lumbda/wasm/python/lumbda-py.js

// wasm/python/lumbda-py.js
// Python tier loader — Pyodide (CPython-in-WASM) hosting lumbda.py.
//
// Exports createPythonTier() -> Promise<{ evalLisp(src) -> Promise<string> }>.
// Output is whatever the program printed (via display/print/write) plus the
// final value's printed form if non-void.

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

async function _bootstrap(baseURL) {
    // Load Pyodide loader script (sets globalThis.loadPyodide).
    if (typeof loadPyodide === "undefined") {
        await new Promise((resolve, reject) => {
            const s = document.createElement("script");
            s.src = PYODIDE_INDEX_URL + "pyodide.js";
            s.onload = resolve;
            s.onerror = () => reject(new Error("pyodide.js load failed"));
            document.head.appendChild(s);
        });
    }

    const pyodide = await loadPyodide({ indexURL: PYODIDE_INDEX_URL });

    // Pull lumbda.py + stdlib.lsp into Pyodide's virtual FS.
    const lumbdaSrc = await (await fetch(baseURL + "lumbda.py")).text();
    const stdlibSrc = await (await fetch(baseURL + "stdlib.lsp")).text();
    pyodide.FS.writeFile("/home/pyodide/lumbda.py", lumbdaSrc);
    pyodide.FS.writeFile("/home/pyodide/stdlib.lsp", stdlibSrc);

    // Initialize the lumbda environment once. We swap sys.stdout to a StringIO
    // buffer per eval to capture program output.
    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)

def _lumbda_eval(src):
    buf = io.StringIO()
    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
    return out
`);

    return {
        async evalLisp(src) {
            // Pass src in via globals to avoid escaping issues.
            pyodide.globals.set("_src_in", src);
            const result = await pyodide.runPythonAsync("_lumbda_eval(_src_in)");
            return result;
        },
    };
}

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