jflexcup

Parse EOF token in CUP


I'm having trouble making my CUP parser parse the EOF token. I read in the documentation that using the %cup flag in my Jflex code implies that there is something present like this:

%eofval{
  return new java_cup.runtime.Symbol(<CUPSYM>.EOF);
%eofval}
%eofclose

This is all good and well, but when I try the following first rule in my grammar (CUP file):

program                 ::=   program declaration EOF
                          | /* Empty */
                          ;

I get the error message that EOF is not declared by CUP.

Error : java_cup.runtime.Symbol "EOF" has not been declared

Allrighty, so I add the following to my CUP file:

terminal EOF;

No, because then CUP tells me:

Fatal : JavaCUP Internal Error Detected: Duplicate terminal (EOF) created
enter code here

However, without defining the terminal EOF, and I have a look in the sym.java class that Cup generates I do find:

  public static final int EOF = 0;

So I'm pretty lost on how to fix this. The documentation for both is really vague on the issue.

Edit: The main reason I want to parse the EOF token is because I want to print out my symbol table in the end and other stuff for debugging purposes.


Solution

  • Okay, so instead of explicitly parsing the EOF token to execute some code I added the following "wrapper" to my grammar, which allows me to do exactly what I wanted to do.

    Instead of:

    program                 ::=   program declaration
                              | /* Empty */
                              ;
    

    I now have:

    initial                 ::=   program   {: /* Code for EOF here */ :}
                              ;
    program                 ::=   program declaration EOF
                              | /* Empty */
                              ;
    

    This allows me to execute code at the end of every succesful parse.