--- Jeni Tennison <jeni@[...].com>  wrote:
 
>  Sure. The XPath 2.0 WD gives only two distinct examples of the for
>  expression, and neither of them would be achievable using the simple
>  mapping operator.
>  
>  The first one has two range variables, as follows:
>  
>    for $i in (1, 2),
>        $j in (3, 4)
>    return ($i, $j)
>  
>  which returns the sequence:
>  
>    (1, 3, 1, 4, 2, 3, 2, 4)
>  
>  and is equivalent to:
>  
>    for $i in (1, 2)
>    return for $j in (3, 4)
>           return ($i, $j)
>  
>  This iterates over two sequences - (1, 2) and (3, 4) - within the same
>  for expression, to create the sequence that contains pairs of possible
>  combinations (ish - obviously in flat sequences the 'pairedness' isn't
>  explicit).
>  
>  The second example has two for expressions. The inner for expression
>  creates a sequence to iterate over using the range variable from the
>  outer for expression within a predicate:
>  
>    for $a in distinct-values(//author)
>    return ($a,
>            for $b in //book[$b/author = $a]
>            return $b/title)
>  
>  I don't think that you can do either of these with the operator syntax
>  because you lose track of what *was* the context node as you go from
>  one step to the next. If the outer context item was available with the
>  current() function, say, then you could do:
>  
>    (1, 2) -> ((3, 4) -> (current(), .))
>  


Maybe something like this:

( (x, y) | x ->  (1,2) | y -> (3,4) )



>  and:
>  
>    distinct-values(//author) ->
>      (//book[author = current()] -> (current(), title))
>  
>  but without range variables, you can't manage these situations.
>  

And:

 ( (y, x ) | x->  //book[author = y]/title | y -> distinct-values(//author) )


Cheers,

Dimitre Novatchev.

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