Purpose of $default and $end

[Samkit Jain]

Hi,

And I created a small program to test some small fundamentals and found that
there is a lot of difference between the below 2 rules.

sentence:   /* empty */
 |          sentence line optional_comma '$'        { printf("\nInput line:
>>>%s ::: %s <<<\n", $2, $3);   }
 ;


sentence:   sentence line optional_comma '$'        { printf("\nInput line:
>>>%s ::: %s <<<\n", $2, $3);   }
 ;

I am using scanf in yylex (my own yylex), which always accepts some string.

And now I am confused as to why is "/* empty */" necessary even when empty
cannot be returned by yylex.

When I checked the states generated by the parser, I found that there is a
difference in the way $default and $end are created for some states.

Can someone please tell me basic principle behind $end and $default terminal
symbols.


: Samkit Jain