[commit: ghc] ghc-kinds: Fix use of decomposeCo in Simplify; fixes a Lint error (7c2d9a8)

[Simon Peyton Jones]

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

On branch  : ghc-kinds

http://hackage.haskell.org/trac/ghc/changeset/7c2d9a8f3ccba8d095b807a22937171d61339495

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

commit 7c2d9a8f3ccba8d095b807a22937171d61339495
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Mon Nov 7 08:25:40 2011 +0000

    Fix use of decomposeCo in Simplify; fixes a Lint error

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

 compiler/simplCore/Simplify.lhs |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs
index 853815c..4bb20fa 100644
--- a/compiler/simplCore/Simplify.lhs
+++ b/compiler/simplCore/Simplify.lhs
@@ -980,8 +980,13 @@ simplCoercionF env co cont
     simpl_co co (CoerceIt g cont)
        = simpl_co new_co cont
      where
-       new_co = mkSymCo g0 `mkTransCo` co `mkTransCo` g1
-       [g0, g1] = decomposeCo 2 g
+       -- g :: (s1 ~# s2) ~# (t1 ~#  t2)
+       -- g1 :: s1 ~# t1
+       -- g2 :: s2 ~# t2
+       new_co = mkSymCo g1 `mkTransCo` co `mkTransCo` g2
+       [_reflk, g1, g2] = decomposeCo 3 g
+            -- Remember, (~#) :: forall k. k -> k -> *
+            -- so it takes *three* arguments, not two
 
     simpl_co co cont
        = seqCo co `seq` rebuild env (Coercion co) cont