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Sure, type systems are very practical. I wouldn't want to program without a good one any more. But that's not really why I find them interesting. Mostly, I jus

by tikhonj 14y ago

Sure, type systems are very practical. I wouldn't want to program without a good one any more. But that's not really why I find them interesting. Mostly, I just find most type theory simple and beautiful. It's fun and gives me a new perspective on how to think about computation (as transformations between types). Also, while a type system restricts the set of possible programs, it can actually make a language more expressive. Haskell's typeclasses make a whole bunch of things much nicer: custom numeric types, overloaded string literals, monads, QuickCheck... All this is far uglier in a language without typeclasses. Coincidentally, I'm very excited that Rust is promising to bring much of the typeclassy goodness to low-level programming. It really does make life much nicer, and promises to bring some progress to the otherwise seemingly stagnant field of systems languages. I think that's the sort of innovation we really need rather than Go, but I'm obviously very biased :).

ufo 14y ago
don't common lisp multimethods do kind of the same thing as typeclasses but on a dynamic language?
- tikhonj 14y ago
  They're missing one very important part: dispatching on the return type. All my examples require that. That is, in Haskell, numeric literals are polymorphic on the type they are supposed to be: the type system can infer whether you need an Int, an Integer, a Double, a Word or even a Word18--which my last project did--just from using a literal number. In every other language I know, you would have to specify which one you wanted somehow, either by using a current syntax (like 0L or 0.1) or calling a function on the number. In Haskell, the type system can figure it out for you.
  - FreeFull 14y ago
    The way this happens underneath is that every type that has a Num instance has a fromInteger function. If a literal like 3435 is encountered, the fromInteger function gets called on it to convert it to the appropriate type.

by tikhonj 14y ago

ufo 14y ago

don't common lisp multimethods do kind of the same thing as typeclasses but on a dynamic language?

tikhonj 14y ago
They're missing one very important part: dispatching on the return type. All my examples require that. That is, in Haskell, numeric literals are polymorphic on the type they are supposed to be: the type system can infer whether you need an Int, an Integer, a Double, a Word or even a Word18--which my last project did--just from using a literal number. In every other language I know, you would have to specify which one you wanted somehow, either by using a current syntax (like 0L or 0.1) or calling a function on the number. In Haskell, the type system can figure it out for you.
- FreeFull 14y ago
  The way this happens underneath is that every type that has a Num instance has a fromInteger function. If a literal like 3435 is encountered, the fromInteger function gets called on it to convert it to the appropriate type.