--- a/core/src/luan/modules/Utils.java	Tue Mar 01 07:29:01 2016 -0700
+++ b/core/src/luan/modules/Utils.java	Thu Mar 03 12:38:24 2016 -0700
@@ -19,29 +19,49 @@
 
 	static final int bufSize = 8192;
 
-	private static void checkNotNull(LuanState luan,Object v,String expected) throws LuanException {
+	private static void checkNotNull(LuanState luan,Object v,String expected,int pos) throws LuanException {
 		if( v == null )
-			throw new LuanException(luan,"bad argument #1 ("+expected+" expected, got nil)");
+			throw new LuanException(luan,"bad argument #"+pos+" ("+expected+" expected, got nil)");
+	}
+
+	public static void checkNotNull(LuanState luan,String s,int pos) throws LuanException {
+		checkNotNull(luan,s,"string",pos);
 	}
 
 	public static void checkNotNull(LuanState luan,String s) throws LuanException {
-		checkNotNull(luan,s,"string");
+		checkNotNull(luan,s,1);
+	}
+
+	public static void checkNotNull(LuanState luan,byte[] b,int pos) throws LuanException {
+		checkNotNull(luan,b,"binary",pos);
 	}
 
 	public static void checkNotNull(LuanState luan,byte[] b) throws LuanException {
-		checkNotNull(luan,b,"binary");
+		checkNotNull(luan,b,1);
+	}
+
+	public static void checkNotNull(LuanState luan,LuanTable t,int pos) throws LuanException {
+		checkNotNull(luan,t,"table",pos);
 	}
 
 	public static void checkNotNull(LuanState luan,LuanTable t) throws LuanException {
-		checkNotNull(luan,t,"table");
+		checkNotNull(luan,t,1);
+	}
+
+	public static void checkNotNull(LuanState luan,Number n,int pos) throws LuanException {
+		checkNotNull(luan,n,"number",pos);
 	}
 
 	public static void checkNotNull(LuanState luan,Number n) throws LuanException {
-		checkNotNull(luan,n,"number");
+		checkNotNull(luan,n,1);
+	}
+
+	public static void checkNotNull(LuanState luan,LuanFunction fn,int pos) throws LuanException {
+		checkNotNull(luan,fn,"function",pos);
 	}
 
 	public static void checkNotNull(LuanState luan,LuanFunction fn) throws LuanException {
-		checkNotNull(luan,fn,"function");
+		checkNotNull(luan,fn,1);
 	}
 
 	public static String readAll(Reader in)