There was a an indie 2D platformer game called "Nikki and the Robots" that came out a few years ago; the base "engine" and level editor is free (and I did buy the extra story content which was great). It's still available on github: https://github.com/nikki-and-the-robots/nikki.
The game didn't do very well for commercial reasons, but it ran smoothly - no noticeable GC pauses.
Game programming section misses link to "Nikki and the robots". One of the most serious gamedev projects made in Haskell
https://github.com/nikki-and-the-robots/nikki http://steamcommunity.com/sharedfiles/filedetails/?id=107105028