[commit: ghc] master: Comments fix to Trac #9140 (27c99a1)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/27c99a1f8399fd6cb8931c17385102747556b6cc/ghc

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

commit 27c99a1f8399fd6cb8931c17385102747556b6cc
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Wed Aug 20 09:12:55 2014 +0100

    Comments fix to Trac #9140


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

27c99a1f8399fd6cb8931c17385102747556b6cc
 compiler/typecheck/TcBinds.lhs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/compiler/typecheck/TcBinds.lhs b/compiler/typecheck/TcBinds.lhs
index 14a5704..9db4125 100644
--- a/compiler/typecheck/TcBinds.lhs
+++ b/compiler/typecheck/TcBinds.lhs
@@ -1456,6 +1456,10 @@ checkStrictBinds top_lvl rec_group orig_binds tc_binds poly_ids
 
     is_unlifted id = case tcSplitSigmaTy (idType id) of
                        (_, _, rho) -> isUnLiftedType rho
+          -- For the is_unlifted check, we need to look inside polymorphism
+          -- and overloading.  E.g.  x = (# 1, True #)
+          -- would get type forall a. Num a => (# a, Bool #)
+          -- and we want to reject that.  See Trac #9140
 
     is_monomorphic (L _ (AbsBinds { abs_tvs = tvs, abs_ev_vars = evs }))
                      = null tvs && null evs