[antlr-interest] Antlr Book Chapter 3 troubles

[Terence Parr]

Oh, crap. that's antlr's atom rule...not yours! Ooops. sorry. adding  
to list.
Ter
On Sep 5, 2008, at 1:40 PM, Tim Halloran wrote:

> Thanks Jim,
>
> Yes, I typo-ed the example it was
>   | ^('=' ID expr)
> not
>   | ^('=' ID.expr)
> on page 65 of the book.
>
> A bit tricky to diagnose, hopefully this will improve in future  
> releases.  In particular, your heuristic approach could be used  
> inside the tool implementation to at least report which rule has  
> some sort of problems.
>
> Thanks,
> Tim
>
>
> On Fri, Sep 5, 2008 at 4:26 PM, Jim Idle <jimi at temporal-wave.com>  
> wrote:
> On Fri, 2008-09-05 at 13:17 -0700, Terence Parr wrote:
>>
>> On Sep 5, 2008, at 12:44 PM, Tim Halloran wrote:
>> > [15:36:28] error(10):  internal error: /Users/tim/Source/antlr- 
>> Work/
>> > Ch3 Expr AST/src/Eval.g : java.lang.NullPointerException
>> > org.antlr.codegen.CodeGenTreeWalker.atom(CodeGenTreeWalker.java: 
>> 1959)
>>
>> I don't see rule atom.
>
> That's the ANTLR stack trace not the grammar trace. This is  
> happening because something in the input source for the tree grammar  
> is wrong, but the v3 grammar doesn't catch it and produces a tree  
> that causes NPE.
>
> At the moment, the only way to work out what it is, is to remove  
> your actions one at a time and try, then remove any parameters or  
> returns and so on, and suddenly it will compile - then you will know  
> which bit is in error.
>
> However I can save you a little trouble by pointing out that the  
> problem is this:
>
> | ^('=' ID.expr)
>
> You have put ID.expr in the grammar spec and it needs to be just ID.
>
> Jim
>>
>> Ter
>> >
>>
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