ludic/COMPILING.md

Compiling Ludic

Note (2026-08-27): ludicc is now written in Ludic (selfhost/*.ludic) and built from a checked-in IR seed — the C compiler this document describes has been deleted. The native pipeline below (Ludic → LLVM IR → object → binary) is unchanged. ludicc now drives clang itself (via an os_system intrinsic), so ludicc app.ludic -o bin/app and --emit-llvm work directly, and a sibling command ludic app.ludic compiles to a temporary binary and runs it in one step. Build both with ./build-cli.sh. build.sh remains as a convenience wrapper. --fmt is reimplemented as a lex+parse gate (the doc-check hook). The --target/cross-compile and --shared paths are still features of the old C driver not yet re-implemented on the self-hosted toolchain. See BOOTSTRAP.md §5.7.

./build-cli.sh                          # build ./ludicc and ./ludic (from the seed)
./ludicc examples/snake.ludic -o bin/snake     # compile
./ludic  examples/snake.ludic                  # compile + run

The binaries are multi-call (one native binary under two names): invoked as ludicc it compiles, as ludic it compiles-and-runs. A .ludic file with systems is a game and links windowed by default; --headless and --windowed force the mode. The runtime (runtime/native/cocoa.ll) is found via $LUDIC_HOME, defaulting to the directory the binary sits in — keep them at the repo root, or set LUDIC_HOME and put them on PATH. $LUDIC_CC overrides the assembler/linker (default clang).

ludicc is a compiler, not a translator. It lexes, parses, checks and lowers Ludic to LLVM IR itself, then hands that IR to the system toolchain to be assembled and linked. There is no C in the middle: no generated .c file, no C runtime compiled alongside your game, and no transpiling step you could inspect and find your program rewritten in another language.

   app.ludic
      │  ludicc — lex, parse, check, lower              (compiler/ludicc.c,
      ▼                                                  compiler/native.c)
   app.ll        LLVM IR: your systems, your components, your runtime
      │  IR assembler                                   (compiler/driver.c)
      ▼
   app.o         Mach-O / ELF / COFF object code
      │  system linker
      ▼
   app     or    libapp.dylib / .so / .dll

clang appears in that pipeline twice — as the IR assembler and as the linker driver — which is the same role rustc and swiftc give it. Set LUDIC_CC to point at a different LLVM toolchain if you have one.

Artifacts

you want	command
a windowed native executable	ludicc game.ludic -o build/game
a headless executable	ludicc game.ludic --headless -o build/game
the IR, to read	ludicc src.ludic --emit-llvm -o src.ll
a shared library †	ludicc lib.ludic --shared -o build/liblib.dylib
a game that runs in a browser †	ludicc game.ludic --target wasm32-unknown-unknown -o build/web/game.wasm
an object file †	ludicc src.ludic -c -o src.o

† --shared, --target/cross-compile, -c and the wasm path were features of the old C driver and are not yet re-implemented on the self-hosted toolchain (see the note at the top). The rows above the line work today via the self-hosted ludicc.

build.sh wraps the common cases:

./build.sh examples/snake.ludic              # -> build/snake        (native)
./build.sh examples/lib/combat.ludic --lib   # -> build/libcombat.*  (library)
./build.sh examples/snake.ludic --headless   # -> build/snake_headless (out.ppm)
./build.sh examples/snake.ludic --web        # -> build/web/            (browser)

Programs and libraries

Not yet on the self-hosted toolchain. --shared and the nm/library workflow below describe the old C driver's behavior; the self-hosted ludicc builds executables only for now. The module/export fn semantics are unchanged — only the packaging step is pending.

A source file opens with game Name { … } or module Name { … }.

• A game gets an entry point and the phase-ordered frame loop (Start, then Input → FixedUpdate → Update → LateUpdate → Render each tick).
• A module gets neither. It is a library, and only its export fns become public symbols; everything else stays private to the library.

# doc-check: skip — illustrative: elided body
module Combat {
  export fn damage(attack: int, armour: int, roll: int) -> int { … }
  fn curve(level: int) -> int { … }          # private: not a symbol
}

ludicc examples/lib/combat.ludic --shared -o build/libcombat.dylib
nm -gU build/libcombat.dylib
#  T _damage   T _hits_to_kill   T _xp_for        (no _curve)

Those are ordinary C-ABI symbols, so anything that can call a shared library can call Ludic. To call them from another Ludic program, declare them and link:

extern fn damage(attack: int, armour: int, roll: int) -> int = "damage"

ludicc examples/lib/arena.ludic -o build/arena -Lbuild -lcombat

Libraries are linked as @rpath/… ($ORIGIN on Linux) and executables search next to themselves, so a built pair keeps working when you move it.

