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-module(bf).
-export([bf/1, test/0]).

-include_lib("kernel/include/file.hrl").

jump(reverse, [[DH | DT], D, [EH | ET]]) ->
	if
		D =:= '[' -> [DT, DH, [D | [EH] ++ ET]];
		true      -> jump(reverse, [[D | [DH] ++ DT], EH, ET])
	end;
jump(forward, [[DH | DT], D, [EH | ET]]) ->
	if
		D =:= ']' -> [DT, DH, [D | [EH] ++ ET]];
		true      -> jump(forward, [DT, DH, [D | [EH] ++ ET]])
	end.

bf({[[IHH | IHT], I, [ITH | ITT]], [[AHH | AHT], A, [ATH | ATT]]}) ->
	bf(case I of 
		'+' -> {[IHT, IHH, [I | [ITH] ++ ITT]], [[AHH | AHT], A + 1, [ATH | ATT]]};
		'-' -> {[IHT, IHH, [I | [ITH] ++ ITT]], [[AHH | AHT], A - 1, [ATH | ATT]]};
		'>' -> {[IHT, IHH, [I | [ITH] ++ ITT]], [AHT, AHH, [A | [ATH] ++ ATT]]};
		'<' -> {[IHT, IHH, [I | [ITH] ++ ITT]], [[A | [AHH] ++ AHT], ATH, ATT]};
		'.' -> 
			io:format("~s", [[A]]),
			{[IHT, IHH, [I | [ITH] ++ ITT]], [[AHH | AHT], A, [ATH | ATT]]};
		',' ->
			[O | _] = io:get_chars('', 1),
			{[IHT, IHH, [I | [ITH] ++ ITT]], [[AHH | AHT], O, [ATH | ATT]]};
		'[' -> {if 
				A == 0 -> jump(forward, [[IHH | IHT], I, [ITH | ITT]]);
				true   -> [IHT, IHH, [I | [ITH] ++ ITT]]
			end,
								[[AHH | AHT], A, [ATH | ATT]]};
		']' -> {if 
				A =/= 0 -> jump(reverse, [[IHH | IHT], I, [ITH | ITT]]);
				true   -> [IHT, IHH, [I | [ITH] ++ ITT]]
			end,					[[AHH | AHT], A, [ATH | ATT]]};
		 _  -> {[IHT, IHH, [I | [ITH] ++ ITT]], [[AHH | AHT], A, [ATH | ATT]]}
	end);
bf(_) -> [].

test() ->
	bf({[['>','+','+','+','+','+','+','[','<','-','-','-',
		'-','-','-','-','-','>','-',']',',','[','<','+','>','-',']','<','.', eoi], ',', [0]], [[0, 0], 0, [0, 0]]}).