在F＃中构建一个应用程序的强大记录 [英] Constructing a record with a power of Applicative in F#

问题描述

假设有一个类型r = {A：int; B：字符串; C：int; D：string} 和一些值：
$ b

  let aOptional： int option = ... 
 let bOptional：string option = ... 
 let cOptional：int option = ... 
 let dOptional：string option = ... 
  

如何 r可选可以由他们构建eleganty（不嵌套这些是如何在haskell中完成的 Control.Applicative ：
$ b

data R = R {a :: Integer，b :: String， c :: Integer，d :: String}

R $ $> a可选的* b可选的* c可选的* dOptional ::也许R


在fsharp中寻找等价的东西。

<我知道的唯一方法（使用applicatives）是通过创建一个函数来构造记录：

<$ p

$ p> let rabcd = {A = a; B = b; C = c; D = d}


然后你可以这样做：

 > r< / map /> a可选的* b可选的* c可选的*可选;; 
 
 val it：R选项
  

您可以定义 map 和< *> ，但是如果您想要一个通用实现，请使用 F＃+ ，或者如果您想使用 FsControl 直接你可以这样编写代码：

  #rFsControl.Core.dll
 
 open FsControl.Operators 
 
 let（< /）=（|>）
 let（/>）fxy = fyx 
 
 / /示例代码
 type R = {A：int; B：字符串; C：int; D：string} 
 let r a b c d = {A = a; B = b; C = c; D = d} 
 
 let aOptional = Some 0 
 let bOptional = Some
 let cOptional = Some 1 
 let dOptional = Somesome string
 
r< / map /> a可选的* b可选的* c可选的* d可选
 // val it：R选项=一些{A = 0; B =; C = 1; D =some string;} 
  

$ b 更新： Nuget软件包现已发布。

Suppose there is a type r = {A : int; B : string; C : int; D : string} and a some values:

let aOptional : int option = ...
let bOptional : string option = ...
let cOptional : int option = ...
let dOptional : string option = ...

How can r optional could be constructed from them eleganlty (without nested case-stuff, etc.)?

---

Btw, here is how it could be done in haskell with Control.Applicative:

data R = R { a :: Integer, b :: String, c :: Integer, d :: String}

R <$> aOptional <*> bOptional <*> cOptional <*> dOptional :: Maybe R

Looking for something equivalent in fsharp.

解决方案

The only way I know (using applicatives) is by creating a function to construct the record:

let r a b c d = {A = a; B = b; C = c; D = d}

Then you can do:

> r </map/> aOptional <*> bOptional <*> cOptional <*> dOptional ;;

val it : R option

You can define map and <*> yourself, but if you want a generic implementation try that code with F#+ or if you want to use FsControl directly you can write the code this way:

#r "FsControl.Core.dll"

open FsControl.Operators

let (</) = (|>)
let (/>) f x y = f y x

// Sample code
type R = {A : int; B : string; C : int; D : string}
let r a b c d = {A = a; B = b; C = c; D = d}

let aOptional = Some 0
let bOptional = Some ""
let cOptional = Some 1
let dOptional = Some "some string"

r </map/> aOptional <*> bOptional <*> cOptional <*> dOptional
// val it : R option = Some {A = 0; B = ""; C = 1; D = "some string";}

UPDATE: Nuget packages are available now.

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