f#

问题 I'm learning F#. I'm here because I had something hard to understand about value restriction. Here are the examples from the book I'm studying with. let mapFirst = List.map fst Since I had learned FP with haskell, I was pretty sure that this code would be well compiled, but it was not the case. It resulted error FS0030 (Sorry that I can't copy-paste fsi error message, since it was written in korean). Instead, I had to provide an explicit argument like: let mapFirst inp = List.map fst inp //

问题 With the latest VS for mac installed (8.5 preview) and the latest net core sdk (3.1.200) F# 4.7 should be supported. When I run the dotnet fsi, indeed language features are supported and the FSI shows F# 4.7 as the F# version. In VS for mac, in the preferences settings the exact command: /usr/local/share/dotnet/dotnet fsi is the path to the F# compiler. However, when creating a new fix file and trying F# language features, it doesn’t work and the FSI in VS for mac doesn’t compile the code.

问题 With the latest VS for mac installed (8.5 preview) and the latest net core sdk (3.1.200) F# 4.7 should be supported. When I run the dotnet fsi, indeed language features are supported and the FSI shows F# 4.7 as the F# version. In VS for mac, in the preferences settings the exact command: /usr/local/share/dotnet/dotnet fsi is the path to the F# compiler. However, when creating a new fix file and trying F# language features, it doesn’t work and the FSI in VS for mac doesn’t compile the code.

问题 This question already has answers here : F# how to return have value a tuple or null (3 answers) Closed 24 days ago . I have this type-correct C# function: static System.Tuple<int,int> f(int n) { switch (n) { case 0: return null; default: return System.Tuple.Create(n,n+1); } } I try to re-implement it in F#: let f = function | 0 -> null | n -> System.Tuple.Create(n, n+1) Type-checker disagrees, though: error FS0001: The type '('a * 'b)' does not have 'null' as a proper value. How do I re

问题 I want to process to types of a message Add x makes program remember number x Print makes it print all remembered numbers Why would I write this: open System type Message = | Add of int | Print let mailbox = new MailboxProcessor<Message>(fun inbox -> let rec loop history = async{ let! msg=inbox.Receive() match msg with | Add x -> return! loop(history + x.ToString()+" ") | Print -> printfn "%s" history return! loop(history) } loop "" ) [<EntryPoint>] let main argv = mailbox.Start() mailbox

问题 The msdn page documenting Records (F#) details record expressions for record construction and record patterns for deconstruction, the latter without naming them as such. Here's an example which uses both techniques for an arithmetic operator: // Simple two-dimensional generic vector defintion type 'a UV = { U : 'a; V : 'a } static member inline (+) ({ U = au; V = av }, { U = bu; V = bv }) = { U = au + bu; V = av + bv } This appears unwieldy and not very readable. For deconstruction, there are

问题 I have a set of F# scripts that call various libraries that we have created, many of them exposing asynchronous methods originally written in C#. Recently I found out the scripts stopped working (I think it's about half a year since I used them last time and they worked back then). I was trying to isolate the problem and came up with the following code that reproduces it: First, let's consider a library containing the following C# class: public class AsyncClass { public async Task<string>

问题 When I try to create some class like type MyType () = let func<'T> () = () The compiler says that there's an error: Explicit type parameters may only be used on module or member bindings But the MSDN says: A let binding at the module level, in a type, or in a computation expression can have explicit type parameters. A let binding in an expression, such as within a function definition, cannot have type parameters. Why documentation and compiler say different things? 回答1: This appears to be a

问题 When I try to create some class like type MyType () = let func<'T> () = () The compiler says that there's an error: Explicit type parameters may only be used on module or member bindings But the MSDN says: A let binding at the module level, in a type, or in a computation expression can have explicit type parameters. A let binding in an expression, such as within a function definition, cannot have type parameters. Why documentation and compiler say different things? 回答1: This appears to be a

问题 When I try to create some class like type MyType () = let func<'T> () = () The compiler says that there's an error: Explicit type parameters may only be used on module or member bindings But the MSDN says: A let binding at the module level, in a type, or in a computation expression can have explicit type parameters. A let binding in an expression, such as within a function definition, cannot have type parameters. Why documentation and compiler say different things? 回答1: This appears to be a