Charles,
Am 02.01.2014 22:36, schrieb Charles Duffy:
While I know how to do this in a few other functional languages (for
instance, in Clojure with its atoms), I'm a bit lost in XQuery. Could I
ask for a bit of clue?
I think you are looking for `fn:fold-left(...)` and/or
`fn:fold-right(...)` [1]. They can be used to thread some kind of state
through while iterating over a sequence. `fn:fold-left($seq, $z, $f)`
behaves similar to the following imperative snippet:
$accum <- $z;
foreach($item in $seq) {
$accum <- $f($accum, $item);
}
return $accum;
Your algorithm could be written like this (untested):
fn:fold-left(
$inputs,
map:new(),
function($already-seen, $element) {
if(local:map-contains-prefix-of($already-seen, $element))
then $already-seen
else (
let $result := expensive-operation($element)
return map:new((
$already-seen,
map:entry(get-key($element), $result)
))
)
}
)
Hope that helps,
Leo
[1] http://www.w3.org/TR/xpath-functions-30/#func-fold-left
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