patch applied (ghc): Fix Trac #4917: try a bit harder to unify on-the-fly

[Simon Peyton Jones]

Tue Jan 25 03:01:12 PST 2011  simonpj at microsoft.com
  * Fix Trac #4917: try a bit harder to unify on-the-fly
  
  This is generally a modest improvement but, more important,
  it fixes a "unify-under-forall" problem.  See Note [Avoid deferring].
  
  There's still a lurking unsatisfactory-ness in that we can't
  defer arbitrary constraints that are trapped under a forall.

    M ./compiler/typecheck/TcUnify.lhs -8 +28

View patch online:
http://darcs.haskell.org/cgi-bin/darcsweb.cgi?r=ghc;a=darcs_commitdiff;h=20110125110112-1287e-6dd7830ea6b1527440ba1b0109a9bb2ef898228d.gz