beginnings of a parser

parser/parser.cpp

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+#include <string>
+#include <iostream>
+
+#include <pegtl.hh>
+
+using namespace pegtl;
+
+namespace query
+{
+    // strings
+    struct unicode : list< seq< one< 'u' >, rep< 4, must< xdigit > > >, one< '\\' > > {};
+    struct escaped_char : one< '"', '\\', '/', 'b', 'f', 'n', 'r', 't' > {};
+    struct escaped : sor< escaped_char, unicode > {};
+    struct unescaped : utf8::range< 0x20, 0x10FFFF > {};
+    struct char_ : if_then_else< one< '\\' >, must< escaped >, unescaped > {};
+
+    struct string_content : until< at< one< '"' > >, must< char_ > > {};
+    struct string : seq< one< '"' >, must< string_content >, any >
+    {
+        using content = string_content;
+    };
+
+    // numbers
+    struct minus : opt< one< '-' > > {};
+    struct dot : one< '.' > {};
+
+    struct float_num : sor<
+        seq< plus< digit >, dot, star< digit > >,
+        seq< star< digit >, dot, plus< digit > >
+    > {};
+    struct hex_num : seq< one< '0' >, one< 'x', 'X' >, plus< xdigit > > {};
+    struct int_num : plus< digit > {};
+
+    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< '.' > > {};
+
+    // expressions and operators
+    struct expr : sor< string, key_path, number > {};
+    struct oper : sor< one< '=' >, istring< '=', '=' >, istring< '!', '=' >, one< '<' >, istring< '<', '=' >, one< '>' >, istring< '>', '=' > > {};
+
+    // predicates
+    struct pred : seq< expr, plus< blank >, oper, plus< blank >, expr > {};
+
+    // rules
+    template< typename Rule >
+    struct action : nothing< Rule > {};
+    template<> struct action< expr >
+    {
+        static void apply( const input & in, std::string & string_value )
+        {
+            std::cout << in.string() << std::endl;
+        }
+    };
+}
+
+int main( int argc, char ** argv )
+{
+    if ( argc > 1 ) {
+        std::string intstring;
+        parse< must< query::expr, eof>, query::action >( 1, argv, intstring);
+    }
+}
+

parser/query.abnf

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+
+
+pred     	= expr 1*WSP oper 1*WSP expr 
+;pred 		=/ "(" *WSP pred *WSP ")"
+;pred 		=/ ("NOT" / "!") 1*WSP pred 
+;pred 		=/ pred 1*WSP ("OR" / "||") !*WSP pred 
+;pred 		=/ pred 1*WSP ("AND" / "&&") 1*WSP pred
+
+oper		= "=" / "==" / "!=" / "<" / "<=" / ">" / ">="
+
+expr		= string / num / key-path
+
+key-path	= key *("." key)
+key 		= 1*(ALPHA / "_")
+
+string 		= dq-string / sq-string
+sq-string 	= "'" *(%x20-ffffffff) "'"
+dq-string 	= DQUOTE *("\\" / %x20-21 / %x23-ffffffff) DQUOTE
+
+num 		= float-num / int-num / hex-num
+float-num	= ["-"] (*DIGIT "." 1*DIGIT / "." 1*DIGIT)
+int-num		= ["-"] 1*DIGIT
+hex-num		= ["-"] ["0"] "x" 1*HEXDIG