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declare variable $n as xs:integer external := 1000;
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let $put := function($map as map(*), $key as xs:anyAtomicType, $value as item()*) as map(*)
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{ Q{http://www.w3.org/2005/xpath-functions/map}put($map, $key, $value) },
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$gen1ToInf :=
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map{
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"initialized": true(),
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"endReached": false(),
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"getCurrent": function($this as map(*)) { $this?last + 1},
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"moveNext": function($this as map(*))
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{
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if(not($this?initialized)) then $put($this, "initialized", true())
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else $put($this, "last", $this?last +1)
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},
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"last" : 0
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},
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$emptyGenerator := function()
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{
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map{
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"initialized" : true(),
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"endReached": true(),
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"getCurrent": function($this as map(*)) {error()},
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"moveNext": function($this as map(*)) {error()}
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}
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},
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$skip-helper := function($gen as map(*), $n as xs:integer, $self as function(*))
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{
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if($n eq 0) then $gen
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else
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(
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let $gen := if(not($gen?initialized)) then $gen?moveNext()
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else $gen
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return
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if(not($gen?endReached)) then $self($gen?moveNext($gen), $n -1, $self)
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else $gen
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)
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},
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$skip := function($gen as map(*), $n as xs:integer)
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{
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$skip-helper($gen, $n, $skip-helper)
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},
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$take-helper := function($gen as map(*), $n as xs:integer, $self as function(*))
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{
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let $gen := if(not($gen?initialized)) then $gen?moveNext()
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else $gen
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return
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if( $gen?endReached or $n eq 0) then $emptyGenerator()
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else $put($gen, "moveNext", $self($gen?moveNext($gen), $n -1, $self))
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},
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$take := function($gen as map(*), $n as xs:integer)
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{
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$take-helper($gen, $n, $take-helper)
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},
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$subrange := function($gen as map(*), $m as xs:integer, $n as xs:integer) as map(*)
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{
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$take($skip($gen, $m -1), $n)
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},
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$at := function($gen as map(*), $ind as xs:integer)
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{
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let $genResult :=$subrange($gen, $ind, 1)
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return
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$genResult?getCurrent($genResult)
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}
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return
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$at($gen1ToInf, $n)
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.