7.2.4.2 Marking a Right-Hand Side ¶

The #r… specifier marks a right-hand side of a production of a source PCFG. The right-hand side consists of nonterminal symbols.

The specifier has the format:

#rIndexOfRightHandSide

where IndexOfRightHandSide is a non-negative integer number. It is the identifier of a right-hand side of a nonterminal symbol in a source PCFG.

There are a few kinds of places where inserting an #r… specifier is necessary:

1. At the end of the right-hand side of a production in a bottom-up template grammar if that right-hand side is not a set of alternatives separated by ‘|’.

   Example

   A #l-A: B C D #r0 ;
   

2. At the end of each alternative in a set of alternatives separated by ‘|’.

   Example 1

   A #l-A: E #r2
         | F F #r0
         | G G G #r1
   ;
   

   The source PCFG productions might have the form

   A: F F
    | G G G
    | E
   ;
   

   Example 2

   A #l-A: B C D #l-_A_1C ( F F #r1
                          | G G G #r2
                          | E #r0
                          ) ...
   ;
   

   The source PCFG productions for the nonterminal symbol _A_1C might have the form

   _A_1C: E
        | F F
        | G G G
   ;
   

3. At the end of a subexpression quantified by ‘*’.

   Example

   S #l-S: B C ( #l-_S_1A D D #r0 )* ...