元类型（0阶类型）；nullary type， data types
一元类型（一阶类型）：unary adj. [数] 一元的 
二元类型：
is the kind of a binary type
高阶类型：
：关注类型的变换；
a kind is the type of a type constructor or, less commonly, the type of a higher-order type operator.
, pronounced "type", is the kind of all data types seen as nullary type constructors, and also called proper types in this context. This normally includes function types in functional programming languages.- is the kind of a unary type constructor, e.g. of a list type constructor.
- is the kind of a binary type constructor (via currying), e.g. of a pair type constructor, and also that of a function type constructor (not to be confused with the result of its application, which itself is a function type, thus of kind )
- is the kind of a higher-order type operator from unary type constructors to proper types.[2]
https://www.cnblogs.com/feng9exe/p/9155649.html
https://en.wikipedia.org/wiki/Kind_(type_theory)
type多指具体的
kind多指抽象的
kind - 种类
type - 类型