This post was first published inline to the Haskell Discourse, where there was some discussion about the debugger:

The Haskell Debugger for GHC 9.14

The Haskell Debugger is ready to use with GHC-9.14!

The installation, configuration, and talks can be found in the official website. The tl;dr first step is installing the debugger:

$ ghc --version # MUST BE GHC 9.14
The Glorious Glasgow Haskell Compilation System, version 9.14.1

$ cabal install haskell-debugger \
    --allow-newer=base,time,containers,ghc,ghc-bignum,template-haskell \
    --enable-executable-dynamic # ON WINDOWS, DO NOT PASS --enable-executable-dynamic
...

$ ~/.local/bin/hdb --version # VERIFY IT'S THE LATEST!
Haskell Debugger, version 0.11.0.0

The second step is configuring your editor to use the debugger via the Debug Adapter Protocol (DAP). - For VSCode, install the haskell debugger extension. - For Neovim, install nvim-dap and configure it for haskell-debugger - For other editors, consult your DAP documentation and let others know how!

Bug reports and discussions are welcome in the haskell-debugger issue tracker.

My MuniHac 2025 talk also walks through the installation, usage, and design of the debugger. Do note much has been improved since the talk was given, and much more will still improve.

A little bit more info

The debugger work is sponsored by Mercury. It’s the project in which I’ve spent most of my full working days (for almost a full year now), with the invaluable help from my team at Well-Typed.

The debugger is meant to work both on trivial files and on large and complex codebases¹. It is a GHC application so all features are supported. Like HLS, it also uses hie-bios to automatically configure the session based on your cabal or stack project.

Robustness is a main goal of the debugger. If anything doesn’t work, or if you have performance issues, or something crashes, please don’t hesitate to submit a bug. We’ve got a small but respectable testsuite, and have tested performance by debugging GHC itself, but there’s much still to be fixed and improved.

Roadmap: There’s a lot to do. I’m currently working on callstacks and multi-threaded support. Do let me know what features would be most important to you, so I can also factor that into the future planning.