[commit: ghc] master: Comments only (f20312f)

[Simon Peyton Jones]

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/f20312f90db4a0c8dc9d6e91b2a4b3a370b2f9c9

>---------------------------------------------------------------

commit f20312f90db4a0c8dc9d6e91b2a4b3a370b2f9c9
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Thu Feb 14 11:41:30 2013 +0000

    Comments only

>---------------------------------------------------------------

 compiler/typecheck/TcSimplify.lhs |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index b69962f..de19b91 100644
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -266,6 +266,7 @@ simplifyInfer _top_lvl apply_mr name_taus wanteds
                             meta_tvs   = filter isMetaTyVar (varSetElems (tyVarsOfCts quant_cand)) 
                       ; ((flats, _insols), _extra_binds) <- runTcS $ 
                         do { mapM_ (promoteAndDefaultTyVar untch gbl_tvs) meta_tvs
+                                 -- See Note [Promote _and_ default when inferring]
                            ; _implics <- solveInteract quant_cand
                            ; getInertUnsolved }
                       ; return (map ctPred $ filter isWantedCt (bagToList flats)) }
@@ -910,6 +911,7 @@ have an instance (C ((x:*) -> Int)).  The instance doesn't match -- but it
 should!  If we don't solve the constraint, we'll stupidly quantify over 
 (C (a->Int)) and, worse, in doing so zonkQuantifiedTyVar will quantify over
 (b:*) instead of (a:OpenKind), which can lead to disaster; see Trac #7332.
+Trac #7641 is a simpler example.
 
 Note [Float Equalities out of Implications]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~