F# 与复杂类型匹配

Question

我是 F# 新手，我正在尝试对复杂类型进行简单的模式匹配，但我找不到这样做的方法。请参阅下面的伪代码来解释我想要做的模式匹配。

type Vector= {X:int; Y:int}

let calculateDirection vector = 
match vector with
| vector.X=0 && vector.Y>0 -> "N"    // pseudo code 
| vector.X>0 && vector.Y>0 -> "NE"   // pseudo code 
| vector.X>0 && vector.Y=0 -> "E"    // pseudo code 
| vector.X>0 && vector.Y<0 -> "SE"   // pseudo code 
| vector.X=0 && vector.Y<0 -> "S"    // pseudo code 
| vector.X<0 && vector.Y<0 -> "SW"   // pseudo code 
| vector.X<0 && vector.Y=0 -> "W"    // pseudo code 
| vector.X<0 && vector.Y>0 -> "NW"   // pseudo code 
| _ -> "Error"

我读了一些教程( https://fsharpforfunandprofit.com/posts/match-expression/ )，但它总是简单的场景，对我没有多大帮助。或者我只是不明白他们。

提前致谢。

Answer 1

使用事件模式，您可以获得非常可读的代码，如下所示:

type Vector= {X:int; Y:int}

let (|West|_|) v = if v.X < 0 then Some () else None
let (|East|_|) v = if v.X > 0 then Some () else None
let (|North|_|) v = if v.Y > 0 then Some () else None
let (|South|_|) v = if v.Y < 0 then Some () else None

let calculateDirection = function
    | North & East -> Some "NE"
    | North & West -> Some "NW"
    | North -> Some "N"
    | South & East -> Some "SE"
    | South & West -> Some "SW"
    | South -> Some "S"
    | East -> Some "E"
    | West -> Some "W"
    | _ -> None