[commit: ghc] master: Comments only (2d0e1db)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/2d0e1db3e5d6400b50d349ec1fedc328c35c1af1/ghc

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

commit 2d0e1db3e5d6400b50d349ec1fedc328c35c1af1
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Mon Nov 9 09:38:53 2015 +0000

    Comments only


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2d0e1db3e5d6400b50d349ec1fedc328c35c1af1
 compiler/typecheck/TcInteract.hs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/compiler/typecheck/TcInteract.hs b/compiler/typecheck/TcInteract.hs
index 47147d7..180ddd3 100644
--- a/compiler/typecheck/TcInteract.hs
+++ b/compiler/typecheck/TcInteract.hs
@@ -602,12 +602,13 @@ we keep?  More subtle than you might think!
          See Note [Solving superclass constraints] in TcInstDcls
 
        - Keep the one that has a non-trivial evidence binding.
-         Note [Tracking redundant constraints] again.
             Example:  f :: (Eq a, Ord a) => blah
-            then we may find [G] sc_sel (d1::Ord a) :: Eq a
+            then we may find [G] d3 :: Eq a
                              [G] d2 :: Eq a
+              with bindings  d3 = sc_sel (d1::Ord a)
             We want to discard d2 in favour of the superclass selection from
             the Ord dictionary.
+         Why? See Note [Tracking redundant constraints] in TcSimplify again.
 
   * Finally, when there is still a choice, use IRKeep rather than
     IRReplace, to avoid unnecessary munging of the inert set.