| > In my actual industry practice, type information never did anything to "preserve the internal invariants of other modules." Most languages don't have abstract types (not to be confused with abstract classes!), so there's that. Abstract types protect invariants of modules from external tampering. This is a mathematical fact. > However, that was your example. My argument is that's a really poor example. And now you are abandoning it. I'm not abandoning anything. I'm only saying that the use cases of parametricity go far beyond parametric collections. > I also like separating concerns. Good! Then what do you gain from the existence of reflection (which is pretty much the opposite of type abstraction), or the possibility of sending wrong messages? This is as anti-separation-of-concerns as it gets. Even more worrisome is what you have said in another post: “Decompilation in Smalltalk is trivially perfect, excluding local variable names, so closed source was fairly pointless.” (https://news.ycombinator.com/item?id=12340864) How can you pretend this is compatible with separating concerns? You're talking about inspecting the structure of arbitrary parts of a program! > I'm also not a dynamic typing bigot, though you seem to be imagining you are arguing with one. I've just made technical claims. I haven't personally attacked you. If you think I did, my apologies. > How in the heck did you get here from parametric algorithms? This smacks of intellectual dishonesty. I also request that you refrain from making personal attacks. Anyway. Parametricity means more than you think. The inability to inspect the representation of an abstract type is an example of parametricity too. > And earlier, you were claiming something about refactoring. Do you see a contradiction here? Nope, I don't see it. Refactoring produces a different program with a different fixed structure. And the difference shows up when the old and new programs have different types. The reason why types are helpful is precisely because they guide the evolution from the old to the new program. |