Question

这是Provided方法的简化代码段，它接受可变数量的参数，在这种情况下为3

ProvidedMethod(methodName = "GetContext", 
               parameters = [ for i in [ 1..3 ] do
                                  yield ProvidedParameter("Param" + string i, typeof<string>) ], 
               IsStaticMethod = true, returnType = typeof<string>, 
               InvokeCode = (fun args -> 
                   <@@ 
                       let dim1 : string = %%args.[0] : string
                       let dim2 : string = %%args.[1] : string
                       let dim3 : string = %%args.[2] : string
                 //    let dims = [for %%arg in args do yield (arg : string) ]// [1] error below
                 //    let dims = [for arg in args do yield (%%arg : string) ]// [2] error below
                       let dims = [ dim1; dim2; dim3 ] //this works
                       String.Join("--", dims)
                   @@>))

我想将所有参数收集在一个列表中。

我在代码中引用了我尝试过但没有起作用的内容。

[1]: [FS0010] Unexpected prefix operator in expression
     [FS0594] Identifier expected

[2]: [FS0446] The variable 'arg' is bound in a quotation but is used as part of a spliced expression. This is not permitted since it may escape its scope.

Answer 1

以以下方式破解您的解决方案实际上可以编译

InvokeCode = (fun args -> 
    let dims: string[] = Array.zeroCreate args.Length
    let mutable i = 0
    let inc () = i <- i + 1
    <@@
        while i < args.Length do
            dims.[i] <- %%args.[i]
            inc ()
        String.Join("--", dims)
    @@>

但是我怀疑您想将Quotations.Expr[]形状的[|Value ("a"); Value ("b"); Value ("c")|]转换为单个Quotations.Expr。

您可以通过以下方式使用Microsoft.FSharp.Quotations.Patterns中的模式从表达式中提取内容

InvokeCode = (fun args -> 
    let dims =
        args
        |> Array.choose (function | Value(value, _) -> value |> string |> Some | _ -> None)
        |> fun arr -> String.Join("--", arr)
    <@@ dims @@>

Answer 2

这种解决方案也可以基于评论中建议的答案：F# Type Provider development: When providing a method, how to access parameters of variable number and type?

ProvidedMethod(methodName = "GetContext", 
           parameters = [ for i in [ 1..3 ] do
                              yield ProvidedParameter("Param" + string i, typeof<string>) ], 
           IsStaticMethod = true, returnType = typeof<string>, 
           InvokeCode = (fun args -> 
               let dims = List.fold ( fun state e -> <@@ (%%string)::%%state @@>) <@@ []:List<string> @@> args
               <@@ 
                   String.Join("--", dims)
               @@>))

收集列表中的TypeProvider ProvidedMethod参数值

2 个答案: