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# Snack Break Problem #20: Brain***k compiler!

Let's get right to it: this week's Snack Break problem involves writing a compiler for a computer language. Don't worry, though! It's an extremely basic programming language with few rules and instructions.

Brain***k is a funny little language. It should be a fun task to implement a version of it in Lua! From Wikipedia:

Brain***k is an esoteric programming language created in 1993 by Urban Müller, and notable for its extreme minimalism.

The language consists of only eight simple commands and an instruction pointer. While it is fully Turing-complete, it is not intended for practical use, but to challenge and amuse programmers.

You can use this online Brain***k compiler to get some more examples and experiment with the language.

## Breakdown

The concept of the language is simple. Imagine you have a row of cells or an array. The data pointer points to an index of this array. Two instructions in the language can increment or decrement the data pointer, so as to adjust the active index of the array. Two other instructions can increment or decrement the value at the index, e.g. data[pointer] = data[pointer] + 1.

Here is a list of all the instructions in the language. Every instruction in Brain***k is one-character long, so that makes it easy to parse.

Character Meaning
> Increment the data pointer by one.
< Decrement the data pointer by one.
+ Increment the value at the data pointer by one.
- Decrement the value at the data pointer by one.
. Output the byte at the data pointer as an ASCII character (Lua's string.char will come in handy for this!)
[ Loop start: If the value at the current data pointer is not zero, continue. If it is zero, jump to after the matching ]
] Jump to the matching [

Any other characters that aren't in the list above are ignored.

## Examples of the language in action

++ --- 2
++ --- 2


#### Multiply 5 x 13

> ---- Move data pointer over to cell 1 (remember, it starts at 0!)
+++++ ----- We want to run the below loop 5 times, so set the value at cell 1 to 5
[ ---- Loop start
- ----- Subtract one from cell 1 (this is the cell that keeps track of how many times our loop runs)
< ---------- Move data pointer back to cell 0, this is where we are storing our result
+++++ +++++ +++ ---- Increment cell 0 13 times.
> ------ Move data pointer back to cell 1, since it needs to be back there at the beginning of the loop when we subtract 1 from it again
] ---- End of loop
< -------- Move back to cell 0, which is where we stored our result
. ------ Print the contents of cell 0 in an ascii character. REMEMBER that this isn't a number, it's actually the letter "A", because "A" is at index 65 in the ASCII table! (and 5 x 13 is 65)


#### Hello World

++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.


Add the final instruction, a ,, which accepts one byte of input from the user and stores it in the value of the current data pointer.

Good luck!

### Commentary

EzraNehemiah_TF2 says: November 15, 2016
Wow cursing evaera?!?! What an all-time low!! ( ?° ?? ?°)
Programical says: November 15, 2016
This is the simplest, and yet the most complicated language I have ever seen... Wait, that doesn't make sense...
The given definition for [ and ] is incorrect. The data pointer isn't 'stored' when [ is reached, it's simply tested. If it's 0, it jumps to the next instruction after the matching ]. And ] jumps to the instruction after the matching [ if it's NOT 0.
OldPalHappy says: November 16, 2016
If we finish the challenge, is there a place to submit our solutions?
D_ctorScript says: November 17, 2016
BOOOOOOOORING
buoyantair says: November 17, 2016
Cool
DepressionSensei says: November 18, 2016
cool
CMVProduction says: November 23, 2016
Next on the list, "Ook!" programming language. Yeah, this exist!
OldPalHappy says: November 24, 2016
Some Shakespeare, maybe? :3
EzraNehemiah_TF2 says: November 26, 2016
Do LOLCode next.
aquathorn321 says: January 10, 2017
I remember using this in the chemi***k in space station 13
LisaF854 says: November 16, 2018
Oh wow, I recently made this on repl.it Literally during my free time. It was fun, not hard though. I even went as far as making it display the memory, the stuff it is currently executing, etc. Really fun. https://repl.it/@Q_verCubes/Brainf There you go, if you have no idea how to use it, the code is written on the stdin input. At the end of your code, always put a \0.01 as it indicates the end.