Learn UNLAMBDA with Real Code Examples

Unlambda is based on SKI combinatory logic, where programs are constructed from function applications.

It does not have named variables or conventional control structures.

Output and input are handled via the '.' and ',' operators, respectively.

Unlambda programs are often challenging to read due to their extreme minimalism.

It is primarily used for academic, experimental, and recreational programming.

Primary combinators: `s`, `k`, `i`, `v`, `c`, `d`, `@`

Function application is left-associative

Output with `.` operator

Input with `,` operator

Conditional logic via combinator constructs

Combinators - fundamental building blocks (`s`, `k`, `i`)

Application - left-associative function application

Output - `.` operator prints characters

Input - `,` operator reads characters

Conditional logic - implemented using combinators like `c` and `d`

Single `.ul` file containing combinator expressions

No directories or modules by default

Optional comments in some interpreters

Input/output handled inline

Entire logic embedded in combinator chains

Write combinator expressions in a text file

Use left-associative application to chain combinators

Add input/output combinators if needed

Run the program in an interpreter

Debug by reducing combinator expressions step-by-step

Beginner: run existing Unlambda programs

Intermediate: modify programs and trace execution

Advanced: write small original programs

Expert: implement Turing-complete algorithms

Architect: explore complex combinator-based systems

Unlambda vs Brainfuck -> Both esoteric, Unlambda: combinatory logic, Brainfuck: memory tape

Unlambda vs Haskell -> Haskell: practical functional programming, Unlambda: minimal theoretical demonstration

Unlambda vs Lisp -> Lisp: macros and variables, Unlambda: no variables, only combinators

Unlambda vs C -> C: imperative, practical, Unlambda: minimal and academic

Unlambda vs Lambda Calculus -> Unlambda implements lambda calculus via combinators

1999 - Unlambda created by David Madore

2000 - Initial C interpreter released

2001 - Online interpreters begin appearing

2005 - Minor updates and community examples

2010–2025 - Used in academic and recreational contexts

Combinator - a function with no free variables

Application - applying one combinator to another

Turing-complete - capable of performing any computation

Esoteric language - designed for theoretical or recreational purposes

SKI calculus - foundation of Unlambda combinatory logic