Really bad code for single method dictionaries?

I was reading the stream fusion code today and came across a comment stating that single element dictionaries interacted poorly with GHC's optimizer: class Unlifted a where [...] expose [...] -- | This makes GHC's optimiser happier; it sometimes produces really bad -- code for single-method dictionaries -- unlifted_dummy [...] A cursory search on GHC's Trac shows no corresponding bug; is this no longer a problem? A small problem? I would like to know more about it. -- Jason Dusek |...stream fusion code...| http://www.cse.unsw.edu.au/~dons/code/streams/list/Data/Stream.hs