zlacker

>>andsoi+(OP)
Big "college freshman" energy in this take:

  I personally prefer to make the error state part of the objects: Streams can be in an error state, floats can be NaN and integers should be low(int) if they are invalid (low(int) is a pointless value anyway as it has no positive equivalent).

It's fine to pick sentinel values for errors in context, but describing 0x80000000 as "pointless" in general with such a weak justification doesn't inspire confidence.

>>mwkauf+M2
I have been burned by sentinel values every time. Give me sum types instead. And while I’m piling on, this example makes no sense to me:

    proc fib[T: Fibable](a: T): T =
      if a <= 2:
        result = 1
      else:
        result = fib(a-1) + fib(a-2)

Integer is the only possible type for T in this implementation, so what was the point of defining Fibable?

>>sevens+QKb
You're completely missing the point of this casual example in a blog post ... as evidenced by the fact that you omitted the type definition that preceded it, that is the whole point of the example. That it's not the best possible example is irrelevant. What is relevant is that the compiler can type check the code at the point of definition, not just at the point of instantiation.

And FWIW there are many possible types for T, as small integer constants are compatible with many types. And because of the "proc `<=`(a, b: Self): bool" in the concept definition of Fibable, the compiler knows that "2" is a constant of type T ... so any type that has a conversion proc for literals (remember that Nim has extensive compile-time metaprogramming features) can produce a value of its type given "2".