lambda

Basic untyped lambda calculus interpreter. Running the program will drop you into a repl where you can type an expression in lambda calculus. Upon parsing this, you will be put into a new repl, where pressing enter will beta reduce the current term by one step. You can exit this by typing 'q' and pressing enter. I would recommend using rlwrap, as the repls are rather basic.

Here's an example interaction showing each step of the beta reduction.

> (lambda x y z. x z (y z)) (lambda x y. x) (lambda x y. x)
(λx y z. x z (y z)) (λx y. x) (λx y. x)
?
(λy z. (λx y. x) z (y z)) (λx y. x)
?
λz. (λx y. x) z ((λx y. x) z)
?
λz. (λy. z) (λy. z)
?
λz. z
? q

It will even handle name collisions and automatically alpha-rename.

> (lambda x y. x y) (lambda x. y)
(λx y. x y) (λx. y)
?
λz. (λx. y) z
?
λz. y
? q