在Scala和Haskell中要求类型的类型

Question

当我在Haskell中询问那种情况时[Int],[]我得到:

Prelude> :k [Int]
[Int] :: *
Prelude> :k []
[] :: * -> *

这是有道理的:第一个是合适的类型,第二个是更高的类型.

但是当我在Scala中做同样的事情时:

scala> :k -v List[Int]
scala.collection.immutable.List's kind is F[+A]
* -(+)-> *
This is a type constructor: a 1st-order-kinded type.

scala> :k -v List
scala.collection.immutable.List's kind is F[+A]
* -(+)-> *
This is a type constructor: a 1st-order-kinded type.

......它说都是更高级的类型.为什么第一个没有被归类为合适的类型？造成这种差异的原因是什么？

Answer 1

似乎完全看好scala这[Int]部分List[Int],但选择忽略它并且总是刻意地看待"外部"类型.

如果这不是真的,那么type ListOfInt = List[Int]接下来:k -v ListOfInt会产生*不是,* -> *但事实并非如此:

scala> :k -v List
scala.collection.immutable.List's kind is F[+A]
* -(+)-> *
This is a type constructor: a 1st-order-kinded type.

scala> :k -v List[Int]
scala.collection.immutable.List's kind is F[+A]
* -(+)-> *
This is a type constructor: a 1st-order-kinded type.

scala> type ListOfInt = List[Int]
defined type alias ListOfInt

scala> :k -v ListOfInt
scala.collection.immutable.List's kind is F[+A]
* -(+)-> *
This is a type constructor: a 1st-order-kinded type.