Add indexMaybe and synonym to ShortByteString

haskell · Aug 21, 2020 · d755b17 · d755b17
1 parent f2e918c
commit d755b17
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Showing 2 changed files with 22 additions and 3 deletions.
diff --git a/Data/ByteString/Short.hs b/Data/ByteString/Short.hs
@@ -77,7 +77,7 @@ module Data.ByteString.Short (
     unpack,
 
     -- * Other operations
-    empty, null, length, index,
+    empty, null, length, index, indexMaybe, (!?),
 
     -- * Low level conversions
     -- ** Packing 'Foreign.C.String.CString's and pointers

diff --git a/Data/ByteString/Short/Internal.hs b/Data/ByteString/Short/Internal.hs
@@ -31,7 +31,7 @@ module Data.ByteString.Short.Internal (
     unpack,
 
     -- * Other operations
-    empty, null, length, index, unsafeIndex,
+    empty, null, length, index, indexMaybe, (!?), unsafeIndex,
 
     -- * Low level operations
     createFromPtr, copyToPtr,
@@ -107,7 +107,8 @@ import Prelude ( Eq(..), Ord(..), Ordering(..), Read(..), Show(..)
                , String, userError
                , Bool(..), (&&), otherwise
                , (+), (-), fromIntegral
-               , return )
+               , return
+               , Maybe(..) )
 
 
 -- | A compact representation of a 'Word8' vector.
@@ -215,6 +216,24 @@ index sbs i
   | i >= 0 && i < length sbs = unsafeIndex sbs i
   | otherwise                = indexError sbs i
 
+-- | /O(1)/ 'ShortByteString' index, starting from 0, that returns 'Just' if:
+--
+-- > 0 <= n < length bs
+--
+-- @since 0.10.10.0
+indexMaybe :: ShortByteString -> Int -> Maybe Word8
+indexMaybe sbs i
+  | i >= 0 && i < length sbs = Just $ unsafeIndex sbs i
+  | otherwise                = Nothing
+
+-- | /O(1)/ 'ShortByteString' index, starting from 0, that returns 'Just' if:
+--
+-- > 0 <= n < length bs
+--
+-- @since 0.10.10.0
+(!?) :: ShortByteString -> Int -> Maybe Word8
+(!?) = indexMaybe
+
 unsafeIndex :: ShortByteString -> Int -> Word8
 unsafeIndex sbs = indexWord8Array (asBA sbs)