快樂中的%%是什麼？

Question

我建立與快樂的解析器，發現這是online documentation：

YACC一樣，我們包括%%這裏，沒有真正的理由。

%%

必須有一個原因，不過，即使是微不足道的。有誰知道它是什麼？

Answer 1

它分隔Yacc源文件中的部分。例如見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