F#值不是函数错误

Question

通过尝试使用递归重新创建一个简单的二分法来继续我的F#学习,这里我使用MathNet库继承Beta分布.

我收到函数'search'(二进制搜索方法)的错误the value is not a function and cannot be applied.

//Beta class inheriting from MathNet Beta distribution
//Extends the class by implementing an InverseCDF function

type newBeta(alpha:double, beta:double) =
    inherit MathNet.Numerics.Distributions.Beta(alpha, beta)

member this.InverseCDF(p: float) =
    let rec search (min: float, max: float, acc: uint32) = 
        let x = (min + max) / 2.0
        let error = 0.001
        let maxiters : uint32 = 1000u
        let cdf = this.CumulativeDistribution(x)

        match cdf, (Math.Abs(cdf - p) < error || acc > maxiters) with   //while statement
        | _ , true                  -> cdf      //auto match cdf and if while statement evaluates true then break and return cdf result
        | p , _                     -> cdf      //if exactly matches p then break and return cdf result
        | p , false when p > cdf    -> search (min) (x) (acc + 1)   //if p > cdf then set max = x and increment then call func with new params
        | p , false when p < cdf    -> search (x) (max) (acc + 1)   //if p < cdf then set min = x and increment then call func with new params

    search (0.0) (1.0) (0)  //Call the bisection method with initial parameters

有人可以帮忙吗？显然,任何关于如何使这个更"功能"的输入都会很酷.但由于错误,尚未能运行此测试.鉴于我正在尝试返回当前值,我的前2个匹配模式看起来很可疑cdf.

Answer 1

正如@John所说,你的根本错误是你以元组形式声明了函数,但是以curry形式使用它.

我注意到你的图案匹配cdf带p.新值p将跟随参数p的this.InverseCDF; 因此,该参数不再可用于比较.你实际上cdf与cdf自己相比,when总是有两个守卫false,你完全不想要.

一些更正:

1. cdf从模式匹配中删除,因为您只想比较其值p,而不是与特定文字匹配.
2. 向上移动两名when警卫.最后的模式不应该是一个when后卫; 在这种情况下,编译器会抱怨不完整的模式匹配.
3. u对任何算术运算使用后缀acc(属于类型unint32).

新search功能:

let rec search (min: float) (max: float) (acc: uint32) = 
    let x = (min + max) / 2.0
    let error = 0.001
    let maxiters : uint32 = 1000u
    let cdf = this.CumulativeDistribution(x)

    match abs(cdf - p) < error || acc > maxiters with   // while statement
    | false when p > cdf    -> search min x (acc + 1u)   // if p > cdf then set max = x and increment then call func with new params
    | false when p < cdf    -> search x max (acc + 1u)   // if p < cdf then set min = x and increment then call func with new params 
    | _                     -> cdf      // if exactly matches p or returns true then break and return cdf result

search 0.0 1.0 0u  // call the bisection method with initial parameters