Unlambda

Unlambda is a minimal functional programming language based upon the lambda calculus but not supporting the lambda operator. It relies mainly on two builtin functions (s and k) and an "Apply" operator (written `, the backquote character); these alone make it Turing-complete, but there are also some I/O functions to make it possible to interact with the user.

As an esoteric programming language, Unlambda is meant as a demonstration of very pure functional programming rather than for practical use. Its main feature is the lack of conventional operators and data types -- the only kind of data in the program is one-parameter functions. Data can nonetheless be represented with curried functions.