[antlr-interest] Tree Grammar for loops

[Jim Idle]

Try input.mark() and input.release() instead?

Jim

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Christian Pontesegger
> Sent: Thursday, February 18, 2010 8:18 AM
> To: antlr-interest at antlr.org
> Subject: [antlr-interest] Tree Grammar for loops
> 
> Hi there,
> 
> I hope this list is intendend to ask for support.
> 
> I am desperately trying to write a tree grammar for a do-while loop. I
> got the following so far:
> 
> The source for the loop:
> ----------------------------
> 
>     int $loop = 0
>     do {
>         $loop = $loop + 1
>         foo()
>     } while ($loop < 3)
> 
> 
> for such a loop my parser gives me:
> ---------------------------------------
> 
>     (= int ($ loop) 0) (do { (= ($ loop) (+ ($ loop) 1)) foo } (< ($
> loop) 3))
> 
> 
> TreeGrammar.g:
> -----------------------
> 
> doWhileStatement
>     :
>         ^(
>         head='do' '{'                     {    int loopHead =
> ((CommonTree) head).getTokenStartIndex(); }
>             statementList
>         '}' e=expression              {    if (e.isTrue()) {
> 
> input.seek(loopHead);
> 
> doWhileStatement();
>                                                         }
>                                                     }
>         )
>     ;
> 
> the TreeGrammar is able to recognize the loop, but I am not able to run
> the loop a second time. as calling doWhileStatement() runs into an
> exception. How can I traverse parts of my tree again?
> 
> I was looking for tutorials and found:
> http://www.antlr.org/wiki/display/CS652/Tree-based+interpreters
> 
> ... but it seems a bit out of date.
> 
> any help is appreciated
> regards
> Christian
> 
> 
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