diff --git a/src/Language/Brainfuck.hs b/src/Language/Brainfuck.hs
index c348315..0681be7 100644
--- a/src/Language/Brainfuck.hs
+++ b/src/Language/Brainfuck.hs
@@ -1,5 +1,4 @@
 {-# LANGUAGE ImportQualifiedPost #-}
-{-# LANGUAGE ViewPatterns #-}
 {-# LANGUAGE DerivingStrategies #-}
 {-# LANGUAGE LambdaCase #-}
 module Language.Brainfuck (parse, ParseFailure, render) where
@@ -16,10 +15,11 @@ import Data.Vector.Mutable qualified as MutableVector
 
 import Language.Brainfuck.Instruction ( Instruction(..) )
 import qualified Data.List as List
+import Numeric.Natural (Natural)
 
 data ParseFailure
-  = UnexpectedClosingBracket Int -- closing bracket position
-  | UnmatchedOpenBracket Int -- opening bracket position
+  = UnexpectedClosingBracket Natural -- closing bracket position
+  | UnmatchedOpenBracket Natural -- opening bracket position
   deriving stock (Show, Eq)
 
 -- | Convert a Text to a list of instructions, discard all comments.
@@ -30,48 +30,51 @@ parse :: Text -> Either ParseFailure (Vector Instruction)
 parse text = runST $ do
   collectorVector <- MutableVector.new (Text.length text)
 
-  result <- go text collectorVector 0
+  result <- parseBlock text collectorVector 0
 
   pure $ case result of
 
     Right (instructions, rest) -> case rest of
       Text.Empty -> Right instructions
-      _ -> Left (UnexpectedClosingBracket $ Text.length text - Text.length rest)
+      _ -> Left (UnexpectedClosingBracket . fromIntegral $ Text.length text - Text.length rest)
 
     Left failure -> Left failure
 
   where
 
-    go :: Text -> MVector s Instruction -> Int -> ST s (Either ParseFailure (Vector Instruction, Text))
-    go (Text.Empty  ) instructions index = do
+    -- | Parses the supplied text until the next closing bracket., the closing bracket will be returned in the rest.
+    --
+    -- Assumes the vector has enough space to hold all the instructions. Assumes all elements until the Int index have already been initialized.
+    parseBlock :: Text -> MVector s Instruction -> Int -> ST s (Either ParseFailure (Vector Instruction, Text))
+    parseBlock Text.Empty instructions index = do
       let populatedSlice = MutableVector.take index instructions
       frozen <- Vector.force <$!> Vector.freeze populatedSlice
       pure . Right $ (frozen, Text.empty)
-    go t@(c Text.:< cs) instructions index = let
-      
-      recognizeInstruction i cont = do
-        MutableVector.write instructions index i
-        go cont instructions (succ index)
+    parseBlock t@(c Text.:< cs) instructions index = let
 
-      in case c of
-        '+' -> recognizeInstruction Increment cs
-        '-' -> recognizeInstruction Decrement cs
-        '>' -> recognizeInstruction MoveRight cs
-        '<' -> recognizeInstruction MoveLeft  cs
-        ',' -> recognizeInstruction ReadByte  cs
-        '.' -> recognizeInstruction PutByte   cs
-        ']' -> do
-          let populatedSlice = MutableVector.take index instructions
-          frozen <- Vector.force <$!> Vector.freeze populatedSlice
-          pure $ Right (frozen, t)
-        '[' -> do
-          innerVector <- MutableVector.new (Text.length cs)
-          innerResult <- go cs innerVector 0
-          case innerResult of
-            Right (body, ']' Text.:< rest) -> recognizeInstruction (Loop body) rest
-            Right _ -> pure $ Left (UnmatchedOpenBracket $ Text.length text - Text.length t)
-            _ -> pure innerResult
-        _   -> go cs instructions index
+              recognizeInstruction i cont = do
+                MutableVector.write instructions index i
+                parseBlock cont instructions (succ index)
+
+              in case c of
+                '+' -> recognizeInstruction Increment cs
+                '-' -> recognizeInstruction Decrement cs
+                '>' -> recognizeInstruction MoveRight cs
+                '<' -> recognizeInstruction MoveLeft  cs
+                ',' -> recognizeInstruction ReadByte  cs
+                '.' -> recognizeInstruction PutByte   cs
+                ']' -> do
+                  let populatedSlice = MutableVector.take index instructions
+                  frozen <- Vector.force <$!> Vector.freeze populatedSlice
+                  pure $ Right (frozen, t)
+                '[' -> do
+                  innerVector <- MutableVector.new (Text.length cs)
+                  innerResult <- parseBlock cs innerVector 0
+                  case innerResult of
+                    Right (body, ']' Text.:< rest) -> recognizeInstruction (Loop body) rest
+                    Right _ -> pure $ Left (UnmatchedOpenBracket . fromIntegral $ Text.length text - Text.length t)
+                    _ -> pure innerResult
+                _   -> parseBlock cs instructions index
 
 
 -- >>> parse $ Text.pack "<<>>,,..<,.>"
@@ -100,6 +103,7 @@ render = Text.concat . List.map renderSingle . Vector.toList
 
 -- >>> import Test.QuickCheck.Instances.Vector ()
 -- >>> import Test.QuickCheck.Arbitrary (arbitrary)
+-- >>> import Test.QuickCheck.Gen as Gen
 -- >>> render <$> Gen.generate arbitrary
--- "<,<>,<,."
+-- "-<,.<<,>++.[]<+>.<.-,"
 
diff --git a/stack.yaml b/stack.yaml
index c092d1d..8e55f30 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -18,6 +18,7 @@
 # snapshot: ./custom-snapshot.yaml
 # snapshot: https://example.com/snapshots/2024-01-01.yaml
 snapshot: nightly-2025-06-16
+compiler: ghc-9.12.1
 
 # User packages to be built.
 # Various formats can be used as shown in the example below.