OCaml

Question

所以我有这段代码：

let rec minBound s =
    match s with
    Rect (s,i)-> Rect(s,i)
    |Circle (c,r)-> getRectOutCircle (c,r)
    |Union(l,r)-> 
        let Rect(sl, il) = (minBound l) in
        let Rect(sr, ir) = (minBound r) in
        let (xsl,ysl) = sl in 
        let (xil,yil) = il in
        let (xsr,ysr) = sr in   
        let (xir,yir) = ir in           
        Rect( ((min xsl xsr), (min ysl ysr)) , 
              (( max xil xir), (max yil yir)) )
    |Intersection(l,r)-> 
        let Rect(sl, il) = (minBound l) in
        let Rect(sr, ir) = (minBound r) in
        let (xsl,ysl) = sl in 
        let (xil,yil) = il in
        let (xsr,ysr) = sr in   
        let (xir,yir) = ir in           
        Rect( ((min xsl xsr), (min ysl ysr)) , 
              (( max xil xir), (max yil yir)) )
    |Subtraction(l,r) -> 
        let Rect(sl, il) = (minBound l) in
        let Rect(sr, ir) = (minBound r) in 
        let (xsl,ysl) = sl in   
        let (xil,yil) = il in           
        let (xsr,ysr) = sr in                   
        let (xir,yir) = ir in
        Rect( ((min xsl xsr), (min ysl ysr)) , 
              (( max xil xir), (max yil yir)) )                 
;;

谁能解释一下为什么会出现以下警告？

Warning 8: this pattern-matching is not exhaustive.
Here is an example of a value that is not matched:
(Circle (_, _)|Union (_, _)|Intersection (_, _)|Subtraction (_, _))val minBound : shape -> shape = <fun>

这里有更多信息可以提供帮助！！

type point = float*float;;

type shape = Rect of point*point
       | Circle of point*float
       | Union of shape*shape
       | Intersection of shape*shape
       | Subtraction of shape*shape
;;

Answer 1

您的函数 minBound return 类型 shape。但是你的递归调用假设它只能 return 一种形状。编译器警告您它可能 return 其他类型的形状。

这是一个常见问题。基本上你知道 minBound 总是 return 是一个 Rect，但编译器不知道。

一个可能的解决方案是 minBound return point * point.

OCaml - 谁能解释一下 "pattern-matching is not exhaustive"

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