[xquery-talk] Removing douplicate elements

[Michael Kay]

Actually, the error message looks rather like a Saxon message. Saxon does
have tail-call optimization, and it's not obvious why it's not being used
here (which version are you using?). There isn't a built-in limit on the
depth of function calls; rather Saxon catches the StackOverflowException and
turns it into this error message.

Having said that, the algorithm looks pretty inefficient, and I'm sure one
could do better.

Michael Kay
http://www.saxonica.com/


> -----Original Message-----
> From: talk-bounces at xquery.com 
> [mailto:talk-bounces at xquery.com] On Behalf Of Martin Probst
> Sent: 10 August 2005 17:17
> To: EXTERNAL Kruse Peter (Praktikant;CR/AEA1-Si)
> Cc: talk at xquery.com
> Subject: Re: [xquery-talk] Removing douplicate elements
> 
> Hi,
> your function is recursive relative to the number of elements. As your
> processor obviously does not have tail call optimization, the
> (processors) recursion level is dependent on the number of 
> elements, and
> to prevent a StackOverFlowException (or sth worse with C) the 
> processor
> seems to have a built in limit.
> The solution is to have a non recursive function.
> 
> declare function local:notIn($pivot as node(),$list as node()*) as
> xs:boolean {
> 	if ( for $elem at $index in $list
> 		return
> 		    if ( deep-equal($pivot, $elem) )
> 		    then true()
>         	    else ()
> 	   ) then true()
> 	else false()
> }
> 
> The trick is to return a list of boolean values, but only 
> return a true
> value if the node is deep-equal, otherwise return nothing. 
> The outer if
> will try to evaluate the EBV of the condition and receive an empty
> sequence (--> false) if none of the elements was deep-equal, a list
> starting with the value true otherwise.
> You just need the outer if to make sure it's exactly one boolean btw.
> 
> Martin
> 
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