in reply to The Virtue of Laziness

Why do you think that dereferencing is the issue here?

Is map faster if you use a literal array @ar?

Update

I doubt it.

map expects a list as input, and those lists can be chained, like in the Schwarzian Transform

map {} grep {} map {} @list

To allow those constructs to be lazy, they would have to stop returning lists.

IIRC... the reason why foreach can be efficient is that it has special magic if the THING inside brackets is one array (starts with @) or a range operator. In that case it'll switch to iteration by index.

That's actually something the earliest versions of perl5 couldn't do.

So it's not real lazyness but just an optimized edge case.

I doubt that a for ("a",@ar,"z") {} is still that performant, because the heuristics might not detect anymore the array in between

Short version

This perceived lazyness depends on heuristics, which are hard to extend and normally won't bring much benefit.

Cheers Rolf
(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery

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Re^2: The Virtue of Laziness
by jo37 (Curate) on May 05, 2024 at 07:14 UTC
    I doubt that a for ("a",@ar,"z") {} is still that performant, because the heuristics might not detect anymore the array in between

    LanX, you are right: 

    cmpthese(0, {
        map => sub {map_die(\@arr)},
        for => sub {for_die(\@arr)},
    });

sub map_die ($ar) {
    eval {map {die} 0, @$ar};
}

sub for_die ($ar) {
    eval {
        for (0, @$ar) {
            die;
        }
    }
}
__DATA__
      Rate for map
for 1390/s  -- -1%
map 1404/s  1%  --

    [download]

    Greetings,
    🐻

    $gryYup$d0ylprbpriprrYpkJl2xyl~rzg??P~5lp2hyl0p$
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[select]
      Well, you could ask p5p if it's possible to catch the edge cases of iterating over a following array variable
      • map {} @array
      • grep {} @array

      But, I'm sceptical they have resource left for that.

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      see Wikisyntax for the Monastery

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[d/l]
[select]
Re^2: The Virtue of Laziness
by jo37 (Curate) on May 12, 2024 at 21:46 UTC
[reply]

In Section Meditations