For example, the type of α lists is defined by datatype α list = Cons of α * α list | Empty Lists of natural numbers, then, are of type nat list, while lists of strings are of string list.
比如 α lists 的类型被定义为 datatype α list = Cons of (α, list) | Empty. 数的列表，接着是有类型 Nat list，而字符串的列表有类型 String list。