[antlr-interest] Converting Tree operands ('^' '!') to rewrite rules ( '-> ^(...)')

[Jens Boeykens]

Bounced on a problem:

What should be the rewrite rule for this operand rule:
*rule   :    id ('+'^ id)*;

*I can't even find one. Tried several things, and I assume you are forced to
use recursion, or are there other (as simple as possible) ways?

*rule :  id | (id '+' rule) -> ^('+' id rule);
**rule :  | id rule | ('+' id rule);

*But these rules don't parse because the first alternative is unreachable in
both cases. I don't understand why though... id doesn't have an empty
alternative or a '+'.

Jens

2008/7/11 Jens Boeykens <jens.boeykens at gmail.com>:

> Hello,
>
> I'm a student in computer science and for the moment I'm doing internship
> in a  company (Sigasi <http://www.sigasi.com/>) mainly working on hardware
> refactoring.
> So far, I have written a program which can read a .g grammar as input,
> parse it into a tree and automatically regenerate the grammar by using a
> stringtemplate I have written. This regeneration allows some useful things.
> e.g. I have written something to sort the rules alphabetically using the
> trees, and then  regenerate the  grammar from the tree resulting in a
> grammar with sorted rules.
>
> The next step is to convert tree operands to rewrite rules. Eg.
>
> *rule : a b^ c d^ e;*
> will be automatically converted to*
> rule: a b c d e -> ^(d  ^(b a c) e);*
>
> My question is: does there already exists something that I could reuse (and
> where to find it) or can you give me some tips to achieve this? The
> convertion will probably be done on the trees which are created with my
> (slightly modified) ANTLRv3.g. Thus for the previous example:
>
> *(RULE rule (BLOCK (ALT a (^ b) c (^ d) e EOA) EOB) EOR) *
> needs to be converted somehow to
> *(RULE rule (BLOCK (ALT a b c d e EOA) (-> (ALT (TREE_BEGIN d (TREE_BEGIN
> b a c) e) EOA)) EOB) EOR)*
>
> My regenerator will then read in the second tree and thus generate a
> grammar with a tree rewrite rule.
> The conversion itself is not very simple so any  help is appreciated.
> Difficulties are rules with alternatives which have complex trees:
> *rule : (a^ | b^) c ;*
>
> Am I correct that rules like *rule : (a b)^ c ;   *and* **rule : (a b)! c
> ; *are no longer allowed? It parses but doesn't really make sense in my
> oppinion.
>
> So why would I want to do all this? Well with the rewrite rules it is
> easier to create the tree walker from a parser. This is the final goal: when
> you have written a parser grammar for a language, you can give it to my
> tool, and it will automatically generate a tree grammar from it. Thus no
> need to do it manually or to create 2 grammars.
>
> Best regards,
> Jens
>
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