The playground

The playground is the zero-install way to run rut: the whole engine — lexer, parser, compiler, VM — compiled to WebAssembly and served as a static page. It is deployed at https://playground.rut.hpp2334.com.

The layout

• Case list — prepared programs, ordered the way the repo’s own gate runs them: algorithms first (sieve, quicksort, matrix multiply), then language-surface tours (classes, closures & generics, structs, literals, checked arithmetic, str views, bytes, opaque, when, maps & sets, type aliases), then memory shapes (node cycle, tree, weak cache).
• Editor — the case’s source, live-editable. The cases are read from the same .rut files the repository’s native test gate compiles and runs, so what you edit is the real corpus, not a copy.
• Output / AST / IR panes — every run shows the program’s real output plus the two compile views: the parsed AST and the typed IR the compiler lowers to. rut dump <file> prints the same structures from the CLI.
• Budget control — each run executes under an explicit fuel + heap budget (default 10,000,000 fuel / 4 MiB heap). A budget that bites is a feature, not a bug: one prepared case parks on the out-of-fuel trap on purpose, and the Resume control adds fuel and continues the same frame — that is structured-concurrency-grade resumption, not a restart.

No silent fallback

The page probes the wasm artifact at boot. If the engine or the syntax-highlighting module is missing or invalid, you get a full-page error naming the exact build command — the panes never mount in a degraded mode. On the deployed site this never happens; when you run a local build (below), the preflight exists so a stale artifact cannot masquerade as a working playground.

Running it locally

cd demo
npm install
npm run build:wasm   # builds rut.wasm + rut-lsp.wasm, copies to public/
npm run dev          # http://localhost:8080 with live reload

Other lanes:

npm run build        # static build into dist/
npm run smoke        # headless gate: every case really runs
npm run dev:channel  # dev server + a throwaway public https URL for demos

The corpus itself is documented in the playground corpus, with the bigger end-to-end projects under Examples.