f#

问题 I have installed Visual Studio 2017 with F# support on my PC and I have MSBuild targets in C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\Microsoft\VisualStudio\v15.0\FSharp and F# 4.1 SDK in C:\Program Files (x86)\Microsoft SDKs\F#\4.1 I have installed Build Tools for Visual Studio 2017 (from https://www.visualstudio.com/thank-you-downloading-visual-studio/?sku=BuildTools&rel=15 ) but there is no option to install F# SDK so building F# projects using MSBuild 15 fails.

问题 I implemented a Fisher-Yates shuffle recently, which used List.permute to shuffle the list, and noted that as the size of the list increased, there was a significant performance decrease. I suspect this is due to the fact that while the algorithm assumes it is operating on an array, permute must be accessing the list elements by index, which is O(n). To confirm this, I tried out applying a permutation to a list to reverse its element, comparing working directly on the list, and transforming

问题 I implemented a Fisher-Yates shuffle recently, which used List.permute to shuffle the list, and noted that as the size of the list increased, there was a significant performance decrease. I suspect this is due to the fact that while the algorithm assumes it is operating on an array, permute must be accessing the list elements by index, which is O(n). To confirm this, I tried out applying a permutation to a list to reverse its element, comparing working directly on the list, and transforming

问题 I'm trying to query data with F# SqlDataProvider but I got strange error when I'd like to use groupBy function my init code : r# "packages/FSharp.Data.2.2.5/lib/net40/FSharp.Data.dll" r# "packages/SQLProvider.1.0.0/lib/FSharp.Data.SQLProvider.dll" r# "packages/FSharp.Data.TypeProviders.5.0.0.2/lib/net40/FSharp.Data.TypeProviders.dll" open FSharp.Data open FSharp.Data.Sql open FSharp.Data.TypeProviders open FSharp.Linq open System.Text.RegularExpressions open System open System.Data type

问题 Is it possible to add constant field values to F# discriminated unions? Can I do something like this? type Suit | Clubs("C") | Diamonds("D") | Hearts("H") | Spades("S") with override this.ToString() = // print out the letter associated with the specific item end If I were writing a Java enum, I would add a private value to the constructor like so: public enum Suit { CLUBS("C"), DIAMONDS("D"), HEARTS("H"), SPADES("S"); private final String symbol; Suit(final String symbol) { this.symbol =

问题 I am struggling with the following: I have a system that has its main flow and has two background threads that can be started and stopped, but they're generally very long running as they stop only during configuration changes. I found that the cancellation token in F# gets checked at async points in the code. The worker threads do not perform any async operations; they are doing background work but nothing is asynchronous. A simplified version looks like that: let workerThread (someParameters

问题 I know how to catch specific exceptions as in the following example: let test_zip_archive candidate_zip_archive = let rc = try ZipFile.Open(candidate_zip_archive.ToString(), ZipArchiveMode.Read) |> ignore zip_file_ok with | :? System.IO.InvalidDataException -> not_a_zip_file | :? System.IO.FileNotFoundException -> file_not_found | :? System.NotSupportedException -> unsupported_exception rc I am reading a bunch of articles to see if I can use a generic exception in the with , like a wildcard

问题 This is a question about working with FParsec's ParserResult. Is there a cleaner implementation of match_result to pull out the XKEYVALUE or XATTRIBUTES contained inside the ParserResult without two nested matches? The following code works as a F# console app... // Learn more about F# at http://fsharp.org open System open FParsec // Types type XKEYVALUE = string * string type XATTRIBUTES = Map< string, string> type PARSER_RESULT_XML = | PR_XKEYVALUE of ParserResult<XKEYVALUE, unit> | PR

问题 This is a question about working with FParsec's ParserResult. Is there a cleaner implementation of match_result to pull out the XKEYVALUE or XATTRIBUTES contained inside the ParserResult without two nested matches? The following code works as a F# console app... // Learn more about F# at http://fsharp.org open System open FParsec // Types type XKEYVALUE = string * string type XATTRIBUTES = Map< string, string> type PARSER_RESULT_XML = | PR_XKEYVALUE of ParserResult<XKEYVALUE, unit> | PR

问题 I am trying to use FSharp.Data's HTML Parser to extract a string List of links from href attributes. I can get the links printed out to console, however, i'm struggling to get them into a list. Working snippet of a code which prints the wanted links: let results = HtmlDocument.Load(myUrl) let links = results.Descendants("td") |> Seq.filter (fun x -> x.HasClass("pagenav")) |> Seq.map (fun x -> x.Elements("a")) |> Seq.iter (fun x -> x |> Seq.iter (fun y -> y.AttributeValue("href") |> printf "%A