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Writing terminal applications with Unison

January 03, 2026

The Terminus library in Unison is a terminal interaction library designed to provide a rich set of functions for working with the terminal. Here’s a summary of its functionality and what makes it unique:

Summary of Terminus Library

  • Purpose: Terminus allows Unison developers to interact with the terminal in a powerful and ergonomic way. It is particularly useful for building command-line applications, games, and interactive tools directly in Unison.
  • Core Features:
    • Text Output: Write text to the terminal screen with precise control.
    • User Input: Read input from the user interactively.
    • Cursor Control: Store, move, and reset the cursor position on the screen, enabling advanced terminal UI features like menus, progress bars, and animations.
    • Example Use Case: The library includes a sample Snake game, demonstrating its capabilities for building interactive terminal applications.

Functionality

  • Terminal Manipulation: Terminus provides low-level control over the terminal, such as moving the cursor, clearing the screen, and styling text, which is essential for building complex terminal-based interfaces.
  • Interactive Applications: It enables the creation of interactive applications without needing external libraries or complex setup, leveraging Unison’s pure functional paradigm.
  • Integration with Unison’s Ecosystem: Since Unison is content-addressable and purely functional, Terminus benefits from the language’s ability to manage dependencies and versions seamlessly, making it easy to share and reuse terminal-based code.

Why It Stands Out

  • Simplicity: Terminus abstracts away the complexity of managing terminal I/O, allowing developers to focus on application logic rather than low-level details.
  • Unison’s Unique Features: By leveraging Unison’s content-addressable code and effect system, Terminus ensures that terminal applications are reliable, reusable, and easy to distribute.

Example

To try Terminus, you can pull the library and run the included Snake game example using Unison’s code manager (UCM):

run examples.snake.main

This demonstrates how Terminus can be used to build engaging terminal applications with minimal effort.