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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 ''
<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
|