[antlr-interest] Tree-based interpreters

[Terence Parr]

Hi. they use a custom AST node.
Ter
On Mar 25, 2009, at 9:58 AM, Joern Gebhardt wrote:

> Hi,
>
> I found in the wiki (http://www.antlr.org/wiki/display/CS652/Tree-based+interpreters 
> ) a page that describes how an if-statement could be processed based  
> on an AST.
>
> The grammar stated there looks like this:
>
> ifstat
>     :   ^('if' c=expr s=. e=.?) // ^('if' expr stat stat?)
>         {
>         int next = input.index();
>         if ( ((Boolean)$c.value).booleanValue() ) {
>
>             input.seek($s.start.streamIndex);
>             stat();
>         }
>         else if ( $e!=null ) {
>             input.seek($e.start.streamIndex);
>             stat();
>         }
>         input.seek(next);
>
>         }
>     ;
>
> I tried this out but wasn't able to extract the "streamIndex" out of  
> the statement CommonTree objects "s" and "e" (by the way, this is  
> already stated as comment on the wiki).
> I only found was the "startIndex" and "stopIndex" but I guess that  
> these attribute refer to the token position in the token stream  
> created by the lexer.
>
> Is there any possibility to get the index of the  
> CommonTreeNodeStream (and not the token stream)? Or do you have any  
> other suggestions how I could use a tree-grammar
> to process if-statements?
>
> Thanks in advance,
> Joern
>
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