Why my Haskell game sometimes responds differently to the same arguments? [closed] - haskell

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I am working on a simple Gtk/Cairo game:
https://github.com/bigos/cairo-example/blob/9ac6f39d53cd27f36cad53a265e05f3e45564a37/src/Main.hs
I have noticed a problem where sometimes my snake doesn't eat food. I have figured out how to log subsequent versions of global state.
I have this debuggator function, which tests versions dumped by the logger.
debuggator =
let m1 = Model {debugData = "", eaten = 5, foodItems = [(6,2)], gameField = Move, snakeLength = 0, heading = HeadingUp, height = 400, lastKey = 65362, scale = 25, snake = [(6,3),(6,4),(5,4),(4,4),(3,4),(2,4),(1,4),(0,4),(-1,4),(-2,4),(-2,3),(-2,2),(-2,1),(-2,0),(-1,0),(0,0),(1,0),(2,0),(3,0),(4,0)], tickInterval = 500.0, seed = 36, width = 600}
m2 = Model {debugData = "", eaten = 5, foodItems = [(6,2)], gameField = Move, snakeLength = 0, heading = HeadingUp, height = 400, lastKey = 65362, scale = 25, snake = [(6,2),(6,3),(6,4),(5,4),(4,4),(3,4),(2,4),(1,4),(0,4),(-1,4),(-2,4),(-2,3),(-2,2),(-2,1),(-2,0),(-1,0),(0,0),(1,0),(2,0),(3,0)], tickInterval = 500.0, seed = 36, width = 600}
m3 = Model {debugData = "", eaten = 5, foodItems = [(6,2)], gameField = Move, snakeLength = 0, heading = HeadingRight, height = 400, lastKey = 65363, scale = 25, snake = [(6,1),(6,2),(6,3),(6,4),(5,4),(4,4),(3,4),(2,4),(1,4),(0,4),(-1,4),(-2,4),(-2,3),(-2,2),(-2,1),(-2,0),(-1,0),(0,0),(1,0),(2,0),(3,0)], tickInterval = 500.0, seed = 37, width = 600}
ma = updateGlobalModel Tick m1
mb = updateGlobalModel Tick ma
in
[ma,mb]
which returns the following:
λ> debuggator
[Model {debugData = "", eaten = 5, foodItems = [(6,2)], gameField = Move, snakeLength = 0, heading = HeadingUp, height = 400, lastKey = 65362, scale = 25, snake = [(6,2),(6,3),(6,4),(5,4),(4,4),(3,4),(2,4),(1,4),(0,4),(-1,4),(-2,4),(-2,3),(-2,2),(-2,1),(-2,0),(-1,0),(0,0),(1,0),(2,0),(3,0)], tickInterval = 500.0, seed = 36, width = 600},
Model {debugData = "(\"** eaten **\",(6,2),[(6,2)])", eaten = 6, foodItems = [(2,5),(0,2),(10,4)], gameField = Move, snakeLength = 3, heading = HeadingUp, height = 400, lastKey = 65362, scale = 25, snake = [(6,1),(6,2),(6,3),(6,4),(5,4),(4,4),(3,4),(2,4),(1,4),(0,4),(-1,4),(-2,4),(-2,3),(-2,2),(-2,1),(-2,0),(-1,0),(0,0),(1,0),(2,0),(3,0)], tickInterval = 500.0, seed = 36, width = 600}]
In this example ma corresponds to m2 which values was copied from the real game. Processing ma leads to mb, which shows that snake has eaten the food, but in real game progressing from m2 to m3 did not lead to snake eating food. the snake head has moved over the food item and the list of food items did not change. In the repl example mb has 3 food items because the last food item was eaten and 3 more were generated.
Why does function respond differently to the same arguments? does calling a pure function from IO have some unexpected effects?
Function that checks id the snake has eaten food is at line 110:
foodEaten :: Model -> Bool
foodEaten model =
any id (map (\c -> (fst c)==cx && (snd c)==cy) (foodItems model))
where hsm = head (snake model)
cx = fst hsm
cy = snd hsm
That in turn is called by cook function at line 293:
cook :: Model -> Model
cook model =
if foodEaten model
then model { gameField = detectCollision model
, snakeLength = (snakeLength model) +3
, foodItems = filter (\c -> not (foodUnderHead c model)) (foodItems model)
, debugData = (debugData model) ++ (show ("** eaten **" :: String, head (snake model), (foodItems model)))
, eaten = (eaten model) + 1 }
else model { gameField = detectCollision model
, snakeLength = shrink (snakeLength model)
, debugData = "" }
For some reason the snake does not detect if the food was eaten. One commenter has suggested to check if my code is thread safe.
Debuggator function at line 273 tries to illustrate simple case that always works. function cook that fails in some situations is called indirectly at main function line line 295. There a timer events are defined which call updateGlobalModel Tick
_ <- GI.GLib.timeoutAdd GI.GLib.Constants.PRIORITY_DEFAULT 500 ( modifyIORef' globalModel (updateGlobalModel Tick) >>
Gtk.widgetQueueDraw canvas >> return True)
Debuggator function illustrates how I can call it in REPL. However, as someone suggested that could be a thread problem. My Haskell skills are still poor and I do not know how to investigate it properly.