Infinite Scroll: Lazy Lists in the Brick TUI Library

location_city Melbourne schedule May 15th 12:15 - 12:45 PM AEST place Red Room people 54 Interested

The Brick terminal UI library provides a rich library of widgets for building console applications in Haskell. These include a list widget, which uses a packed vector type under the hood: a major problem when working with lists that are very large or expensive to compute.

In this case study I will review, step by step, how I generalised Brick's list widget to admit different underlying container types and achieved lazy loading of list items. The presentation will address several topics including:

  • The advantages of more general (polymorphic) code, including parametricity
  • Ensuring adequate test coverage before refactoring or generalising
  • Maintaining backwards compatibility
  • Assessing and documenting asymptotic performance
  • Using Brick list widget in a real-world application (purebred MUA) for lazy loading where I/O is involved
  • How to evaluate a lazy structure in the background (and why you might want to)
  • Can we really achieve infinite scroll, or is my presentation title just clickbait?

Code examples will abound, and live demonstrations will both justify the work that was done, and show the pleasing results. The presentation uses Haskell exclusively but principles and advice for generalising code apply to many languages.


Outline/Structure of the Talk

  • Overview of Brick and the list widget
  • Live demo: the performance issue
  • The generalisation work, in detail
  • Live demo: the results
  • Concurrent evaluation of lazy structures
  • Live demo: concurrent evaluation
  • Infinite scroll

Learning Outcome

Attendees will learn the benefits of, and general guidelines for generalising code. They will be familiar with the Brick list widget implementation and know how to choose (or define) the right container type to use with it. A firm grasp on laziness and lazy I/O in Haskell.

Target Audience


Prerequisites for Attendees

Familiarity with Haskell syntax.



schedule Submitted 3 years ago