[antlr-interest] to stop walking into a subtree

[poroshpathor poroshpathor]

Gary,
Your solution makes a lot of sense to me. I was absolutely looking for some 
solution like that.
Thank you very much.

Martijn
As I was new in the area, I didnt know that i could do the tree operation.
Now, I am fine with it. Thanks a lot.

Porosh
>Hello,

>I personally prefer a manual tree-visitor (which walks the AST), that
>way you can just evaluate a node and based on the result take
>appropriate action, it also allows more control (e.g. multi-phases if
>needed). The main reason I do it that way is I don't want any of my
>grammars getting cluttered with hard to maintain code in between (Java
>e.g..) Disadvantage is, if your grammar is large, your visitor may get
>complex. So it both has its advantages and disadvantages.

>Cheers!
>Martijn

On Wed, Apr 6, 2011 at 3:13 AM, Gary Miller <miller.garym at gmail.com> wrote:
> Hi Porosh,
>
> One way to do this is to skip the walk of the second operand (op2) is
> the tree grammar and call some java code to continue the walk if
> necessary. See example (this is sample code and is not expected to
> compile as is) below.
>
> Question: Does anyone know and a way this can be done without needing
> to create a new TreeNodeStream? Maybe using a predicate to acess the
> op2 without changing the position in the TreeNodeStream?
>
> Regards
>
> Gary
>
>
> Sample code.
>
> @members {
>
> ?boolean continueBooleanexpression(TreeParser walker, Tree op) throws
> RecognitionException {
>
> ? ?// Save the current TreeNodeStream
>
> ? ?TreeNodeStream tns = walker.getTreeNodeStream();
>
> ? ?boolean result =
> ? ?try {
> ? ? ?CommonTreeNodeStream nodes = new CommonTreeNodeStream(op);
> ? ? ?nodes.setTokenStream(walker.getTreeNodeStream().getTokenStream());
>
> ? ? ?// Use the same walker so state (scope, member etc.) is preserved.
> ? ? ?walker.setTreeNodeStream(nodes);
>
> ? ? ?// Continue the walk
>
> ? ? ?// Probably doesn't return a boolean,
>
> ? ? ?// might need to be something like walker.booleanexpression().result;
> ? ? ?result = walker.booleanexpression();
> ? ?} finally {
>
> ? ? ?// Resort original TreeNodeStream
> ? ? ?walker.setTreeNodeStream(tns);
> ? ?}
> ? ?return result;
>
> ?}
>
> }
>
> booleanexpression returns[boolean result]
> : ?^(AND op1=booleanexpression op2=.)
> ? ?{
> ? ? ?if( $op1 ) {
> ? ? ? ?boolean op2Result = continueBooleanexpression(this, $op2);
> ? ? ? ?if( op2Result ) {
> ? ? ? ? ?result = true;
> ? ? ? ?} else {
> ? ? ? ? ?result =false;
> ? ? ? ?}
> ? ? ?} else {
> ? ? ? ?result = false;
> ? ? ?}
> ? ?}
> ;
>
>> booleanexpression returns[boolean result]
>
>> :* ?^(AND op1 = booleanexpression op2 = booleanexpression) {if(op1&&op2) result 
>>= *> true; else result =false;}
>> ;
>>
>> My question:
>> I want to stop walking once I found op1 as false. In that case, I don't need 
>to
>> evaluate op2 anymore, the result is false anyway.
>>
>> Is there any way to implement this?
>
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