The example file place from which I had copied the code from works perfectly fine. However, this error is thrown when I try to run the game.
After doing some debugging, I had noticed the code I had copied from which worked perfectly fine in it’s own place but lags a lot when copied and pasted into my own place.
Line 131 in question:
The example file:
A Pathfinding.rbxl (25.8 KB)
My place:
Pathfinding Algorithms.rbxl (28.6 KB)
Add a wait() to the while loop.
If you took a look at the files I posted, the code I had referred to didn’t have a wait function in this while loop.
You are expecting too much out of scripting support lol.
Anyways, make sure the goal is reached to ensure the path has a solution in the first place before tracing back the path.
And ensuring the while condition follows the general psuedo code:
While currentPath ~= start do
--find path
One time I printed it out and it just went back and forth between start and goal because I messed up the while condition, I suggest putting a wait() and printing it out to make sure the logic follows.
I highly recommend this resource, the best visual A star tutorial on the web:
And looking at the path construction psuedo code:
The code to reconstruct paths is simple: follow the arrows backwards from the goal to the start. A path is a sequence of edges, but often it’s easier to store the nodes:
current = goal
path = []
while current != start:
path.append(current)
current = came_from[current]
path.append(start) # optional
path.reverse() # optional
I believe you are missing this line specifically
current = came_from[current]
which is causing the recursion error.
Shameless self bump
Studio freezes whenever I try to print out the previous node, adding wait() to the while loop does little to help this either.
Strangely enough, when I published the file I had copied the code from, that place begins to experience a lot of lag as well.
Wouldn’t this just be Temp = Temp.previous in my case?
Not really because your loop isn’t check Temp, it’s checking Temp.previous which is unchanged.
It should be
Temp.previous = cameFrom[Temp.previous]
But you didn’t show your full code 
so I don’t know what variable is your cameFrom dictionary.
Don’t screen shot
Then I have no clue what cameFrom is supposed to be.
And I seriously don’t understand why you can’t just download the place file.
--local OpenList = workspace:WaitForChild("Path"):GetChildren()
local OpenList = {}
local CloseList = {}
local Grid = {}
-- Rows and columns in a grid
local Rows = 100
local Columns = 100
local Start_Node
local End_Node
local Path = {}
-- Module
local NodeModule = require(script:WaitForChild("NodeModule"))
local function SetUp() -- Createa a grid to use for pathfinding
for x = 1, Rows do
Grid[x] = {}
for y = 1, Columns do
local IsPath = true -- 1,1 and 100,100 are not path nodes as they are the start and end
if x == 1 and y == 1 then -- Starting node
IsPath = false
end
if x == Rows and y == Columns then -- End node
IsPath = false
end
Grid[x][y] = NodeModule.new(x, y, IsPath) -- Construct an object class for the node called Grid[x][y]
end
end
for x = 1, Rows do
for y = 1, Columns do
Grid[x][y]:Show() -- VIsualize the node
Grid[x][y]:AddNeighbours(Grid)
end
if x%5 == 0 then
-- e.g: 10%5 = 0, or 15%5 = 0, so multiples of 5
-- I have no idea why you need this
wait(0.1)
end
end
end
local function RemoveFromTable(OpenList, CurrentNode)
for i = 1, #OpenList do
if OpenList[i] == CurrentNode then
-- if its the current node remove it
table.remove(OpenList, i)
break
end
end
end
local function Is_Valid_Neighbour(List, NeighbourNode)
for i = 1, #List do
if List[i] == NeighbourNode then
return true
end
end
return false
end
local function Start()
Start_Node = Grid[1][1]
End_Node = Grid[Rows][Columns]
table.insert(OpenList, Start_Node)
while #OpenList > 0 do
wait()
if #OpenList > 0 then
local Min = 1
for i = 1, #OpenList do
if OpenList[i].f < OpenList[Min].f then -- Still dont really understand this bit
Min = i
end
end
-- Get the current node
-- let the currentNode equal the node with the least f value
local CurrentNode = OpenList[Min]
-- if currentNode is the goal
if CurrentNode == End_Node then
break
end
RemoveFromTable(OpenList, CurrentNode)
table.insert(CloseList, CurrentNode)
local Neighbours = CurrentNode.neighbours
for i = 1, #Neighbours do
-- Neighbour is one object, Neighbours is the table
local Neighbour = Neighbours[i]
local NewPath = false
if not Is_Valid_Neighbour(CloseList, Neighbours) and not Neighbour.Wall then
local _TempG = CurrentNode.g + 1
if Is_Valid_Neighbour(OpenList, Neighbour) then
if _TempG < Neighbour.g then -- if current node g is less than neighbour node g, but what does that mean?
Neighbour.g = _TempG
NewPath = true
end
else
Neighbour.g = _TempG
NewPath = true
table.insert(OpenList, Neighbour)
end
end
if NewPath then
Neighbour:Heuristic(End_Node)
Neighbour.f = Neighbour.g + Neighbour.h
Neighbour.previous = CurrentNode
end
end
-- visualize the nodes
for i = 1, #CloseList do
CloseList[i]:ShowClosed()
end
for i = 1, #OpenList do
OpenList[i]:ShowOpen()
end
Path = {}
local Temp = CurrentNode
table.insert(Path, Temp) -- insert path node into the table
local Value = 1
while Temp.previous do -- Insert path nodes into path table
-- exhaused allowed exectuion time
Value += 1
table.insert(Path, Temp.previous)
Temp = Temp.previous
end
for i = 1, #Path do
Path[i]:ShowPath()
end
end
end
end
SetUp()
wait(1)
Start()
Because it’s a lot of work, I’m busy with an A star pathfinding commision right now at the moment in fact 
enough to get paid for.
I suggest looking at this excellent community resource which formats the A star path finding better and modularizing it according to the RedBlob games A star path finding article with the aformentioned data structures PriorityQueue.
If you don’t have a cameFrom dictionary then you might need to add on.
Removing the while loop, everything else works perfectly fine. If anyone has any suggestions or alternatives to construct a path, it’d be appreciated.