Created: 2008-06-02 21:00
Updated: 2018-03-10 17:17
License: other



Chance is a library for exploring uncertainty in code. Maybe you always wanted to program with probability, to be boldly indecisive, to roll the dice without scratching your head? That's what we're all about here.

The idea originated with Numeric#percent and Kernel#maybe, which Marcel Molina posted to Projectionist, a tumblelog. This led to various snippets for executing code in a fuzzier way than usual, and this library has since been used in the production of the game Firewatch and several others. You get such handy, wishy-washy methods as:

Date#at_some_point rather than Date#midnight Array#pick(percentage) rather than iterating over every element

"maybe" is a Kernel method that randomly evaluates to true or false when it is called.

bob.lucky_winner? = maybe
# => true

chauncey.lucky_winner? = maybe
# => false

Maybe can also be supplied with a block, which will be called only if the Chance happens:

maybe do

Behind the scenes, maybe is just constructing a Chance object. It's equivalent to the statement 50.percent.chance.of {rotate_logs}

By themselves, Chance objects either "happen" or they don't- the probability for each is evaluated the first time you call Chance.happen?, and thereafter it's set in stone. See the schroedinger.rb example if this interests you.

Chance Case Statements

Chance Cases take any number of args, each one being a probability statement with an outcome block attached. The probabilities must add to 100 percent (sorry, for once in your life you will have to give less than 110%). Only one outcome will be evaluated, as you would expect:

outcome =
  70.percent.chance.will {'snow'},
  20.percent.chance.will {'sleet'},
  8.percent.chance.will  {'sun'},
  1.percent.chance.will  {'knives'}

Running examples and specs

Check out the specs for a better idea of how to use Chance. Make sure you have Bundler installed- then run bundle exec rake.

Game Dev

As we've found in our experience making games like Firewatch, Chance is perfect for use in making video games— it's an insanely easy to read and use DSL for introducing uncertainty into games. Basically, anywhere a random number generator might make your code harder to understand, Chance is a good fit.

For example, the weather system above is a succinct form of the logic you'd find running the hourly weather cycles in a game like Breath of the Wild. See weather.rb for more examples!


LICENSE for the copying and use of this code is "MIT-Alike" the file COPYING for license details.

"CHANCE" is Copyright (c) 2008—2017 Chance/Agency, All Rights Reserved

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