On Nov 6, 2008, at 4:32 PM, Brice Figureau wrote:
>
> On 27/10/08 16:59, Luke Kanies wrote:
>> On Oct 25, 2008, at 8:48 AM, Brice Figureau wrote:
>>> I choose to push the comments on the stack on each LBRACE and pop on
>>> each RBRACE. I also fetch a reset the current stack level on each
>>> statement reduction. This way I can attach comment precisely to the
>>> puppet statement they belong to.
>>
>> Seems reasonable. I did something similar when I had some code that
>> needed to know whether it was in a define or not, and I think it's a
>> pretty common pattern. It's clumsy, but then, LALR parses always
>> are,
>> it seems.
>
> Except my proposed solution doesn't work all the time.
>
> This (simple) example fails:
>
> # comment
> node test {
> include klass
> }
>
> When we read the comment we push "comment" on the comment stack.
> When the parser calls the lexer to read the { we push a new stack
> level.
> When the parser calls the lexer to read the } we pop the stack.
> Then the parser noticing the }, will reduce the include function, with
> will fetch the current comment level as it documenation. Unfortunately
> we already popped it, so the function include will get the #comment
> comment as documenation instead of an empty level.
>
> Really, the only real fix is to push/pop on token shifting.
> Unfortunately, this isn't possible with Racc at this time, except by
> playing games (ie enable debug, override the methods that prints
> when a
> shift happens to push or pop our comment stack...arghhh...)
>
> The only other alternative I can think of is to change the grammar to
> understand comments and deal with them directly in the parser
> instead of
> in the lexer (which has no knowledge of the language).
>
> If someone has a better idea, please speak up.
> Otherwise, I'll start with the comment-enhanced parser grammar :-(
The only other approaches I can think of involve keying off the
tokens. E.g., you see a 'CLASS' token, and somehow associate the
preceding comment with that token, either involving a hash table
lookup in the lexer, or finding a way to pass the comment with the
token and its value to the parser.
Neither seems particularly fun, but then, neither does hte comment-
enhanced parser.
--
I can't understand why a person will take a year to write a novel when
he can easily buy one for a few dollars. -- Fred Allen
---------------------------------------------------------------------
Luke Kanies | http://reductivelabs.com | http://madstop.com
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