That was really well written. As I was reading through the example code in the section about closures

    let add_one = |x| x + 1;
    let five = add_one(4);

I thought to myself "hmm I wonder what happens if I were to call the code with a float rather than an int?"

Answered my question a few paragraphs down. Kudos.

Is it possible to write a generic closure? i.e something that would add 1 to any numeric type.