py-four

py-four is a Python interpreter for the 4 esoteric programming language. You can try it in your browser on Try it Online! thanks to @DennisMitchell.

For a quick introduction with 4 code, scroll to the 4 Guide.

The four directory is a package for the interpreter; The samples directory contains 4 code samples.

Quickstart

To use the interpreter, either pass a file name or the raw code through the -e option:

$ python four samples/hello.4
Hello World!

$ python four -e 3.60072601735005014
HI

The transpiled python source can be viewed with the -v | --verbose option.

Optimizations are available under the -o | --optimize option (currently unstable).

4 Guide

4 is a simple language with a small instruction set, created by Vriskanon. This guide contains a brief summary of the esolangs page documentation.

Every program starts with 3. and ends with 4, and uses a memory area with 100 numeric cells, numbered 00-99.

The code consists of several instructions, starting with an 1-byte opcode, followed by [0 to 3] 2-bytes operands.

Operations

In the following examples G[x] denotes the array cell at x.

Also, 4 code should not contain ant non-numeric characters. Spaces and brackets here are for demonstration..

Assignment: set (opcode 6) performs G[operand 1] = operand 2, so 6 00 01 will set G[0] value to 1.

Math: add (opcode 0), subtract (opcode 1), multiply (opcode 2), and floor divide (opcode 3), each has three operands, and performs G[operand 1] = operation(G[operand 2], G[operand 3]), so 2 00 01 02 will multiply G[1] and G[2] into G[0].

IO: input (opcode 7) and output (opcode 5) each read a byte into or write a byte from G[operand 1], so 5 00 outputs G[0] in unicode.

Branching: begin loop (opcode 8) and end loop (opcode 9) instructions execute all the instructions between them until the counter at G[operand 1] is 0, so 8 01 [7 00] 9 (without brackets) will input a byte into G[0] until G[1] is zero (possibly never).

exit (opcode 4) exits the program.

Example

The program 3.70080050070094 outputs a string received as input. Lets break it down:

3.     |
7 00   | input a byte into G[0]
8 00   | while grid[0] is not null
  5 00 |     output G[0] as a byte
  7 00 |     input a byte into G[0]
9      | close loop
4      |