[Versa] Problem with splitting the grammar

[Michael Olson]

On Sep 27, 2005, at 3:13 PM, Uche Ogbuji wrote:

> On Tue, 2005-09-27 at 14:07 -0600, Michael Olson wrote:
>> If we split the grammar, then the production (in bind) for a function
>> definition must be something like
>>
>> @function function_name = ([^;])+ ';'
>>
>> Basically, the bind parser does not know the grammar of the function,
>> so it just gives it everything.
>>
>> This causes a problem back in versa land for a query that looks like
>>
>> @prefix ft = foo
>> @function myFunc () = ft:s - ft:p -> ft:o;
>> @prefix ft = bar;
>> myFunc()
>>
>>
>> Because "myFunc" would not be parsed until after the complete bind
>> expression is parsed.
>>
>> Is this bad?
>>
>> We could just disallow redefining, probably the best.
>
> I'm not sure I follow, but if I do, this is a semantic issue, not a
> grammar issue.  In the above specific case, line 3 would pretty much be
> a no-op.  An implementation would implement the semantics of the
> function using the prefixes in scope at the time, which are foo.  That
> function would always have those constant URIs using the foo prefix,
> regardless of the next line.
>
> I don't really see a problem.
>

The problem is with the first statement I made.  By splitting the  
grammars, we have 2 parsers.  One for bind and one for what every  
language bind is binding.  So, from binds POV, the string "ft:s - ft:p  
-> ft:o" is opaque.  So to use this new approach, we would first create  
a bind parser and parse the context query.  That would result in a  
bunch of variables, functions and the end query that are just opaque  
strings.  Then, a Versa parser is created to parse the variables,  
functions and finally the query.  Because of the two-step, we lose  
order of the context grammar and the function "myFunc" would use the  
second, overriding, prefix definition for ft.

Mike

>
> --  
> Uche Ogbuji                               Fourthought, Inc.
> http://uche.ogbuji.net                    http://fourthought.com
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>
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Mike Olson                                                Principal  
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