From experience (the last time slides for a talk by Stephen Diehl made its way to the HN frontpage), there's a lot of information in the actual (recorded) talk that the slides are going to be missing.

There are a lot of advanced techniques in these slides, but if you care about program behaviour, in a functional context that mostly reduces to caring about the types of your functions. E.g., in Haskell if you have a function of type `a -> a` you know that it must be the identity function (leaving aside exceptions and undefined).

Taking this further, you can define functions of types that specify your desired behaviour exactly, e.g. guess what this does:

    foo :: List a -> SortedList a

Or this:

    bar :: VerificationToken -> Email Unverified -> Email Verified

That's really the main idea. If you specify the types in the right way, you can make them describe the function quite nicely.

Very interesting, What is the programming language used in the code examples ?

Is the talk recorded? Can we find it somewhere?

Sorry for being off-topic, but those slides are beautiful. Does anyone know what they're made in?