@@ -71,20 +71,20 @@
 	Value eval( Str e, Layer lay, Table ctx, bool overwriteCtx=CascadeCtx )
 	{
 		if( isASTLayer(lay) )
 			return ast2table(e, (AST e){return eval(e,lay,ctx);});
-		if( lay==ValueLayer )
-			return new StrValue(e.data);
-		return lift(new StrValue(e.data), lay, ctx, e.pos);
+		if( isUserDefinedLayer(lay) )
+			return lift(new StrValue(e.data), lay, ctx, e.pos);
+		return new StrValue(e.data);
 	}
 
 	Value eval( Int e, Layer lay, Table ctx, bool overwriteCtx=CascadeCtx )
 	{
 		if( isASTLayer(lay) )
 			return ast2table(e, (AST e){return eval(e,lay,ctx);});
-		if( lay==ValueLayer )
-			return new IntValue(e.data);
-		return lift(new IntValue(e.data), lay, ctx, e.pos);
+		if( isUserDefinedLayer(lay) )
+			return lift(new IntValue(e.data), lay, ctx, e.pos);
+		return new IntValue(e.data);
 	}
 
 	Value eval( Var e, Layer lay, Table ctx, bool overwriteCtx=CascadeCtx )
 	{
@@ -92,11 +92,11 @@
 			if( isMacroLayer(lay) && ctx.has(e.name,MacroLayer) )
 				return ctx.get(e.name, MacroLayer, e.pos);
 			else
 				return ast2table(e, (AST e){return eval(e,lay,ctx);});
-		if( lay==ValueLayer || ctx.has(e.name, lay) )
-			return ctx.get(e.name, lay, e.pos);
-		return lift(ctx.get(e.name, ValueLayer, e.pos), lay, ctx, e.pos);
+		if( isUserDefinedLayer(lay) && !ctx.has(e.name, lay) )
+			return lift(ctx.get(e.name, ValueLayer, e.pos), lay, ctx, e.pos);
+		return ctx.get(e.name, lay, e.pos);
 	}
 
 	Value eval( App e, Layer lay, Table ctx, bool overwriteCtx=CascadeCtx )
 	{
@@ -137,9 +137,10 @@
 	{
 		Table newCtx = overwriteCtx ? ctx : new Table(ctx, Table.Kind.NotPropagateSet);
 		if( isASTLayer(lay) )
 			return ast2table(e, (AST ee){
-				if(ee is e.expr) // need this for correct scoping (outer scope macro variables must be hidden!)
+				// need this for correct scoping (outer scope macro variables must be hidden!)
+				if(ee is e.expr)
 					newCtx.set(e.name, ValueLayer, new UndefinedValue);
 				return eval(ee,lay,newCtx);
 			});
 		else
@@ -254,16 +255,19 @@
 			override const(Parameter[]) params() { return ast.params; }
 			override Table definitionContext()   { return defCtx; }
 
 			this(Fun ast, Table defCtx) { this.ast=ast; this.defCtx=defCtx; }
-			override string toString() const { return sprintf!"(function:%x:%x)"(cast(void*)ast, cast(void*)defCtx); }
+			override string toString() const
+				{ return sprintf!"(function:%x:%x)"(cast(void*)ast, cast(void*)defCtx); }
 			override int opCmp(Object rhs) {
 				if(auto r = cast(UserDefinedFunValue)rhs) {
-					if(auto i = this.ast.opCmp(r.ast))
-						return i;
+					auto a = cast(void*)this.ast;
+					auto b = cast(void*)r.ast;
+					if(a<b) return -1;
+					if(a>b) return +1; // [TODO] avoid using pointer value...
 					return this.defCtx.opCmp(r.defCtx);
 				}
-				if(auto r = cast(Value)rhs)    return typeid(this).opCmp(typeid(r));
+				if(auto r = cast(Value)rhs) return typeid(this).opCmp(typeid(r));
 				throw genex!RuntimeException("comparison with value and something other");
 			}
 			mixin SimpleToHash;
 
@@ -297,9 +301,9 @@
 			override string toString() { return sprintf!"(native:%x)"(dg.funcptr); }
 			override int opCmp(Object rhs) {
 				if(auto r = cast(NativeFunValue)rhs) return typeid(typeof(dg)).compare(&dg,&r.dg);
 				if(auto r = cast(Value)rhs)          return typeid(this).opCmp(typeid(r));
-				throw genex!RuntimeException(LexPosition.dummy, "comparison with value and something other");
+				throw genex!RuntimeException("comparison with value and something other");
 			}
 			mixin SimpleToHash;
 
 			R delegate(T) dg;
@@ -314,14 +318,16 @@
 
 			override Value invoke(Layer lay, Table ctx, LexPosition pos)
 			{
 				if( lay != defLay )
-					throw genex!RuntimeException(pos, text("only ", defLay, " layer can call native function: ", name));
+					throw genex!RuntimeException(pos,
+						text("only ", defLay, " layer can call native function: ", name));
 				T typed_args;
 				foreach(i, Ti; T) {
 					typed_args[i] = cast(Ti) ctx.get(text(i), ValueLayer, pos);
 					if( typed_args[i] is null )
-						throw genex!RuntimeException(pos, sprintf!"type mismatch on the argument %d of native function: %s"(i+1,name));
+						throw genex!RuntimeException(pos,
+							sprintf!"type mismatch on the argument %d of native function: %s"(i+1,name));
 				}
 				try {
 					return dg(typed_args);
 				} catch( RuntimeException e ) {