Most languages, sure, but not all; Haskell doesn’t have NULL. You can express the absense of a value with a Maybe: Just “value” -> Maybe String Nothing

Most languages, sure, but not all; Haskell doesn’t have NULL. You can express the absense of a value with a Maybe: Just “value” -> Maybe String Nothing -> Maybe a If your function returns a “Maybe String”, it can either be just a value, or Nothing. However, if a function returns a “String”, you can’t return Nothing, only an actual String. There’s no null in Haskell.