Scheme status

I’ve written here before about my efforts to write a Scheme interpreter from scratch.  The last update was in May, but I’m still working on it.  I’ve made 60 git commits since then.  The major thing I’m trying to do is implement macros, but I’m having a hard time of it.  No matter.  When they’re done, I’ll understand macros thoroughly.

Scheming, part 7. The Reader.

I haven’t ‘blogged about my Scheme interpreter in ages.  Development stopped from January through March, but I’ve been working on it again.  Here are links to the earlier articles.

• Scheming, part 6
• Scheming, part 5
• Announcing kbscheme
• Scheming, part 3
• Scheming, part 2
• Scheming, part 1
• Not another Scheme interpreter!

The biggest new development  is the reader.  Most developers call them parsers, but Lisp people call them readers.  I have written six readers for Scheme now, and I’ve effectively completed a class in advanced parsing theory.  The current reader works very well, and I do not want to write another.

Scheming, part 6

This morning I added vectors to my Scheme interpreter.  It was surprisingly easy.  It was nearly test-driven development — now that the scheme interpreter has a full unit test harness built in, I got the tests written before I finished the code (though not before I started).

Scheming, part 5

Call/cc works!

That’s the big news.  Lots of little tweaks and cleanup, but call/cc is the big deal.  I’d designed the evaluator to handle call/cc way back when, so it wasn’t a major rewrite.  It was just a matter of figuring out exactly what it had to do.

Announcing kbscheme

I published my scheme interpreter on gitorious.  Now you can follow along.  It needed a name, so I called it kbscheme.  Not a brilliant name but it’ll do.

Here’s the project blurb.

kbscheme

This vanity project is yet another implementation of the Scheme programming language.

Project goals:

• I want to learn Scheme.
• I want to write something in C. I’ve been using higher level languages and my C is rusty.
• I want to write a garbage collector. They’ve always fascinated me, but I’ve never written one.
• I have some research ideas about garbage collection that I want to explore.

Project non-goals:

• a production-quality Scheme interpreter
• full implementation of the language

Check it out, Brandon.

Hint to the git-ignorant (as I was very recently).  Go to the repositories/mainline page and click on the “More info…” links,  Those will show the exact commands needed to copy (clone) the tree onto your local disk.

Actually, I’m still git-ignorant.  Gotta work on that…

Scheming, part 3

GC is hard.  Let’s go shopping.

I’ve been working on my scheme interpreter a lot.  But I don’t have much to show for it.  What I do have, finally, is a working garbage collector (GC).  GC is a real pain to debug.  Every error shows up as a memory corruption bug.

Scheming, part 2

I’ve been working on my Scheme interpreter.  I just got the nonrecursive evaluator working, so it seems like a good time to take stock.

Scheming, part 1

I have a Scheme interpreter.

~/scheme> ./scheme
> ()
> 123
123
> +
#<C-proc 0x804ad19>
> (+ 12 34)
46
> (lambda (x) x)
#<proc 0x80590f8>
> ((lambda (x) (+ x x)) 3)
6
> [Ctrl-D]
~/scheme>

Not another Scheme interpreter!

I’m getting psyched about the idea of writing a Scheme interpreter.  I’m wondering what’s the absolute minimum amount of C code you have to write to be able to bootstrap it.