I built a Game Boy emulator in F#

I built a Game Boy emulator in F# to understand how retro gaming hardware works and to challenge myself with a complex functional programming project. The emulator can run most Game Boy ROMs, though some games still have timing issues that need refinement.

Why Did You Choose F# for This Project?

I selected F# because I wanted to explore functional programming patterns while building something tangible. The immutable data structures and pattern matching features in F# made it particularly well-suited for emulating hardware registers and memory states.

What Was the Most Challenging Part of the Process?

The most challenging aspect was accurately emulating the Game Boy's timing system. The original hardware has several timing-sensitive operations, and getting these right required careful analysis of the official documentation and trial-and-error testing.

How Did You Approach Debugging Issues?

I used a combination of logging, unit tests, and visual debugging. For example, I wrote a test harness that could compare the emulator's behavior against a reference implementation to identify discrepancies. Visual debugging involved overlaying the emulator's output with annotations to track state changes.

What Functional Programming Techniques Did You Use?

I heavily utilized F#'s pattern matching to handle different CPU instructions and interrupt vectors. I also employed discriminated unions to model the different states of the emulator, such as running, paused, or halted. Immutable data structures helped prevent subtle bugs related to shared state.

What Are Your Future Plans for the Emulator?

I plan to add support for the Game Boy Color and improve the emulation accuracy. I'm also considering adding features like save states and a debugger for educational purposes. Ultimately, I hope to make it a tool for learning about retro gaming hardware.

• Used F#'s pattern matching to handle CPU instructions
• Employed immutable data structures to prevent shared state issues
• Built a test harness to compare against reference implementations
• Overlaid visual annotations to track state changes during debugging

Functional programming provided a unique perspective on hardware emulation, forcing me to think about the problem in terms of transformations rather than mutable state.

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