[antlr-interest] Dangling ELSE on Cobol

[Juancarlo Añez]

Nilo,

It's a lot of lookahead, but it solves your problem:

command :
    ifCmd
    | 'INIT'
    | 'MOVE'
    ;

ifCmd:
    'IF' 'EXPRE' ((command)=>command)+
    (
        ('ELSE')=> 'ELSE' ((command)=>command)+
    |
        ()
    )
    ;

The ambiguity warning were saying that ANTLR didn't know to which nesting
level to add the next "command". The lookaheads tell it to be greedy and
match them against the closest IF or ELSE.

Cheers,

-- Juanca

On Thu, Sep 20, 2012 at 2:50 PM, Nilo Roberto C Paim <nilopaim at gmail.com>wrote:

> Hi, folks.
>
> I'm trying to parse Cobol sources using Antlr 3.4 (ANTLR Parser Generator
> 3.4 Jul 19, 2011 11:35:12. actually).
>
> I'm stuck with the old dangling ELSE problem. Here the relevant piece of
> code of my grammar that shows me the problem:
>
>
>         command :
>                 ifCmd
>                 |       initializeCmd
>                 |       moveCmd
>                 |       openCmd
>                 ;
>
>         ifCmd:
>                         IF expr command+ ( (ELSE)=> ELSE command+)?
>                 ;
>
>
> I cannot put a terminator on the commands 'cause commands in Cobol may end
> or with a '.' or with the following command. This is true including the
> ifCmd itself.
>
> The code above shows me the following messages:
>
> warning(200): /SuperCobol/src/SC.g:229:13:
> Decision can match input such as "IF" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> IF expr command+ ( (ELSE)=> ELSE command+)?
>
> warning(200): /SuperCobol/src/SC.g:229:13:
> Decision can match input such as "MOVE" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> IF expr command+ ( (ELSE)=> ELSE command+)?
>
> warning(200): /SuperCobol/src/SC.g:229:13:
> Decision can match input such as "OPEN" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> IF expr command+ ( (ELSE)=> ELSE command+)?
>
> warning(200): /SuperCobol/src/SC.g:229:13:
> Decision can match input such as "INITIALIZE" using multiple alternatives:
> 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> IF expr command+ ( (ELSE)=> ELSE command+)?
>
> warning(200): /SuperCobol/src/SC.g:229:38:
> Decision can match input such as "IF" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> IF expr command+ ( (ELSE)=> ELSE command+)?
>
> warning(200): /SuperCobol/src/SC.g:229:38:
> Decision can match input such as "MOVE" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> IF expr command+ ( (ELSE)=> ELSE command+)?
>
> warning(200): /SuperCobol/src/SC.g:229:38:
> Decision can match input such as "OPEN" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> IF expr command+ ( (ELSE)=> ELSE command+)?
>
> warning(200): /SuperCobol/src/SC.g:229:38:
> Decision can match input such as "INITIALIZE" using multiple alternatives:
> 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> IF expr command+ ( (ELSE)=> ELSE command+)?
>
>
> 8 warnings
>
> Please, any hints?
>
> Thanks in advance,
> Nilo
> Brazil
>
>
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-- 
Juancarlo *Añez*