subtype_code2]

在 MoonBit 代码中我们将 $S \vee T$ 实现为 s | t，将 $S \wedge T$ 实现为 s & t。这两个运算符的定义如下：

impl BitAnd for Type with land(s, t) {
  match (s, t) {
    (TyFun(xs1, v, p), TyFun(xs2, w, q)) if xs1 == xs2 => {
      guard v.length() == w.length() else { TyBot }
      TyFun(xs1, v.zip(w).map(z => z.0 | z.1), p & q)
    }
    (s, t) if s.subtype(t) => s
    (s, t) if t.subtype(s) => t
    _ => TyBot
  }
}

impl BitOr for Type with lor(s, t) {
  match (s, t) {
    (TyFun(xs1, v, p), TyFun(xs2, w, q)) if xs1 == xs2 => {
      guard v.length() == w.length() else { TyTop }
      TyFun(xs1, v.zip(w).map(z => z.0 & z.1), p | q)
    }
    (s, t) if s.subtype(t) => t
    (s, t) if t.subtype(s) => s
    _ => TyTop
  }
}