Something that hit me tonight: Last GSoC gave us GHC compiler plugins. We have examples, but no documented significant uses, suitable for production code. Plugins, in essence, as I understand them, let us extend the type system in useful ways. Haskell has libraries for units[1], but no lightweight (i.e. without simulated dependent types or a dsl) way to embed units in Haskell calculations. Units in a functional language are possible, and implemented in, e.g., F# [2] The punchline: With GHC plugins, it should be possible, and reasonable, to add a proper unit system for Haskell. Given a suitable SoC candidate, I'd love to see this, and if it worked reasonably enough, I'm sure that I would use it. Cheers, Sterl. [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ dimensional, http://liftm.wordpress.com/2007/06/03/ scientificdimension-type-arithmetic-and-physical-units-in-haskell/, http://hackage.haskell.org/cgi-bin/hackage-scripts/package/caldims [2] http://blogs.msdn.com/andrewkennedy/archive/2008/09/04/units-of- measure-in-f-part-three-generic-units.aspx