Re: [Exist-development] bug @fn:string

[Pieter D. <pie...@gm...>]

On Mon, Aug 9, 2010 at 6:29 AM, Dmitriy Shabanov <sha...@gm...>wrote:

>  On Sun, 2010-08-08 at 23:28 +0200, Pieter Deelen wrote:
>
>
> The spec you refer to states:
> "The behavior of the function if the argument is omitted is exactly
> the same as if the context item had been passed as the argument.",
> i.e., string() is equivalent to string(.). Hence, ()/string() should
> return exactly the same value as ()/string(.).
>
>
> I totally agree that it must be same, but the question "what should
> empty(()/string(.)) return?"
>
> Let go step by step:
> ()/string(.) have equivalent string( () ). The spec quite clear on this (
> http://www.w3.org/TR/xpath-functions/#func-string ) :
>
> ===================================================================
> 2.3 fn:string
> fn:string() as xs:string
> fn:string($arg as item()?) as xs:string
>
> Summary: Returns the value of $arg represented as a xs:string. If no
> argument is supplied, the context item (.) is used as the default argument.
> The behavior of the function if the argument is omitted is exactly the same
> as if the context item had been passed as the argument.
>
> If the context item is undefined, error [err:XPDY0002]XP is raised.
>
>
> *If $arg is the empty sequence, the zero-length string is returned.*
> ===================================================================
>
> So, getting empty( xs:string("") ) and it return false, because (
> http://www.w3.org/TR/xpath-functions/#func-empty )
>
> ===================================================================
> 15.1.4 fn:empty
> fn:empty($arg as item()*) as xs:boolean
>
> Summary: If the value of $arg is the empty sequence, the function returns
> true; otherwise, the function returns false.
> ===================================================================
>
> the xs:string("") is not a empty sequence.
>
> That mean empty( ()/string(.) ) == empty( ()/string() ) == false
>

Let's forget about the string function for a moment and introduce function
f:

declare function local:f($elt as element()) {
  "f"
};

Then if I evaluate the following expression

(<a/>, <b/>)/local:f(.)

I expect (and get from both eXist 1.4 and Saxon 9)

("f", "f")

So the function f is called twice, the first time with <a/> as parameter,
and the second time with <b/>.

Similarly, (<a/>)/local:f(.) returns ("f"): the function f is called once,
for <a/>.

So if I evaluate

()/local:f(.)

I would expect the function f to be called not at all and the empty sequence
as result. Instead, eXist shows the following error:

"The actual cardinality for parameter 1 does not match the cardinality
declared in the function's signature: local:f($a as element()) item()*.
Expected cardinality: exactly one, got 0."

I.e., eXist tries to call the function f, but this fails because the
function's signature does not allow it.

Saxon gives me the result I expect.

Pieter

>