--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/luan/interp/ConcatExpr.java	Wed Nov 21 06:57:09 2012 +0000
@@ -0,0 +1,27 @@
+package luan.interp;
+
+import luan.Lua;
+import luan.LuaNumber;
+import luan.LuaException;
+import luan.LuaState;
+
+
+final class ConcatExpr extends BinaryOpExpr {
+
+	ConcatExpr(Expr op1,Expr op2) {
+		super(op1,op2);
+	}
+
+	@Override Object eval(LuaState lua) throws LuaException {
+		Object v1 = op1.eval(lua);
+		Object v2 = op2.eval(lua);
+		check(v1);
+		check(v2);
+		return Lua.toString(v1) + Lua.toString(v2);
+	}
+
+	private static void check(Object v) throws LuaException {
+		if( !(v instanceof String || v instanceof LuaNumber) )
+			throw new LuaException( "attempt to concatenate a " + Lua.type(v) + " value" );
+	}
+}