Co to jest %% w Happy?

Question

buduję parser z szczęśliwy i zauważyłem to online documentation:

jak yacc zaliczamy %% tutaj, bez żadnego powodu.

%%

Musi być jakiś powód, chociaż, nawet jeśli jest to trywialne. Czy ktoś wie, co to jest?

Answer 1

Oddziela sekcje w źródłowym pliku Yacc. na przykład Zobacz http://dinosaur.compilertools.net/yacc/

Names refer to either tokens or nonterminal symbols. Yacc requires token names 
to be declared as such. In addition, for reasons discussed in Section 3, it is 
often desirable to include the lexical analyzer as part of the specification 
file; it may be useful to include other programs as well. Thus, every 
specification file consists of three sections: the declarations, (grammar) 
rules, and programs. The sections are separated by double percent ``%%'' marks. 
(The percent ``%'' is generally used in Yacc specifications as an escape 
character.) 

In other words, a full specification file looks like 

     declarations 
     %% 
     rules 
     %% 
     programs 
The declaration section may be empty. Moreover, if the programs section is 
omitted, the second %% mark may be omitted also; thus, the smallest legal Yacc 
specification is 

     %% 
     rules