rell-playground

Backend-less SPA for trying Rell in the browser. Live: https://chromiaproject.github.io/rell-playground/

Three modes:

• Run — paste a complete program, click Run. For pure functions, print, expression evaluation, struct/enum defs, etc. Output appears in the right pane. (Entity / query / operation declarations aren't allowed here — use SQL dry-run for those.)
• SQL dry-run — declare entities + a query main(); the playground compiles every @-expression to SQL and shows the statements postchain would issue in the SQL pane. Nothing actually executes (there's no database), so queries run against an empty result set.
• REPL

The Rell compiler + interpreter is compiled ahead-of-time to JavaScript by TeaVM. The browser loads the resulting ESM module directly — no JVM bytecode interpreter, no CheerpJ runtime, just a single .js file.

Architecture

flowchart TD
    SPA["SPA — TypeScript, Vite"]
    Worker["Web Worker (ESM)"]
    Bridge["rell-playground-bridge.js<br/>TeaVM AOT JS"]
    API["PlaygroundJsBridge<br/>@JSExport static API<br/>version / runFile / runModule / repl*"]
    Repl["ReplSession<br/>wraps ReplInterpreter<br/>(Run + REPL modes)"]
    Module["ModuleSession<br/>compiles source as module 'main'<br/>(SQL dry-run)"]
    Sql["CapturingSqlManager<br/>records SQL before<br/>returning empty results"]
    Channel["BufferedReplChannel<br/>emits a JSON event envelope"]

    SPA --> Worker
    Worker --> Bridge
    Bridge --> API
    API --> Repl
    API --> Module
    Repl --> Sql
    Module --> Sql
    Repl --> Channel
    Module --> Channel

Loading

The worker imports rell-playground-bridge.js as ESM and calls the @JSExport-annotated static methods (version, runFile, runModule, replCreate, replExecute, replDispose) directly. Each call returns a JSON envelope {"ok": bool, "events": […]} whose events are stdout lines, REPL value prints, compiler diagnostics, runtime errors, and sql entries. The worker forwards each as a postMessage; main.ts routes them — sql → SQL pane, everything else → the output panel.

SQL capture

CapturingSqlManager replaces Rell's NoConnSqlManager. Every SQL string Rell hands the executor is appended to the event channel; the executor then returns an empty result (rather than throwing "no database connection"), so a whole routine's worth of statements is captured in one run instead of just the first. This is something the stock rell.sh can't do — without --db-url it bails on the first SQL call.

Build

./gradlew assembleAll        # → web/dist/

# Or, for dev:
./gradlew dev                # http://localhost:5173

The bridge JS lands at web/public/teavm/rell-playground-bridge.js (mirrored there by :bridge:copyTeavmToWeb). Vite copies web/public/ verbatim into web/dist/, so the worker's static /teavm/rell-playground-bridge.js import resolves both in dev and prod.

CI / deployment

.github/workflows/ci.yml runs three jobs:

• bridge — runs :bridge:build, uploads web/public/teavm/ as an artifact.
• build — downloads the bridge artifact and runs :web:assemble to produce web/dist/. Also runs the Vitest survival kit against the bridge.
• deploy — on master, publishes web/dist/ to GitHub Pages.