TODO

Template struct Declarations

struct Pair(type Left, type Right) {
    left:   Left
    right:  Right
}

fn fst(pair: Pair(<Left>, _)): Left =
    pair.left

fn snd(pair: Pair(_, <Right>)): Right =
    pair.right

fn sum(pair: Pair(<T>, T))
    case (T.is::arithmetic): T =
        pair.fst + pair.snd

fn main() {
    let p = Pair(int, int)(2, 3)
    return p.sum - 5
}

TODO