I have this page on my "TODO" list. What is your opinion about it? I see already that you are recommending it but maybe you can give some more details. Thanks in advance.
Shameless self-promotion: I wrote a Lisp interpreter in a single assembly file for Raspberry Pi. It also starts from scratch at an even lower level, to the point of ignoring standard libraries.
https://github.com/marcpaq/arpilisp
I was inspired by jonesforth, which, if you haven't read it, is a beautiful piece of work.
This really makes me want to blow the dust off the RaspberryPi (we all bought one and never used it: admit it) and get this up and running, just to see it working.
/* excerpt from builtin_op function */
while (a->count > 0) {
/* Pop the next element */
lval* y = lval_pop(a, 0);
if (strcmp(op, "+") == 0) { x->num += y->num; }
if (strcmp(op, "-") == 0) { x->num -= y->num; }
if (strcmp(op, "*") == 0) { x->num *= y->num; }
if (strcmp(op, "/") == 0) {
if (y->num == 0) {
lval_del(x); lval_del(y);
x = lval_err("Division By Zero!"); break;
}
x->num /= y->num;
}
lval_del(y);
}
One thing that you might be interested in knowing about is that this book uses a few libraries which means you don't end up writing everything from scratch. For example, in the chapter on parsing, the grammar is implemented using a library called MPC (https://github.com/orangeduck/mpc) written by the author himself.
I didn't quite reach till the very end so didn't have a chance to implement Macros (the author does mention them in Chapter 16), so if that's something you can very keen on implementing then you might have to look someplace else.