@@ -44,8 +44,14 @@
 	mixin SimpleConstructor;
 	alias data call;
 	override string toString() const { return sprintf!"(function:%s:%s)"(data.ptr,data.funcptr); }
 }
+
+class UndValue : Value
+{
+	mixin SimpleClass;
+	override string toString() const { return "<undefined>"; }
+}
 
 /// Layer ID
 
 alias string Layer;
@@ -69,13 +75,16 @@
 	}
 
 	Value get(string i, Layer lay, in LexPosition pos=null)
 	{
-		if( i in data )
+		if( i in data ) {
+			if( lay !in data[i] )
+				throw genex!RuntimeException(pos, sprintf!"variable %s is not set in layer %s"(i,lay));
 			return data[i][lay];
+		}
 		if( prototype is null )
 			throw new RuntimeException(pos, sprintf!"variable %s not found"(i));
-		return prototype.get(i, lay);
+		return prototype.get(i, lay, pos);
 	}
 
 private:
 	Table                prototype;