Idris

Idris is a general-purpose functional programming language with dependent types, designed to enable type-driven development and formal verification within software. It blends ideas from Haskell with a dependent type system that allows types to depend on values. The language aims to make it practical to encode properties of programs in types and to extract executable code from constructive proofs.

The Idris type system supports dependent types, type inference with explicit dependent annotations, as well as type classes, implicits, and first-class families. A distinctive feature is totality checking, which analyzes functions to ensure they terminate and are total, helping to guarantee program safety. Idris programs are written in a Haskell-like syntax and are elaborated by a compiler that checks types and then generates executable code. Idris emphasizes interactive development through a REPL and an elaborator that guides the programmer in writing correct code. It also integrates with theorem-proving ideas, enabling lightweight proofs alongside ordinary programs.

Historically, Idris originated in academic research at the University of St Andrews in the 2010s. It has seen multiple major releases, with Idris 2 delivering a redesigned core language and improved tooling. The language is used primarily in research and education to explore type-driven design, program verification, and dependently typed programming, though it has not achieved the same level of industry-wide adoption as some other languages.

Examples illustrate the power of dependent types: a vector type may encode its length in the type system, so operations like append can have types that reflect the resulting length.