higher-order-functions | 易学教程

Constructing a qi::rule with a function attribute

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问题 I'm trying to create a rule that returns a function<char(char const *)> constructed by currying a Phoenix expression. E.g., start = int_[_val = xxx]; rule<Iterator, function<char(char const *)> start; What should xxx be so that parsing the string "5" should give me a function that gives me the fifth character of its input? I've tried things like lambda(_a = arg1)[arg1[_a]](_1) might work, but I've not been able to hit on the magic formula. In other words, I'd like the attribute to curry arg2

Flow error when passing props through flow-typed higher ordered components

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问题 Consider the following code. Wrapper1 renders Wrapper2 , passing into it the Final component as a prop, along with a couple props that Final ultimately expects, finalProp and w2prop . Wrapper2 then renders the component passed into it, passing along all its props to that rendered component. In this case, the Final component is getting rendered by Wrapper2 , and it is receiving its needed props. However, Flow does not understand this. I'm receiving the following two errors: property finalProp

Can someone explain to me how this function works?

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问题 I'm learning to code and I'm trying to understand Higher Order Functions and abstractions. I don't understand how this piece of code runs to return "true". function greaterThan(n) { return function(m) { return m > n; }; } var greaterThan10 = greaterThan(10); console.log(greaterThan10(11)); Thanks for the help. 回答1: The function greaterThan returns a function when called. The returned function has access to all the members of the outer function even after the function has returned. This is

reversing a list in OCaml using fold_left/right

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问题 UPDATE - Solution Thanks to jacobm for his help, I came up with a solution. // Folding Recursion let reverse_list_3 theList = List.fold_left (fun element recursive_call -> recursive_call::element) [] theList;; I'm learning about the different ways of recursion in OCaml (for class) and for some exercise, I'm writing a function to reverse a list using different recursion styles. // Forward Recursion let rec reverse_list_forward theList = match theList with [] -> [] | (head::tail) -> (reverse

Different brackets style on Scala function definition parameter list

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问题 What is the difference of the following two function definitions in Scala: 1) def sum(f: Int => Int)(a: Int, b: Int): Int = { <code removed> } 2) def sum(f: Int => Int, a: Int, b: Int): Int = { <code removed> } ? SBT's console REPL gives different value for them so looks if they are somehow different: sum: (f: Int => Int, a: Int, b: Int)Int sum: (f: Int => Int)(a: Int, b: Int)Int 回答1: The first definition is curried, so that you can provide a and b at another time. For instance, if you know

How to map scalar twig filter to array

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问题 I have a simple array of floats. And I need to show it as comma separated string. {{ arr|join(', ') }} is bad solution because of excessive insignificant accuracy. {% for val in arr %} {{val|number_format(2)}}, {% endfor %} is bad because of extra comma at the end. I would like to do something like this: {{ arr|map(number_format(3))|join(', ') }} but I have not found filter map or similar filter it Twig. Аnd I don't know how to implement such filter. 回答1: Quick Answer (TL;DR) This question

How can I create shared state for HOC?

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问题 I have created LoadBookHOC which is wrapped with BookDetails and BookSummary component. LoadBookHOC.js const LoadBookHOC = InnerComponent => class LoadBook extends React.Component { constructor(){ super(); this.state={ book: [] }; } set= obj => this.setState(obj); render(){ return( <InnerComponent {...this.props} hocState={this.state} hocSetState={this.set} /> ); } } BookDetails.js this.hocSetState({book: <new data>}); BookSummary.js this.hocSetState({book: <new data>}); Whenever this.props

How to do Nested For Loops in Functional Style

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I'm in the process of learning functional programming, and completely getting rid of for loops has been a challenge sometimes, because they provide so much control and freedom. Below is an example of checking if a string is an isogram or not (no letters should be repeated). With nested for loops, it became an easy solution. Is there a way to do this the functional way with any high order functions or anything else? Any suggestion would be a huge help. Code: function isIsogram(string) { let array = string.split(''); let condition = true; for (let i = 0; i < string.length; i++) { //first loop

Confusing Scala Higher order function call syntax [duplicate]

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This question already has answers here : What is the formal difference in Scala between braces and parentheses, and when should they be used? (8 answers) Closed 6 years ago . I am a little confused by the various uses of the 'block' {...} contruct in scala especially when calling a higher order function like in the following example. def higherOrder(func: Int => Int): Int = { func(4) } val f = ((x: Int) => x*x) Then I can call higherOrder like so: higherOrder(f) , or higherOrder {f} , or higherOrder { x => x*x } (1) is obvious, but I can not wrap my head around how the syntax for (2) and (3)

reversing a list in OCaml using fold_left/right

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UPDATE - Solution Thanks to jacobm for his help, I came up with a solution. // Folding Recursion let reverse_list_3 theList = List.fold_left (fun element recursive_call -> recursive_call::element) [] theList;; I'm learning about the different ways of recursion in OCaml (for class) and for some exercise, I'm writing a function to reverse a list using different recursion styles. // Forward Recursion let rec reverse_list_forward theList = match theList with [] -> [] | (head::tail) -> (reverse_list_1 tail) @ [head];; // Tail Recursion let rec reverse_list_tail theList result = match theList with [