Day 5 - alternate solution using unboxed vectors, but unfortunately they're not any faster

5.hs

@@ -1,4 +1,4 @@
-import Data.IntMap (IntMap, insert, size, fromList, findWithDefault)
+import Data.IntMap (IntMap, insert, fromList, findWithDefault)
 
 type Length = Int
 type Index = Int

5_alt.hs

@@ -0,0 +1,26 @@
+import Data.Vector.Unboxed (Vector, fromList, (!), (//))
+import qualified Data.Vector.Unboxed as V (length)
+
+type Length = Int
+type Index = Int
+type Steps = Int
+type State = (Steps, Index, Vector Int)
+type Update = Int -> Int
+
+next :: Update -> State -> State
+next f (steps, i, jumps) =
+    let value = jumps ! i
+        nextI = i + value
+        nextJumps = jumps // [(i, f value)]
+    in  (steps + 1, nextI, nextJumps)
+
+getExitSteps :: Update -> State -> Int
+getExitSteps f (steps, i, jumps) =
+    if i >= V.length jumps then steps else getExitSteps f $! next f (steps, i, jumps)
+
+main :: IO ()
+main = do
+    input <- readFile "5.txt"
+    let jumpsList = fromList $ map read $ lines input
+    print $ getExitSteps (+1)                                    (0, 0, jumpsList)
+    print $ getExitSteps (\v -> if v >= 3 then v - 1 else v + 1) (0, 0, jumpsList)