I wrote the pickle.load comment [1]. I want to defend it here. King (the author) places "dynamically typed" and "statically typed" in opposition. But keep in m

I wrote the pickle.load comment [1]. I want to defend it here. King (the author) places "dynamically typed" and "statically typed" in opposition. But keep in mind that many languages have both: Java, ObjC, TypeScript, C#, etc. I like to say that a a language "has" static and/or dynamic types, but "is" dynamic if it supports runtime features like reflection - of course this is a sliding scale. King observes that static types allow you to make explicit what you know. After calling `pickle.load` you don't know anything about the result, so its static type is going to be something quite constraining like `String -> Object`. It seems we are in violent agreement on this point. King then goes on to make a different claim: that it is possible to implement `pickle.load` in Java and also in Haskell. It is possible in Java but not in Haskell. Here's the key line for Java: However, nothing is stopping you from passing Serializable.class and branching on the type later Notice the subtle shift in meaning for "type": from static type to runtime tag. It is possible to branch on the type at runtime, because the type is available at runtime, because Java has dynamic types. They're awkward and painful to use, but it is possible. For Haskell: Can we do this in Haskell, too? Absolutely—we can use the serialise library, which has a similar API to the Java one mentioned above. Absolutely you cannot! The Serialise libary requires you to list all of the possible result types up-front, "by providing a set of type class instances." There is no way for a Haskell program to deserialise a value whose static type was not visible when the program was compiled. There is no way in Haskell to "get a list of all types" (it's hard to even formulate this). Implementing Python-style pickle isn't really about types, it's about the language's dynamic features. Can you look up a types by name, reflect on a value at runtime? Dynamic features really do bring new capabilities to programs. 1: https://news.ycombinator.com/item?id=21479933 https://news.ycombinator.com/item?id=21479933