LTypen

LTypen is a fictional programming language and type system designed for educational purposes in computer science literature. It emphasizes precise resource management through linear types and a compact core syntax, enabling formal reasoning about program safety and side effects.

The project aims to illustrate how types can encode usage rules, preventing common errors such as use-after-free or duplicate ownership. Its design favors simplicity, modularity, and a clear separation between ordinary data types and resource types.

LTypen's type system combines static typing with linear and affine concepts. Linear types require values to be used exactly once, while affine types permit at most one use. The system supports parametric polymorphism, algebraic data types, and a small effect system for I/O and state.

Programs in LTypen often feature explicit resource flows. Functions consuming linear resources produce new values and must adhere to transfer rules that the compiler checks, ensuring resources are neither leaked nor duplicated.

Origin and influence: LTypen was introduced in instructional materials and hypothetical compiler projects in the 2010s and early 2020s. While not adopted as a practical language, it serves as a teaching tool for type theory and language design.

Implementations are experimental and research-oriented. Several toy compilers and interpreters implement core features, focusing on type safety proofs and formal verification rather than performance.

See also: linear types, affine types, resource management, type systems in Rust, Haskell, Idris.