A compiler small enough to read, written in itself.

mc compiles a schoolbook-C language — seven types, one opaque pointer, loop and if — into Mach-O for AArch64. A 2,846-line C23 seed is compiled by clang exactly once; after that mc compiles its own source, writes and signs the executable itself, and reaches a fixed point where one generation is byte-identical to the next. Everything the core leaves out — while, for, +=, a second backend, a whole object model — you teach it from ordinary mc source.

Getting started Reference Examples

It compiles itself

clang builds the C23 seed once, and never runs again. The seed compiles src/mc.mc; that compiler compiles the same source a second time, and the third generation comes out byte for byte identical to the second.

cmp mc2.o mc3.o → identical
Syntax you teach it

while, for, += and ++ are not in the core — they are 37 lines of lib/prelude.mc. Directives add lexemes, operators and statements; pass() and backend() add AST passes and code generators; syntax handlers add whole constructs.

#rule · #token · #infix · pass() · backend()
Executables, not homework

mc --exe prog.mc -o prog lays out the segments, resolves every relocation, writes the bind and rebase opcodes and ad-hoc signs the result. No linker, no codesign — the backend that does it is itself an mc program.

codesign --verify → valid on disk

The whole idea, in one file

The core has no while. This program adds one, then uses it — the dotted underline marks every word that came from the surface rather than the core.

#include <sys>

// a statement the core does not have, taught in two lines
#rule stmt: while ( expr $c ) block $b
    => loop { if (!$c) break; $b }

i64 main(i64 argc, uptr argv) {
    i64 i = 0;
    while (i < 3) {
        write(1, "mc\n", 3);
        i = i + 1;
    }
    return 0;
}

core keyword
taught word
directive
$hole
"string"
42
// comment

A compiler small enough to read, written in itself.

It compiles itself

Syntax you teach it

Executables, not homework

The whole idea, in one file