Parser.cup

package Example;

import java_cup.runtime.*;

parser code {:
	public static void main(String args[]) throws Exception {
		SymbolFactory sf = new DefaultSymbolFactory();
		if (args.length==0) new Parser(new Scanner(System.in,sf),sf).parse();
		else new Parser(new Scanner(new java.io.FileInputStream(args[0]),sf),sf).parse();
	}
:}

// Here the terminal values for the parser are declared. They are linked to the tokens defined in the lexer file. The tokens TRUE, FALSE, NUMBER and STRING have a Java data type defined so that they could later be used in Java code inside the parser. 


terminal COMMA, COLON, LSQBRACKET, RSQBRACKET, LCLBRACKET, RCLBRACKET, NULL;
terminal Boolean TRUE, FALSE;
terminal Double NUMBER;
terminal String STRING;

//The non-terminal values that will be used in the grammar are defined here.

non terminal object, array, value, value_list, pair_list, string_value_pair;

//These non terminals are used to test the code by printing out the values in an array and the name/value pairs in an object.

non terminal Object print_value;

non terminal String print_string;



// Here the grammar is defined. This closely follows the JSON specification. 

//A value in JSON can be a string, number, boolean, null, object or array. The extra code in here prints out the values.

value::= STRING:n {: RESULT = n; :}|NUMBER:n {: RESULT = n; :}|TRUE:n {: RESULT = n; :}|FALSE:n {: RESULT = n; :}|NULL:n {: RESULT = n; :}|object:n {: RESULT = n; :}|array:n {: RESULT = n; :} ;

//this will print the value in an array or a JSON object. this includes all types of value, not just string or numerical. 
print_value ::= value:e {: System.out.println("value: "+e+""); :};

//An object in JSON can be a list of 1 or more string/value pairs or it can be a left curly bracket followed by a right curly bracket with nothing inside. The individual string/value pairs are a string followed by a colon followed by a  value and the pairs are separated by commas within the list.

//Error handling was added so that when the parser encounters an error within object, the parsing will stop until the end of the current curly bracket (i.e. a right curly bracket).
 
object ::=  LCLBRACKET pair_list RCLBRACKET | LCLBRACKET RCLBRACKET| error RCLBRACKET ;
pair_list ::=  pair_list COMMA string_value_pair |string_value_pair;
string_value_pair ::= print_string COLON print_value ;

// this will print the name in a name/value pair within a JSON object. 

print_string ::= STRING:s  {: System.out.println(" name: "+s+""); :};


//An array in JSON can be a list of 1 or more values or it can be a left square bracket followed by a right square bracket with nothing inside. The individual values within the list are separated by commas.  

//Error handling was added so that when the parser encounters an error within array, the parsing will stop until the end of the current square bracket (i.e. a right sqaure bracket).

array ::= LSQBRACKET value_list RSQBRACKET | LSQBRACKET RSQBRACKET| error RSQBRACKET;
value_list ::= value_list COMMA print_value  | print_value  ;