f# 带参数的函数调用并转换为度量单位

Question

我喜欢用 F# 编写一些数学函数并在 C# 中使用它们。由于 F# 使用度量单位，因此进行编译时检查真的很棒。在 C# 中，我已经有一个 Length（转换为 m、mm、km 等的索引器）类，因此我想使用 F# 函数将其用作 C# 中的参数，并将其转换为浮点数或更具体的浮点数。

由于我有两个参数，我很难调用这些函数。我想这与currying有关。

module Static
open Xunit
open Units.Contract // here is my Length class defined in C#

[<Measure>] type m
[<Measure>] type slabThickness = m
[<Measure>] type kN
[<Measure>] type freshConcreteDensity = kN/m^3
[<Measure>] type freshConcreteLoad = kN/m^2


let FreshConcreteLoad(slabThickness:float<m>, freshConcreteDensity:float<kN/m^3>) = slabThickness * freshConcreteDensity // 1. works

let FreshConcreteLoadL(slabThickness:Length, freshConcreteDensity:Length) = slabThickness.[Length.Units.m] *  freshConcreteDensity.[Length.Units.m] //2. works

let FreshConcreteLoadLUseMeasure(slabThickness:Length, freshConcreteDensity:Length) =  FreshConcreteLoad (slabThickness.[Length.Units.m]:float<m> freshConcreteDensity.[Length.Units.m]:float<kN/m^3>)  //3. here I struggel

// Related to 1. and works
[<Fact>]
let FreshConcreteLoad_Test() = 
    let thickness =  0.2<slabThickness>
    let density =  25.0<freshConcreteDensity> 
    let load:float<freshConcreteLoad> = FreshConcreteLoad(thickness,density)  
    Assert.Equal(load, 5.0<kN/m^2>) 

// Related to 2. and works
[<Fact>]
let FreshConcreteLoadL_Test() = 
    let thickness = new Length(0.2)
    let density = new Length(25.0) // dont care that this is now also a length, just for testing. in real live here would be a class for kN
    let load:float = FreshConcreteLoadL(thickness,density)  
    Assert.Equal(load, 5.0)

// Related to 3. and I struggle with the function call
[<Fact>]
let FreshConcreteLoadLUseMeasure_Test() = 
    let thickness = new Length(0.2)
    let density = new Length(25.0) // dont care that this is now also a length, just for testing. in real live here would be a class for kN
    let load:float = FreshConcreteLoadLUseMeasure(thickness,density)  
    Assert.Equal(load, 5.0)

Answer 1

您的 3. 函数定义不是有效的 F# 函数定义。如果您需要调用另一个函数“FreshConcreteLoad()”，则不能在函数调用中使用类型注释。 也许您想将函数参数转换为度量单位，但无法执行此转换，因为 C# 中不存在 F# 度量单位，因此无法将 C# 值直接转换为它。

您可以做的是创建几个转换 F# 函数的助手，例如：

let convToLength (inp: float) = inp * 1.0<m>
let convToDensity (inp: float) = inp * 1.0<kN/m^3>

并将第三个函数定义为：

let FreshConcreteLoadLUseMeasure(slabThickness:Length, freshConcreteDensity:Length) =  FreshConcreteLoad (convToLength slabThickness.[Length.Units.m], convToDensity freshConcreteDensity.[Length.Units.m]) 

或者直接在调用中进行转换：

let FreshConcreteLoadLUseMeasure(slabThickness:Length, freshConcreteDensity:Length) =  FreshConcreteLoad (1.0<m> * slabThickness.[Length.Units.m], 1.0<kN/m^3> * freshConcreteDensity.[Length.Units.m])