patch applied (ghc): new version of ZipDataflow

[nr at eecs.harvard.edu]

Sat May  3 15:42:08 PDT 2008  Norman Ramsey <nr at eecs.harvard.edu>
  * new version of ZipDataflow
  This version combines forward/backard into a type class
  (actually two classes) of analysis and transformation.
  These type classes will always be expanded away at the client,
  so SLPJ may wonder why they exist: it is because the interface
  to this module is already very broad, and by overloading the functions 
  for forward and backward problems, we cut the cognitive load on the
  clients in half.

    A ./compiler/cmm/ZipDataflow.hs

View patch online:
http://darcs.haskell.org/ghc/_darcs/patches/20080503224208-39dff-3b956189b224096ec22ba60fc0122323c63c9505.gz