f#

问题 I'm trying to figure out how to properly test exceptions with FsUnit. Official documentation states, that to test for exceptions I have to right something like this: (fun () -> failwith "BOOM!" |> ignore) |> should throw typeof<System.Exception> But, if I don't mark my test method with [<ExpectedException>] attribute it will always fail. Sounds reasonable because if we want to test for exceptions we have to add such attribute in C# + NUnit. But, as long as I've added this attribute it doesn't

问题 Looking at http://msdn.microsoft.com/en-us/library/dd287191(v=vs.110).aspx, it seems that ConcurrentDictionary and all of its friends in the System.Collections.Concurrent namespace are available for use in a Portable Class Library. However, when I create either an F# or C# Portable Class Library, even if I explicitly add a reference to mscorlib.dll , the compilation fails when using ConcurrentDictionary . Why? 回答1: The term "Portable" should be loosely applied right now. When you create the

问题 It is nice to have a wrapper for every primitive value, so that there is no way to misuse it. I suspect this convenience comes at a price. Is there a performance drop? Should I rather use bare primitive values instead if the performance is a concern? 回答1: Yes, there's going to be a performance drop when using single-case union types to wrap primitive values. Union cases are compiled into classes, so you'll pay the price of allocating (and later, collecting) the class and you'll also have an

问题 I am currently experimenting with F#. The articles found on the internet are helpful, but as a C# programmer, I sometimes run into situations where I thought my solution would help, but it did not or just partially helped. So my lack of knowledge of F# (and most likely, how the compiler works) is probably the reason why I am totally flabbergasted sometimes. For example, I wrote a C# program to determine perfect numbers. It uses the known form of Euclids proof, that a perfect number can be

问题 Hi I am wanting to create in F# a 2D array of size 1000x1000, with the value in the array at any position to be initialized as the same vaue of its index using the 2DArray class. i.e. position [1,1] would have value (1,1). I have looked at the syntaxt of Array2D.create, but am not sure how to use it properly... Any help would be appreciated... 回答1: Use Array2D.init to pass a function to specify the initial value of each. let a = Array2D.init 3 3 (fun x y -> (x,y)) printfn "%A" a 来源： https:/

问题 I find that I tend to write long source files in F#. Some open source projects in F# also have long source files, e.g. FPersec and F# for excel. So it would be very helpful if code folding (even very limited support) is available in VS for F#. E.g. in a module, we can fold out functions that are stable, only leave functions that are subject to change unfold. Is this feature easy to be supported, e.g. by a third party vendor? 回答1: Unfortunately, this feature is not available in F# (neither

问题 I have been teaching myself F# lately, and I come from an imperative (C++/C#) background. As an exercise I have been working on functions that can do stuff with matrices, like add, multiply, get determinants, etc. Everything is going well in this regard, but I find that maybe I am not making the best decisions when it concerns handling invalid inputs, for example: // I want to multiply two matrices let mult m1 m2 = let sizeOK = validateDims m1 m2 // Here is where I am running to conceptual

问题 I have the following sample code. The objective is to run SQL statement with multiple input parameters. [<Literal>] let connectionString = @"Data Source=Localhost;Initial Catalog=Instrument;Integrated Security=True" [<Literal>] let query = "SELECT MacroName, MacroCode FROM Instrument WHERE MacroCode IN (@codeName)" type MacroQuery = SqlCommandProvider<query, connectionString> let cmd = new MacroQuery() let res = cmd.AsyncExecute(codeName= [|"CPI";"GDP"|]) |> Async.RunSynchronously However,

问题 Curried functions in F#. I get the bit where passing in a subset of parameters yields a function with presets. I just wondered if passing all of the parameters is any different. For example: let addTwo x y = x + y let incr a = addTwo 1 let added = addTwo 2 2 incr is a function taking one argument. Is added an int or a function? I can imagine an implementation where "added" is evaluated lazily only on use (like Schroedinger's Cat on opening the box). Is there any guarantee of when the addition

问题 I've started researching some ideas in algorithms using VS2010 and F# interactive. So, I've created a DebugScript.fsx , I write some code there and eventually send it to F#Int to test it. At some some moment I need to catch a bug. But I can't place a breakpoint even in a simple for loop: for i in stringarray do printfn "%s" i When I press F9 to set a breakpoint, the VS show a red circle with a warning sign. The hint for it is "The breakpoint will not currently be hit". Surely, I did open