[antlr-interest] manual AST construction: what am I doing wrong?

[Ric Klaren]

On Sun, Jun 15, 2003 at 01:26:35PM +0200, Jorge Scandaliaris wrote:
> 	How can I generate for a rule a single AST node, using manual
> tree construction?

In a nutshell:

myrule ! : st:SOME_TOKEN
{ ## = #([MY_IMAG_AST_NODE, st->getText()]);
  ##->setSomeAttrib( sumthin );
}
;

Alternatively you can also use #myrule in stead of ##.

> 	I have created created a custom AST class. I have defined the
> option ASTLabelType = "RefMyAST";	It is sort of working. I say
> this 'cause I came over some issues and I am not sure if it is ANTLR'
> expected behaviour or I did something wrong.

> 	In view of this I decided that I don't need to generate all the
> nodes corresponding to all sub rules, but that I only need the node
> corresponding to the rule.
> 	I tried using ! at the rule and sub rules levels, but here is
> where problems appear. If I use say:
> rule!
> : .....
> { ## = #[##];
>   #->addSrc(...); // addSrc() is defined for MyAST
> }
> I have a run-time error in addSrc(). I think this is due to a missing
> astFactory->addChild(...)in the generated code compared to when
> automatic AST building is done (what is the purpose of this anyway? And
> why it is only there for automatic tree building?).

The addChild stuff is used to generate the tree e.g. to link sibling/child
nodes together. If you turn it off you have to do this manually via the
#( .. ) syntax. If you have rules with multiple parts which may return AST
trees you may have to label them and then put them together yourself.

e.g.

some_rule: p1:other_rule p2:ignore_rule p3:great_other_rule
{
   ## = #( #p1, #p3 ); // only link up p1 and p3
};

Hmmm lemme refer to this old post of Mike Barnett for some more stuff:

http://wwwhome.cs.utwente.nl/~klaren/antlr/treebuilding.txt

> Please, if someone can enlighten me on this, or point me to some
> resources (I didn't find a lot). Maybe I got the semantics of AST
> completely wrong?

There might be some jewels in the archives, maybe even still something
usefull in the FAQ site.

Cheers,

Ric
--
-----+++++*****************************************************+++++++++-------
    ---- Ric Klaren ----- j.klaren at utwente.nl ----- +31 53 4893722  ----
-----+++++*****************************************************+++++++++-------
  "You can't expect to wield supreme executive power just because some
   watery tot throws a sword at you!"
  --- Monty Python and the Holy Grail

 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/