X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcUnify.lhs;h=23cc9e21760724b982b42322863af6001fe1b13b;hb=0f800dc9f3dc695cd06d0fdd7799a52c37241752;hp=187f055ff7136d4c512d4a1d3869e85e83bcd230;hpb=4c7b8ec3e7852f88f4c355de2745dc594d120819;p=ghc-hetmet.git

diff --git a/ghc/compiler/typecheck/TcUnify.lhs b/ghc/compiler/typecheck/TcUnify.lhs
index 187f055..23cc9e2 100644
--- a/ghc/compiler/typecheck/TcUnify.lhs
+++ b/ghc/compiler/typecheck/TcUnify.lhs
@@ -67,7 +67,7 @@ import VarSet		( emptyVarSet, mkVarSet, unitVarSet, unionVarSet, elemVarSet, var
 import VarEnv
 import Name		( Name, isSystemName )
 import ErrUtils		( Message )
-import Maybes		( fromJust, isNothing )
+import Maybes		( expectJust, isNothing )
 import BasicTypes	( Arity )
 import UniqSupply	( uniqsFromSupply )
 import Util		( notNull, equalLength )
@@ -1197,7 +1197,8 @@ checkTauTvUpdate orig_tv orig_ty
 	     ; case mb_tys' of
 		Just tys' -> return (TyConApp tc tys')
 				-- Retain the synonym (the common case)
-		Nothing   -> go (fromJust (tcView (TyConApp tc tys)))
+		Nothing   -> go (expectJust "checkTauTvUpdate" 
+					(tcView (TyConApp tc tys)))
 				-- Try again, expanding the synonym
 	     }
 \end{code}