bf[program_, input_] :=
  Module[{p = Characters[program], pp = 0, m, mp = 0, bc = 0,
      instr = StringToStream[input]},
    m[_] = 0;
    While[pp < Length@p,
      pp++;
      Switch[p[[pp]],
        ">", mp++,
        "<", mp--,
        "+", m[mp]++,
        "-", m[mp]--,
        ".", BinaryWrite["stdout", m[mp]],
        ",", m[mp] = BinaryRead[instr],
        "[", If[m[mp] == 0,
          bc = 1;
          While[bc > 0, pp++; Switch[p[[pp]], "[", bc++, "]", bc--]]],
        "]", If[m[mp] != 0,
          bc = -1;
          While[bc < 0, pp--; Switch[p[[pp]], "[", bc++, "]", bc--]]]]];
    Close[instr];];
bf[program_] := bf[program, ""]