bf

bf is an optimizing Brainfuck interpreter written in Elixir. Use it as a library or from the command line.

Documentation

Documentation for the latest release is available at hexdocs.pm.

Library usage

Add bf to your dependencies in mix.exs:

def deps do
  [
    {:bf, "~> 2.0.0"}
  ]
end

Parse a program with Bf.parse/1, then run it with Bf.run/2, which takes the input as a string and returns the output:

iex> {:ok, program} = Bf.parse(",[.,]")
iex> Bf.run(program, "hello")
"hello"

Bf.run/3 streams instead. It reads from any enumerable of binaries, only as far as the program needs, and puts each byte the program writes into any collectable right away:

iex> Bf.run(program, File.stream!("input.txt", 1), File.stream!("output.txt"))

Parse errors tell you which bracket doesn't match:

iex> Bf.parse("+[")
{:error, %Bf.ParseError{reason: :unmatched_open, line: 1, column: 2}}

Command line

Install the bf escript with mix:

mix escript.install hex bf

Or build it from source:

git clone https://github.com/lukad/bf.git
cd bf
MIX_ENV=prod mix do escript.build, escript.install

Run a program, with stdin and stdout as its input and output:

$ cat <<EOF> hello.bf
+++++ +++++             initialize counter (cell #0) to 10
[                       use loop to set the next four cells to 70/100/30/10
    > +++++ ++              add  7 to cell #1
    > +++++ +++++           add 10 to cell #2
    > +++                   add  3 to cell #3
    > +                     add  1 to cell #4
    <<<< -                  decrement counter (cell #0)
]
> ++ .                  print 'H'
> + .                   print 'e'
+++++ ++ .              print 'l'
.                       print 'l'
+++ .                   print 'o'
> ++ .                  print ' '
<< +++++ +++++ +++++ .  print 'W'
> .                     print 'o'
+++ .                   print 'r'
----- - .               print 'l'
----- --- .             print 'd'
> + .                   print '!'
> .                     print '\n'
EOF

$ bf hello.bf
Hello World!

bf ast hello.bf prints the optimized program instead of running it.

Interpreter Info

• Cells are 8 bits wide
• Cells wrap around 256
  • 255 + 1 = 0
  • 0 - 1 = 255
• The tape is 30000 cells large
• The tape pointer wraps around 30000
• Input and output are bytes
• Reading at the end of the input sets the cell to 0