Binary lambda calculus
Binary lambda calculus (BLC) is an extremely small Turing-complete language which can be represented as a series of bits or bytes. Unlike Binary combinatory logic, another binary language with a similar acronym, it is capable of input and output.
BLC Syntax
The BLC program is a sequence of bits read left to right. The following commands are defined. Feel free to change how the commands are explained if you think it's too confusing.
00x= Lambda function with body xx0, where x is one or more "1" bits = the number of "1" bits serves as the De Bruijn index, 1-indexed- For example
10corresponds to a De Bruijn index of 1,110to 2,1110to 3, etc. - To be clear, this means 10 refers to the final lambda, 110 to the second-last, 1110 to the third-last, etc.
- For example
01xy, where x and y are more code = x is applied to y.- By default, the output of a lambda is one term in this language. Using 01 allows the function to output both x and y, which is the same as applying x to y in lambda calculus because both of the outputs are also lambdas.
- If you want to take in one input and output it once, you would write 0010 = 00 10.
- If you want to take in one input and output it twice, you would write 00011010 = 00 01 10 10.
- If you want to take in two inputs and output the first one three times, you would write 00000101110110110 = 00 00 01 01 110 110 110.
- If you want to output code directly starting with 00, it doesn't need to have 01 directly before it. If there is a term before the function, then 01 is needed before the term.
It is possible for the code to have padding at the right end, i.e. code which doesn't affect the result of the command. This fact is especially useful when trying to use bytes to represent this language.
Basic Program Information
A program is a lambda calculus term that transforms an input to an output. Standard input is represented as a list of boolean values, and standard output has the same format.
A 0 bit in BLC is 0000110 (True), and a 1 bit is 000010 (False), which are the normal lambda calculus representations of these values.
0000110 = 00 00 110 *taking two inputs (with the two lambda functions represented by 00), return the second argument from the inside i.e. the first argument 000010 = 00 00 10 *taking two inputs (with the two lambda functions represented by 00), return the innermost / last argument i.e. the second argument
The empty list, called nil, is 000010 (False).
A list with multiple elements is represented by the pairing or cons function 00010110xy, where x is the head of the list and y is the tail.
00010110xy = 00 01 01 10 x y *taking one input, output that input, the head of the list, and the tail of the list
You might expect programs to consist of multiple bytes, considering all of these have been six bits or over. However, printing out input in this language is done through the code 0010, which takes one input (which is the innermost by default) and prints it out. Because padding is ignored and lambdas only output one term by default in this language, a program consisting of just a cat can be represented by any bytes between 32 (00100000) and 47 (00101111) because everything after 0010 is ignored (remember that you have to type 00011010 to output the input twice).
SKI combinator calculus
The encoding of lambda term S is λxλyλz.((xz)(yz)), which is written as λλλ.((3 1)(2 1)) using De Bruijn indexes instead of names, and as 00 00 00 01 01 1110 10 01 110 10 in BLC.
The K combinator is written as λxλy.x or λλ.2 in a corresponding format, so it would be 00 00 110 in BLC.
The identity function I is the same as the cat: 00 10.
Therefore, you can implement SKI combinator calculus in BLC.
BLC8
BLC operates on a stream of bits (values of 0 and 1), while BLC8 is the same, but operates on a stream of bytes (values from 0 - 255) with the most significant bit in the smallest value (big-endian). In the following programs, BLC and BLC8 programs are put into different parts.
Programs (BLC)
self-interpreter
01010001
10100001
00000001
10000001
01110011
00001111
11100001
01110011
1111100000
011110000001
01110111001101
1110011111111000
01111111 10000101
11101001 11010010
11111010 01011010
10011010 00011001
00011010 00011010
prime number sieve
000100011001100101000110100 000000101100000100100010101 11110111 101001000 11010000 111001101 000000000010110111001110011 11111011110000000011111001 10111000 00010110 0000110110
Brainfuck interpreter
0000000 01a15144 02d55584 223070b7 00f032ff 0000020 7f85f9bf 956fe15e c0ee7d7f 006854e5 0000040 fbfd5558 fd5745e0 b6f0fbeb 07d62ff0 0000060 d7736fe1 c0bc14f1 1f2eff0b 17666fa1 0000100 2fef5be8 ff13ffcf 2034cae1 0bd0c80a 0000120 e51fee99 6a5a7fff ff0fff1f d0049d87 0000140 db0500ab 3bb74023 b0c0cc28 10740e6c 0000160
Universal Turing Machine
0101000110100001000000011000000101110011000011111 1100001011100111111100000011110000001011101110011 0111100111111110000111111110000101111010011101001 0111110100101101010011010000110010001101000011010
Programs (BLC8)
self-interpreter
19468
05580
05f00
bfe5f
85f3f
03c2d
b9fc3f8
5e9d65e5f
0decb f0fc3
9befe 185f7
0b7fb 00cf6
7bb03 91a1a
There is also a universal Turing machine written in BLC8 which is slightly longer than the one in BLC.
Computational Class
Lambda calculus is Turing-complete, and because binary lambda calculus is a way of writing lambda calculus, it is also Turing-complete. It can also implement SKI combinator calculus as seen above, so it is Turing-complete in that way. As a final indication of Turing-completeness, Brainfuck and a Universal Turing Machine have both been represented in this language.