[Versa] statements function

[Michael Olson]

>
>> Though you would be able to express it as
>>
>> statements( type (rss:item), ns:age, . > 18)
>
> I don't see how this would work.  Do you mean:
>
> statements( type (rss:item), ns:age, ". > 18")
>

No, the quotes make it a constant.  Without quotes it is a filter  
expression, which is a valid argument to a function call.

Just like it works with

type(rss:item) - ns:stage -> . > 18

the . > 18 portion is evaluated once per result statement.


>>> Basically
>>>
>>> anon-function ::= '(!' param-list ':' expr ')'
>>>
>>> Or to give an example using the statements function:
>>>
>>> statements(type(rss:item), dc:creator, (!x: $x - ns:age -> gt(18))
>>>
>>> I prefer naming the parameter (functional macro-like) rather than  
>>> using
>>> the magic "." particle.  We also then get the flexibility of  
>>> functions
>>> with multiple parameters, etc.
>>
>> I like this better then currying, though I don't see how you would
>> specify an anon function with more then one parameter.  Maybe
>>
>> ( !x = ., !y = "foo" :  $x - ns:age -> gt($y)
>>
>> and the default of (!x : query) would default "x" to the current
>> context.
>
> Well, based on the grammar snippet above:
>
> anon-function ::= '(!' param-list ':' expr ')'
>
> You wouldn't have a ! in front of each parameter.  For 2 parameters:
>
> (! x, y:  $x - ns:age -> gt($y))
>
> You're right that I haven't accounted for a syntax for "defaulting" a
> parameter, but considering that anon functions will probably only be
> passed in at the spot they're used, is this such a big deal?
>
> What I mean is that in every spot you might want to type
>
> (! x, y=18:  $x - ns:age -> gt($y))
>
> Wouldn't you already know well enough to just write
>
> (! x:  $x - ns:age -> gt(18))
>

Only if it was a constant, like 18.  What if it is the results of a sub  
query?

(!x,y = all() - rdf:type -> rdfs:Class : $y - rdfs:subClassOf -> * |  
all() - rdfs:subClassOf -> $y)


Something tells me this may be getting out of hand....

> When I was talking about multiple parameters, I honestly didn't have a
> use case for it, but I guess I should think that through as part of  
> this
> whole exercise.
>
> I did consider that if you did want to do such things as defaulting
> functions, you could go back to the state (formerly known as
> context? :-) ) operations we've been discussing:
>
> @def f(x, y=18): $x - ns:age -> gt($y)
>

Right, and maybe this is the case for multi params and anon-functions  
just take a single argument, dot, and are soley used to clean up  
quotes.  I'm OK with that.

>
>> In the current grammar, I supported something similar to this with the
>> reuse of the "{}" symbols.  It just did not support parameters.
>
> OK.  I kind of wondered whether these two uses were compatible, but I
> wasn't sure, so I went with new symbols.  Maybe we should generalize {}
> a bit and also use it for the anon funct syntax:
>
> {x: $x - ns:age -> gt(18)}
>

I'm OK with either.  However if anon-functions are going to always be  
single parameter, and the parameter value is always DOT, then I think  
it should just be DOT.

Mike

>
> --  
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Mike Olson                                                Principal  
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