For those who don't speak Haskell, its worth noting that "<>" is the monoid concatenation operator. The "~>" operator returns a function type "a -> Maybe String

For those who don't speak Haskell, its worth noting that "<>" is the monoid concatenation operator. The "~>" operator returns a function type "a -> Maybe String". A function type is a monoid if its return type is a monoid, so this works.