Re: EBNF definition for RPG?

Charles E. Bortle, Jr. <cbrtjr@ix.netcom.com> writes
>Our moderator wrote:
>> [Oh, you can certainly write a lexer that turns column positions
>> into tokens. But the syntax of RPG is so simple that BNF seems like
>> overkill. -John]
>
>Yes. I have been planning to do a RPG II for a long time, and I would
>never consider a formal parser. If I were coding the compiler in
>Pascal I would use variant records, and use the RPG record type as a
>tag field. Just read a line at a time fromt he source into the
>record. Now, based on the RPG record type in the tag field, just
>access the fields directly....no need to scan/parse since the record
>type automatically parses it for us into appropriate "buckets" :-)
>
>Just do semantic processing on a record by record basis since the
>record automatically pre-parses the input.
>
>The generated code is really just a pre-designed fixed logic
>algorithm, with allowances for the record type and control indicators.


I think you may have particular trouble with the "I" specifications;
its format varies according to what columns are used. For example it
could be a multi-line file description, a constant definition, a
rename of a field, part of a data structure plus quite a few other
possibilities, some of them machine dependent.
--
Jeremy Boden

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