[antlr-interest] Implementation decision help

[Gustaf Johansson]

Hello!

I am trying to implement the ETSI TTCN-3 BNF into Antlr.
The major part is done and working as it should but there are some
quirks which i don't know how to solve.

I have rules like this:
stm : stmGroup1 | stmGroup2 ... | stmGroupX;

And all/some of these stmGroup's can start with the same type of
token, but they are distinguishable by some token along the line
further down the parse tree.

I have tried to solve this by using backtrack=true which didn't work.

My current solution is a specific order of the stmGroup's and a few
syntactic predicates. But i don't like this solution since i don't
know if it will work for all possible input (the grammar is really
complex).

Basically what i want to accomplish is make Antlr try all of the rules
in "stm" and only report error if none of them matches. Currently it
reports errors even though a rule later in the list will match the
input completely, just because the rule reporting the error matches it
partly.

The only solution other then syntactic predicates and backtrack i can
think of is to combine the stmGroup's into a rule which has truly
distinctive paths depending on the next token.
Is this the way to do it?
It will require a huge amount of work since all the stmGroup's are
quite large and complex themselves. Also it will make the grammar
almost unreadable.



An example of a problematic rule is:
http://www.trex.informatik.uni-goettingen.de/trac/wiki/ttcn-3_4.0.4#FunctionStatement

These are two parts of that problem:
-> ConfigurationStatements -> StartTCStatement
-> TimerStatements -> StartTimerStatement

PS. backtrack is not used at all in the grammar.

BR Gustaf