Re: COBOL Parsers

Mark Rickan wrote:
>
> Does anyone have any insights/experience on options for parsing COBOL?
> I am working on a project where we will need to extract data file
> declarations and access these files using other applications using
> multiplatform C/C++.


In fact, grammar of Cobol is fairly tricky at times.


Example: Cobol grammar is non LALR(1), that is it requires lookaheads
of more than one.


Example: to distinguish between 2 forms of PERFORM statement
PERFORM A OF B TIMES COMPUTE X=Y+Z END-PERFORM and
PERFORM A OF B COMPUTE X=Y+Z
we need a lookahead of 4 tokens.


In the 1st form A OF B is data item name
that contains conuter for PERFORM ... TIMES ... END-PERFORM stmt.
In the 2nd form A OF B is paragraph name performed
by PERFORM statement.


It probably can be made with some heavy symbol-table-based trickery,
but it does not really work here, because is some dialects A OF B can
be both paragraph name and data item name (2 diffrent names can have
the same name!).


So really doing your own Cobol grammar -- the one that works -- is too
expensive, as there are many pitfalls on the way. It tooks us 3 years
to get it right, which I would not qualify as easy.


Vadim Maslov
Siber Systems

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