Cross-compilation

Not yet on the self-hosted toolchain. --target and -c were old C-driver flags; the self-hosted ludicc builds only for the host today. The section below records the intended design — object code for ELF, COFF and Mach-O from one source — which the IR pipeline already supports in principle.

--target takes an LLVM triple and retargets the whole pipeline:

ludicc game.ludic --target x86_64-unknown-linux-gnu  -c -o game-linux.o
ludicc game.ludic --target aarch64-unknown-linux-gnu -c -o game-arm64.o
ludicc game.ludic --target x86_64-pc-windows-msvc    -c -o game-win.o

Object code for ELF, COFF and Mach-O comes out of the same source with no per-platform branches in the compiler. Linking a foreign target additionally needs that platform's linker and sysroot, as with any cross toolchain.

The runtime is written in Ludic

runtime/native/core.ludic implements the framebuffer, fill_rect, the 5×7 bitmap text, the registers, the RNG, input and the frame dump — in Ludic. ludicc splices it into every native build, and a builtin call in a game resolves to a runtime function by name: clear(c) calls rt_clear(c). Replace that file and you have replaced the runtime; pass --freestanding to build without it.

Underneath the runtime there is exactly one layer, and it is not C: a set of compiler intrinsics that lower to direct calls into the platform ABI.

intrinsic	lowers to
mem_alloc(n) -> ptr, mem_free, mem_copy, mem_set	malloc, free, memcpy, memset
peek8/peek32(p, i) -> int, poke8/poke32(p, i, v)	load / store
ptr_add(p, n) -> ptr, ptr_null(), ptr_is_null(p)	getelementptr, null
file_open(path, mode) -> ptr, file_read, file_write, file_close	fopen, fread, fwrite, fclose
read_byte() -> int, write_byte(c), print_str(s), print_int(n)	getchar, putchar, printf
str_len(s) -> int, os_exit(code), os_time() -> int	strlen, exit, time

That is the operating system's interface — the floor Rust and Swift stand on too. Everything above it, including all the graphics, is Ludic.

The runtime protocol is four optional functions. Define them (or let the prelude define them) and the entry point calls them:

function	when
rt_init()	once, before the Start systems
rt_poll() -> int	once per frame; its result is what key() reads
rt_running() -> bool	each frame; false ends the loop
rt_shutdown()	after the loop

The window

runtime/native/cocoa.ll is the macOS platform layer, written in LLVM IR. It talks to the Objective-C runtime through its C ABI — objc_getClass, sel_registerName, objc_msgSend — and to Quartz through CoreGraphics, which is what a compiled .m file does anyway; this just skips the .m. AppKit paints through -drawRect:, so the view class is built at runtime with objc_allocateClassPair and an IR function is installed as its IMP.

ludicc assembles it exactly like the program's own IR and hands both objects to the linker, adding -framework Cocoa. A --headless build omits it entirely, reads keys from stdin and writes the last frame to out.ppm; the win_* intrinsics compile to nothing there, so a headless binary never references a symbol the window would have provided.

Other platforms build headless today. A Win32 or X11 port is another .ll file with the same five entry points — win_open, win_poll, win_present, win_running, win_close — and no compiler change.

The web

WebAssembly is a target, not a port. The front end, the type checker, the ECS lowering and the Ludic-written runtime are the same ones a macOS build uses; only the triple changes.

   game.ludic
      │  ludicc — the same lex, parse, check and lower
      ▼
   game.ll        LLVM IR, triple wasm32-unknown-unknown
      │  IR assembler
      ▼
   game.o    +    wasm.o        (runtime/web/wasm.ll, the platform layer)
      │  wasm-ld
      ▼
   game.wasm  +  index.html  +  platform.js  +  assets.json  +  the assets

./build.sh examples/chronorift.ludic --web
python3 -m http.server -d build/web 8000     # then open http://localhost:8000/

build/web/ is self-contained: copy it to any static host — GitHub Pages, S3, itch.io — and the game runs. It needs no server-side anything, and no cross-origin isolation headers.

No game logic passes through JavaScript. The systems, the queries, the fixed-point arithmetic, the PNG decoder, the TrueType rasteriser and the UI are all compiled Ludic executing as wasm. platform.js is 300 lines and implements the same five-function window protocol cocoa.ll implements, plus the host services wasm has no OS to ask for. It is the web's Cocoa, not an interpreter.

The toolchain

A wasm build needs an LLVM with the WebAssembly backend and wasm-ld. Linux distributions ship both in clang and lld, so nothing extra is needed there or in CI. Apple's clang is built without the WebAssembly target, so on macOS:

brew install llvm

ludicc looks in /opt/homebrew/opt/llvm/bin and /usr/local/opt/llvm/bin before falling back to PATH. $LUDIC_CC and $LUDIC_WASM_LD override both, so any LLVM works — a distro one, a downloaded release, zig cc, wasi-sdk.

