Question

在以下示例中，我收到错误＆＃34;没有重载符合方法＆＃39; op_Subtraction＆＃39;。＆＃34;

open System

type EmployeeStatus = 
    | Active
    | NotActive

type EnrollmentPeriod = 
    | JanuaryFirst
    | JulyFirst
    | PeriodNotApplicable

let DetermineTargettedEnrollmentDate targettedEnrollmentDate (relativeDate : DateTime) = 
    match targettedEnrollmentDate with
    | EnrollmentPeriod.JanuaryFirst -> new DateTime(relativeDate.Year + 1,1,1)
    | EnrollmentPeriod.JulyFirst -> new DateTime(relativeDate.Year,7,1)
    | EnrollmentPeriod.PeriodNotApplicable -> relativeDate

let ProjectDaysWorkedSinceJan1 employeeStatus targettedEnrollmentPeriod (relativeDate : DateTime) =
    let januaryFirst = DateTime(relativeDate.Year,1,1)
    let targettedEnrollmentDate = DetermineTargettedEnrollmentDate targettedEnrollmentPeriod
    match employeeStatus with
    | Active -> int (januaryFirst - targettedEnrollmentDate).TotalDays
    | NotActive -> 0

targettedEnrollmentDate函数确定DetermineTargettedEnrollmentDate似乎并非如此。

我在哪里错了？

Answer 1

您只向DetermineTargettedEnrollmentDate提供第一个参数：

let targettedEnrollmentDate = DetermineTargettedEnrollmentDate targettedEnrollmentPeriod

结果是等待第二个参数的函数，即targettedEnrollmentDate是一个以relativeDate为参数的函数。

因此，您尝试做的是从日期中减去一个函数，这是编译器抱怨的内容。

Answer 2

我真的不明白你的问题。代码显然没有编译。

DetermineTargettedEnrollmentDate定义为

val DetermineTargettedEnrollmentDate :
  targettedEnrollmentDate:EnrollmentPeriod ->
    relativeDate:DateTime -> DateTime

这意味着，它需要两个参数：EnrollmentPeriod和DateTime并返回另一个DateTime。稍后在ProjectDaysWorkedSinceJan1中，您只使用一个参数：

let targettedEnrollmentDate = DetermineTargettedEnrollmentDate targettedEnrollmentPeriod

由于partial application，这会使targettedEnrollmentDate成为一个函数，需要DateTime并返回另一个DateTime。但是当你试图从中减去另一个DateTime时，你会尝试使用它，就像它是一个值一样。

      | Active -> int (januaryFirst - targettedEnrollmentDate).TotalDays
  ----------------------------------^

(...)

Possible overload: 'DateTime.op_Subtraction(d1: DateTime, d2: DateTime) : TimeSpan'. Type constraint mismatch. The type 
    DateTime -> DateTime    
is not compatible with type
    DateTime

你可能想要的是用DetermineTargettedEnrollmentDate来代替relativeDate：

let ProjectDaysWorkedSinceJan1 employeeStatus targettedEnrollmentPeriod (relativeDate :  DateTime) =
    let januaryFirst = DateTime(relativeDate.Year,1,1)
    let targettedEnrollmentDate = DetermineTargettedEnrollmentDate targettedEnrollmentPeriod relativeDate
    match employeeStatus with
    | Active -> int (januaryFirst - targettedEnrollmentDate).TotalDays
    | NotActive -> 0

这使得它使用以下结果进行编译：

val ProjectDaysWorkedSinceJan1 :
  employeeStatus:EmployeeStatus ->
    targettedEnrollmentPeriod:EnrollmentPeriod -> relativeDate:DateTime -> int

在F＃中将函数作为参数传递

2 个答案: