[antlr-interest] RES: COBOL grammar

[Nilo Roberto C Paim]

Thanks, Parsiad, for your help.

Indeed the ambiguities are 'solved'... but using your solution, only the
first 'command' of the first 'block' of the first 'paragraph' are parsed!

And I don't have something I can call 'END_BLOCK', as you suggested. This
thing would be a '.', that can be preceded by a 'command' either... and the
problem returns...

What else am I missing?

TIA,
Nilo - Brazil

-----Mensagem original-----
De: antlr-interest-bounces at antlr.org
[mailto:antlr-interest-bounces at antlr.org] Em nome de Parsiad Azimzadeh
Enviada em: segunda-feira, 11 de julho de 2011 14:36
Para: antlr-interest at antlr.org
Assunto: Re: [antlr-interest] COBOL grammar

Hi Nilo,

The problem is that a paragraph contains any number of blocks and a block
contains any number of commands (the ambiguity here is that some paragraph
with two commands can be perceived as containing either two blocks each with
one command or a single block with two commands).

The fix is simple, remove the * symbol from the line:
paragraph : ID '.' block* '.';

If multiple blocks holds semantic value, you might need to use a symbol to
denote the end of a block. For example, instead of using the fix above you
could change the block rule to:

block: (command END_BLOCK)*;

-- 
Parsiad Azimzadeh
http://sfu.ca/~paa4

On Mon, Jul 11, 2011 at 9:46 AM, Nilo Roberto C Paim
<nilopaim at gmail.com>wrote:

> Hi all,
>
> I'm facing a problem on my grammar that I don't know how to solve
> (Antlr3.3)...
>
> Let me show you my grammar. Simplified, of course. It's just to show you
my
> trouble.
>
>
>
>
>
> grammar Cobol;
>
> options {
>  language = Java;
> }
>
> program : 'procedure' 'division' '.' section*;
>
> section : ID 'section' '.' paragraph*;
>
> paragraph : ID '.' block* '.';
>
> block : command*;
>
> command: (cmdA | cmdB | cmdC ) '.'?;
>
> cmdA: 'A';
>
> cmdB: 'B';
>
> cmdC: 'C';
>
> fragment Digit : '0'..'9';
>
> fragment Letter : ('a'..'z' | 'A'..'Z');
>
> ID : Letter ( Letter | Digit | '-' )*;
>
>
>
>
>
> Using this grammar, I'm having the following errors and warnings:
>
> warning(200): /Cobol/src/Cobol.g:14:12: Decision can match input such as
> "{'.', 'A'..'C'}" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> ID '.' block* '.';
>
> error(201): /Cobol/src/Cobol.g:14:12: The following alternatives can never
> be matched: 2
>  |---> ID '.' block* '.';
>
> warning(200): /Cobol/src/Cobol.g:17:5: Decision can match input such as
> "'B'" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> command*;
>
> warning(200): /Cobol/src/Cobol.g:17:5: Decision can match input such as
> "'A'" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> command*;
>
> warning(200): /Cobol/src/Cobol.g:17:5: Decision can match input such as
> "'C'" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>  |---> command*;
>
>
> 4 warnings
>
> 1 error
>
> BUILD FAIL
>
>
>
> My real problem is:
>
> 1) any 'command' can be followed by a '.'
> 2) any sequence of 'command's not followed by '.' forms a 'block'
> 3) wherever I can use a 'command', I can use a 'block'
> 4) the '.' signifies the end of a 'block'
> 5) I can use any number of 'block's to form a 'paragraph'
> 6) I can use any number of 'paragraph's to form a 'section'
> 7) I can have any number of 'section's on a 'program'
>
> Any hints or help about what am I doing wrong? I'm completely stuck on it,
> 'cause I'm a little newbie using Antlr...
>
> TIA,
> Nilo - Brazil
>
>
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