Who owns the frame loop

A native build runs the loop:

ludic_boot(); while (ludic_alive()) ludic_frame(); ludic_teardown();

A browser tab cannot be held inside that loop — it would never paint, and the key events the loop is waiting on would never be delivered. So a web build exports those four functions instead of main, and platform.js calls ludic_frame from requestAnimationFrame. Both targets emit the four from the same code in ll_emit_loop_parts, so the systems that run, and the phase order they run in, are identical; only the owner of the loop differs.

The floor

wasm32-unknown-unknown has no libc, so runtime/web/wasm.ll is the floor — hand-written LLVM IR, assembled by the same toolchain as everything else:

what	how
malloc / free	a first-fit free list over linear memory, growing it with memory.grow
memcpy / memset	the memory.copy / memory.fill instructions (-mbulk-memory)
strlen	a byte loop
fopen / fread / fwrite / fclose / fseek / ftell	wasm imports, over a preloaded asset image and localStorage
getchar / putchar / print_str / time / exit	wasm imports
win_open / win_poll / win_present / win_running / win_close	wasm imports, implemented against a <canvas>

Nothing above that file changes for the web: core.ludic, image.ludic, inflate.ludic, truetype.ludic and ui.ludic compile to wasm unmodified.

Assets and saves

The browser has no synchronous file access, and file_open() is synchronous, so a web build ships an image of its files instead of a filesystem. ludicc records every string literal in the program that names a file existing at compile time, writes the list to assets.json, and copies the files into the bundle; platform.js fetches them all before the first frame. file_open() then resolves exactly the paths it resolves natively.

That is a heuristic, and a deliberately visible one: a path the compiler never sees written down is a path the browser cannot be told to fetch ahead of time, and a path outside the project (/System/Library/Fonts/…) is refused with a warning rather than silently dropped.

Writes go the other way. file_open(path, "wb") buffers and commits to localStorage on close, so save() / load() survive a page reload, and a read prefers a save the player has made over the shipped asset of the same name.

Testing a wasm build

--headless --target wasm32-unknown-unknown produces a bare module with no page, driven by a runner instead of a browser:

node tools/ludic-web/run.mjs build/web/snake_headless.wasm --stdin=ddss

Because Ludic is fixed-point and its RNG is seeded, the native headless binary and the wasm one must render byte-identical frames from the same input. test.sh asserts exactly that, which is a much stronger check on the backend than "it started".

What a build contains

Everything: components and archetypes, spawn/despawn, queries with bindings, where filters and archetype filters, match, machine/become, scene/layer/enter, module state (var), const, int and Q16.16 fixed-point arithmetic, control flow, functions, extern fn FFI, strings, the entity allocator, save/load snapshots, the frame loop, the window, and the whole graphics stack — framebuffer, PNG decoding, sprites, 9-slice, TrueType text and the retained UI.

None of it goes through C. ./test.sh asserts that directly: no C source survives in runtime/, no C emitter survives in ludicc, and the examples all build, run and render from IR alone.

Every flag

The self-hosted ludicc/ludic (built with ./build-cli.sh) accept:

  <file.ludic>       the program to compile (first non-flag argument)
  -o <path>          output binary; with --emit-llvm, the IR path.
                     Parent directories are created. With no -o and not
                     invoked as `ludic`, the IR is written to stdout.
  --windowed         force a windowed (Cocoa) build
  --headless         force a headless build (stdin input, out.ppm output)
  --emit-llvm        stop at LLVM IR — write it and exit, no clang
  --fmt              lex + parse only; exit 0 if it parses, 1 on a parse error
                     (the check-docs gate; canonical formatting not yet restored)
  --save-temps       keep the intermediate .ll
  --run              compile then run (implicit when invoked as `ludic`)
  (unknown -flags are ignored with a warning, never taken as the input file)

environment:
  LUDIC_CC           the LLVM that assembles IR and drives the linker (clang)
  LUDIC_HOME         where runtime/native/ lives (default: the binary's dir)

Mode is automatic when neither --windowed nor --headless is given: a program with systems (a game) links windowed, anything else headless.

Not yet re-implemented on the self-hosted toolchain (old C-driver flags): --shared, --emit <kind>, -c, --target/cross-compile, --freestanding, -v, and the explicit link inputs (-L/-l/-framework/ -Wl). Those, plus LUDIC_WASM_LD/LUDIC_RUNTIME_DIR/LUDIC_RUNTIME, describe the previous driver and are documented here as intended design.

There is one backend. ludicc has no mode that emits C, and no part of a build compiles or links a C translation unit — including the web one, where the platform layer is LLVM IR and the loader is 300 lines of JavaScript that never sees a game rule.