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Re: cheerful static typing (was: Any and Every... (was: Eval))
> We have had a "type system" like that in CL for years.
"we" ~= "the world" and "like that" ~= "like Curl's".
Please show me for a small essential core model of Curl
what typing means. The more I see about Curl's type system
the more I am confused. Let me point to two examples
that most people on the list should know and understand.
When the Java type checker performs its task, we know exactly what the
underlying type language is (the specified interface and class hierarchy,
including the imported Java libs, plus the basic types specified in the
Java report. When it reports an error, it's pretty easy to see what I need
to fix, because the typing rules are published and the explanations make
sense. Finally, when the Java program runs, I am guaranteed that what the
type checker proved holds during an evaluation. For example, the type
checker proved that the machine will never attempt to add the bit
representation of 10998 to the bit representation of "hello world".
That's called type safety. If you discover that your particular
compiler/rt system violates this last part, you can go to the vendor and
Compare this to the C++ type checker:
1. Yes, the types are specified in the same way.
2. Yes, the typing rules are specified alright for plain classes.
If you get into parametric polymorphism, things don't look that easy
anymore when we get to type errors and fixing type errors.
3. When you run a C++ program, you have absolutely no guarantee that it
doesn't add the bit representation of some integer to the bit
representation of some string. That's called "lack of type safety".
When you add a type system to a language, you should investigate these
three aspects. That's what research on type systems over the past 25 years
points to and when we invent new languages we should understand
that. Otherwise our interpreters and compilers look like those that
undergraduates write as Simon Cozen argued during LL1.