This module defines the ByteStringUTF8 newtype wrapper around ByteString, together with its TextualMonoid instance. The FactorialMonoid instance of a wrapped ByteStringUTF8 value differs from the original ByteString: the prime factors of the original value are bytes, while UTF8 character byte sequences make up the wrapped value's prime factors. The following example session demonstrates the relationship:

> let utf8@(ByteStringUTF8 bs) = fromString "E=mc\xb2"
> bs
"E=mc\194\178"
> factors bs
["E","=","m","c","\194","\178"]
> utf8
"E=mc²"
> factors utf8
["E","=","m","c","²"]

The TextualMonoid instance follows the same logic, but it also decodes all valid UTF8 sequences into characters. Any invalid UTF8 byte sequence from the original ByteString is preserved as a single prime factor:

> let utf8'@(ByteStringUTF8 bs') = ByteStringUTF8 (Data.ByteString.map pred bs)
> bs'
"D<lb\193\177"
> factors bs'
["D","<","l","b","\193","\177"]
> utf8'
"D<lb\[193,177]"
> factors utf8'
["D","<","l","b","\[193,177]"]