A language that knows how to wait. pause as a first-class primitive.
In ordinary languages, a running program's mid-execution state is ephemeral. If the process dies, the state dies with it. You write checkpoint files, queues, retries, idempotency layers to survive failure.
Modern durable-execution frameworks (Temporal, Inngest, Restate, DBOS) add that infrastructure on top of ordinary languages. They work — and they force you to structure programs around activity/step/await boundaries.
Penelope dissolves these boundaries by making pause/resume a language primitive, not a framework feature.
let x = 10;
let y = pause; // process exits, state saved to disk
print(to_str(x + y)); // a later process resumes, prints 15The variable x survives across processes. The user wrote no checkpoint, no restore, no await. Just let y = pause. That is the entire ergonomic claim.
Execution is data. A running program is a value.
If the runtime state is just JSON, it can be persisted to disk, forked, inspected, migrated, compared, transmitted, scheduled — like any other value. Everything else in Penelope follows from this axiom.
| Phase | What | Status |
|---|---|---|
| Phase 1 | Foundations: lexer + parser + step-machine + snapshot | ✅ done |
| Phase 2 | Effect system: 8 effects + strings + agent runtime | ✅ done |
| Phase 3 | Bytecode VM + 5-pass optimizer + snapshot v3 | ✅ done |
| Polish R1 | wait_for value injection · source positions · REPL · LSP | ✅ done |
| Polish R2 | list/dict · type checker · profiler · VSCode ext · docs site | ✅ done |
| Polish R3 | Rust-style errors · LSP hover · snippets · web playground | ✅ done — try the Playground |
| Polish R4 | pen fmt · pen test · LSP completions + go-to-def · --watch · color | ✅ done |
| Phase 4 | Self-hosting · live editing · time-travel | future |
git clone https://github.com/airingursb/Penelope
cd Penelope
npm install && npm run build
# Run a program
bin/penelope run examples/01-toplevel-pause.pen
# Compile to bytecode
bin/penelope build -O2 examples/09-fib.pen
# Drop into a REPL
bin/penelope repl
# Type-check
bin/penelope check examples/08-24h-agent.pen