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- Subject: Re: Okay, lets talk assemblers and Lua (was Re: A bit more on bits...)
- From: Sean Conner <sean@...>
- Date: Wed, 22 Feb 2023 13:36:12 -0500
It was thus said that the Great Johann ''Myrkraverk'' Oskarsson once stated:
> On 2/17/2023 7:18 PM, Luiz Henrique de Figueiredo wrote:
> >Can we please go back to discussing Lua? Thanks.
> I have done project 1-1, more or less, in the book /Assemblers and
> Loaders/  in Lua. It was a bit unusual for me to create data
> structures out of Lua tables, but once the initial hurdles were over
> and I had figured out binary output, it turned out to be rather easy.
A few years ago I did an assembler for the Motorola 6809 in Lua.
> It turns the example input of
> STO 50
> STO 51
> BZE X
> ADD 50
> BRA Y
> X LOD 50
> ADD 50
> Y STO 52
> 00000000: 7000 2032 7000 2033 400d 3032 8000 6011 p. 2p. 3@.02..`.
> 00000010: 1032 3032 2034 0000 .202 4..
> with the 2pass assembler.
Yup, my Lua 6809 assembler is also a two pass assembler.
> As per the book, I changed the binary
> format slightly between the 1pass and 2pass assemblers. 
> Parsing is something I did with a line by line reader, and
> string.match(), which works fine for a very rigid syntax. Later
> on, I'm pretty sure I'll have to resort to something more flexible
> like recursive descent or something.
I used LPEG for my assembler, only because parsing expressions like:
ldd #(ACIA_CONTROL_RESET * 256) + ACIA_CONTROL_DEFAULT
a lot easier. It also helped with index-based addressing modes. But even
with LPEG, I still do line-by-line parsing. The only portion of my
assembler that is recursive is my "include" directive, which to me, is a
"nice to have" rather than a "hard requirement."