Execute Brain****/OCaml

Execute Brain****/OCaml is an implementation of Brainf***. Other implementations of Brainf***.

Execute Brain****/OCaml is part of RCBF. You may find other members of RCBF at Category:RCBF.

Quick implementation of a Brainfuck interpreter in OCaml.

Like the Haskell version but without the lazy lists:

Pairs of lists are used to implement both the two-side infinite band of cells, and the program storage.

run interprets a Brainfuck program as a list of characters and reads integers from stdin and outputs them to stdout.

A more efficient implementation could for example only admit well-bracketed brainfuck programs, and parse bracket blocks first, to replace the match_left and match_right which need linear time.

<ocaml> let move_left (x::l, r) = (l, x::r) let move_right (l, x::r) = (x::l, r)

let rec match_left d =

 match d with
   '['::_, _ ->
     d
 | ']'::_, _ ->
     match_left (move_left (match_left (move_left d)))
 | _ ->
     match_left (move_left d)

let rec match_right d =

 match d with
   _, '['::_ ->
     move_right d
 | _, '['::_ ->
     match_right (match_right (move_right d))
 | _ ->
     match_right (move_right d)

let pad = function

   [], [] -> [0], [0]
 | [], r  -> [0], r
 | l,  [] -> l,   [0]
 | d      -> d;;

let modify f (l, x::r) = l, f x :: r

let dec x =

 if x = 0 then 0
 else x - 1

let rec exec p d =

 match p, d with
   (_, []),     _         -> ()
 | (_, '>'::_), _         ->
     exec (move_right p) (pad (move_right d))
 | (_, '<'::_), _         ->
     exec (move_right p) (pad (move_left  d))
 | (_, '+'::_), _         ->
     exec (move_right p) (modify succ d)
 | (_, '-'::_), _         ->
     exec (move_right p) (modify dec  d)
 | (_, ','::_), _         ->
     let c = read_int () in
       exec (move_right p) (modify (fun _ -> c) d)
 | (_, '.'::_), (_, x::_) ->
     print_int x;
     print_newline ();
     exec (move_right p) d
 | (_, '['::_), (_, 0::_) ->
     exec (match_right (move_right p)) d
 | (_, '['::_), _         ->
     exec (move_right p) d
 | (_, ']'::_), (_, 0::_) ->
     exec (move_right p) d
 | (_, ']'::_), _         ->
     exec (match_left (move_left p)) d

let run s = exec ([], s) ([0], [0]) </ocaml>

Example output:

# let char_list_of_string s =
  let result = ref [] in
    String.iter (fun c -> result := c :: !result) s;
    List.rev !result;;
val char_list_of_string : string -> char list = <fun>

# run (char_list_of_string ",[>+<-].>.");;
5
0
5
- : unit = ()