GoKawiilLasm lets developers compile Lean 4 code to WebAssembly for Node, edge and browser apps
Lasm is a new toolchain that ahead-of-time compiles standard Lean 4 programs into WebAssembly, letting a single codebase run as a Node server, serverless or edge function, WASI/Fastly module, or browser app. It ships via npm bundling Lean and its Lake build tools, requiring only Node, Bun, or Deno. Its flagship demo, a RealWorld-spec app called Conduit, includes 117 formally proved theorems.
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Bringing a formal proof assistant like Lean into mainstream JavaScript deployment targets could let developers verify correctness properties of production web code rather than relying solely on tests. By packaging Lean's toolchain through npm, the project lowers the barrier for JS developers to try formal verification without separate installs, which may broaden interest in provably correct software beyond academic or safety-critical niches.
- Lasm compiles Lean 4 to WebAssembly, targeting Node, serverless/edge platforms, WASI/Fastly, and browsers from one codebase.
- The project provides Lean frameworks for HTTP, UI, RPC, DOM, and key-value storage to support typical web app needs.
- Its example app, Conduit, demonstrates formal verification with 117 proved theorems, showcasing the verification angle of the toolchain.
Source: github.com, 2026-10-30
Published there as: “Show HN: Lasm – Write formally verified webapps in Lean for Node/serverless/edge”
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