Brainfuck part 1: what is it?

This article is part of a series on brainfuck, a weird programming language:

  1. Brainfuck part 1: what is it?
  2. Brainfuck part 2: an interpreter in JavaScript
  3. Brainfuck part 3: a brainfuck → JavaScript transpiler

Brainfuck is an esoteric programming language using only eight characters ><+-.,[]. It has no pratical use but it’s fun and challenges the mind.

Design

The language has only eight commands: the eight characters. Any other character is ignored and can be use for commenting.

The programming model is simple: you have a 30,000 cells data array and a pointer to the current cell. You can modify the value of this cell, print it (ASCII output) or replace it with the value of the keyboard input.

  • > move the data pointer forward
  • < move the data pointer backward
  • + increments (+1) the current cell
  • - decrements (-1) the current cell
  • . outputs the current cell as an ASCII character
  • , reads one character from the input and writes it in the current cell
  • [ makes the program jump to the instruction after the matching ] if the current cell’s value is 0.
  • ] makes the program jump to the instruction after the matching [ if the current cell’s value is not 0.

Having only these commands is the ‘’fuck’’ part of brainfuck.

Examples

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******************
* print 'foobar' *
******************

init variables
==============
+++++ +++++          a = 10
[                    while(a != 0)
    > +++++ +++++        add 10 to b
    > +++++ +++++ +      add 11 to c
    <<-                  decrement a
]                    end of while:
                       b = 100 (close to 'f' 'b' 'a')
                       c = 110 (close to 'o' 'r')

adjust variables and print
==========================
>
++ .    b = 102; print 'f'
>
+ .     c = 111; print 'o'
  .              print 'o'
<
---- .  b = 98;  print 'b'
- .     b = 97;  print 'a'
>
+++ .   c = 114; print 'r'

Crazy, huh?

Now an “echo” program. It reads your input and just outputs it.

Serial version (reads all, prints all)

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> +     mem = (O 1) ; you need a non zero cell to enter the loop
[>,]    read until there is a 0 (= convention for end of input)
<[<]    move data pointer backwards until there is a 0 (condition to exit the loop)
>>[.>]  move forwards and print until 0

Parallel version (reads one, prints one) 

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, read first char
[ while the last read value is not 0
    .   print it
    [-] reset the cell to 0
    ,   read next char
]

Exercices

If you don’t think it’s fun, please close your browser. Otherwise, here are some exercices (the number of * indicates the difficulty):

How do you:

  • Duplicate a cell? *
  • Move a cell? *
  • Add 2 cells? *
  • Multiply 2 cells? **

Write the brainfuck equivalent of:

  • If(a){code} *
  • While(a && b){a—; b—} **
  • If(x){code1}else{code2} *

My solutions.

Conclusion

Brainfuck is a well chosen name.

This article is part of a series on brainfuck, a weird programming language:

  1. Brainfuck part 1: what is it?
  2. Brainfuck part 2: an interpreter in JavaScript
  3. Brainfuck part 3: a brainfuck → JavaScript transpiler