That is indeed exactly what Fin is. The first n natural numbers is a finite set of n elements after all. I'll elaborate a bit in the tutorial. I guess the trouble with writing a tutorial when you're completely familiar with a language is that it's hard to know what will and won't make sense!
There'd also be nothing wrong to use a natural number, along with a proof that it's bounded by the length, to index the vector.
I don't think I've claimed it has C-style speed anywhere. At least, not in general - we have observed it in some cases though, and it is a goal to make it as efficient as possible. Dependent types plus partial evaluation gives you some nice opportunities for optimisation. Early days yet...
That is indeed exactly what Fin is. The first n natural numbers is a finite set of n elements after all.
Ah, right! I must admit that it feels like an odd definition to me indeed. I see how "the first n natural numbers" is a finite set of n elements, but I don't see how the reverse is true. I mean, look here, a finite set of n elements: {1, 1, 1, 1}. 4 elements, and they're all valued 1. They're also not ordered. So your concept of taking an element from a finite set (in this case, let's say, 1, or maybe 1 instead) to uniquely identify an element in a vector sounds a bit odd to me :-)
Clearly, I'm the noob here, and maybe in this stage Idris just isn't meant for people not on Lambda the Ultimate, but if not, it's good that you intend do something about it :-)
Cause once again, I love the concept, and I'd love to program with this.
There'd also be nothing wrong to use a natural number, along with a proof that it's bounded by the length, to index the vector.
I don't think I've claimed it has C-style speed anywhere. At least, not in general - we have observed it in some cases though, and it is a goal to make it as efficient as possible. Dependent types plus partial evaluation gives you some nice opportunities for optimisation. Early days yet...