转换F＃报价为LINQ表达式 [英] Converting F# Quotations into LINQ Expressions

问题描述

我可以转换类型 Expr的℃的报价;'A - > 'B> 来通过下面的代码片段一个LINQ表达式：

I can convert a quotation of type Expr<'a -> 'b> to a Linq expression via the following snippet:

/// Converts a F# Expression to a LINQ Lambda
let toLambda (exp:Expr) =
    let linq = exp.ToLinqExpression() :?> MethodCallExpression
    linq.Arguments.[0] :?> LambdaExpression

/// Converts a Lambda quotation into a Linq Lamba Expression with 1 parameter
let ToLinq (exp : Expr<'a -> 'b>) =
    let lambda = toLambda exp
    Expression.Lambda<Func<'a, 'b>>(lambda.Body, lambda.Parameters)

现在我想转换型报价 Expr的<A *b - > C> 或者甚至 Expr的<'A - > B - > C> 来型的Linq Lambda表达式表达式来; Func键<'一'B'C>>

Now I want to convert a quotation of type Expr<'a * 'b -> 'c> or maybe even Expr<'a -> 'b -> 'c> to a Linq Lambda Expression of type Expression<Func<'a,'b'c>>.

我怎样才能做到这一点？

How can I do this?

问候，
forki

Regards, forki

推荐答案

我不知道这是直接由F＃PowerPack中提供的LINQ模块的支持。但是，您可以实现通过F＃库产生的LINQ表达自己的后处理把它变成了一般形式的C＃lambda函数：

I'm not sure if this is directly supported by the LINQ modules available in the F# PowerPack. However, you can implement your own post-processing of the LINQ expression produced by F# libraries to turn it into a C# lambda function of the usual form:

下面的函数取其被构造为单个参数的多个嵌套 LambdaExpression 表达式（即，被F＃翻译产生的结构），并返回所述内的参数的列表和身体LINQ表达式 - 大多数表达式：

The following function takes a LINQ expression which is constructed as multiple nested LambdaExpression expressions of a single parameter (that is, the structure produced by F# translator) and returns a list of parameters and body of the inner-most expression:

let rec translateExpr (linq:Expression) = 
  match linq with
  | :? MethodCallExpression as mc ->
      let le = mc.Arguments.[0] :?> LambdaExpression
      let args, body = translateExpr le.Body
      le.Parameters.[0] :: args, body
  | _ -> [], linq

现在你可以用它来获得一个普通的 Func键委托出去的类型，例如 INT - > INT - > INT - > INT 是这样的：

Now you can use it to get an ordinary Func delegate out of type such as int -> int -> int -> int like this:

let linq = (<@@ fun a b c -> (a + b) * c @@>).ToLinqExpression()
let args, body = translateExpr liq
let f = Expression.Lambda<Func<int, int, int, int>>
          (body, args |> Array.ofSeq)
f.Compile().Invoke(10, 11, 2)

这篇关于转换F＃报价为LINQ表达式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！