Anyone know this book?

Hi


I bought myself a copy of "Compiler Construction" by N. Wirth in the
hope of learning how to write a simple compiler. While it's generally
very interesting and good fun, I have a problem when I get to a bit I
have trouble working out: since I am not following a course, I don't
have a tutor or other students to discuss things with. I would love to
correspond with someone who has used this book in a course and might
be able to explain a couple of points.


For example, in one section he discusses generating a "table" to
represent a grammar. A construct like
    p = t { '+' | '-' t }.
gets represented as
                    +-----------------+
                    v |
    p --> [ ] --> [ '+' ] --|
      ----/ | |
    / [ '-' ] --+
    t |
                                    [ EMP ]


(Does that make sense? That's one reason I'd like to write to someone
who has the book - so as not to have to copy the diagrams!)


but what I don't understand is: why the pseudo-terminal symbol "EMP"
(indicating a lack of an alternative terminal symbol) is needed. I'm
doing the exercise of writing a program to parse EBNF files and
generate such a graph and I can't figure out where to put the empties!


Thanks


Frank
--

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