Brainfuck

October 4, 2011

In 1993, Urban Müller invented the brainfuck programming language, which is a simple-minded programming language, similar to a Turing machine, with a very terse syntax. The data store consists of 30000 cells, each a single byte initialized to 0; a data pointer points to one of the cells. Programs consist of the eight characters +-.,[] with the following meanings:

< move the data pointer one cell left
> move the data pointer one cell right
+ increment the cell at the current data pointer
- decrement the cell at the current data pointer
. output the cell at the current data pointer as a character
, input the next character to the cell at the current data pointer
[ if the cell at the current data pointer is zero, move the instruction pointer to the matching ]
] move the instruction pointer to the matching [

The brainfuck interpreter runs through a program performing each instruction as it appears, ignoring all characters other then +-.,[], advancing the instruction pointer after each instruction (including after [ and ]); a program halts by running off its end. Here’s a sample brainfuck program, which prints “Hello World!” when it is run; additional sample programs appear on the next page:

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

Your task is to write a brainfuck interpreter. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

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