kw op

ImplMember  = { Attr } [ Vis ] ( Receiver ( "fn" | "op" ) Sig ( Block | "=>" Expr )
            | "override" "fn" Sig ( Block | "=>" Expr ) | "open" "fn" Sig ( Block | "=>" Expr )
            | "init" Sig ( Block | "=>" Expr ) | "dep" Ident ":" Type | Rpc | Const ) ;

impl Vec3 {
  static op +(a: Vec3, b: Vec3) -> Vec3 => Vec3(a.x + b.x, a.y + b.y, a.z + b.z)
  static op *(v: Vec3, k: f32) -> Vec3 => Vec3(v.x * k, v.y * k, v.z * k)
  static op -(v: Vec3) -> Vec3 => v * -1.0
  op [](i: usize) -> f32 { … }            // read by index
  var op [](i: usize) -> &var f32 { … }   // write by index
  op ()(t: f32) -> Vec3 { … }             // call as a function
  static op <=>(a: Vec3, b: Vec3) -> Ordering { … }
  op as Vec4 => Vec4(x, y, z, 1.0)
}