Why don't we have two nulls?

Question

I\'ve often wondered why languages with a null representing \"no value\" don\'t differentiate between the passive \"I don\'t know what the value is\"

Answer 1

In haskell you can define something like this:

data MaybeEither a b = Object a
                     | Unknown b
                     | Null
                       deriving Eq
main = let x = Object 5 in
       if x == (Unknown [2]) then putStrLn ":-("
       else putStrLn ":-)"

The idea being that Unknown values hold some data of type b that can transform them into known values (how you'd do that depends on the concrete types a and b).

The observant reader will note that I'm just combining Maybe and Either into one data type :)