The C ABI has long been the de facto bridge for calling code across languages, but it cannot express generics—placeholders for types that are filled in later. That limitation forces Rust libraries to be stripped down to raw primitives when used from other languages. Evan Ovadia, creator of the Valen language, set out to solve this by making Rust itself the interoperability layer.
His solution has two parts. First, he runs the Rust compiler as a library, embedding rustc directly into Valen's memory space. Second, he patches Rust so that when it encounters non-Rust Valen types, it hands control to the Valen compiler and waits for the compiled result. This allows generic functions and types to flow in both directions—Valen can call Rust generics, and Rust can call back into Valen.
The patch is only about 100 lines of code, but Ovadia calls it the "nuclear option." It is hacky, assumes Rust uses LLVM for code generation, and is not upstreamable. Still, the experiment demonstrates a genuine step forward in language interoperability, and it has drawn praise from programmers on forums like Reddit and Lobste.rs, even as some question whether Rust is the ideal base for such a bridge. If refined, this approach could reduce reliance on the creaky C ABI and make it easier to bootstrap new languages from Rust's rich ecosystem.