Re: java parsing problem

<shirleytemple@my-deja.com> wrote:
>
> Is this left-recursion?


Yes. ("left-recursion" means there's a recursion in the productions that
threads through the leftmost symbol in each production.)


You'll have to rewrite the grammar to make it LL.
A simple-minded rewrite would be to expand productions until you get
something like


    Primary:
        ... -- Other productions 1
        Primary . Identifier
        ... -- Other productions 2
and to rewrite this as
    Primary:
        Simple_Primary
        Simple_Primary . Primary_Sequence
    Simple_Primary:
        ... -- Other productions 1
        ... -- Other productions 2


which is LL.
More intelligent rewrite techniques might exist; the above is textbook
knowledge.


I'm not 100% sure, but I dimly remember that not all LR languages are LL
(and vice versa). If that's the case, I suspect that there's no general
algorithm for transforming an LR grammar into an LL one; grammar
transformations tend to run into undecidability issues pretty quickly.


Regards,
Joachim

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