7.2.4.1 Marking a Left-Hand Side ¶

The #l-… specifier marks the left-hand side of a production of a source PCFG. The production has nonterminal symbols at the right-hand side.

The specifier has the format:

#l-NonterminalSymbolOfSourcePCFG

where NonterminalSymbolOfSourcePCFG is the name of a nonterminal symbol at the left-hand side of a production of a source PCFG. That name is a sequence of English letters, digits, and the characters ‘_’.

There are a few kinds of places where inserting a #l-… specifier is necessary:

1. At the left-hand side of a production of a bottom-up template grammar.

   Example

   A/10 #l-A: B/3 C/3 D/4 ... ;
   

   The #l-A specifier here sets A as a nonterminal symbol at the left-hand side of a source PCFG production for the expression ‘B/3 C/3 D/4’. The source PCFG production might have the form

   A: B C D ... ;
   

2. Before ‘(’ … ‘)’ containing a set of alternatives separated by ‘|’.

   Example

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

   The #l-_A_1C specifier here sets _A_1C as a nonterminal symbol at the left-hand side of source PCFG productions for the expression ‘E … | F … | G …’. The source PCFG productions might have the form

   _A_1C: E ...
        | F ...
        | G ...
   ;
   

   If the right-hand side of a nonterminal symbol of a bottom-up template grammar is a set of alternatives separated by ‘|’, an #l-… specifier just after the nonterminal symbol contains a source nonterminal symbol at the left-hand side of source PCFG productions separated by ‘|’.

   Example

   A #l-A: E ...
         | F ...
         | G ...
   ;
   

   The #l-A specifier here sets A as a nonterminal symbol at the left-hand side of source PCFG productions for the expression ‘E … | F … | G …’. The source PCFG productions might have the form

   A: E ...
    | F ...
    | G ...
   ;
   

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

   Example

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

   The #l-_S_1A specifier here sets _S_1A as a nonterminal symbol at the left-hand side of a source PCFG production for a repeatable expression ‘D …’. The source PCFG production might have the form

   _S_1A: D ... ;