Yet-another Grammar Grammar (YGG)

YGG is a generative grammar metasyntax interpreter and compiler, made with bots in mind.

Example

(
    = name |("James" "Jones" "Michael")
    "Hello there " name ", it's "
    |("lovely" "very nice" "wonderful")
    " to meet you. "
    |(
        ("Care to join me " |("for a drink" "for dinner") "?")
        "I've heard much about you."
    )
)

generates

Hello there Jones, it's lovely to meet you. I've heard much about you.
Hello there Michael, it's wonderful to meet you. I've heard much about you.
Hello there James, it's very nice to meet you. Care to join me for dinner?
...

Quick Start

For command line usage:

npm install --global @miguelmurca/ygg
ygg --help

after compiling to a file (for example mine.js),

const {
    generate
} = require('./mine.js');
console.log(generate('Some input'));

For programmatic usage:

npm install @miguelmurca/ygg

and then

const ygg = require('@miguelmurca/ygg');
const GRAMMAR = `( "Hello world!" )`; // Your grammar here
const interpreter = ygg.interpret(GRAMMAR);
console.log(interpreter('Some input.'));

What?

ygg plays 3 separate roles.

First, it's a definition of a metasyntax notation (like, for example, BNF). What this means is that it defines a way for you to define generative grammars (i.e., acceptable sentences). You can find more information about this under syntax.

Secondly, ygg is a command-line utility for "compiling" files defining grammars into javascript files that expose a generating function. This means you can pass in a file with your grammar to ygg on the command line, and produce a javascript file you can use to make, e.g., your Telegram bot. See the CLI section for more information.

Finally, ygg is an npm package, which you can call upon programmatically. You can parse and/or compile grammars on the fly with it. See the npm package section for more information.

Why?

I often make joke bots in Telegram or Twitter. Every so often, or whenever someone messages them, they tweet out or reply with a dynamically generated sentence which has something to do with whatever the bot's about.

It's not hard to write code to generate these texts, but it can be hard to iterate over the code, and keep it readable. I wrote ygg to reduce the amount of boilerplate code I have to write for each bot, and to ease the iteration process.

Syntax

ygg uses a Polish notation-like syntax:

• ? <optional expression> is reduced to either the expression or nothings (with equal likelihood);
• | (<option 1> <option 2> ...) is reduced to one of the options (with equal likelihood);
• = <identifier> <expression> attributes expression to the identifier, and reduces to nothing;
• & "<regex>" <expression> <expression> reduces to first/second expression if regex matches/doesn't match the input;
• <identifier> reduces to value of the identifier (which can be made up of numbers and letters);
• ( <expression> <expression> ... ) is reduced to the concatenated expressions;
• "<literal expression>" is reduced to the text itself, which can be delimited by " or '.

A ygg grammar specification, then, is just one big grouped expression, reducing to a string:

( ... )

CLI

Supposing grammar.ygg is a text file containing the grammar,

ygg grammar.ygg generator.js

will produce a javascript file named generator.js . This file exposes a single function, generate , which takes in the user input as a string argument, and returns a string in the defined grammar.

npm Package

ygg can be used as a module to do things on the fly. For this, the ygg package exposes two functions, compile and interpret .

compile(grammar: String, output_file: String) -> undefined

compile exposes the CLI behaviour; given a string of a grammar, it will write the compiled generator into the specified output file (specified by its name).

interpret(grammar: String) -> ((String) => String)

interpret will take in the grammar as a string and return a function that generates members of the grammar for the provided input.

License

This tool is licensed under an MIT license. See LICENSE for details.

Support

💕 If you liked ygg , consider buying me a coffee.