为什么一元 tuple不是type constructor

Bug提交
1

pub impl[U:ToAny] ToAny for (U) with to_any(self : (U)) → Any {
let (first) = self
Any::Array([first.to_any()])
}
///|
pub impl[U : ToAny, V : ToAny] ToAny for (U, V) with to_any(self : (U, V)) → Any {
let (first, second) = self
Any::Array([first.to_any(), second.to_any()])
}

2元可以编译通过， 一元的报错 Invalid type for “self”: must be a type constructor
https://docs.moonbitlang.com/en/latest/language/error_codes/E4053.html
按照这个文档， 应该一元tuple 也是 type constructor

2

MoonBit里没有一元tuple，所以也没有一元tuple的type constructor。(Type)相当于Type：

let x : Int = 5
let y : (Int) = (5)
// x 和 y 的类型都是Int