Re: [basex-talk] First non-null value?

[Graydon Saunders]

On Fri, Sep 14, 2018 at 4:51 AM Andy Bunce  wrote:

> If you put your "possibles" in an array rather than a sequence  then the
> index of the first non-empty item
> identifies the match.
>

Thank you!  That does it nicely.

It's going to be a little while before I feel like I've comprehended the
hof:until() example, but "use an array" is clearly the way to go, here, and
I had flat forgotten there _were_ arrays.

-- Graydon

Re: [basex-talk] First non-null value?

[Andy Bunce]

 If you put your "possibles" in an array rather than a sequence  then the
index of the first non-empty item
identifies the match.

let $results := [$possible1,$possible2,$possible3,$possible4,$
possible5,'FAILED']

let $index:= array:fold-left($results,
   -1,
   function($acc,$this){
  if($acc gt 0)then $acc else
  if (exists(array:get($results,-$acc))) then
-$acc else $acc -1
  })

let $foundIt:= array:get($results,$index)

This seems a bit tricksy, using the BaseX specific higher order function
hof:until [1] is cleaner

let $index:= hof:until(
  function($index){ exists(array:get($results,$index)) },
  function($index){ $index+1 },
  1)

/Andy

[1] http://docs.basex.org/wiki/Higher-Order_Functions_Module#hof:until


On 14 September 2018 at 07:38, Liam R. E. Quin 
wrote:

> On Thu, 2018-09-13 at 16:18 -0400, Graydon Saunders wrote:
> > let $possible1 as xs:string* := (: go looking for a value via one
> > route :)
> > let $possible2  (: all the other routes in preference order :)
> > 
> > let $foundIt as xs:string :=
> > ($possible1,$possible2,$possible3,$possible4,$possible5,'FAILED')[1]
> >
> > This works nicely in terms of "I got the value by the least-bad
> > route".
> > What I'm blanking on is "how do I tell which was the first
> > possibility to
> > match?" without resorting to sprawl of if-then-else statements.  I
> > have the
> > idea that there must be a compact way but I have no idea what it is
> > if
> > there is.
>
> Don't use variables - just construct a sequence,
> let $possibles as xs:string := (
>stuff to make possible1,
>stuff to make possible 2,
>. . .
>'fallback value'
>)[1]
> >
>
> Liam
>
>
> --
> Liam Quin, https://www.holoweb.net/liam/cv/
> Web slave for vintage clipart http://www.fromoldbooks.org/
> Available for XML/Document/Information Architecture/
> XSL/XQuery/Web/Text Processing/A11Y work/training/consulting.
>
>

Re: [basex-talk] First non-null value?

[Liam R. E. Quin]

On Thu, 2018-09-13 at 16:18 -0400, Graydon Saunders wrote:
> let $possible1 as xs:string* := (: go looking for a value via one
> route :)
> let $possible2  (: all the other routes in preference order :)
> 
> let $foundIt as xs:string :=
> ($possible1,$possible2,$possible3,$possible4,$possible5,'FAILED')[1]
> 
> This works nicely in terms of "I got the value by the least-bad
> route".
> What I'm blanking on is "how do I tell which was the first
> possibility to
> match?" without resorting to sprawl of if-then-else statements.  I
> have the
> idea that there must be a compact way but I have no idea what it is
> if
> there is.

Don't use variables - just construct a sequence,
let $possibles as xs:string := (
   stuff to make possible1,
   stuff to make possible 2,
   . . .
   'fallback value'
   )[1]
> 

Liam


-- 
Liam Quin, https://www.holoweb.net/liam/cv/
Web slave for vintage clipart http://www.fromoldbooks.org/
Available for XML/Document/Information Architecture/
XSL/XQuery/Web/Text Processing/A11Y work/training/consulting.