brainfuck

--Brainf*ck interpreter (c) 2013 by victorious3
--Usage: use brainfuck <filename> to run brainf*ck program
--       add extra "-debug" for testing

local tArgs = {...}

local yieldTime = os.clock() --yield timer
local function yield()
  if os.clock() - yieldTime > 2 then
    os.queueEvent("yield") --post fake "yield" event
    os.pullEvent()
    yieldTime=os.clock() --reset yield timer
  end
end

local function run(program, debug)

  local lenght = program:len() --Total program lenght
  local pointers = {} --all memory cells
  local pointer = 1 --currently selected memory cell
  local counter = 1 --program counter
  local jumpers = {} --jumpers for the "]" command
  local jumper = 0 --current jumperlevel

  --fill pointers and jumpers with 0
  for i = 1, 30000 do
    pointers[i] = 0
    jumpers[i] = 0
  end

  while counter ~= lenght + 1 do --while program not at the end
    --current character in the program
    local command = string.sub(program, counter, counter)
    local isCommandValid = true

    if command == "+" then
      pointers[pointer] = pointers[pointer] + 1 --increment current cell
    elseif command == "-" then
      pointers[pointer] = pointers[pointer] - 1 --decrement current cell
    elseif command == ">" then
      if pointer < 30001 then --increment cell pointer
        pointer = pointer + 1
      else
        pointer = 1
      end
    elseif command == "<" then
      if pointer > 1 then --decrement cell pointer
        pointer = pointer - 1
      else
        pointer = 30000
      end
    elseif command == "." then
      write(string.char(pointers[pointer])) --ouput current cell as ASCII character
    elseif command == "[" then
      if pointers[pointer] ~= 0 then --if current cell ~= 0 then add new jumper at jumperlevel
        jumper = jumper + 1
        jumpers[jumper] = counter
      else
        local i = counter + 1
        local j = 1
        while i ~= lenght do
          if string.sub(program, i, i) == "]" then
            j = j - 1
          elseif string.sub(program, i, i) == "[" then
            j = j + 1
          end

          if j == 0 then
            counter = i --if current cell == n�B40 then go to the matching "]"
            break
          end

          i = i + 1
        end
      end
    elseif command == "]" then
      if pointers[pointer] ~= 0 then
        counter = jumpers[jumper] --if current cell ~= 0 then go to matching "[" (jumper)
      else
        jumper = jumper - 1
      end
    elseif command == "," then
      local event, key = os.pullEvent("char") --wait for character input and store ASCII Code in current cell
      pointers[pointer] = string.byte(key)
    else
      isCommandValid = false
    end

    if debug and isCommandValid then
      os.pullEvent() --wait for os event
      write("{"..command.." "..pointer..":"..pointers[pointer].."@"..counter.."} ") --write debug information
    end

    counter = counter + 1 --increment program counter
    yield() --used to prevent "Too long without yielding" - error
  end
end

if tArgs[1] == nil then
  error("Argument 1 must be a filename!")
end

local file = fs.open(tArgs[1], "r") --open program file
local debug = tArgs[2] == "-debug"

if file == nil then
  error("Argument 1 is not a valid file!")
end

local program = file.readAll() --read program file into a string
file.close()
term.clear()
term.setCursorPos(1,1)
run(program, debug) --run the program
write("\n")