# Hello today I am a unicorn

Designed by | Hakerh400 |
---|---|

Appeared in | 2020 |

Computational class | Turing complete |

Major implementations | Interpreter |

File extension(s) | `.txt` |

**Hello today I am a unicorn** is a Turing-complete programming language that has only two variables.

## Contents

## Overview

There are only two variables: `x`

and `y`

. Both are non-negative integers of unlimited size.

Source code consists of zero or more instructions. Any instruction can be prefixed by a label.

Each instruction begins with the variable name it uses (`x`

or `y`

), then operator that is applied and operands.

### Operator Xor

Denoted by `~`

. No operands. Inverts the lowest bit of the variable. Example:

x~

Value of `x`

before: `123`

Value of `x`

after: `122`

### Operator Shift left

Denoted by `+`

. No operands. Performs binary shift to the left. Example:

y+

Value of `y`

before: `5`

Value of `y`

after: `10`

### Operator Shift right

Denoted by `-`

. No operands. Performs binary shift to the right. Example:

x-

Value of `x`

before: `15`

Value of `x`

after: `7`

### Operator If

Denoted by `?`

. Two operands (and they are labels). If the lowest bit is `1`

jump to the first label, otherwise jump to the second label. Example:

y? label1 label2 label1: x+ label2: x-

If `y`

is odd, `x`

will be shifted left and then shifted right. If `y`

is even, `x`

will only be shifted right.

Note: all instructions except this simply increment instruction pointer.

## I/O format

Input is a non-negative number. It is written in the `x`

variable before program starts, while `y`

is initially `0`

. When program terminates, `y`

contains the output.

## Examples

### Cat

Note: assuming the same I/O format as described here for converting from/to ASCII strings.

x? copy exit copy: x- y+ y~ y+ x? flip next flip: y~ next: x- x? copy exit exit: x~

## Computational class

The variables `x`

and `y`

effectively implement two stacks of bits; you can push to these via a left-shift (possibly followed by an xor), pop them via a right-shift, and test the bottom bit via the if operator. Because the language also allows arbitrary control flow, this allows two-stack machines to be implemented more or less directly (a two-counter machine can also be implemented via treating the counter as a stack of multiple 0 bits above a single 1 bit), making the language Turing complete.