intercalate -base +bytestring

intercalate :: ByteString -> [ByteString] -> ByteString
bytestring Data.ByteString, bytestring Data.ByteString.Char8, bytestring Data.ByteString.Lazy, bytestring Data.ByteString.Lazy.Char8
O(n) The intercalate function takes a ByteString and a list of ByteStrings and concatenates the list after interspersing the first argument between each element of the list.