lumbda/wasm/python/lumbda-py.js

// wasm/python/lumbda-py.js
// Python tier loader — Pyodide (CPython-in-WASM) hosting lumbda.py.
//
// ES module form so it works in both window and Web Worker contexts.
// Exports createPythonTier() -> Promise<{ evalLisp(src) -> Promise<string>,
//                                          setBendUrl(url) -> void,
//                                          heapStats() -> {used,total} }>.

const PYODIDE_VERSION = "0.27.2";
const PYODIDE_INDEX_URL = `https://cdn.jsdelivr.net/pyodide/v${PYODIDE_VERSION}/full/`;

async function _bootstrap() {
    // Dynamic ES-module import works in both window and Worker (module type)
    // contexts. The CDN ships pyodide.mjs alongside pyodide.js.
    const { loadPyodide } = await import(PYODIDE_INDEX_URL + "pyodide.mjs");
    const pyodide = await loadPyodide({ indexURL: PYODIDE_INDEX_URL });

    // Pull lumbda.py + stdlib.lsp into Pyodide's virtual FS. Paths resolve
    // relative to THIS loader (under python/) for both window and Worker.
    const pyURL = new URL("./lumbda.py", import.meta.url).href;
    const stdlibURL = new URL("./stdlib.lsp", import.meta.url).href;
    const lumbdaSrc = await (await fetch(pyURL)).text();
    const stdlibSrc = await (await fetch(stdlibURL)).text();
    pyodide.FS.writeFile("/home/pyodide/lumbda.py", lumbdaSrc);
    pyodide.FS.writeFile("/home/pyodide/stdlib.lsp", stdlibSrc);

    // bend dispatch closure. Browser can't open raw TCP, so we POST
    // the S-expression payload to the configured worker URL and read
    // the response text back. Sync XHR is the only sync HTTP available
    // in a Web Worker; perfect for the blocking eval model lumbda
    // primitives expect.
    const refs = { bendUrl: null, currentOnChunk: null, pauseFlag: null };
    // Cooperative pause check — lumbda.py polls _lumbdaPyPauseRequested
    // every ~1024 leval iterations. Returns true when the REPL has
    // signalled a pause via the SharedArrayBuffer atomic (index 0).
    // Falls back to false when SAB isn't available (no COOP/COEP),
    // turning the poll into a no-op.
    globalThis._lumbdaPyPauseRequested = () => {
        if (!refs.pauseFlag) return false;
        try { return Atomics.load(refs.pauseFlag, 0) ? true : false; }
        catch (e) { return false; }
    };
    // Streaming output bridge — sys.stdout in pyodide is replaced
    // (during _lumbda_eval) with a class whose write() calls back
    // here. We forward to the current onChunk so the worker can
    // postMessage chunks to the UI as work happens, instead of the
    // user staring at a blank panel during a long bend dispatch.
    globalThis._lumbdaPyEmitChunk = (s) => {
        if (refs.currentOnChunk && s) refs.currentOnChunk(s);
    };
    globalThis._lumbdaPyBendCall = (payload) => {
        if (!refs.bendUrl) return "no bend URL configured";
        try {
            const xhr = new XMLHttpRequest();
            xhr.open("POST", refs.bendUrl, false);  // sync
            xhr.setRequestHeader("Content-Type", "text/plain; charset=utf-8");
            xhr.send(payload);
            return xhr.responseText || "";
        } catch (e) {
            return `bend error: ${e.message || String(e)}`;
        }
    };

    await pyodide.runPythonAsync(`
import sys, io
sys.path.insert(0, "/home/pyodide")
import lumbda
_env = lumbda.make_global_env()
for _e in lumbda.read_all(lumbda.PRELUDE):
    lumbda.leval(_e, _env)

# bend!-call primitive — bridges to JS XHR via globalThis._lumbdaPyBendCall.
# Argument: a string payload (the S-expression text). Returns response text.
# Wire the pause hook so leval polls SAB via the JS callback.
from js import _lumbdaPyPauseRequested as _js_pause_requested
lumbda._lumbda_pause_hook = lambda: bool(_js_pause_requested())

from js import _lumbdaPyBendCall as _js_bend_call
def _bend_call_prim(args, env):
    if not args:
        return ""
    payload = args[0]
    if not isinstance(payload, str):
        payload = lumbda.show(payload)
    return str(_js_bend_call(payload))
_env.define(lumbda.S('bend!-call'), _bend_call_prim)

