Re: Converting regex to DFA - rule diagram

Peter Friend wrote:


> I am working on building a regex compiler, and I am using the rules
> from the "Dragon Book" to convert the parsed regex to a DFA. To help
> with this, I have copied the diagram from page 138 and expanded it a
> bit to include lastpos and followpos. I am still working on the
> followpos entry for the '?' operator.


There should be no entry. You can think of e? as a | \epsilon. From
this you can derive that firstpos of e? is firstpos of e and there
should be no followpos rule (as there are none for | or \epsilon).


BTW, you need to replace all references to firstpos(e_1) and
firstpos(e_2) in the lastpos column by lastpos(e_1) and lastpos(e_2).


Torben Mogensen (torbenm@diku.dk)
--

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