+++.>+++++.[<+>-]<.With comments
sum of two cells
+ cell(0) = 1
. print
> move to cell(1)
++ cell(1) = 2
. print
[ go to matching bracket if this cell is non zero
< go back to cell(0)
+ increment cell(0)
> go to cell(1)
- decrement
] go back to matching bracket if this cell is zero
<. print result+++++.[-]++.
With comments
Replace the value of a cell
+++++. load a value
[-] clear the cell
++++++. the new value
+++++. load a value
[
- decrement
> move
+ increment
< go back
]
+++++.
[
- decrement
> move
+ increment
> move
+ increment
<< go back
]
+++++. load 5
[->+>+<<] copy contents into a new cell
>>
[->
+++ multiply by 3
<]
>. print result
swaps cell(0) and cell(1)
+++++.>++++++++.< load some values
[->>+<-<]
>[-<+>]
>[-<+<+>>]The shortest known bf code to generate 42
--[>+<++++++]>-Simpler code to generate 42. Compare this to the multiplications example. Do you see the trick?
>>++[-<+++[-<+++++++>]>]<<.++++>+.>+<<[->>.[->+>+<<]>>[-<<+>>]<<<[->+<]>>[-<<+>>]<<<]>>.With comments.
Fibonacci
number of iterations
++++ This program will print this many fibonacci numbers
plus the first two terms we initialize here
>
+. 1 (put 2 here for the Lucas numbers)
>
+ 1
<<
start loop
[-
copy second term
>>.
[->+>+<<]
move copy to blank cell
>>
[-<<+>>]
sum first and second terms
<<<
[->+<]
move (old) second to first place
>>
[-<<+>>]
go to first cell to restart loop
<<<
]
>>. print last termThe Brainf*ck Language
| Instruction | Description |
|---|---|
> |
Move the tape pointer to the right |
< |
Move the tape pointer to the left |
+ |
Increment the tape cell under the pointer |
- |
Decrement the tape cell under the pointer |
[ |
Jump past the matching right bracket if the cell under the pointer is 0 |
] |
Jump back to the matching left bracket if the cell under the pointer is nonzero |
, |
Input a character and store it in the cell at the pointer |
. |
Output the character signified by the cell at the pointer |
| Anything else | Ignored |
Brainf*ck Keywords
Adapted from esolangs.org
Brainf*ck (or BF) is one of the most famous "esoteric" programming languages. Invented in 1993 by Urban
Müller, it was intentionally designed to be an extremely small language. The language consists of
only 8 keywords meant to correspond to the behavior of a Turing machine. Every program starts on the first cell of an
infinite tape of cells, and each cell can hold a value between 0 and 255. You can move the tape "pointer" left
or right and increment or decrement the values in a cell. The most difficult part to get your head around is
using the brackets ([ and ]) to repeat a block of code over and over again. But it is
this ability to conditionally run a block of code which promotes BF from a language which just puts
values in cells to a
full-fledged Turing-complete programming language.
Notes
- I opted for a "wrapping" implementation of brainf*ck, meaning that if you decrement a cell with a 0 in it, it will wrap around to 255. Similarly, if a cell contains 255, incrementing will cause it to wrap to 0.
-
In most implementations of BF, output is interpreted as the ascii encoding of a character. So for example,
to print the character 'A', you need to increment a cell to 65, and then output with the "
." instruction. However, I felt this would make even simple programs take far too long to animate, so, by default, output is just the literal number in a cell. - I had the idea to make a Turing machine interpreter for brainf*ck a while ago and couldn't find any examples of this online. Until, of course, right after I completed it. Here is a very similar page created by Fatih Erikli. He has some other really neat things on his page, so check it out!
- In my Recursion Theory class, my teacher showed us a website which lets you play with Turing machines in a similar way. You can check it out at turingmachinesimulator.com.