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I think your warnings about complexity in the type system are prudent, but your comment about casting is off. Casting (with the exception of primitive types) is a very blunt hammer to bash your way out of a type system. The MLs have a simple type system, yet you almost never need to cast. It's worthwhile from a language design perspective to try to eliminate the need to cast entirely, and I believe you don't have to complicate your type system to do so.

Also, you note that "many people prefer static typing", but then you suggest Clojure...




Well, avoiding casts AND supporting inheritance AND having a simple type system is pretty hard. You can usually just pick two of the three.

Many prefer static typing, and many don't. BTW, Clojure is indeed dynamically typed, but it has a "type philosophy" that keeps things nice and orderly, namely no encapsulation and uniform data access.

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Java avoids casts in most cases with generics, it supports inheritance, and it has a simple type system. Ditto with C#. (I also haven't heard people complain about the complexity of F#'s type system, so I'd point to it, but I don't know F# enough to be able to say whether it's a good point or bad point in the space here.) OCaml also supports inheritance, although its object system is kinda weird (in that it doesn't really fit with the rest of the language; I wouldn't say it's overly complex though).

Basically I don't think that Scala's complexity should burn us on type safety in general. I think Go and Dart, for example, are an overreaction to the complexities of type systems like those of Scala (no generics and null pointers in the former, and unsound covariant generics and null pointers in the latter). There is room for a statically typed language that brings the benefits of type safety that make programming easier without the complexities that make programming harder; the fact that we haven't found that sweet spot yet doesn't mean that we should just throw up our hands. I'm not convinced that the sweet spot is either unsound or requires casts.

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