Untyped Lambda calculus to JavaScript compiler

Latest on Hackage:

This package is not currently in any snapshots. If you're interested in using it, we recommend adding it to Stackage Nightly. Doing so will make builds more reliable, and allow to host generated Haddocks.

GPL-3 licensed by Matej Kollar
Maintained by

Welcome to lambda2js

Before you get any further: lambda2js is mainly a fun project. So if you are not in the mood simply leave as it is not for you.

If you need something serious, try PureScript, Haste, elm, or Fay.

As you can guess just by looking at the name, lambda2js is compiler that takes simple syntactically sugared untyped lambda calculus and produces JavaScript code. Though this project is meant as fun, it actually works.

Lambda2js is open source (licensed under GPL-3) and patches are welcome.


Have you ever found yourselves writing JavaScript code and thinking: “Oh my… How nice would it be to have this function with flipped arguments. And now I have to write wrapper function, or at least some anonymous function that will do what I need. In functional language I would simply use flip and that would be it!” Well, now it is your time as lambda2js was brought to light.


In examples you can find simple example, that will get compiled into

K = function(x){return function(y){return x}}
S = function(f){return function(g){return function(x){return f(x)(g(x))}}}
I = S(K)(K)
Dot = function(f){return function(g){return function(x){return f(g(x))}}}
Flip = function(f){return function(x){return function(y){return f(y)(x)}}}
True = K
Not = Flip
False = Not(True)
If = I
Zero = function(s){return function(z){return z}}
Succ = function(n){return function(s){return function(z){return n(s)(s(z))}}}
IsZero = function(n){return n(K(False))(True)}
Add = function(m){return function(n){return function(s){return function(z){return m(s)(n(s)(z))}}}}
Mul = function(m){return function(n){return function(s){return function(z){return m(n(s))(z)}}}}
Pow = function(m){return function(n){return function(s){return function(z){return n(m)(s)(z)}}}}
One = Succ(Zero)
Two = Succ(One)
Three = Succ(Two)
Tup = function(x){return function(y){return function(p){return p(x)(y)}}}
Fst = function(t){return t(K)}
Snd = function(t){return t(Flip(K))}
Fac = function(n){return Snd(n(function(t){return t(function(x){return function(y){return Tup(Succ(x))(Mul(x)(y))}})})(Tup(One)(One)))}

which is fully functional (pun intended) JavaScript. It can be played with: combined with small helper library for seamless integration, one can compute (2+3)!.


Flipping arguments can be as simple as


…and much more.


I was playing with JavaScript the other day, pondering higher functions. Trying the usual stuff like Church numerals and other. I found myself under avalanche of JavaScript boilerplate. Just compare function(x){return x} and \ x . x.

And then it occurred to me: this can be easily automated! I can write code I like and get code I need. So I sat down to my console and in just couple of moments I came up with 10 commandm^W^Wthis little project. Enjoy.

Depends on 2 packages:
Used by 1 package:
comments powered byDisqus