Q: <fail>, and context-aware rules

[Vasily Chekalkin]

Austin Hastings wrote:
>>
>> token typedef_name {
>>     <identifier> <?{ is_a_typedef(~$0) }>
>> }
>>
> 
> Yeah, except it would be <?{{ ... pir ... }}>, and I'd prefer to code it 
> in NQP if possible. That's why I was wondering if there's a "fail from 
> within" function available in the Action methods.

It's definitely not possible within Actions. Because actions invoked for 
already parsed tree. OTOH you can use

token typedef_name {
     <identifier> <.ensure_typedef>
}

and implement Close::Grammar::ensure_typedef in NQP.

-- 
Bacek