F#中这种惯用的Option用法吗? [英] Is this usage of Option idiomatic in F#?

问题描述

我具有以下功能，该功能检查数据源中customer的存在并返回ID.这是使用Option类型的正确/惯用方式吗?

I have the following function that checks the existance of a customer in a data source and returns the id. Is this the right/idiomatic way of using the Option type?

let findCustomerId fname lname email = 
    let (==) (a:string) (b:string) = a.ToLower() = b.ToLower()
    let validFName name (cus:customer) =  name == cus.firstname
    let validLName name (cus:customer) =  name == cus.lastname
    let validEmail email (cus:customer) = email == cus.email
    let allCustomers = Data.Customers()
    let tryFind pred = allCustomers |> Seq.tryFind pred
    tryFind (fun cus -> validFName fname cus && validEmail email cus && validLName lname cus)
    |> function 
        | Some cus -> cus.id
        | None -> tryFind (fun cus -> validFName fname cus && validEmail email cus)
                  |> function
                    | Some cus -> cus.id
                    | None -> tryFind (fun cus -> validEmail email cus)
                              |> function
                                | Some cus -> cus.id 
                                | None -> createGuest() |> fun cus -> cus.id

推荐答案

当您缩进缩进时再好不过了，因此值得一看，看看您能对此做些什么.

It's never good when you have indent upon indent, so it'd be worthwhile seeing what you can do about it.

这是通过引入一些辅助功能来解决该问题的一种方法:

Here's one way to address the problem, by introducing a little helper function:

let tryFindNext pred = function
    | Some x -> Some x
    | None -> tryFind pred

您可以在findCustomerId函数中使用它来展平后备选项:

You can use it inside the findCustomerId function to flatten the fallback options:

let findCustomerId' fname lname email = 
    let (==) (a:string) (b:string) = a.ToLower() = b.ToLower()
    let validFName name (cus:customer) =  name == cus.firstname
    let validLName name (cus:customer) =  name == cus.lastname
    let validEmail email (cus:customer) = email == cus.email
    let allCustomers = Data.Customers()
    let tryFind pred = allCustomers |> Seq.tryFind pred
    let tryFindNext pred = function
        | Some x -> Some x
        | None -> tryFind pred
    tryFind (fun cus -> validFName fname cus && validEmail email cus && validLName lname cus)
    |> tryFindNext (fun cus -> validFName fname cus && validEmail email cus)
    |> tryFindNext (fun cus -> validEmail email cus)
    |> function | Some cus -> cus.id | None -> createGuest().id

这与此处概述的方法非常相似.

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