From 49ccdd84d85bf9d75947456ae3782b78c831730b Mon Sep 17 00:00:00 2001
From: sof <unknown>
Date: Mon, 25 Aug 1997 22:28:37 +0000
Subject: [PATCH] [project @ 1997-08-25 22:28:37 by sof] new function:
 zonkSigTyVar

---
 ghc/compiler/typecheck/TcType.lhs |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/ghc/compiler/typecheck/TcType.lhs b/ghc/compiler/typecheck/TcType.lhs
index 0af7c44..a4b7474 100644
--- a/ghc/compiler/typecheck/TcType.lhs
+++ b/ghc/compiler/typecheck/TcType.lhs
@@ -27,7 +27,7 @@ module TcType (
   tcInstType, tcInstSigType, tcInstTcType, tcInstSigTcType,
   tcInstTheta, tcInstId,
 
-  zonkTcTyVars,
+  zonkTcTyVars, zonkSigTyVar,
   zonkTcType,
   zonkTcTypeToType,
   zonkTcTyVar,
@@ -410,6 +410,16 @@ zonkTcTyVar tyvar
 	BoundTo other		    -> zonkTcType other
 	other			    -> returnNF_Tc (TyVarTy tyvar)
 
+-- Signature type variables only get bound to each other,
+-- never to a type
+zonkSigTyVar :: TcTyVar s -> NF_TcM s (TcTyVar s)
+zonkSigTyVar tyvar 
+  = tcReadTyVar tyvar		`thenNF_Tc` \ maybe_ty ->
+    case maybe_ty of
+	BoundTo ty@(TyVarTy tyvar') -> returnNF_Tc tyvar'	-- tcReadTyVar never returns a bound tyvar
+	BoundTo other		    -> panic "zonkSigTyVar"	-- Should only be bound to another tyvar
+	other			    -> returnNF_Tc tyvar
+
 zonkTcType :: TcType s -> NF_TcM s (TcType s)
 
 zonkTcType (TyVarTy tyvar) = zonkTcTyVar tyvar
-- 
1.7.10.4