Specialize packBytes and packChars for empty input (haskell#291)

* Specialize packBytes and packChars for empty input * mempty -> Empty
phadej · Oct 1, 2020 · d701a2a · d701a2a
1 parent d79b997
commit d701a2a
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/Data/ByteString/Lazy/Internal.hs b/Data/ByteString/Lazy/Internal.hs
@@ -142,6 +142,7 @@ instance Data ByteString where
 -- Packing and unpacking from lists
 
 packBytes :: [Word8] -> ByteString
+packBytes [] = Empty
 packBytes cs0 =
     packChunks 32 cs0
   where
@@ -150,6 +151,7 @@ packBytes cs0 =
       (bs, cs') -> Chunk bs (packChunks (min (n * 2) smallChunkSize) cs')
 
 packChars :: [Char] -> ByteString
+packChars [] = Empty
 packChars cs0 = packChunks 32 cs0
   where
     packChunks n cs = case S.packUptoLenChars n cs of