[commit: ghc] type-nats: Just a note. (fca0545)

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

On branch  : type-nats

http://hackage.haskell.org/trac/ghc/changeset/fca0545b4713183f7f7c5a8a23c77b1ff2ea3234

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

commit fca0545b4713183f7f7c5a8a23c77b1ff2ea3234
Author: Iavor S. Diatchki <[email protected]>
Date:   Sat Sep 22 11:35:30 2012 -0700

    Just a note.

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

 compiler/typecheck/TcTypeNats.hs |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/compiler/typecheck/TcTypeNats.hs b/compiler/typecheck/TcTypeNats.hs
index b17b431..e815f55 100644
--- a/compiler/typecheck/TcTypeNats.hs
+++ b/compiler/typecheck/TcTypeNats.hs
@@ -101,6 +101,11 @@ typeNatStage ct
   | isGiven ev =
     case solve ct of
       Just _ -> return Stop              -- trivial fact
+                -- Note: we don't interact givens with wanteds or derived
+                -- because we assume that they are added before them
+                -- Otherwise we'd basically have to kick-out all of the
+                -- wanteds and restart them, to check if they might be solvable
+                -- with the new assumption.
       _      -> checkBad =<< computeNewGivenWork ct
 
   | isWanted ev =