ord.rs

// NOTE:
//
// Matthias's code below and inline.
//
// (define (<-card c1 c2)
//   (match-define (card f1 t1) c1)
//   (match-define (card f2 t2) c2)
//   (or (<-trait t1 t2) (and (equal? t1 t2) (< f1 f2))))

// (define (<-card c1 c2)
//
// Here the notion of `<-card` is encoded in the type system as
// `impl Ord for Card` and that trait requires a a function named `cmp`,
// which takes in two `&Card`s.
impl Ord for Card {
    fn cmp(&self, other: &Card) -> Ordering {
        //   (match-define (card f1 t1) c1)
        //   (match-define (card f2 t2) c2)
        //
        // This is a straightforward translation. `let` in Rust destructures
        // just as `match-define` does. In fact our data models for the game
        // must be practically identical.
        let Card(f1, t1) = *self;
        let Card(f2, t2) = *other;
        // This line I'll line up to show how cool it is that these two
        // different languages encode the idea of order in a similar, yet
        // different way.
        //
        // (or (<-trait t1 t2) (and (equal? t1 t2) (< f1 f2))))
           match t1.cmp(&t2) { Equal => f1.cmp(&f2), o => o }
        // Rust's is shorter :P
    }
}