Index: polemy/eval.d
==================================================================
--- polemy/eval.d
+++ polemy/eval.d
@@ -10,64 +10,55 @@
 import polemy.ast;
 import polemy.parse;
 import polemy.value;
 import std.typecons;
 import std.stdio;
+
+// [todo] move to value.d
+
+FunValue nativef(Value delegate(immutable LexPosition pos, Layer lay, Value[] args) dg)
+{
+	return new FunValue(dg);
+}
+
+FunValue native(R,T...)(R delegate (T) dg)
+{
+	return nativef( delegate Value(immutable LexPosition pos, Layer lay, Value[] args) {
+		if( lay != "@v" )
+			throw genex!RuntimeException(pos, "only @v layer can call native function");
+		if( T.length != args.length )
+			throw genex!RuntimeException(pos, "argument number mismatch!");
+		T typed_args;
+		foreach(i, Ti; T)
+		{
+			typed_args[i] = cast(Ti) args[i];
+			if( typed_args[i] is null )
+				throw genex!RuntimeException(pos, sprintf!"type mismatch on the argument %d"(i));
+		}
+		try {
+			return dg(typed_args);
+		} catch( RuntimeException e ) {
+			throw e.pos is null ? new RuntimeException(pos, e.msg, e.file, e.line) : e;
+		}
+	});
+}
 
 ///
 Table createGlobalContext()
 {
 	auto ctx = new Table;
-	// [TODO] autogenerate these typechecks
-	ctx.set("+", "@v", new FunValue(delegate Value(immutable LexPosition pos, Layer lay, Value[] args){
-		if( args.length != 2 )
-			throw genex!RuntimeException(pos, "+ takes two arguments!!");
-		if( auto x = cast(IntValue)args[0] )
-			if( auto y = cast(IntValue)args[1] )
-				return new IntValue(x.data+y.data);
-		throw genex!RuntimeException(pos, "cannot add non-integers");
-	}));
-	ctx.set("-", "@v", new FunValue(delegate Value(immutable LexPosition pos, Layer lay, Value[] args){
-		if( args.length != 2 )
-			throw genex!RuntimeException(pos, "- takes two arguments!!");
-		if( auto x = cast(IntValue)args[0] )
-			if( auto y = cast(IntValue)args[1] )
-				return new IntValue(x.data-y.data);
-		throw genex!RuntimeException(pos, "cannot subtract non-integers");
-	}));
-	ctx.set("*", "@v", new FunValue(delegate Value(immutable LexPosition pos, Layer lay, Value[] args){
-		if( args.length != 2 )
-			throw genex!RuntimeException(pos, "* takes two arguments!!");
-		if( auto x = cast(IntValue)args[0] )
-			if( auto y = cast(IntValue)args[1] )
-				return new IntValue(x.data*y.data);
-		throw genex!RuntimeException(pos, "cannot multiply non-integers");
-	}));
-	ctx.set("/", "@v", new FunValue(delegate Value(immutable LexPosition pos, Layer lay, Value[] args){
-		if( args.length != 2 )
-			throw genex!RuntimeException(pos, "/ takes two arguments!!");
-		if( auto x = cast(IntValue)args[0] )
-			if( auto y = cast(IntValue)args[1] )
-				return new IntValue(x.data/y.data);
-		throw genex!RuntimeException(pos, "cannot divide non-integers");
-	}));
-	ctx.set("<", "@v", new FunValue(delegate Value(immutable LexPosition pos, Layer lay, Value[] args){
-		if( args.length != 2 )
-			throw genex!RuntimeException(pos, "< takes two arguments!!");
-		if( auto x = cast(IntValue)args[0] )
-			if( auto y = cast(IntValue)args[1] )
-				return new IntValue(BigInt(to!int(x.data < y.data)));
-		throw genex!RuntimeException(pos, "cannot compare non-integers");
-	}));
-	ctx.set(">", "@v", new FunValue(delegate Value(immutable LexPosition pos, Layer lay, Value[] args){
-		if( args.length != 2 )
-			throw genex!RuntimeException(pos, "> takes two arguments!!");
-		if( auto x = cast(IntValue)args[0] )
-			if( auto y = cast(IntValue)args[1] )
-				return new IntValue(BigInt(to!int(x.data>y.data)));
-		throw genex!RuntimeException(pos, "cannot compare non-integers");
-	}));
+	ctx.set("+", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(lhs.data + rhs.data);} ));
+	ctx.set("-", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(lhs.data - rhs.data);} ));
+	ctx.set("*", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(lhs.data * rhs.data);} ));
+	ctx.set("/", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(lhs.data / rhs.data);} ));
+	ctx.set("%", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(lhs.data % rhs.data);} ));
+	ctx.set("<", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(BigInt(lhs.data < rhs.data ? 1: 0));} ));
+	ctx.set(">", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(BigInt(lhs.data > rhs.data ? 1: 0));} ));
+	ctx.set("<=", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(BigInt(lhs.data <= rhs.data ? 1: 0));} ));
+	ctx.set(">=", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(BigInt(lhs.data >= rhs.data ? 1: 0));} ));
+	ctx.set("==", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(BigInt(lhs.data == rhs.data ? 1: 0));} ));
+	ctx.set("!=", "@v", native( (IntValue lhs, IntValue rhs){return new IntValue(BigInt(lhs.data != rhs.data ? 1: 0));} ));
 	ctx.set("print", "@v", new FunValue(delegate Value(immutable LexPosition pos, Layer lay, Value[] args){
 		foreach(a; args)
 			write(a);
 		writeln("");
 		return new IntValue(BigInt(178));
@@ -107,36 +98,36 @@
 }
 
 /// Entry point of this module
 /// If splitCtx = true, then inner variable declaration do not overwrite ctx.
 /// lay is the layer ID for evaluation (standard value semantics uses "@v").
-import std.typetuple;
+
 Value eval(AST e, Table ctx, bool splitCtx, Layer lay)
 {
 	return e.match(
 		(StrLiteral e)
 		{
 			Value v = new StrValue(e.data);
 			if( lay == "@v" )
 				return v;
-			else
+			else // rise
 				return (cast(FunValue)ctx.get(lay, "(system)", e.pos)).call(e.pos, "@v", [v]);
 		},
 		(IntLiteral e)
 		{
 			Value v = new IntValue(e.data);
 			if( lay == "@v" )
 				return v;
-			else // are these "@v"s appropriate???
+			else // rise
 				return (cast(FunValue)ctx.get(lay, "(system)", e.pos)).call(e.pos, "@v", [v]);
 		},
 		(VarExpression e)
 		{
 			try {
 				return ctx.get(e.var, lay, e.pos);
 			} catch( RuntimeException ) {
-				// rise
+				// rise from @v
 				return (cast(FunValue)ctx.get(lay, "(system)", e.pos)).call(e.pos, "@v", 
 					[ctx.get(e.var, "@v", e.pos)]
 				);
 			}
 		},
@@ -164,11 +155,12 @@
 				return f.call(e.pos, lay, args);
 			}
 			throw genex!RuntimeException(e.pos, "Non-funcion is applied");
 		},
 		(FunLiteral e)
-		{
+		{
+			// funvalue need not be rised
 			return new FunValue(delegate Value(immutable LexPosition pos, string lay, Value[] args){
 				if( e.params.length != args.length )
 					throw genex!RuntimeException(e.pos, sprintf!"Argument Number Mismatch (%d required but %d given)"
 						(e.params.length, args.length));
 				Table ctxNeo = new Table(ctx, Table.Kind.NotPropagateSet);