach of the other guile-lightning, to make a 
list and then assemble it, was that it seemed inelegant and possibly slow to 
have to iterate through instructions twice whenever I compiled something, first 
to generate the list and then to compile it. However, I doubt it would be very 
slow, and thinking about it now it might even be faster if the iteration 
programs became smaller and fit in cache.

As for doing it all in C, I am concerned about this because if there were 
bindings available in Scheme, then it might be possible to write a nice 
compiler in Scheme someday, which would do clever things like inlining and 
interprocedural optimization. (Or, more easily, persuade the MIT Scheme or 
Bigloo people to donate their compilers.) Writing it in C could make that more 
difficult - but if it also made Guile programs faster right now, then it might 
be worth doing anyway.

What do you think of this? What way should I try to implement this?

Noah


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