lambda-calculator.js is an implementation of the world's oldest functional programming language, λ-calculus. It implements Alonzo Church's original, untyped variant with call-by-value semantics and modern, dot-based syntax. As such, it differs substantially from conventional functional programming language interpreters.
user@host:~$ sudo npm install --global lambda-calculator.js
user@host:~$ lambda-calculator.js
> (\ x y . y x) a b
b a
> Use Ctrl-C to quit.