FAQ Database Discussion Community


Higher order python functions and setting their attributes correctly

python,higher-order-functions
I'm currently writing a function that makes and returns a new function to create polynomial expressions. I want the function to store the coefficients of the polynomial and the polynomial itself in string form. However, it doesn't seem that I can set either of the attributes without the interpreter insisting...

Creating a function that can be invoked a given number of times and no more

javascript,function,higher-order-functions
Say you have a function that you can input an alert with "hey" and you want to allow that to happen a given number of times — say 2, or 3, or whatever you want — and then after that given number alerts the same amount of times a negative...

Higher order function: “Cannot invoke 'map' with an argument list of type '((_) -> _)'”

swift,higher-order-functions
I would like to use a swift higher order function (map) to remove all Subviews from a given UIView.subviews array. The line (cell.contentView.subviews as [UIView]).map { $0.removeFromSuperView() } causes the error "Cannot invoke 'map' with an argument list of type '((_) -> _)'" I would like to know what the...

TypeScript doesn't seem to allow higher-order function argument generics

generics,typescript,higher-order-functions
I've run into a weird problem in my TypeScript code, which causes it to bail out of compilation with the following error: src/mutable_list.ts(47,25): 1005 ',' expected. The code I'm trying to compile is as follows: 44 export function flatMap<V,I,W,J>( 45 list: IMutableList<V,I>, 46 getFn: (V) => IList<W,J>, 47 setFn: (IList<W,J>)...

How to effectively get indices of 1s for given binary string using Scala?

scala,functional-programming,higher-order-functions
Suppose we have a binary string such as 10010010. All I want is a function returning indices of 1s for that string: indicesOfOnes("10010010") -> List(0, 3, 6) indicesOfOnes("0") -> List() And what I implemented is: def indicesOfOnes(bs: String): List[Int] = { val lb = ListBuffer[Int]() bs.zipWithIndex.foreach { case (v, i)...

Understanding higher order functions in PHP [closed]

php,higher-order-functions
I find this piece of code complicated to understand. I will be grateful if i can understand this with illustrations and details. $data = array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); function get_algorithm($rand_seed_fnc) { return (odd_even($rand_seed_fnc())) ? function($value) { return $value * $value; } : function($value) use...

Having trouble stepping through function that reduces an array of functions

javascript,functional-programming,reduce,higher-order-functions
When using the reduce method on an array of functions I am having difficulty tracing through how reduce works on the array exactly. comboFunc(num, functionsArr) { return functionsArr.reduce(function (last, current) { return current(last); }, input); } so with functionsArr = [add, multi] and the functions add and multi being function...

Is recursion a smell (in idiomatic Clojure) because of of zippers and HOFs?

recursion,clojure,higher-order-functions,idiomatic,zipper
The classic book The Little Lisper (The Little Schemer) is founded on two big ideas You can solve most problems in a recursive way (instead of using loops) (assuming you have Tail Call Optimisation) Lisp is great because it is easy to implement in itself. Now one might think this...

Why can't I pass a trait to a Scala function and call it: response[A: T](r: A) = { r(value) }

scala,higher-order-functions,trait
I'm trying to implement a generic response function that takes an Int and an object, then calls apply(e: Int) on the provided object (which will return a new instance). Here's what I have so far: trait GPResponse { abstract def apply(error: Int) } trait GPResponseMapping { def response[A: GPResponse](error: Int,...

Trouble understanding a basic concept in Javascript Higher Order Functions

javascript,higher-order-functions
I am having a little bit of trouble understanding Higher Order Functions in javascript. Can someone explain to me the difference of what's going on in these two situations? Scenario 1: // A function that takes in a number (x) and adds one to it. function doMath(x){ return function (x){...

Higher order javascript functions

javascript,anonymous-function,higher-order-functions
can someone explain to me what is going on in the following code. The function is receiving n as parameter, so where is the m coming from? The whole code is confusing.. if someone can explain? function greaterThan(n) { return function(m) { return m > n; }; } var greaterThan10...

What's the proper way of passing named functions to Javascript's higher-order functions?

javascript,functional-programming,higher-order-functions
I'm trying to use Javascript's higher-order functions for functional programming. However, they are producing unexpected results: ['1','2','3','4'].map(parseInt) // [1, NaN, NaN, NaN] ['1','2','3','4'].map(function(x){ return parseInt(x) }) // [1, 2, 3, 4] I expected these two calls to Array.prototype.map to both return [1, 2, 3, 4]. How can I map parseInt()...

Create a quotient-lifted type with polymorphism over working set and equivalence relation in Isabelle/HOL

set,higher-order-functions,isabelle,theorem-proving,isar
I would like to create a quotient type with quotient_type in Isabelle/HOL in which I would left "non-constructed" the non-empty set S and the equivalence relation ≡. The goal is for me to derive generic properties w.r.t. S and ≡ over the quotient-lifted set S/≡. In this way, it would...

Using the reduce method to eliminate any duplicated numbers

javascript,reduce,higher-order-functions
I am trying to use the reduce method as follows to eliminate duplicates however, it is not quite working: var unique = function(array) { array = array.sort(function(a,b) {return a-b;}); var noDup = [array[0]]; array.reduce(function(c,d) { if(c!==d) { noDup.push(d); return d; } }); return noDup; }; var x = [9,2,1,5,9,1,1,4,2,9];//==>[1, 1,...

JavaScript function not working as intended

javascript,higher-order-functions
I've been working through a question and need some help! I've created my own each function below: var myArray = [1,2,3,4,5]; // this will be running through the collection parameter var each = function (collection, callback) { if (Array.isArray(collection)) { for (i=0; i<collection.length; i++) { callback(collection[i]); }; } else {...

Swift compiler error: “Cannot invoke 'map' with an argument list of type '((_) -> _)'”

ios,swift,higher-order-functions
I have a range that I'm trying to map on, but I'm getting the error “Cannot invoke 'map' with an argument list of type '((_) -> _)'” Here's what the code looks like let patterns = (0...5).map { verseNum in let verseNumberStartPattern = "\"verse-num\">\(verseNum)</span>(?:\\s?<span>)?(.*?)<" let chapterStartPattern = "\"chapter-num\">\\s\(parsedVerse.chapterStart)\\s</span>" if verseNum...

Is juxt the opposite of map? (In Clojure)

dictionary,clojure,higher-order-functions
In Clojure we see the following examples of using map: (map inc [1 2 3 4 5]) ;;=> (2 3 4 5 6) We observe that map takes a function and applies it to each element in a collection. In Clojure we see the following example of using juxt: ((juxt...

Python: Higher Order Functions with Methods

python,higher-order-functions
In Python, is there anyway to pass a method to a higher order function, as you would if passing a regular function? For example, let's say I have a string, "str", and depending on some condition, "cond", I want to apply some arbitrary method, "meth", to the string and return...

How to use swift flatMap to filter out optionals from an array

swift,functional-programming,optional,higher-order-functions,flatmap
I'm a little confused around flatMap (added to Swift 1.2) Say I have an array of some optional type e.g. let possibles:[Int?] = [nil, 1, 2, 3, nil, nil, 4, 5] In Swift 1.1 I'd do a filter followed by a map like this: let filtermap = possibles.filter({ return $0...