[antlr-interest] How to create many AST trees from one rule

[Indhu Bharathi]

Use scope variables to remember what you saw in a rule and emit it in
another rule further down in the chain. This will create the tree you want.
But I feel 'TYPE' node is not needed. It is good to build your AST as terse
as possible.

 

grammar Test;

options {

                output=AST;

}

 

tokens {

                DECL;

                TYPE;

}

 

decl

scope {

                Token typeTkn;

}

                :               type {$decl::typeTkn=$type.start;} varList
-> varList

                ;

                

type:     INT

                ;

                

varList

                :               var (COMMA var)* -> var+

                ;

                

var          :               ID -> ^(DECL ID ^(TYPE {$decl::typeTkn}))

                ;

                

INT         :               'int'

                ;

 

ID            :               'a'..'z'+

                ;

                

COMMA

                :               ','

                ;

 

WS         :               (' ' | '\t' | '\n')+ {$channel=HIDDEN;}

                ;

                

 

Cheers, Indhu

S7 Software

 

 

From: antlr-interest-bounces at antlr.org
[mailto:antlr-interest-bounces at antlr.org] On Behalf Of Jared Klumpp
Sent: Friday, October 30, 2009 1:14 AM
To: antlr-interest at antlr.org
Subject: [antlr-interest] How to create many AST trees from one rule

 

I'm trying to create a new DECL for each identifier - if this were C, int a,
b; would become (DECL A (TYPE INT)) (DECL B (TYPE INT)).

My rules (untested):
decl: type IDENTS SEMI
-> ^(DECL idents ^(TYPE $type));

idents: IDENT (COMMA IDENT)*
-> IDENT+;

My problem is this creates (DECL A B (TYPE INT)), how can I split this into
multiple trees when idents collects the identifiers into one tree?

Thanks,
Jared 

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