state
How are mutable arrays implemented in Haskell?
How are arrays, having O(1) time to access or modify an indexed element, implemented in Haskell They are implemented via primitive operations in the runtime system for memory reads and writes. The safety of the side effecting action of destructively writing to memory is ensured via the use of monads to linearize access to the … Read more
How to maintain the state of widget in ListView?
Add the AutomaticKeepAliveClientMixin mixin to your State of your StatefulWidget (Item widget), override the wantKeepAlive method and return true. class _MarkWidgetState extends State<MarkWidget> with AutomaticKeepAliveClientMixin{ … @override Widget build(BuildContext context) { // call this method. super.build(context); … } @override bool get wantKeepAlive => true; } More info here: https://docs.flutter.io/flutter/widgets/AutomaticKeepAliveClientMixin-mixin.html
Can a `ST`-like monad be executed purely (without the `ST` library)?
tl;dr: It’s not possible without adjustments to the definition of PT. Here’s the core problem: you’ll be running your stateful computation in the context of some sort of storage medium, but said storage medium has to know how to store arbitrary types. This isn’t possible without packaging up some sort of evidence into the MkRef … Read more
ReactJS How do you switch between pages in React?
I’d recommend you to check react-router to solve this situation It easily allows you to create custom routes like this: import React from “react”; import { BrowserRouter as Router, Route, Link } from “react-router-dom”; const BasicExample = () => ( <Router> <div> <ul> <li> <Link to=”/”>Home</Link> </li> <li> <Link to=”/about”>About</Link> </li> <li> <Link to=”/topics”>Topics</Link> </li> … Read more
In javascript, how can I uniquely identify one browser window from another which are under the same cookiedbased sessionId
you could set your own window name, the exact syntax escapes me right now, but you can use the current time and session id to create a unique id on window load, then use that id This would be done the same way you set a name in the javascript window.open() function, (but you can … Read more
Should you use “extends” or “with” keyword for ChangeNotifier? – Flutter
You can use either extends (to inherit) or with (as a mixin). Both ways give you access to the notifyListeners() method in ChangeNotifier. Inheritance Extending ChangeNotifier means that ChangeNotifier is the super class. class MyModel extends ChangeNotifier { String someValue=”Hello”; void doSomething(String value) { someValue = value; notifyListeners(); } } If your model class is … Read more
I do not understand the concept of Non Deterministic Turing Machine [closed]
In a Non Deterministic Turing machine, in each branch – you do both possibilities – and only when you are done you “choose” which one is the one you need for the solution (if one exists). For example, let’s look at the subset sum problem, with S = {a,b,c… }. The Non Deterministic Turing machine … Read more
Incrementing state value by one using React
Because you are using the handleClick function incorrectly. Here: handleClick = (prevState) => { …. } prevState will be an event object passed to handleClick function, you need to use prevState with setState, like this: handleClick = () => { this.setState(prevState => { return {count: prevState.count + 1} }) } Another issue is, setState is … Read more