[英]Does F# have a language construct to access the lexical scope (like python locals()/globals())
When writing tests in F# I am trying to generate useful messages about the state that caused errors. 用F#编写测试时,我试图生成有关导致错误的状态的有用消息。 In python I would include all the locals(), so they are easily accessible in the test trace. 在python中,我将包括所有locals(),因此可以在测试跟踪中轻松访问它们。
Is there a similar construct in F#? F#中是否有类似的构造?
I have been searching the web and the excellent fsharpforfunandprofit site, as well as gone through the list of reserved keywords. 我一直在搜索网络和出色的fsharpforfunandprofit网站,并浏览了保留关键字列表。
Here is some code I would like to be able to do. 这是我想做的一些代码。
[<Property>]
let some_test x =
let example_inner_helper y =
let z = y + x
// Example of the meta-construction i am looking for
let scope = {|
local = {| y = y; z = z |};
capture = {|
local = {| x = x |};
capture = {| (* ... *) |};
|};
|}
x = z |@ sprintf "require %A=%A (%A)" x y scope
example_inner_helper (x+x)
Which would produce the very useful output 这将产生非常有用的输出
Tests.some_test
Source: Tests.fs line 105
Duration: 51 ms
Message:
FsCheck.Xunit.PropertyFailedException :
Falsifiable, after 1 test (1 shrink) (StdGen (387696160,296644521)):
Label of failing property: require 1=2 ({ capture = { capture = {}
local = { x = 1 } }
local = { y = 2
z = 3 } })
Original:
-1
Shrunk:
1
However, I am having to explicitly capture the information that a construct like "scope" could automatically provide. 但是,我必须明确捕获诸如“范围”之类的结构可以自动提供的信息。 Resulting in ugly, error prone stuff like 导致丑陋,容易出错的东西,例如
let ``firstAscendingLastDescendingPartE Prop`` (a: Extent<int>) b =
let validateT ea eb =
let checkXbeforeY ex ey headx restx =
match restx with
| ValueNone -> // No rest
(ex = headx) |@ sprintf "no rest: ex = headx (%A = %A)" ex headx
.&. ((intersectE ex ey) = ValueNone) |@ sprintf "no rest: ex ∩ ey = ∅ (%A ∩ %A)" ex ey
| ValueSome rex -> // Some rest ->
// headx and restx combines to ex
((expandE headx rex) = ex) |@ sprintf "rest: headx+rex = ex (%A...%A)" headx rex
.&. (exactlyTouchesE headx rex) |@ sprintf "rest: headx ends where rex starts (ex=%A ey=%A headx=%A restx=%A)" ex ey headx restx
.&. (exactlyTouchesE headx ey) |@ sprintf "rest: headx ends where ey starts (ex=%A ey=%A headx=%A restx=%A)" ex ey headx restx
....
(Of course, I don't care about the actual type of the "scope" construct) (当然,我不在乎“ scope”构造的实际类型)
I already looked at unquote which is quite cute and looks about right. 我已经看过unquote了,它很可爱,看起来不错。 But it limits the code quite a bit: 但是它限制了代码很多:
I have code that looks a bit like: 我有看起来像的代码:
[<Struct>]
type X<'T when 'T: comparison and 'T: equality> =
val public first: 'T
val public last: 'T
new (first: 'T, last: 'T) = {
first =
(if last <= first then
invalidOp (sprintf "first < last required, (%A) is not < (%A)" first last)
else first)
last = last;
}
// ..
So I have issues with tests using the two constructs below (causing the above errors). 因此,我在使用以下两种结构的测试中遇到了问题(导致上述错误)。
let quote_limits () =
let x first last = X(first, last)
let validate (x: X<'a>) = x.first < x.last
let a = X(0, 1)
<@ a.first = 0 @> |> test
<@ validate a @> |> test
The first one i can workaround with functions to access the struct parts, but the limitation on generics is PITA. 我可以使用第一种方法解决访问结构部分的功能,但是泛型的局限性是PITA。
I don't think there is a way to do this, even in principle. 我认为即使在原则上也没有办法做到这一点。 F# code gets compiled to .NET bytecode which is stack based and so local variables do not really (in general) exist in the compiled code. F#代码被编译为基于堆栈的.NET字节码,因此本地变量实际上(通常)并不真正存在于编译后的代码中。 You might be able to get some globals (they are static members) or perhaps use debug information somehow, but I don't think there is a standard way of doing that. 您也许可以获取一些全局变量(它们是静态成员),或者也许以某种方式使用调试信息,但是我不认为有这样做的标准方法。
That said, in your specific case, F# actually has a nice option using the unquote testing framework. 就是说,在您的特定情况下,使用unquote测试框架,F#实际上有一个不错的选择。 This lets you put test code in F# quotations and it then shows how this quotation evaluates. 这使您可以将测试代码放入F#引号中,然后显示该引号的评估方式。 For example: 例如:
let some_test x =
let example_inner_helper y =
<@
let z = y + x
x = z
@> |> test
example_inner_helper (x+x)
some_test 10
Here, I defined the local variable z
inside the quotation. 在这里,我在引号内定义了局部变量z
。 When you run the test, unquote will print the individual evaluation steps and you can see the value of z
there: 运行测试时,取消引用将打印各个评估步骤,您可以在其中看到z
的值:
Test failed:
let z = y + x in x = z
let z = 20 + 10 in x = z
let z = 30 in x = z
false
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