OCaml联合类型(OCaml union types)

 我正在尝试创建一个使用已定义类型的子类型但OCaml不会派生正确值的函数：请考虑以下类型定义： 
 
type fraction = {numerator : int; denominator : int};;

type number =
  | Int of int
  | Fraction of fraction;;
 
 如果我尝试输入interpeter（如果重要的话我使用utop）： 
 
utop # ((fun a-> a>0) (Int 1));;
Error: This expression has type number but an expression was expected of type int 
 
 类型号也是一个int，但我不能理解这个功能，我怎么解决这个问题呢？ 

I'm trying to make a function that uses a subtype of a defined type but OCaml wont derive the correct value : Consider this type definition:
 
type fraction = {numerator : int; denominator : int};;

type number =
  | Int of int
  | Fraction of fraction;;
 
if i try to type into the interpeter (i'm using utop if it matters) :
 
utop # ((fun a-> a>0) (Int 1));;
Error: This expression has type number but an expression was expected of type int 
 
type number is also an int but I cant get the function to understand that, how can I solve this?

原文：https://stackoverflow.com/questions/33845651