What was your "ah ha" moment with Haskell? • Hacker News Board

Post by jonsterling » Tue, Jul 03, 2012, 5:43 PM UTC

spacemanaki wrote: post #43

jonsterling wrote: post #22

Earlier quoted context omitted.

Remember, Maybe and Either are not language features in Haskell, but rather library features! Java is totally capable of hosting them. (Though, there isn't any special syntax for tuples in Java).

But if you implemented Maybe in Java, there still wouldn't be any compile-time guarantee that Nothing would be handled, right? At best you'd have something in code that more strongly encourages a certain convention. Just now I briefly looked at implementations of Maybe in Java and at least one of them fakes this with checked exceptions, while another seems to lean heavily on Guava's Function interface, which is just…

There's also no compiletime guarantee that Nothing is handled in Haskell; there are plenty of unsafe partial functions. In a non-total language, you unfortunately have to avoid partial functions without help from the compiler.

You're quite right that programming with these kinds of types in Java introduces you to a whole new kind of Hell! I'm not sure I'd recommend it.

However, I'm simply pointing out that types like these are _not_ language features. Some languages may be better suited to them than others, but they are definitely library features, and had best not be considered otherwise.