Bounds check for writeCharArray#

cabal.project

@@ -1 +0,0 @@
-packages: .

src-checked/Op.hs

@@ -0,0 +1,14 @@
+module Op
+  ( writeCharArray#
+  ) where
+
+import GHC.Exts ((<#),(>=#))
+import qualified GHC.Exts as Exts
+
+writeCharArray# :: Exts.MutableByteArray# s -> Exts.Int# -> Exts.Char# -> Exts.State# s -> Exts.State# s 
+writeCharArray# arr i v st = case i <# 0# of
+  1# -> error ("writeCharArray#: negative index " ++ show (I# i))
+  _ -> case Exts.getSizeofMutableByteArray# arr st of
+    (# st', sz #) -> case i >=# sz of
+      1# -> error ("writeCharArray#: index " ++ show (I# i) ++ " >= length " ++ show (I# sz))
+      _ -> Exts.writeInt8Array# arr i (Exts.intToInt8# v) st'

src-unchecked/Op.hs

@@ -0,0 +1,5 @@
+module Op
+  ( writeCharArray#
+  ) where
+
+import GHC.Exts (writeCharArray#)