From cf9c58c4998795c51ed4a6741e401d4ce3e8ece6 Mon Sep 17 00:00:00 2001
From: Ranjeet Kumar Ranjan <ranjeetr@composewell.com>
Date: Fri, 14 Jul 2023 19:49:43 +0530
Subject: [PATCH] Change signature of getIndex to return Maybe

---
 .../Streamly/Internal/Data/Array/Generic/Mut/Type.hs   |  6 +++---
 core/src/Streamly/Internal/Data/Array/Mut/Type.hs      | 10 ++++++----
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/core/src/Streamly/Internal/Data/Array/Generic/Mut/Type.hs b/core/src/Streamly/Internal/Data/Array/Generic/Mut/Type.hs
index fdb683c334..93a58d8321 100644
--- a/core/src/Streamly/Internal/Data/Array/Generic/Mut/Type.hs
+++ b/core/src/Streamly/Internal/Data/Array/Generic/Mut/Type.hs
@@ -468,11 +468,11 @@ getIndexUnsafe n MutArray {..} =
 -- | /O(1)/ Lookup the element at the given index. Index starts from 0.
 --
 {-# INLINE getIndex #-}
-getIndex :: MonadIO m => Int -> MutArray a -> m a
+getIndex :: MonadIO m => Int -> MutArray a -> m (Maybe a)
 getIndex i arr@MutArray {..} =
     if i >= 0 && i < arrLen
-    then getIndexUnsafe i arr
-    else invalidIndex "getIndex" i
+    then Just <$> getIndexUnsafe i arr
+    else return Nothing
 
 -------------------------------------------------------------------------------
 -- Subarrays
diff --git a/core/src/Streamly/Internal/Data/Array/Mut/Type.hs b/core/src/Streamly/Internal/Data/Array/Mut/Type.hs
index 2b1a0c81ee..fdc1f6b578 100644
--- a/core/src/Streamly/Internal/Data/Array/Mut/Type.hs
+++ b/core/src/Streamly/Internal/Data/Array/Mut/Type.hs
@@ -994,12 +994,12 @@ getIndexUnsafe i MutArray{..} = do
 -- | /O(1)/ Lookup the element at the given index. Index starts from 0.
 --
 {-# INLINE getIndex #-}
-getIndex :: forall m a. (MonadIO m, Unbox a) => Int -> MutArray a -> m a
+getIndex :: forall m a. (MonadIO m, Unbox a) => Int -> MutArray a -> m (Maybe a)
 getIndex i MutArray{..} = do
     let index = INDEX_OF(arrStart,i,a)
     if i >= 0 && INDEX_VALID(index,arrEnd,a)
-    then liftIO $ peekWith arrContents index
-    else invalidIndex "getIndex" i
+    then liftIO $ Just <$> peekWith arrContents index
+    else return Nothing
 
 -- | /O(1)/ Lookup the element at the given index from the end of the array.
 -- Index starts from 0.
@@ -1038,7 +1038,9 @@ getIndicesD liftio (D.Stream stepi sti) = Unfold step inject
         case r of
             D.Yield i s -> do
                 x <- liftio $ getIndex i (MutArray contents start end undefined)
-                return $ D.Yield x (GetIndicesState contents start end s)
+                case x of
+                    Just v -> return $ D.Yield v (GetIndicesState contents start end s)
+                    Nothing -> error "Invalid Index"
             D.Skip s -> return $ D.Skip (GetIndicesState contents start end s)
             D.Stop -> return D.Stop