Really bad code for single method dictionaries?

Jason Dusek jason.dusek at
Thu Mar 26 19:29:47 EDT 2009

  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

 | fusion code...|

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