# Portal save/resume — REPL bridge. Mirrors the C tier's
# (portal-snapshot! NAME) / (portal-load! NAME): writes/reads
# /tmp/<name>.portal so the JS side can round-trip blobs to vault.
import os
os.makedirs('/tmp', exist_ok=True)

def _portal_snapshot_prim(args, env):
    if not args or not isinstance(args[0], str):
        raise lumbda.LispErr('portal-snapshot!: expected string name')
    path = f'/tmp/{args[0]}.portal'
    g = env.g if env.g else _env
    lumbda.portal_save(g, path)
    return path

def _portal_load_prim(args, env):
    if not args or not isinstance(args[0], str):
        raise lumbda.LispErr('portal-load!: expected string name')
    path = f'/tmp/{args[0]}.portal'
    restored_env, _cont = lumbda.portal_resume(path, _env)
    # Copy bindings from the restored env into our live global env so
    # subsequent evals see them. portal_resume gives us back a fresh
    # env with the loaded bindings; we merge into _env in-place.
    for sym, val in restored_env.b.items():
        _env.b[sym] = val
    return True

_env.define(lumbda.S('portal-snapshot!'), _portal_snapshot_prim)
_env.define(lumbda.S('portal-load!'), _portal_load_prim)

# Streaming stdout wrapper — every write() also calls back into JS so
# the worker can postMessage chunks to the UI during the eval. The
# StringIO behind it still captures everything for the final return.
from js import _lumbdaPyEmitChunk as _js_emit_chunk
class _StreamingStdout(io.StringIO):
    def write(self, s):
        n = super().write(s)
        try:
            _js_emit_chunk(s)
        except Exception:
            pass
        return n

def _lumbda_eval(src):
    buf = _StreamingStdout()
    old = sys.stdout
    sys.stdout = buf
    last = None
    try:
        for e in lumbda.read_all(src):
            last = lumbda.leval(e, _env)
    except Exception as ex:
        sys.stdout = old
        return f"{buf.getvalue()}error: {ex}"
    sys.stdout = old
    out = buf.getvalue()
    if last is not None and not isinstance(last, lumbda._Void):
        rep = lumbda.show(last)
        if out and not out.endswith("\\n"):
            out += "\\n"
        out += rep
        try:
            _js_emit_chunk(("" if out.endswith(rep) else "\\n") + rep)
        except Exception:
            pass
    return out
`);

    return {
        async evalLisp(src, onChunk) {
            pyodide.globals.set("_src_in", src);
            refs.currentOnChunk = onChunk || null;
            try {
                return await pyodide.runPythonAsync("_lumbda_eval(_src_in)");
            } finally {
                refs.currentOnChunk = null;
            }
        },
        setBendUrl(url) { refs.bendUrl = url || null; },
        // Pause hook — wraps the incoming SAB in an Int32Array so the
        // _lumbdaPyPauseRequested callback (installed above) can read
        // the atomic. Null disables (no COOP/COEP).
        setPauseFlag(flag) {
            refs.pauseFlag = flag ? new Int32Array(flag) : null;
        },
        // Portal save/resume bridge to vault — same shape as the C tier
        // loader. Pyodide.FS is the same Emscripten FS, so the path
        // /tmp/<name>.portal is reachable from JS exactly as in C.
        portalSave(name) {
            const path = `/tmp/${name}.portal`;
            try {
                const bytes = pyodide.FS.readFile(path);
                return new TextDecoder().decode(bytes);
            } catch (e) { return null; }
        },
        portalLoad(name, blob) {
            const path = `/tmp/${name}.portal`;
            try { pyodide.FS.mkdir("/tmp"); } catch (e) { /* exists */ }
            pyodide.FS.writeFile(path, blob);
        },
        heapStats() {
            // Pyodide's runtime memory is the Emscripten linear memory.
            // CPython's GC reclaims behind the scenes, so this number
            // rises and falls naturally as objects die.
            const total = pyodide._module.HEAPU8.byteLength;
            return { used: total, total };
        },
    };
}

// Closure-encapsulated singleton (see lumbda-c.loader.js for rationale).
export const createPythonTier = (() => {
    let tier = null;
    return async () => {
        if (!tier) tier = await _bootstrap();
        return tier;
    };
})();