Hi Christian,
Elaborating on the issue below and just thinking out loud.
Would it make sense having to opportunity to evaluate a function body lazily?
Consider the following function:
declare function item:exists
( $item
, $existProcessor
, $emptyValue
)
{ if ( exists( $item))
then $existProcessor( $item)
else $emptyValue
} ;
Even when called with an existing: $item, $emptyValue will be evaluated what could be an expensive evaluation.
Having the possibility of lazy evaluation of the function body would prevent this.
I’ve two questions:
- does the above make sense?
- does it make enough sense to be implemented in basex?
If implemented: for keeping the code clean, specifying this laziness should be done within the function, not within the function call.
I tumbled on the %basex:inline-annotation for global variables. This would do very nicely for specifying laziness for evaluating function bodies.
declare %basex:inline function item:exists
( $item
, $existProcessor
, $emptyValue
)
{ if ( exists( $item))
then $existProcessor( $item)
else $emptyValue
} ;
Best,
Rob
Van: Christian Grün [mailto:christian.gruen@gmail.com] Verzonden: woensdag 13 mei 2015 12:36 Aan: Rob Stapper; BaseX Onderwerp: Re: [basex-talk] unexpected behaviour
If I get it right, you would also expect '!' not to be output in the following query, right?
declare function local:f($a, $b) {
if($a) then $b else ()
};
local:f((), trace('!'))
In this case, you'll have to wrap your trace call in a function:
declare function local:f($a, $b) {
if($a) then $b() else ()
};
local:f((), function() { trace('!') })
Best,
Christian
On Wed, May 13, 2015 at 11:44 AM, Rob Stapper r.stapper@lijbrandt.nl wrote:
Hi Christian,
This is the best I can do without losing the essence of the issue. Sorry about the import, forgot to remove that one.
The clue is in the “Query Info”-window. It shows:
Evaluating:
f1: 1
Compiling:
…….
So function “local:f1#1” is unnecessarely evaluated with value 1.
Success,
Rob
Van: Christian Grün [mailto:christian.gruen@gmail.com] Verzonden: woensdag 13 mei 2015 11:13 Aan: Rob Stapper CC: BaseX Onderwerp: Re: [basex-talk] unexpected behaviour
Hi Rob,
It usually takes me some time to understand new code, so could you possibly simplify the example as much as possible? For example, the import cannot be resolved, an empty squence is bound to $a, which means that one branch will never be called, and maybe you can simplify the partial function application as well..
Thanks in advance,
Christian
On Wed, May 13, 2015 at 9:55 AM, Rob Stapper r.stapper@lijbrandt.nl wrote:
Hi Christian,
Can you have a look at the attached program.
Both items of the returned sequence of the program should do the same thing.
Both do give the same, correct result: an empty sequence, but the first item unnecessarely triggers function: “local:f1#1” , while the second item doesn’t.
This a pity since “local:f1#1” could be a time-consuming function.
Cheers,
Rob
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