tracery

Tracery: a story-grammar generation library for javascript

This is my attempt to package up Tracery as a Node library.

Installation

This is hosted at npm, so it can be installed like so:

$ npm install tracery-grammar --save

Example usage

var tracery = require('tracery-grammar');

var grammar = tracery.createGrammar({
  'animal': ['panda','fox','capybara','iguana'],
  'emotion': ['sad','happy','angry','jealous'],
  'origin':['I am #emotion.a# #animal#.'],
});

grammar.addModifiers(tracery.baseEngModifiers); 

console.log(grammar.flatten('#origin#'));

Sample output:

I am a happy iguana.
I am an angry fox.
I am a sad capybara.

Making Tracery deterministic

By default, Tracery uses Math.random() to generate random numbers. If you need Tracery to be deterministic, you can make it use your own random number generator using:

tracery.setRng(myRng);

where myRng is a function that, like Math.random(), returns a floating-point, pseudo-random number in the range [0, 1).

By using a local random number generator that takes a seed and controlling this seed, you can make Tracery's behavior completely deterministic.

// Stable random number generator
// Copied from this excellent answer on Stack Overflow: https://stackoverflow.com/a/47593316/3306
function splitmix32(seed) {
  return function() {
    seed |= 0; // bitwise OR ensures this is treated as an integer internally for performance.
    seed = seed + 0x9e3779b9 | 0; // again, bitwise OR for performance 
    let t = seed ^ seed >>> 16;
    t = Math.imul(t, 0x21f0aaad);
    t = t ^ t >>> 15;
    t = Math.imul(t, 0x735a2d97);
    return ((t = t ^ t >>> 15) >>> 0) / 4294967296;
  };
}

var seed = 123456;
tracery.setRng(splitmix32(seed));

console.log(grammar.flatten('#origin#'));

Deterministic output:

I am an angry capybara.