4

4, named after the last digit of pi (a joke from the webcomic Homestuck), is an esoteric programming language created by user:Vriskanon.

Program overview
4 is a grid-based language made up of 100 cells found on a 10x10 grid. Each cell is an integer variable. Their location is described by its X value (0-9) and its Y value (0-9), so the top left cell is 00 and the bottom right cell is 99. All cells have a default value of 0.

Parts of the program
All codes in 4 are made up of 3 parts: The beginning, the end and a main 'body' of functions.

The beginning
All 4 codes start with "3.". This does not affect the code. If a code does not begin with "3.", it is considered a syntax error.

The end
All 4 codes end with "4". This does not affect the code. If a code does not end with "4", it is considered a syntax error.

The body
The main bulk of a code will be the body of many function. Functions are made up of 1-4 parts: The function name and 0-3 variables. All function names are 1 digit long (0-9) and all variables attached to them are exactly 2 digits long (00-99).

For example, a code that assigned the value 01 to the cell at 00 would look like this (the spacing is uneccessary, it is simply for aesthetics - it is poor form to have any non-number characters in one's code).

3. 6 00 01 4

Here the code starts with 3., then has one function, 6, which has the variables 00 and 01 attached, followed by 4.

Cat program
3.6000180071051094

Hello World!
3.699206007260181001019960288002029960391003039960499004049960594005059960680006069960733608325005015025025035085045035055025065074

External resources

 * A Ruby interpreter which, for the sake of novelty, accepts the program source as a direct call on the number 4.
 * A Python interpreter.