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Re^3: Smartmatch alternatives

by Anonymous Monk
on Dec 17, 2013 at 16:21 UTC ( #1067493=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Smartmatch alternatives
in thread Smartmatch alternatives

Well, L'U'first returns undef "[li]f BLOCK never returns true or LIST was empty" (as of version 1.32), so need to do check further if value is defined.


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Re^4: Smartmatch alternatives
by LanX (Canon) on Dec 17, 2013 at 16:50 UTC
    so this should be a fast and core fallback if no better module available.

    DB<125> @a=(0)x10 => (0, 0, 0, 0, 0, 0, 0, 0, 0, 0) DB<126> sub any (&@) { my $cr=shift; defined first { &$cr } @_ } DB<127> any {$_==0} @a => 1

    well could be faster if I could avoid '$cr' but my golfing foo is weak today. =)

    update

    got it :)

    DB<138> sub any (&@) { defined &first (shift, @_) } DB<139> any {$_==0} @a => 1

    update

    better :)

    DB<144> sub any (&\@) { defined &first } DB<145> any {$_==0} @a => 1

    UPDATE

    DARN! still buggy with false positives!

    didn't sleep enough...

    update

    this seems to work...

    DB<230> sub any (&@) { my $x=&List::Util::first; defined $x } DB<231> any { $_ eq 0 } @a => "" DB<232> any { $_ eq 5 } @a => 1 DB<233> @a => (1, 2, 3, 4, 5)

    Cheers Rolf

    ( addicted to the Perl Programming Language)

      Works fine until you want to see if an array contains any false values...

      use Data::Dumper; use List::Util (); sub any (&@) { my $x = &List::Util::first; defined $x } my @x = (1..3, undef, 5..10); # undef is false print Dumper(any { !$_ } @a);
      use Moops; class Cow :rw { has name => (default => 'Ermintrude') }; say Cow->new->name
        Thanks, but this can't be fixed.

        The problem is that the design of List::Util first is broken, no result should be an empty list and not undef! At least in list context ! :(

        DB<28> \@x => [1, 2, 3, undef, 5, 6, 7, 8, 9, 10] DB<29> @a=List::Util::first { !$_ } @x; \@a => [undef] DB<30> @a=List::Util::first { $_ eq "never" } @x; \@a => [undef]

        I wished people would learn the lesson that () is always better then undef for failure in list operations like iterators or filters.

        update

        grep does it right!

        DB<38> @a=grep { !$_ } @x; \@a => [undef] DB<39> @a=grep { $_ eq "never" } @x; \@a => []

        Cheers Rolf

        ( addicted to the Perl Programming Language)

        hmm maybe simpler than we thought!

        DB<25> sub first (&@) { my $code=shift; grep {return $_ if &$code} @ +_ } DB<26> first { $_ >5 } 1..10 => 6 DB<27> first { $_ >10 } 1..10 DB<28> sub any (&@) { my $code=shift; grep {return 1 if &$code} @_ ; + ()} DB<29> any { $_ >10 } 1..10 => "" DB<30> any { $_ >5 } 1..10 => 1

        Can you spot problems?

        update

        variation of first for finding position

        DB<40> sub position (&@) { my $code=shift; my $idx=-1; grep {++$idx; + return $idx if &$code} @_ ; ()} DB<41> position { !$_ } 1..10,undef,11..20 => 10

        update

        changed "" to () for false.

        update

        even easier

        DB<53> sub first (&@) { my $code=shift; &$code and return $_ for @_ +; ()} DB<54> sub any (&@) { my $code=shift; &$code and return 1 for @_ ; ( +)}

        Cheers Rolf

        ( addicted to the Perl Programming Language)

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