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include [2021/04/01 13:00] – revuskyinclude [2023/03/03 16:20] (current) – revusky
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 # The INCLUDE Statement # The INCLUDE Statement
  
-JavaCC 21's **INCLUDE** statement allows you to break up your grammar file into multiple physical files. It would look like this typically:+Congo's **INCLUDE** statement allows you to break up your grammar file into multiple physical files. It would look like this typically:
  
     INCLUDE "IncludedGrammar.javacc"     INCLUDE "IncludedGrammar.javacc"
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 In legacy JavaCC, if you defined a token production without specifying a lexical state, any lexical definitions belonged to a lexical state called "DEFAULT". Now, obviously, this is a problem once you have an INCLUDE disposition, because the including and included grammar are liable to have a "DEFAULT" lexical state and, typically, we don't want the respective definitions to clobber one another.  In legacy JavaCC, if you defined a token production without specifying a lexical state, any lexical definitions belonged to a lexical state called "DEFAULT". Now, obviously, this is a problem once you have an INCLUDE disposition, because the including and included grammar are liable to have a "DEFAULT" lexical state and, typically, we don't want the respective definitions to clobber one another. 
  
-Thus, JavaCC 21 introduces a setting called **DEFAULT_LEXICAL_STATE**. That means that any lexical specifications where the lexical state is unspecified are in that state. Thus, a JSON grammar would likely have something like this at the top:+Thus, CongoCC has a setting called **DEFAULT_LEXICAL_STATE**. That means that any lexical specifications where the lexical state is unspecified are in that state. Thus, a JSON grammar would likely have something like this at the top:
  
  
-    DEFAULT_LEXICAL_STATE="JSON";+    DEFAULT_LEXICAL_STATE=JSON;
  
          
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 ## Wrinkles with Code Injection ## Wrinkles with Code Injection
  
-JavaCC still supports the legacy JavaCC constructs of **PARSER_BEGIN...PARSER_END** and **TOKEN_MGR_DECLS**. (For how much longer, I am not making any promises...). However, those constructs are ignored within an **INCLUDE**d grammar. +You can  *inject* code into the generated parser or lexer class, from within an included grammar, but you need to write something like:
- +
-You can still *inject* code into the generated parser or lexer class, from within an included grammar, but you need to write something like:+
  
     INJECT PARSER_CLASS :      INJECT PARSER_CLASS : 
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     }     }
    
-JavaCC 21 will replace the **PARSER_CLASS** and **LEXER_CLASS** aliases with the appropriate names -- i.e. the actual class names of the XXXParser or XXXLexer being generated. So, if you have a Foo language in which you want to embed JSON expressions, so you include a JSON grammar, if that JSON grammar is to include some code within the generated parser, it cannot be:+CongoCC 21 replaces the **PARSER_CLASS** and **LEXER_CLASS** aliases with the appropriate names -- i.e. the actual class names of the XXXParser or XXXLexer being generated. So, if you have a Foo language in which you want to embed JSON expressions, so you include a JSON grammar, if that JSON grammar is to include some code within the generated parser, it cannot be:
  
     INJECT JSONParser :     INJECT JSONParser :
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     }     }
  
-because the parser class we are generating is not JSONParser, it is FOOParser! However, the person writing a a generally useful JSON grammar that can be embedded in other grammars does not know the classname of Parser (or Lexer) that is being generated. So, he needs to use the alias **PARSER_CLASS** or possibly **LEXER_CLASS** for the injected code to be included. +because the parser class we are generating is not JSONParser, it is FooParser! However, the person writing a a generally useful JSON grammar that can be embedded in other grammars does not know the classname of Parser (or Lexer) that is being generated. So, he needs to use the alias **PARSER_CLASS** or possibly **LEXER_CLASS** for the injected code to be included.
- +
-So, do not be surprised when the code within PARSER_BEGIN...PARSER_END is ignored if it is within an INCLUDEd grammar. You need to write INJECT(PARSER_CLASS) to achieve the desired result.+
  
 In fact, the aliases **PARSER_CLASS**, **LEXER_CLASS**, **CONSTANTS_CLASS**, and **PARSER_PACKAGE** can be used in code injections and java actions to make an included grammar (or grammar fragment) more generally useful. In fact, the aliases **PARSER_CLASS**, **LEXER_CLASS**, **CONSTANTS_CLASS**, and **PARSER_PACKAGE** can be used in code injections and java actions to make an included grammar (or grammar fragment) more generally useful.
  
-To see a concrete example of **INCLUDE** in use, you can take a look at https://github.com/javacc21/javacc21/tree/master/src/grammars. Specifically, you can see that the JavaCC.javacc grammar **INCLUDE**s the Java.javacc. Another point is that this Java.javacc grammar file is, on its own quite generally usable. And useful!+To see a concrete example of **INCLUDE** in use, you can take a look at https://github.com/congo-cc/congo-parser-generator/tree/master/src/grammars. Specifically, you can see that the CongoCC.ccc grammar **INCLUDE**s the Java.ccc. Another point is that this Java.ccc grammar file is, on its own quite generally usable. And useful!
  
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