Structuring Uncertainty Using the maybe Statement

One of the reasons programming mobile systems is so hard is the uncertainty created by the wide variety of environments a typical app encounters at runtime. In many cases only post-deployment user testing can determine the right algorithm to use, the rate at which something should happen, or when an app should attempt to conserve energy. Programmers should not be forced to make these choices at development time. But today’s programming languages leave no way for programmers to express and structure their uncertainty about runtime conditions, forcing them to adopt ineffective, fragile, and untested ad-hoc approaches to runtime adaptation. We introduce a new approach based on structured uncertainty through a new language construct: the maybe statement.

Consider the following attempt to adapt to the available battery level by establishing a low-battery code path, which might use a slower but more energy efficient algorithm or retrieve lower resolution but more compact content:

if (plugged == false && batteryLevel < 10) { (1)
  // Try to save energy (2)
} else {
  // Don't try to save energy (2)
}

Although the attempt to adapt and conserve energy is laudable 1, there are two serious problems with this approach:

  1. This threshold is arbitrary. If the app is the user’s favorite, it may never make sense to activate the low-battery path.

  2. The two code paths may or may not produce the desired result. In some cases no energy saving may be achieved, and in others the attempt to save energy may fail and consume more energy than the other code path.

The root of the problem is that today’s languages force programmers to be certain at a moment when they cannot be: at development time. While this problem is endemic to existing programming languages, when developing mobile apps it is magnified by the amount of variation developers must confront. Our solution is simple: (1) provide developers with a way to express structured uncertainty, and (2) use the resulting flexibility to enable a large array of downstream tools for resolving uncertainty by choosing from the alternatives provided by the developer.

We allow programmers to express structured uncertainty through a new language construct: the maybe statement.We allow programmers to express structured uncertainty through a new language construct: the maybe statement. Here’s how we can rewrite the earlier example using a maybe statement.

maybe {
  // Try it one way
} or {
  // Try it another way
}

Note the differences from the previous example. Uncertain about how to adapt to energy availability, the programmer does not have to implement an arbitrary decision threshold, or even determine which code path has what effect on energy consumption. Instead, all she has to do is express uncertainty by indicating that there are multiple ways to perform this task and she is not certain which one to use.

At this point the maybe system can take over and use a variety of approaches—​including post-deployment split testing—​to resolve the uncertainty and make intelligent runtime decisions. For more details please read our HotMobile'15 paper.

We are currently in the process of building a prototype of the maybe system which we will evaluate on the PhoneLab Smartphone Platform Testbed.

Videos

Yihong Chen walk through a screencast of how to set up maybe for your own Android project:

Geoffrey Challen motivates the maybe project at the GDG DevFest Buffalo 2015:

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Created 2/11/2016
Updated 2/11/2016
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