Haskell How to convert Char to Word8

In case you really need Data.ByteString (not Data.ByteString.Char8), you could do what Data.ByteString itself does to convert between Word8 to Char:

import qualified Data.ByteString as BS
import qualified Data.ByteString.Internal as BS (c2w, w2c)

main = do
    input <- BS.getLine
    let xs = BS.split (BS.c2w ' ') input 
    return ()

The Data.ByteString.Char8 module allows you to treat Word8 values in the bytestrings as Char. Just

import qualified Data.ByteString.Char8 as C

then refer to e.g. C.split. It's the same bytestring under the hood, but the Char-oriented functions are provided for convenient byte/ascii parsing.