[commit: ghc] wip/rae-new-coercible: Drop Derived `canRewrite` Derived, as per discussions with SPJ & DV (1383e0d)

[git at git.haskell.org]

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

On branch  : wip/rae-new-coercible
Link       : http://ghc.haskell.org/trac/ghc/changeset/1383e0d72788959c8be9877b7c451e6f271d61f0/ghc

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

commit 1383e0d72788959c8be9877b7c451e6f271d61f0
Author: Richard Eisenberg <eir at cis.upenn.edu>
Date:   Mon Dec 8 12:04:03 2014 -0500

    Drop Derived `canRewrite` Derived, as per discussions with SPJ & DV


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

1383e0d72788959c8be9877b7c451e6f271d61f0
 compiler/typecheck/TcCanonical.hs | 13 -------------
 compiler/typecheck/TcFlatten.hs   |  2 --
 2 files changed, 15 deletions(-)

diff --git a/compiler/typecheck/TcCanonical.hs b/compiler/typecheck/TcCanonical.hs
index fcf5c4e..f903ba8 100644
--- a/compiler/typecheck/TcCanonical.hs
+++ b/compiler/typecheck/TcCanonical.hs
@@ -380,19 +380,6 @@ canHole ev occ hole_sort
 canEqNC :: CtEvidence -> EqRel -> Type -> Type -> TcS (StopOrContinue Ct)
 canEqNC ev eq_rel ty1 ty2
   = can_eq_nc ev eq_rel ty1 ty1 ty2 ty2
-    `andWhenContinue` \ ct ->
-    do { emitReprEq ct
-       ; continueWith ct }
-
-emitReprEq :: Ct -> TcS ()
-emitReprEq (CTyEqCan { cc_ev = ev@(CtDerived {}), cc_tyvar = tv, cc_rhs = rhs
-                     , cc_eq_rel = NomEq })
-  = emitWorkNC [ev { ctev_pred = mkTcReprEqPred (mkTyVarTy tv) rhs }]
-     -- This works only on Deriveds, because nominal Givens can rewrite
-     -- representational equalities. See Note [eqCanRewrite] in TcFlatten
-
--- Nothing to do for other equalities
-emitReprEq _ = return ()
 
 can_eq_nc
    :: CtEvidence
diff --git a/compiler/typecheck/TcFlatten.hs b/compiler/typecheck/TcFlatten.hs
index 1b7698c..4a8b026 100644
--- a/compiler/typecheck/TcFlatten.hs
+++ b/compiler/typecheck/TcFlatten.hs
@@ -1183,8 +1183,6 @@ eqCanRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool
 -- See Note [eqCanRewrite]
 eqCanRewriteFR (Given,   NomEq)  (_,       _)      = True
 eqCanRewriteFR (Given,   ReprEq) (_,       ReprEq) = True
-eqCanRewriteFR (Derived, NomEq)  (Derived, NomEq)  = True
-eqCanRewriteFR (Derived, ReprEq) (Derived, ReprEq) = True
 eqCanRewriteFR _                 _                 = False
 
 canRewriteOrSame :: CtEvidence -> CtEvidence -> Bool