Cajal Technologies released Talos, a WebAssembly interpreter built in Lean 4. The project blends execution and formal reasoning, letting developers run .wat files while proving properties about them. Talos targets languages that compile to Wasm, such as Rust, C++, and Go.

Talos shares a single codebase for execution and proof, eliminating sync gaps between an interpreter and its specification. Its weakest‑precondition calculus supplies a predicate‑transformer framework that supports compositional proofs for loops, branches, and function calls. The team plans to cover the full Wasm spec after passing the W3C test suite, then target arbitrary Rust crates.

The framework ships a proof library called codelib that lifts lemmas and provides helpers for program reasoning. Developers can import codelib to write proofs without importing the interpreter directly, keeping proofs lightweight. A sample proof verifies the GCD algorithm in the popular Rust num‑integer crate, demonstrating Talos’s ability to reason about real‑world code.

Talos runs on Lean 4’s lake build system and depends on wasm‑tools for binary decoding. The project is open source under the GNU Affero GPL v3.0, inviting community contributions. By unifying execution with formal verification, Talos pushes toward a future where software carries a mathematical proof of correctness, potentially curbing exploitation.