1.4 KiB
untyped-lambda-calculus
A simple implementation of the untyped lambda calculus as an exercise.
This implementation lacks many features necessary to be useful,
for example let bindings, built-in functions, binding free variables, or a good REPL.
This project purely exists as an exercise and is not intended for general use.
I will make useful programming languages in the future, but this is not one of them.
Usage
Type in your expression at the prompt: >> .
The result of the evaluation of that expression will then be printed out.
Exit the prompt with Ctrl-C (or however else you kill a program in your terminal).
Bound variables will be printed followed by a number representing the number of binders between it and its definition for disambiguation. This is not guaranteed not to capture free variables.
Examples
>> (\D F I. D (F I)) (\x. x x) (\f. f (f y)) (\x. x)
y y
>> (\T f x. T (T (T (T T))) f x) (\f x. f (f x)) (\x. x) y
y
>> \x. \y. y x
\x. \y. y:0 x:1
Syntax
- Variables are alphanumeric, beginning with a letter.
- Applications are left-associative, and parentheses are not necessary.
- Lambdas are represented by
\\, bind as far right as possible, and parentheses are not necessary.
Examples
- Variables:
x,abc,D,fooBar,f10 - Applications:
(\x. x x) y,a b,((g f) y) - Lambdas:
\x. N,\x y. y,(\x. f x)