[antlr-interest] V3 Rule Action allowing inline tree building?

[Sam Harwell]

Once you get the hang of it, you can do it by hand without too much
trouble. For example, in converting a v2 grammar to v3, I encountered
this in the members section:

 

stringAlias =

        #(#[BLOCK], #(#[ALT], #[STRING_LITERAL], #[EOA]), #[EOB]);

 

Which became this (you can use CommonTree instead of GrammarAST). Note
that this uses the CSharp3 target so the function names are capitalized,
unlike the Java target.

 

/*

 * stringAlias = ^(BLOCK[] ^(ALT[] STRING_LITERAL[] EOA[]) EOB[])

 */

stringAlias = (GrammarAST)adaptor.Create( BLOCK, "BLOCK" );

{

    GrammarAST alt = (GrammarAST)adaptor.Create( ALT, "ALT" );

    adaptor.AddChild( alt, adaptor.Create( STRING_LITERAL,
"STRING_LITERAL" ) );

    adaptor.AddChild( alt, adaptor.Create( EOA, "EOA" ) );

    adaptor.AddChild( stringAlias, alt );

}

adaptor.AddChild( stringAlias, adaptor.Create( EOB, "EOB" ) );

 

In your case, you'd use something like this:

 

CommonTree tree = (CommonTree)adaptor.Nil();

adaptor.AddChild( tree, adaptor.Create( LITERAL_enum, "enum" ) );

adaptor.AddChild( tree, adaptor.Create( ID, enumName ) );

 

Sam

 

From: antlr-interest-bounces at antlr.org
[mailto:antlr-interest-bounces at antlr.org] On Behalf Of Lucien Antlr
Sent: Wednesday, March 18, 2009 11:53 AM
To: antlr-interest at antlr.org
Subject: [antlr-interest] V3 Rule Action allowing inline tree building?

 

Hi folks,

 

I saw back in 2005 there was a bit of discussion around inline tree
building.   ( linked here 

http://markmail.org/message/7zigjknpakugflje
<http://markmail.org/message/7zigjknpakugflje>  ).  For practice I am
converting the freely available C v2 ANTLR .g  and I came over a rule
that has me stuck...

 

It keeps the internal symbol-table by adding part of a tree into the
symbol table along with the C symbol (in this case enum).

 

Normally a v2 rewrite would look like below (from stdcparser.g)

 

enumerator[String enumName]
        :       i:ID                { symbolTable.add(  i.getText(),
                                                        #(   null,
 
#[LITERAL_enum, "enum"],
                                                            #[ ID,
enumName]
                                                         )
                                                     );
                                    }
                (ASSIGN constExpr)?
        ;

#( ) under v2 calls ASTFactory.create(), but under v3 it just appears to
pass straight through into the Java target?  

 

This is true even when re-written, as I guessed it should be below.

 

enumerator[String enumName]  

        :       i=ID         { symbolTable.add(  $i.text,
                                                        ^(   NULL,
 
^(LITERAL_enum),
                                                            ^(ID
$enumName.text)
                                                         )
                                                     );
                                    }
                (ASSIGN constExpr)?
        ;

The only thing I came up with is "rewriting" the rule, and creating a
dummy rule inside and using $dummy.tree inside the action.

 

Any thoughts from the more experienced community?

 

Kind Regards,

 

Luc

 

 

 

 

 

 

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