1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
//! **blc** is an implementation of the
//! [binary lambda calculus](https://esolangs.org/wiki/Binary_lambda_calculus) in Rust.
//! ## Binary lambda calculus basics
//!
//! Binary lambda calculus (BLC) is a minimal, purely functional programming language based on a binary
//! encoding of the untyped [lambda calculus](https://en.wikipedia.org/wiki/Lambda_calculus) with
//! [De Bruijn indices](https://en.wikipedia.org/wiki/De_Bruijn_index).
//!
//! Lambda terms have the following representation in BLC:
//!
//! | term | lambda | BLC |
//! --------------|--------|----------------|
//! | abstraction | λM | 00M |
//! | application | MN | 01MN |
//! | variable | i | 1<sup>i</sup>0 |
//!
//! Since BLC programs are basically lambda calculus terms, they can be applied to other terms. In
//! order to be applicable to binary (but not BLC-encoded) input, it has to be lambda-encoded first.
//! Bytestrings are lambda-encoded as
//! [Church lists](https://en.wikipedia.org/wiki/Church_encoding#One_pair_as_a_list_node) of bytes
//! and bytes are lambda-encoded as Church lists of lambda-encoded bits.
//!
//! Bits 0 and 1 are lambda-encoded as
//! [Church booleans](https://en.wikipedia.org/wiki/Church_encoding#Church_Booleans):
//!
//! | bit | lambda | BLC |
//! |-----|-------------|---------|
//! | 0 | λλ2 (true) | 0000110 |
//! | 1 | λλ1 (false) | 000010 |
//!
//! Example: BLC-encoding steps for a byte representing the ASCII/UTF-8 encoded letter 'a':
//!
//! | encoding | representation |
//! |-----------|----------------|
//! | decimal | 96 |
//! | binary | 01100001 |
//! | lambda | λ1(<b>λλ2</b>)(λ1(<b>λλ1</b>)(λ1(<b>λλ1</b>)(λ1(<b>λλ2</b>)(λ1(<b>λλ2</b>)(λ1(<b>λλ2</b>)(λ1(<b>λλ2</b>)(λ1(<b>λλ1</b>)(λλ1)))))))) |
//! | BLC (hex) | 16 16 c 2c 10 b0 42 c1 85 83 b 6 16 c 2c 10 41 0 |
extern crate lambda_calculus;
pub use run;
pub use ;