[antlr-interest] Possible bug in swapping intermediary terminal?

[Mark Volkmann]

On Feb 1, 2008 2:29 PM, Dejas Ninethousand <dejas9000 at gmail.com> wrote:
> Hi,
>
> I'm having a problem getting a grammar to to accept "foo.bar.Dec" and I'm
> not sure why.  I think it may be a bug.  Consider my initial grammar:
>
> type_identifier
>      : IDENTIFIER
>     |
>     TYPE_IDENTIFIER_FULL
>     ;
>
> IDENTIFIER
>     : ('a'..'z'|'A'..'Z')('a'..'z'|'A'..'Z'|'0'..'9')*
>      ;
>
> PACKAGE_SEPARATOR
>     :    '.'
>     ;
>
> TYPE_IDENTIFIER_FULL
>     : IDENTIFIER (PACKAGE_SEPARATOR IDENTIFIER)+
>     ;
>
> This grammar accepts the "foo.bar.Dec" input no problems.  However, I wanted
> to modify the grammar to eliminate the the intermediary TYPE_IDENTIFIER_FULL
> terminal by taking its rhs and allowing it to directly derive from
> type_identifier:
>
> type_identifier
>     : IDENTIFIER
>     |
>     IDENTIFIER (PACKAGE_SEPARATOR IDENTIFIER)+
>     ;
>
> IDENTIFIER
>     : ('a'..'z'|'A'..'Z')('a'..'z'|'A'..'Z'|'0'..'9')*
>      ;
>
> PACKAGE_SEPARATOR
>     :    '.'
>     ;
>
> Now when I give ANTLRWorks the same "foo.bar.Dec" to interpret, it builds
> the tree :
>
> <grammar XXX>
>  type_identifier
> foo
> .
> bar
> .
> Dec
> NoViableAltException
>
>
> ... and I don't understand why.  These grammars seem equivalent to me.  Is
> there something I'm not seeing or is this a bug?

I hate it when people say "Works for me!"  ;-)
Unfortunately that's what I have to say here. I ran the ANTLRWorks
debugger on the following grammar and gave it your input of
"foo.bar.Dec" and it created the correct parse tree.

grammar package;

type_identifier
  : IDENTIFIER
  | IDENTIFIER (PACKAGE_SEPARATOR IDENTIFIER)+
  ;

IDENTIFIER
  : ('a'..'z'|'A'..'Z')('a'..'z'|'A'..'Z'|'0'..'9')*
  ;

PACKAGE_SEPARATOR: '.';

-- 
R. Mark Volkmann
Object Computing, Inc.