less_retarded_wiki/brainfuck.md

# Brainfuck

Brainfuck is an extremely simple, untyped [esoteric programming language](esoland.md); simple by its specification (consisting only of 8 commands) but intentionally very hard to program in. It works similarly to a pure [Turing machine](turing_machine.md). In a way it is kind of [beautiful](beauty.md) by its [simplicity](minimalism.md). It is very easy to write your own brainfuck [interpreter](interpreter.md).

There exist [self-hosted](self_hosting.md) brainfuck interpreters and compilers (i.e. themselves written in brainfuck) which is pretty fucked up. The smallest one is probably the one called [dbfi](dbfi.md) which has only slightly above 400 characters, that's incredible!!! (Esolang wiki states that it's one of the smallest self interpreters among imperative languages).

The language is based on a 1964 language P´´ which was published in a mathematical paper; it is very similar to brainfuck except for having no [I/O](io.md).

Brainfuck has seen tremendous success in the [esolang](esolang.md) community as the **lowest common denominator language**: just as mathematicians use [Turing machines](turing_machine.md) in proofs, esolang programmers use brainfuck in similar ways -- many esolangs just compile to brainfuck or use brainfuck in proofs of [Turing completeness](turing_complete.md) etc. This is thanks to brainfuck being an actual, implemented and working language reflecting real computers, not just a highly abstract mathematical model with many different variants. For example if one wants to encode a program as an integer number, we can simply take the binary representation of the program's brainfuck implementation.

In [LRS](lrs.md) programs brainfuck may be seriously used as a super simple [scripting language](script.md).

Brainfuck can be trivially translated to [comun](comun.md) like this: remove all comments from brainfuck program, then replace `+`, `-`, `>`, `<`, `.`, `,`, `[` and `]` with `++ ` , `-- `, `$>0 `, `$<0 `, `->' `, `$<0 <- `, `@' ` and `. `, respectively, and prepend `$>0 `.

## Specification

The "vanilla" brainfuck operates as follows:

We have a linear memory of **cells** and a **data pointer** which initially points to the 0th cell. The size and count of the cells is implementation-defined, but usually a cell is 8 bits wide and there is at least 30000 cells.

A program consists of these possible commands:

- `+`: increment the data cell under data pointer
- `-`: decrement the data cell under data pointer
- `>`: move the data pointer to the right
- `<`: move the data pointer to the left
- `[`: jump after corresponding `]` if value under data pointer is zero
- `]`: jump after corresponding `[` if value under data pointer is not zero
- `.`: output value under data pointer as an ASCII character
- `,`: read value and store it to the cell under data pointer

## Implementation

This is a very simple [C](c.md) implementation of brainfuck:

```
#include <stdio.h>

#define CELLS 30000

const char program[] = ",[.-]"; // your program here

int main(void)
{
  char tape[CELLS];
  unsigned int cell = 0;
  const char *i = program;
  int bDir, bCount;
  
  while (*i != 0)
  {
    switch (*i)
    {
      case '>': cell++; break;
      case '<': cell--; break;
      case '+': tape[cell]++; break;
      case '-': tape[cell]--; break;
      case '.': putchar(tape[cell]); fflush(stdout); break;
      case ',': scanf("%c",tape + cell); break;
      case '[':
      case ']':
        if ((tape[cell] == 0) == (*i == ']'))
          break;

        bDir = (*i == '[') ? 1 : -1;
        bCount = 0;
          
        while (1)
        {
          if (*i == '[')
            bCount += bDir;
          else if (*i == ']')
            bCount -= bDir;
          
          if (bCount == 0)
            break;
          
          i += bDir;
        }
        
        break;
      
      default: break;
    }
    
    i++;
  }
}

```

TODO: comun implementation

## Programs

Here are some simple programs in brainfuck.

Print `HI`:

```
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ . + .
```

Read two 0-9 numbers (as ASCII digits) and add them:

```
,>,[<+>-]<------------------------------------------------.
```

TODO: more

## Variants

TODO