F# 中有什么方法可以获取传递给函数的变量的名称吗?
例子:
let velocity = 5
let fn v = v.ParentName
let name = fn velocity // this would return "velocity" as a string
先感谢您
编辑:
为什么这段代码不起作用?它作为值匹配,因此我无法检索“变量”名称。
type Test() =
let getName (e:Quotations.Expr) =
match e with
| Quotations.Patterns.PropertyGet (_, pi, _) -> pi.Name + " property"
| Quotations.Patterns.Value(a) -> failwith "Value matched"
| _ -> failwith "other matched"
member x.plot v = v |> getName |> printfn "%s"
let o = new Test()
let display () =
let variable = 5.
o.plot <@ variable @>
let runTheCode fn = fn()
runTheCode display
最佳答案
为了完成 Marcelo 的回答,是的,您可以为此任务使用引号:
open Microsoft.FSharp.Quotations
open Microsoft.FSharp.Quotations.Patterns
let velocity = 5
let fn (e:Expr) =
match e with
| PropertyGet (e, pi, li) -> pi.Name
| _ -> failwith "not a let-bound value"
let name = fn <@velocity@>
printfn "%s" name
正如您在代码中看到的那样,F# let-bound 顶部定义值(函数或变量)被实现为类的属性。我再也找不到显示如何使用 C# 以功能方式重写一段 F# 代码的链接。看到代码,很明显为什么需要
PropertyGet
图案。现在如果你也想计算表达式,你需要安装 F# powerpack和引用
FSharp.PowerPack.Linq
在你的项目中。它添加了
EvalUntyped
Expr
上的方法类(class)..open Microsoft.FSharp.Linq.QuotationEvaluation
let velocity = 5
let fn (e:Expr) =
match e with
| PropertyGet (eo, pi, li) -> pi.Name, e.EvalUntyped
| _ -> failwith "not a let-bound value"
let name, value = fn <@velocity@>
printfn "%s %A" name value
如果您需要为实例的方法执行此操作,我将这样做:let velocity = 5
type Foo () =
member this.Bar (x:int) (y:single) = x * x + int y
let extractCallExprBody expr =
let rec aux (l, uexpr) =
match uexpr with
| Lambda (var, body) -> aux (var::l, body)
| _ -> uexpr
aux ([], expr)
let rec fn (e:Expr) =
match e with
| PropertyGet (e, pi, li) -> pi.Name
| Call (e, mi, li) -> mi.Name
| x -> extractCallExprBody x |> fn
| _ -> failwith "not a valid pattern"
let name = fn <@velocity@>
printfn "%s" name
let foo = new Foo()
let methodName = fn <@foo.Bar@>
printfn "%s" methodName
只是回到显示 EvalUntyped
用法的代码片段。 ,您可以为 Expr
添加显式类型参数如果您想要/需要保持类型安全,请使用向下转换 ( :?>
):let fn (e:Expr<'T>) =
match e with
| PropertyGet (eo, pi, li) -> pi.Name, (e.EvalUntyped() :?> 'T)
| _ -> failwith "not a let-bound value"
let name, value = fn <@velocity@> //value has type int here
printfn "%s %d" name value
关于function - 如何使用 F# 获取作为参数进入函数的变量的名称?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/2736192/