Melbi

Melbi is an embeddable expression language designed for safe evaluation of user-defined logic.

Feature Highlights

• No runtime errors if it compiles - Type system guarantees logical errors are handled.
• Expression-focused - Everything is an expression. No statements, no surprises.
• Effect tracking - Errors propagate automatically through ! effect. Handle with otherwise or pattern matching.
• Safe sandboxing - Memory and time limits built-in. Safe for untrusted code.
• Type inference - Full Hindley-Milner style inference. No type annotations required.
• Pattern matching - Decompose union types and handle errors explicitly.
• Embeddable anywhere - Rust-native with C FFI for Python, Node.js, Go, Java, and any language with C bindings.
• Fast execution - Arena-based allocation competitive with C++ performance.
• Rich expressions - Arrays, records, maps, lambdas, format strings, and where-bindings.

Use Cases

Email filters, feature flags, A/B testing, ETL transformations, business rules, configuration systems, data validation - anywhere end users need to define logic without modifying your application’s source code.

Project Status

Melbi is in active alpha development. The core language features work, but the API and tooling are still evolving. Not recommended for production use yet.