first-class-functions

问题 In the Swift documentation Apple says this: Closures are self-contained blocks of functionality that can be passed around and used in your code. Closures in Swift are similar to blocks in C and Objective-C and to lambdas in other programming languages. Which I thought was the definition of First-class functions And they also say this: Closures can capture and store references to any constants and variables from the context in which they are defined. This is known as closing over those

问题 i was going through a post post about how observer pattern can be implemented in python . on the same post there are these comments. 1) In python you may as well just use plain functions, the ‘Observer’ class isnt really needed. 2) This is great example of what Java programmers are trying to do once they switch to Python – they feel like Python is missing all that crap and try to “port” it. These comments imply that the observer pattern is not really useful in python and there exists other

问题 i try to write an event handler in a scalaFx app. I found followin solution: import scalafx.scene.control.ListView import javafx.scene.input.MouseEvent import javafx.event.EventHandler ... val list = new ListView[String] { onMouseClicked = new EventHandler[MouseEvent] { override def handle(event: MouseEvent) { doSomething(event) } } } But this seems to be very Java-style boilerplate code. Is there a way to do this with a first class function like this? onMouseClicked = (event: MouseEvent) =>

问题 What is a first class citizen function? Does Java supports first class citizen function? Edit: As mention on Wikepedia First class functions are a necessity for the functional programming style. Is there any other use of first class functions? 回答1: A language that considers procedures to be "first-class" allows functions to be passed around just like any other value . Languages like Java 7 (and earlier) and C "kind of" have this capability: C allows function pointers to be passed around, but

问题 What is a first class citizen function? Does Java supports first class citizen function? Edit: As mention on Wikepedia First class functions are a necessity for the functional programming style. Is there any other use of first class functions? 回答1: A language that considers procedures to be "first-class" allows functions to be passed around just like any other value . Languages like Java 7 (and earlier) and C "kind of" have this capability: C allows function pointers to be passed around, but

问题 I could not find a direct answer to this question yet in SO. Is there a predefined delegate with void (void) signature? 回答1: Action has the signature you're looking for. However, it doesn't mean the same thing as Runnable does: Runnable generally indicates that the run() method is intended to be run on a Thread, while Action makes no indication. For that you'd want ThreadStart, which has the same signature, and does make that indication. If all you need is a delegate with no parameters,

问题 I have the following code in F# live version at https://repl.it/repls/CarefulGiganticExtraction let inline tryParse text = let mutable r = Unchecked.defaultof<_> (^a : (static member TryParse: string * ^a byref -> bool) (text, &r)), r let inline tryParseWithDefault (defaultVal:'a) text = match tryParse text with | true, v -> v | _ -> defaultVal type TextBox(text:string) = member this.Text = text type View() = member this.Name = "View" type State = { count: int } module Binder = let inline

问题 I want to store a function like print in a variable so that I can just type something short like p , e.g: In Scheme : (define print display) (print "Hello world\n") ;; alternate way (define print 'display) ((eval print) "Hello world\n") The same approach does not seem to work in Common Lisp : (defvar p 'print) ;;(print (type-of p)) (p "Hello world") ;; Attempt 1 ((eval p) "Hello world") ;; >> Attempt 2 ((eval (environment) p) "Hello world") ;; Attempt 3 I'm getting this error with Attempt 1

问题 I've been successfully passing no-argument functions around in PowerShell using ScriptBlocks. However, I can't get this to work if the function has arguments. Is there a way to do this in PowerShell? (v2 preferably) Function Add([int] $x, [int] $y) { return $x + $y } Function Apply([scriptblock] $s) { write-host ($s.Invoke(1,2)) } Then Apply { Add } writes 0 to the console. Apply does invoke Add , but doesn't pass any arguments in (i.e. uses the default [int] values of 0 and 0) 回答1: Ok, I

问题 I checked out the latest Ruby version, to play a bit with the latest changes. The first thing I tried to do was call a Ruby lambda/block/proc just like you'd do with a Python callable. a = lambda {|x| puts x} a.call(4) # works, and prints 4 a[4] # works and prints 4 a.(4) # same a(4) # undefined method 'a' for main:Object Why isn't the last call possible? Will it ever be? 回答1: AFAIK it's because ruby doesn't let you define the () method for an object. The reason it doesn't let you define the