Re: [Grammatica-users] Identities

[Per Cederberg]

Just a quick comment:

I think this sounds a lot like the Enumeration design pattern.
Grammatica hasn't been modelled after that simply because I
judged it as unnecessary for the first version. Now, if we'll
progress on the road towards modular grammars a fix for the
node identities is needed.

In the C# version of Grammatica, this is all handled better.
Although not ideal.

/Per

On thu, 2005-09-15 at 21:48 +0300, Matti Katila wrote:
> 
> Hello Grammatica people,
> 
> 
> I have problems with identities used with Grammatica.
> Currently Grammatica has primitive integer identity for tokens and
> patterns. Thus can the user use those identity integers where they need
> them by Node.getId() method, for example when analyzing parsed tree.
> Token ids start from 1000, pattern ids from 2000 and generated pattern ids
> from 3000.
> 
> Well, this sounds like good identity model for the first 10 seconds. Like
> with web, you do not often use some ip address with it's numbers but domain
> name instead.
> 
> I propose that Grammatica should add a grammar header declaration for
> identity namespace which by default is empty. Then, instead of returning
> 
>     int getId();
> 
> in abstract class Node, it should return
> 
>     Object getId();
> 
> The nice thing with integers is that you can compare them with ==
> operator, e.g., Node a, b; /* ... */ a.getId() == b.getId() would say
> whether they are same integer number or not. So to be able to create
> reference comparable objects I propose we use String.intern(). For example
> in Node class:
> 
>     static public Object id(String createReferenceComparableString) {
>        return referenceComparableString.intern();
>     }
> 
> Now you can construct constant file by saying:
> 
>     public static final Object HEADER =
>         Node.id("http://grammatica.percederberg.net/grammar#header";);
> 
>     public static final Object TOKENS = ;
>         Node.id("http://grammatica.percederberg.net/grammar#tokens";);
> 
>     public static final Object PRODUCTIONS =
>         Node.id("http://grammatica.percederberg.net/grammar#productions";);
> 
> The above example would be constructed if namespace
> http://grammatica.percederberg.net/grammar was chosen and you still don't
> need to use a.equals(b) in code.
> 
> Some cons with primitive integers too: they need to be wrapped with
> Integer when put into map for example. That is, we might create a lot
> of objects for every look up.
> 
> And finally to my problem with current identity "model".
> When I use a two parsers in queue, first one as a lexer and the
> second one as a parser, the identities intersect with each other.
> I could fix it just by adding 3000 to parser identities but it would be a
> hack over identity hack and I prefer better code and architechture in
> overall.
> 
> 
>    -Matti
> 
> 
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