functions

types must be specified, i.e. types are only inferred locally.  `return`
returns early, using it at the end of a function is not idiomatic.

rust/book/src/main.rs

fn inc(x: i32) -> i32 {
    if x == 42 {
        return 42
    }
    x + 1
}
fn main() {
    let x = 5;
    } else {
        println!("Meh, it's just a number, {}.", x);
    }
    let n = 10;
    println!("inc({}) = {}", n, inc(n));
    println!("inc(42) = {}", inc(42));
    println!("inc(43) = {}", inc(43));
}