Execute Brain****/OCaml
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.
<lang 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 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 pred 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])</lang>
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 = ()