Re: Cheaper to prepend or append an item to a sequence

@id = //@id except (@id, //meta//@id) - yep... good idea

but i think that even //@id[not(ancestor::meta)] should be calculated
only once since it not depend from current node - is not it? is
optimizer capable to recognize context dependant from context
independant XPath fragments inside predicate and calculate independant
fragments only once instead calculating it every time for each node?

2011/2/22 Dimitre Novatchev <dnovatchev@xxxxxxxxx>:
>> Even with a forward-chained list, you can implement append without copying
>> if you choose, at least for the first append operation to a given list
>> (which 9 times out of 10 will be the only append operation).
>
> What people want is to be able to append one list to another in O(N)
> time, not in O(N^2).
>
> This is why people chose to pre-pend the elements of the second list
> (starting from the last) to the first list.
>
>
> Cheers,
> Dimitre Novatchev
> ---------------------------------------
> Truly great madness cannot be achieved without significant intelligence.
> ---------------------------------------
> To invent, you need a good imagination and a pile of junk
> -------------------------------------
> Never fight an inanimate object
> -------------------------------------
> You've achieved success in your field when you don't know whether what
> you're doing is work or play
> -------------------------------------
> Facts do not cease to exist because they are ignored.
>
>
>
> On Tue, Feb 22, 2011 at 6:32 AM, Michael Kay <mike@xxxxxxxxxxxx> wrote:
>> On 22/02/2011 13:58, Dimitre Novatchev wrote:
>>>
>>> The accepted term in most functional programming languages is "a list".
>>>
>>> A list is a functional data structure (immutable). Appending to a list
>>> causes the whole list to be copied and is O(N). Prepending a list is
>>> making just the "next pointer" of an item point to the list -- an O(1)
>>> operation.
>>>
>>
>> Even with a forward-chained list, you can implement append without copying
>> if you choose, at least for the first append operation to a given list
>> (which 9 times out of 10 will be the only append operation).
>>
>> Michael Kay
>> Saxonica
>>
>>
>
>
>
> --