Perhaps I should have clarified that point.

Here is a more robust implementation of the optional type using Java

The names have changed slightly (to reflect ML-style):

• Maybe -> Option
• Just -> Some
• Nothing -> None

“Therefore, the Maybe data type has 2 and only 2 constructors. It is the “and only 2″ that makes this data type a closed algebraic data type.”

but further down, you say the equivalent is to only allow two subclasses of that type.

Two constructors and two subclasses are very different thing, which is it?

Here is a post that talks about that link:
http://blog.tmorris.net/algebraic-data-types-again/

Nate, don’t give up! Haskell is a deeply beautiful language and learning it will make you a better programmer even if Perl remains your day job! It will make you rethink what a program is and what programming is about.

Don’t let this the too stereotypical conception of functional programmers as played by “Runar” and “Tony” scare you away! Go watch some videos of Simon Peyton Jones and Phillip Wadler. They’re f***ing geniuses who manage to say why they think there are better alternatives to today’s languages without resorting to whining about “cults” or saying that mainstream languages are “useless.” In fact, SPJ jokingly called early attempts at purely functional languages “safe but useless” while traditional imperative languages were “unsafe but useful” http://channel9.msdn.com/showpost.aspx?postid=326762. It’s pure self deprecating humor. Haskell is useful. See Darcs as a very practical example of what Haskell can do.

Don’t let this the too stereotypical conception of functional programmers as played by “Runar” and “Tony” scare you away! Go watch some videos of Simon Peyton Jones and Phillip Wadler. They’re fucking geniuses who manage to say why they think there are better alternatives to today’s languages without resorting to whining about “cults” or saying that mainstream languages are “useless.” In fact, SPJ jokingly called early attempts at purely functional languages “safe but useless” while traditional imperative languages were “unsafe but useful” http://channel9.msdn.com/showpost.aspx?postid=326762. It’s pure self deprecating humor. Haskell is useful. See Darcs as a very practical example of what Haskell can do.

Classic ad hominem (I know this is your favourite, Tony). Tony Morris has committed that most heinous of moral crimes–having a high opinion of himself–and therefore his argument is invalid.

If you look closely, you can also find irony, albeit unintentional (”to be honest”).

I can’t blame you: it’s much more pleasant than considering that you might actually sometimes be wrong.