[commit: ghc] wip/impredicativity: Change rule for canonicalization of <~ (a406ce2)

[git at git.haskell.org]

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

On branch  : wip/impredicativity
Link       : http://ghc.haskell.org/trac/ghc/changeset/a406ce26198357e137b18c2d388899113be86cb6/ghc

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

commit a406ce26198357e137b18c2d388899113be86cb6
Author: Alejandro Serrano <trupill at gmail.com>
Date:   Wed Jul 29 08:46:14 2015 +0200

    Change rule for canonicalization of <~
    
    Now, if the LHS is not a forall, we always turn it into ~.


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

a406ce26198357e137b18c2d388899113be86cb6
 compiler/typecheck/TcCanonical.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/typecheck/TcCanonical.hs b/compiler/typecheck/TcCanonical.hs
index b1ea1da..169faee 100644
--- a/compiler/typecheck/TcCanonical.hs
+++ b/compiler/typecheck/TcCanonical.hs
@@ -1708,7 +1708,7 @@ can_instance_of (CInstanceOfCan { cc_ev = ev, cc_lhs = lhs, cc_rhs = rhs })
   = can_instance_inst ev lhs rhs
     -- case InstanceOf (T ...) sigma --> T ... ~ sigma
     -- case InstanceOf var sigma --> var ~ sigma, var immutable
-  | is_tyapp_or_skolem lhs
+  | not (is_forall lhs)  -- is_tyapp_or_skolem lhs
   = can_instance_to_eq ev lhs rhs
     -- already canonical
   | otherwise = continueWith (CIrredEvCan { cc_ev = ev })