[antlr-interest] Breaking a loop

[John Green]

Many thanks to Eric and to Sergey for suggesting recursion. That's exactly what I needed.

I wish I'd thought of it myself.  :)

Cheers


Eric Mahurin wrote:
> John Green wrote:
>>     I've got a pre-existing language with a requirement like this:
>> 
>>         (    ( (io_opt)* state_end )=> (io_opt)* state_end {break;}
>>         |    .
>>         )*
> 

> 
> Sorry, I meant to post this to the group.  I accidentally did a reply 
> instead of reply-all.  Used to another group where the reply-to field is 
> the group.
> 
> The way to recursively specify this is (not sure if I have the right 
> ANTLR syntax):
> 
> x : ( (io_opt)* state_end )=> (io_opt)* state_end
>    | . x
> 
> I find that many complex loops with strange termination conditions are 
> easier specified with recursion.  Terence, have you considered putting 
> tail-call optimization into ANTLR so that there isn't a downside with 
> specifying loops with recursion (actually infers a loop rather than 
> recursing)?  For reference, here is how I would specify the above in my 
> Grammar parser:
> 
> Tail { |x|
>   (io_opt.repeat0 + state_end).lookahead | # .lookahead equivalent to 
> self as syntactic predicate
>   ANY + x
> }
> 
> or a shorthand I have is (repeat0 method generates a Tail recursion 
> grammar):
> 
> ANY.repeat0((o_opt.repeat0 + state_end).lookahead)