Unlambda

Unlambda is an esoteric functional programming language created by David Madore in 1999, designed around a minimalist combinator calculus in which the only built-in functions are variants of the S, K and I combinators from combinatory logic, and in which ordinary features such as named variables are deliberately absent. Programs are written entirely as combinator applications, making even simple tasks such as printing a fixed string a nontrivial exercise, which is the language's explicit point: to demonstrate that a full, if painfully impractical, model of computation can be built from function application alone.