Developer builds Rust compiler for custom language Seseragi with minimal Rust knowledge using AI

Kentaro Morishita is developing Seseragi, a custom programming language whose compiler is written in Rust, despite having limited ability to read or write Rust himself. He relies heavily on OpenAI's Codex to produce much of the Rust implementation, while focusing his own efforts on language semantics, architecture decisions, and surface design. Morishita notes that AI-accelerated code generation makes poor architectural choices more dangerous, as flawed structures can become fully implemented very quickly before errors are caught. The Seseragi project now includes a compiler, CLI, LSP, formatter, and a WASM Playground, all available publicly on GitHub and via a web playground. He argues that authorship of a programming language rests in controlling its meaning and design, not in personally writing every line of its implementation.