diff --git a/parser/parser.cpp b/parser/parser.cpp
index 5d89918e..ce211a21 100644
--- a/parser/parser.cpp
+++ b/parser/parser.cpp
@@ -2,6 +2,8 @@
 #include <iostream>
 
 #include <pegtl.hh>
+#include <pegtl/analyze.hh>
+#include <pegtl/trace.hh>
 
 using namespace pegtl;
 
@@ -34,32 +36,77 @@ namespace query
     struct number : seq< minus, sor< float_num, hex_num, int_num > > {};
 
     // key paths
-    struct key_path : list< must< sor< alpha, one< '_' > >, star< sor< alnum, one< '_', '-' > > > >, one< '.' > > {};
+    struct key_path : list< seq< sor< alpha, one< '_' > >, star< sor< alnum, one< '_', '-' > > > >, one< '.' > > {};
 
     // expressions and operators
     struct expr : sor< string, key_path, number > {};
-    struct oper : sor< one< '=' >, istring< '=', '=' >, istring< '!', '=' >, one< '<' >, istring< '<', '=' >, one< '>' >, istring< '>', '=' > > {};
+    struct oper : sor<
+        two< '=' >,
+        one< '=' >,
+        pegtl::string< '!', '=' >,
+        pegtl::string< '<', '=' >,
+        one< '<' >,
+        pegtl::string< '>', '=' >,
+        one< '>' >
+    > {};
 
     // predicates
-    struct pred : seq< expr, plus< blank >, oper, plus< blank >, expr > {};
+    struct comparison_pred : seq< expr, pad< oper, blank >, expr > {};
+
+    struct pred;
+    struct group_pred : if_must< one< '(' >, pad< pred, blank >, one< ')' > > {};
+
+    struct single_pred : pad< sor< group_pred, comparison_pred >, blank > {};
+    struct not_pre : pegtl::string< 'N', 'O', 'T' > {};
+    struct atom_pred : seq< opt< not_pre >, single_pred > {};
+
+    struct or_ext : if_must< two< '|' >, atom_pred > {};
+    struct and_ext : if_must< two< '&' >, atom_pred > {};
+
+    struct pred : seq< atom_pred, star< sor< or_ext, and_ext > > > {};
 
     // rules
     template< typename Rule >
     struct action : nothing< Rule > {};
-    template<> struct action< expr >
+    template<> struct action< and_ext >
+    {
+        static void apply( const input & in, std::string & string_value )
+        {
+            std::cout << "<and>" << in.string() << std::endl;
+        }
+    };
+
+    template<> struct action< or_ext >
+    {
+        static void apply( const input & in, std::string & string_value )
+        {
+            std::cout << "<or>" << in.string() << std::endl;
+        }
+    };
+
+    template<> struct action< comparison_pred >
     {
         static void apply( const input & in, std::string & string_value )
         {
             std::cout << in.string() << std::endl;
         }
     };
+
+    template<> struct action< group_pred >
+    {
+        static void apply( const input & in, std::string & string_value )
+        {
+            std::cout << "<group>" << std::endl;
+        }
+    };
 }
 
 int main( int argc, char ** argv )
 {
     if ( argc > 1 ) {
         std::string intstring;
-        parse< must< query::expr, eof>, query::action >( 1, argv, intstring);
+        analyze< query::pred >();
+        parse< must< seq< query::pred, eof > >, query::action >( 1, argv, intstring);
     }
 }