Unlambda

Unlambda is a minimal functional programming language based upon the lambda calculus but not supporting the lambda operator. It relies mainly on three builtin functions and an "Apply" operator, along with some i/o functions to be turing complete.

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.