CFGs (short for Context-Free Grammars) are an essential part of CS. This project aims to make them more accessible by providing a playground.
In the app, a grammar can be entered (see below) and its expansion observed. There is also a box for checking if the grammar accepts a given input or not.
The app is available here.
When opening the web app, on the left side (top on mobile), a grammar can be entered. Currently, two syntaxes are supported, see below. The text entered here will be parsed into a workable grammar while typing. Errors are displayed at the bottom, with a red outline. If the grammar is valid, a green outline is displayed.
On the right top (middle on mobile), a string to test against the grammar can be entered. The app will check if any expansion of the grammar would allow this string, i.e. check if the entered string is part of the language. Matching is performed while typing, and the status will be displayed below and via outline.
The right bottom (bottom on mobile) can be used to generate a list of unique strings from the grammar. For this the app will try to expand non-terminals to all possible branches. To control recursions and deep expansions, there are variables to limit this generation.
In the header, on the right, a settings symbol can be clicked to open a modal. Here, one of two syntaxes can be selected (see below), and the mentioned variables can be controlled under advanced.
Currently, two syntaxes are supported:
- FCS, a common syntax I could not find a name for, so I used the abbreviation of the course where I learned about it. Non-terminals are uppercase letters, terminals lowercase (expect when a non-terminal can't be found). Valid symbols for the empty string are
^andε. - BNF, Backus-Naur form. Non-terminals are surrounded by
<>, terminals by""or''. A branch can't be left empty, at least the empty string has to be given.
Examples for both are available in the app.
This project was bootstrapped with Create React App.
In the project directory, you can run:
Runs the app in the development mode.
Open http://localhost:3000 to view it in the browser.
The page will reload if you make edits.
You will also see any lint errors in the console.
Launches the test runner in the interactive watch mode.
See the section about running tests for more information.
Builds the app for production to the build folder.
It correctly bundles React in production mode and optimizes the build for the best performance.
The build is minified and the filenames include the hashes.
Your app is ready to be deployed!
See the section about deployment for more information.
Note: this is a one-way operation. Once you eject, you can’t go back!
If you aren’t satisfied with the build tool and configuration choices, you can eject at any time. This command will remove the single build dependency from your project.
Instead, it will copy all the configuration files and the transitive dependencies (Webpack, Babel, ESLint, etc) right into your project so you have full control over them. All of the commands except eject will still work, but they will point to the copied scripts so you can tweak them. At this point you’re on your own.
You don’t have to ever use eject. The curated feature set is suitable for small and middle deployments, and you shouldn’t feel obligated to use this feature. However we understand that this tool wouldn’t be useful if you couldn’t customize it when you are ready for it.
You can learn more in the Create React App documentation.
To learn React, check out the React documentation.
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