X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=90ff3a7c8c1611ec906ca4f307294161fb75f1fe;hb=2423c249f5ca7785d0ec89eb33e72662da7561c1;hp=68c5173be2ea3f4d65eab197b7421ea57e748f72;hpb=49c98d143c382a1341e1046f5ca00819a25691ba;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs
index 68c5173..90ff3a7 100644
--- a/compiler/typecheck/TcDeriv.lhs
+++ b/compiler/typecheck/TcDeriv.lhs
@@ -15,7 +15,6 @@ import DynFlags
 
 import Generics
 import TcRnMonad
-import TcMType
 import TcEnv
 import TcGenDeriv	-- Deriv stuff
 import InstEnv
@@ -763,9 +762,10 @@ solveDerivEqns overlap_flag orig_eqns
 	do { let inst_tys = [mkTyConApp tc (mkTyVarTys tyvars)]
 	   ; theta <- addErrCtxt (derivInstCtxt1 clas inst_tys) $
 		      tcSimplifyDeriv orig tc tyvars deriv_rhs
-	   ; addErrCtxt (derivInstCtxt2 theta clas inst_tys) $
-	     checkValidInstance tyvars theta clas inst_tys
-	   ; return (sortLe (<=) theta) }	-- Canonicalise before returning the soluction
+		-- Claim: the result instance declaration is guaranteed valid
+		-- Hence no need to call:
+		--   checkValidInstance tyvars theta clas inst_tys
+	   ; return (sortLe (<=) theta) }	-- Canonicalise before returning the solution
       where
 	
 
@@ -995,10 +995,5 @@ derivCtxt tycon
 
 derivInstCtxt1 clas inst_tys
   = ptext SLIT("When deriving the instance for") <+> quotes (pprClassPred clas inst_tys)
-
-derivInstCtxt2 theta clas inst_tys
-  = vcat [ptext SLIT("In the derived instance declaration"),
-          nest 2 (ptext SLIT("instance") <+> sep [pprThetaArrow theta, 
-						  pprClassPred clas inst_tys])]
 \end{code}