[antlr-interest] Need some help with AST creation

[Jim Idle]

You can just do this:


ddd: a=TOKEN^ B C D { $a.type = INDEX; } ;

Jim

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of John B. Brodie
> Sent: Friday, August 06, 2010 11:14 AM
> To: Luis Pureza
> Cc: antlr-interest at antlr.org
> Subject: Re: [antlr-interest] Need some help with AST creation
> 
> Greetings!
> 
> On Fri, 2010-08-06 at 16:41 +0100, Luis Pureza wrote:
> > Hi,
> >
> > I need some help from the ANTLR wizards :)
> 
> I am not sure I qualify as an ANTLR wizard, but I try to answer your
question
> anyway....
> >
> > I'm trying to match expressions with field accesses and array indexes.
> > For example:
> >
> > costumers.length
> > costumers[0].address
> > costumers[costumers.length - 1].orders[0].total
> >
> >
> > The following rule seems to work:
> >
> > fieldExpr      : atom ('.'^ identifier | ('['^ expr ']'!))*;
> >
> > However, it creates trees with notes annotated with '[', and I'd
> > prefer to have a dummy token like INDEX. For example, costumers[0] now
> > returns
> >
> > ([ (ID costumers) (INT 0))
> >
> > But I'd like it to return
> >
> > (INDEX (ID costumers) (INT 0))
> >
> > I tried to create the AST manually with -> ^(...), but I ended up
> > nowhere. Maybe I should've tried to refactor the grammar, but that
> > would make it a little less readable, so I didn't do it.
> > How do you suggest I do this?
> >
> 
> This is discussed starting on page 174 of Dr. Parr's book The Definitive
ANTLR
> Reference [TDAR]. It may also be somewhere in the wiki -- haven't looked
> for it there...
> 
> Bottom line: you are allowed to refer to the rule's name in a re-write
section.
> 
> but first you need to tell ANTLR about your imaginary tokens by putting
> 
> tokens { INDEX; DOT /* or whatever */; }
> 
> this belongs after the options{} block, if any, but before the first rule
> (possibly before any @members, can't remember...)
> 
> and now your fieldExpr rule becomes:
> 
> fieldExpr : ( a=atom -> $a /*initializes $fieldExpr*/ )
>     ( ( x='.' i=identifier -> ^(DOT[$x,"DOT"] $fieldExpr $i) )
>     | ( x='[' e=expr ']' -> ^(INDEX[$x,"INDEX"] $fieldExpr $e) )
>     )* ;
> 
> (note the above specific meta-syntax is from memory, may have some slight
> errors, but you get the idea, i hope)
> 
> (i think you do need all of those parentheses, as I recall, needed when
mixing
> rewrites in amongst syntax specifications)
> 
> (you can probably not have all of the labels (a=...,x=...,etc), but
somehow to
> my poor brain it is clearer with the labels)
> 
> so in its potentially tersest form:
> 
> fieldExpr :
>     atom ( ('.' identifier -> ^(DOT['.',"DOT"] $fieldExpr identifier)
>            ('[' expr ']' -> ^(INDEX['[',"INDEX"] $fieldExpr expr )
>          )* ;
> 
> 
> Hope this helps...
>    -jbb
> 
> 
> 
> 
> 
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