recursive loop causing vm error

test:26: vm error:
java.lang.ArrayIndexOutOFBoundsException: 256

function meta(func)
  local metaTable = {}
  local metaComm = {
	isIn = function (self, compare)
	  for k, v in pairs(self) do
		if v == comapre then
		  return true
		end
	  end
	  return false
	end,
  }
  local new = {}
  for k,v in pairs(func) do
	new[v] = metaComm[v]
  end
  setmetatable(metaTable, {__index = new})
  return metaTable
end

local function betser(t, tTracker, tabs)
  -- get type and store it
  iType = type(t)
  -- code to check if it is a recursion loop
  local iTracker = tTracker
  if iTracker:isIn(t) and iType == "table" then	 -- line 26
	error("Cannot handle Recrsive loop")
  elseif iType == "table" then
	iTracker[#iTracker+1] = t
  end
  -- Ready tabs
  local tab = ""
  local tabM1 = ""
  for i = 0, tabs, 1 do
	tab = tab .. "\t\t"
	if i ~= 0 then
	  tabM1 = tabM1 .. "\t\t"
	end
  end
  -- begin serialization
  if iType == "table" then
	result = "{\n"
	for k,v in pairs(t) do
	  result = result..tab.."[" .. betser(k, iTracker, (tabs+1)) .. "] = " .. betser(v, iTracker, (tabs+1)) .. ",\n"
	end
	result = result .. tabM1 .. "}"
	return result
  elseif iType == "string" then
	return string.format("%q", t)
  elseif iType == "number" or iType == "boolean" or iType == "nil" then
	return tostring(t)
  elseif iType == "function" then
	return "**function**"
  else
	error("cannot serialize type " .. iType)
  end
end

function serialize(t)
  local nTracker = meta({"isIn"})
  return betser(t, nTracker, 0)
end
-- test table for testing
test = {}
test.test = {}
test.test.beta = "test"
test.beta = "test"
test.aplha = test
--Print what is returned
print(serialize(test))

Bomb Bloke, on 13 April 2014 - 12:11 AM said:

You may want to define an extra table of your own. Whenever you detect a table inside the one you're serialising, shove it in that new table (if it's not already in there), then remove it when you've finished serialising that child entry.

If you encounter a given child table that already exists in your tracking table, then you'll know you've encountered an infinite loop in the serialised table structure and will need to throw up a custom error message stating that it's impossible to continue.

  -- code to check if it is a recursion loop
  local iTracker = tTracker
  if iTracker:isIn(t) and iType == "table" then  -- line 26
	    error("Cannot handle Recrsive loop")
  elseif iType == "table" then
	    iTracker[#iTracker+1] = t
  end

        isIn = function (self, compare)
          for k, v in pairs(self) do
                if v == comapre then

local table1 = {1,2}
local table2 = {table1, table1}

Bomb Bloke, on 13 April 2014 - 12:52 AM said:

		isIn = function (self, compare)
		  for k, v in pairs(self) do
				if v == comapre then

Bomb Bloke, on 13 April 2014 - 12:52 AM said:

I'm also not sure why you define an "iTracker" as a copy of "tTracker". Bear in mind that doing so doesn't clone the table itself, but rather gives you a pointer leading to the one copy of the table in memory. Each instance of the function that's running is already handed such a pointer and shouldn't need another…?

Bomb Bloke, on 13 April 2014 - 12:52 AM said:

local table1 = {1,2}
local table2 = {table1, table1}

Your current system will declare this recursive.

test = {}
test.test = {}
test.test.beta = "test"
test.beta = "test"
test.delta = test.test
test.alpha = test

Termanater13, on 13 April 2014 - 05:26 AM said:

this function allows the table to see if a value is stored in it if it is it returns true, if not returns false. using setmetatable for it really is not needed, but its easier for me to look at the code this way.

Termanater13, on 13 April 2014 - 05:26 AM said:

not it would not, it would display it no problem. When a table shows up twice, it has no problem, unless this causes a loop.

Bomb Bloke, on 13 April 2014 - 05:37 AM said:

That's what you intend it to do. Let's just say that there's a reason I quoted those lines in particular, and that you should read them again. ;)/>

Bomb Bloke, on 13 April 2014 - 05:37 AM said:

Best I can make out, the table pointer issue would need to be resolved for that to be the case.

Termanater13, on 13 April 2014 - 08:14 AM said:

I call that function on line 26 as iTracker:isIn(t), and is equal to iTracker.isIn(iTracker, t). the second one I think is the function call you are thinking of.

Termanater13, on 13 April 2014 - 08:14 AM said:

it works, just not when a loop is created, I tested it in another lua interpreter(SigmaScript for android) since it has nothing involving computercraft in it. The script will not stop if a loop is given. basically if I give it a loop free table it works as intended, but I need to figure out why my preventive measures against loops is not working.

Bomb Bloke, on 13 April 2014 - 08:20 AM said:

Termanater13, on 13 April 2014 - 08:14 AM said:

I call that function on line 26 as iTracker:isIn(t), and is equal to iTracker.isIn(iTracker, t). the second one I think is the function call you are thinking of.

You misspelled "compare" as "comapre". As a result, the function will always return false.

Sorry not to state it simply sooner. I sometimes like to think I have a sense of humor.

Termanater13, on 13 April 2014 - 08:14 AM said:

it works, just not when a loop is created, I tested it in another lua interpreter(SigmaScript for android) since it has nothing involving computercraft in it. The script will not stop if a loop is given. basically if I give it a loop free table it works as intended, but I need to figure out why my preventive measures against loops is not working.

The bit that stops the script is busted due to the above typo. You may need to test this again once you've fixed that.

local function varCopy(var)
  local newVar = {}
  for k,v in pairs(var) do
	newVar[k] = v
  end
  return newVar
end

  -- begin serialization
  if iType == "table" then
        -- These two lines from higher up can be dragged down into this "if" block:
        if tTracker:isIn(t) then error("Cannot handle Recrsive loop") end
        tTracker[#tTracker+1] = t

        -- Serialise:
        result = "{\n"
        for k,v in pairs(t) do
          result = result..tab.."[" .. betser(k, tTracker, (tabs+1)) .. "] = " .. betser(v, tTracker, (tabs+1)) .. ",\n"
        end

        -- Now we've serialised the sub-table, remove it from tTracker and return:
        tTracker[#tTracker] = nil
        result = result .. tabM1 .. "}"
        return result

Bomb Bloke, on 14 April 2014 - 09:12 AM said:

Normally, yeah, but I'm honestly not sure how well that'll handle your metatable. It might miss its function. I dunno how that works.

But personally, I wouldn't bother trying to make another copy of the table - there's really no need. Maybe just do something like this:

function varCopy(var)
  local newVar = meta({"isIn"})
  for k,v in pairs(var) do
    newVar[k] = v
  end
  return newVar
end

the table copying function I made earlier did need some tweaking to get it to work right. you can save a function to a value of a table and it would of worked fine, but if you set it with setmetatable the for loop I guess does not see it since as it is above it did not copy it.

Termanater13, on 14 April 2014 - 04:23 PM said:

In the example you just gave it will error if there is a recursive table, because you do not remove data no longer needed,

local table1 = {1,2}
local table2 = {table1, table1}