functional-programming

问题 I'm coming from C#/PHP and trying to get my head around Javascript's idea that functions are variables/objects and have quasi constructors, etc. Can anyone explain why the following code functions as it does, namely: Why isn't "2" displayed when instantiating the variable/function test ? Why isn't "1" displayed when executing the variable/function test ? code: var setup = function () { console.log(1); return function() { console.log(2); }; }; var test = setup(); // 1 test(); // 2 test(); // 2

问题 I am trying to write a simple procedure in Lisp to insert an element into binary search tree. I represented the tree as a list: the first element in the tree is the root the second element is the left sub-tree the third element is the right sub-tree This is my code: (define Insert (lambda (x T) (if (null? T) (list x '() '()) (if (> x (car T)) (list (car T) (cadr T) (Insert x (list (caddr T)))) (list (car T) (Insert x (cadr T)) (list (caddr T))))))) When I call the procedure like this: (Insert

问题 Lets say I want to do the following: (define (foo lst x) (filter function lst) but function takes in 2 arguments (and function was given to me), one being the list lst it will use, and the other being x . Syntactically, how would I change that line to pass in the second argument? Sorry I am new to Scheme/DrRacket. 回答1: Try this, using curry: (define (foo lst x) (filter (curry function x) lst)) That is, assuming that function takes as first parameter x and as second parameter each one of the

问题 I'm trying to delay evaluation for a bit, and so I prefer to work with functions as long as possible. I have class Function which defines composition and pointwise arithmetics for functions: from functools import reduce def compose(*funcs): ''' Compose a group of functions f1, f2, f3, ... into (f1(f2(f3(...)))) ''' result = reduce(lambda f, g: lambda *args, **kaargs: f(g(*args, **kaargs)), funcs)) return Function(result) class Function: ''' >>> f = Function(lambda x : x**2) >>> g = Function

问题 I know I can do instanceOf checks against Function1 or Function2 etc but is there a generic way to see if something is function or not (it can have arbitray number of args). I tried defining something like this: type FuncType = (Any*) -> Any But that did not work either. Basically I have some code that looks like this: call = (name: Any, args: Any*) -> if name.isFunction then name.castAs[Function].apply(args) else name aFunction = (name: String) => "Hello " + name notAFunction = "Hello rick"

问题 Suppose I have an imperative algorithm that keeps two indices left and right and moves them from left to right and from right to left var left = 0 var right = array.length - 1 while (left < right) { .... } // move left and right inside the loop Now I would like to write this algorithm without mutable indices. How can I do that ? Do you have any examples of such algorithms ? I would prefer a non-recursive approach. 回答1: You can map pairs of elements between your list and its reverse, then go

问题 As an exercise my team is looking at learning functional programming. One of the factors to choose a language is its support in Eclipse. Any language with Eclipse plug-in is fine but what language offers the best free plug-in? Bonus question: the best online/book tutorial for this language. 回答1: I don't know if it is the best, but it is evolving and improving fast: Scala IDE (up to Scala2.8.1RC1 right now) As for the best online Scala book: Programming Scala (Creative Commons Attribution

问题 I already know the benefit of immutability over mutability in being able to reason about code and introducing less bugs, especially in multithreaded code. In creating structs, though, I cannot see any benefit over creating a completely immutable struct over a mutable one. Let's have as an example of a struct that keeps some score: struct ScoreKeeper { var score: Int } In this structure I can change the value of score on an existing struct variable var scoreKeeper = ScoreKeeper(score: 0)

问题 I quite don't understand how the interface thing works in OCaml. Let's see an example: About the 'a So what the meaning of 'a here? I mean I understand that when describing the functions, 'a means arbitrary type . Then what's its meaning here? Does it mean arbitrary set ? Also, Why put 'a in front of set ? abstract When explaining this example, Jason Hickey's Introduction to Objective Caml says: we need to define a polymorphic type of sets ’a set abstractly . That is, in the interface we will

问题 I'm reading a book with the following: sealed trait Currency case object USD extends Currency ... other currency types case class Money(m: Map[Currency, BigDecimal]) { ... methods defined } The discussion goes on to recognize certain types of operations on Money as being Monoidal so we want to create a Monoid for Money . What comes next though are listings I can't parse properly. First is the definition of zeroMoney . This is done as follows: final val zeroMoney: Money = Money(Monoid[Map