Really bad code for single method dictionaries?

[Jason Dusek]

  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