Hello, ByteString is an array of Word8 but it seems to me that people tend to use the Char interface with Data.ByteString.Char8 instead of Word8 interface with Data.ByteString. Since the functions defined in Data.ByteString.Char8 converts Word8 to Char and Char to Word8, it has unnecessary overhead. Yes, the overhead is ignorable in many cases, but I would like to remove it for high performance server. Why do people use Data.ByteString.Char8? I guess that there are two reasons: - There are no standard utility functions for Word8 such as "isUpper" - Numeric literal (e.g 72 for 'H') is not readable To fix these problems, I implemented the Data.Word8 module and uploaded the word8 library to Hackage: http://hackage.haskell.org/packages/archive/word8/0.0.0/doc/html/Data-Word8.... If Michael and Bas like this, I would like to modify warp and case-insensitive to use the word8 library. What do people think this? My concern is that character names start with "_". Some people would dislike this convention. But I have not a better idea at this moment. Suggestions are welcome. --Kazu