将lambda表达式转换为Func [英] Conversion of lambda expressions to Func

问题描述

给出以下内容：

 打开System.Linq 
 
 let seqA = {1 .. 10} 
  

这样做：

  seqA.All（fun n  - > n> 0）
  

然而这并不是：

  let abc = fun n  - > n> 0 
 
 seqA.All（abc）
  

为什么F＃提供隐式转换从lambda表达式到 Func s但不是来自函数？指向我可以阅读这里发生的事情的文档是值得欢迎的。 ： - ）

/research.microsoft.com/en-us/um/cambridge/projects/fsharp/manual/spec.html#_Toc335819028rel =nofollow>方法解决方案，同样在成员调用中的类型定向转换。引用后者：
$ b

如方法应用程序解析中所述（请参阅第14.4节），两个
类型定向转换应用于方法调用。

第一种类型定向转换将匿名函数
表达式和其他函数值参数转换为委托类型。
鉴于：

• 委托类型的正式参数 D


• 已知类型 ty ₁ - > ...> - > ty _n - > rty 的实际参数 farg em>


• 精确 n 参数给委托类型的调用方法 D >

然后：

• 被解释为如下：
  
  new D （ fun arg ₁ ... arg _n - > farg arg ₁ ... arg _n ）

似乎表明这种转换适用于任何函数值，但观察表明它仅适用于匿名函数。

Given the following:

open System.Linq

let seqA = { 1..10 }

this works:

seqA.All (fun n -> n > 0)

However this doesn't:

let abc = fun n -> n > 0

seqA.All (abc)

Why does F# offer implicit conversion from lambda expressions to Funcs but not from functions? Pointers to the documentation where I can read up on what's going on here are welcome. :-)

解决方案

This is covered in the (rather involved) section of the spec on Method Resolution and again in Type-directed Conversions at Member Invocations. Quoting from the latter:

As described in Method Application Resolution (see §14.4), two type-directed conversions are applied at method invocations.

The first type-directed conversion converts anonymous function expressions and other function-valued arguments to delegate types. Given:

• A formal parameter of delegate type D
• An actual argument farg of known type ty₁ -> ... -> ty_n -> rty
• Precisely n arguments to the Invoke method of delegate type D

Then:

• The parameter is interpreted as if it were written:
  new D(fun arg₁ ... arg_n -> farg arg₁ ... arg_n)

It seems to suggest this conversion would be applied to any function value, but observation suggests it's applied only to anonymous functions.

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