in reply to how to avoid using index of array

No problem if you're not constrained in what Perl version you can use:

use v6; my @male = qw/boy boymonkey boydog/; my @female = qw/girl girlmonkey girldog/; for @male Z @female -> $m, $f { say "$m marries $f"; }

(Works fine in niecza and rakudo).

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Re^2: how to avoid using index of array
by davido (Cardinal) on Nov 13, 2011 at 07:51 UTC

    I knew that it would be (and glad that it was) just a matter of time before you posted a Perl6 and zip operator solution.

    I've been trying to figure out how to do that (before you made your post) using Perl 6 and the zip operator. Thanks for posting an example. For some reason I was expecting that the syntax should look more like this:

    for( @male Z @female )->[$m,$f] { # .... }

    But apparently not. ;) Also, how would you push a stringified concatenation onto a new array? In Perl5 either of these would do WIM:

    my @married; foreach( 0 .. $#male ) { push @married, "$male[$_] $female[$_]"; } # OR ..... my @married = map { "$male[$_] $female[$_]" } 0 .. $#male; # OR with List::MoreUtils::pairwise my @married = pairwise{ "$a $b" } @male, @female;

    ...or you could forgo interpolation and use the (.) dot operator.

    I've been puzzling over a Perl6-ish, Zip-operator-ish way to do the same.


    Dave

      For some reason I was expecting that the syntax should look more like this:
      for( @male Z @female )->[$m,$f] { # .... }

      Close. Two things got into your way. The first is syntactic: you need a space between for and (. The reason is that (nearly) everything of the form identifier(...) is parsed as a subroutine call. That way keywords don't conflict with function names, making it more robust to introduce new syntax.

      The second one is a bit more interesting. In a signature, [$m, $f] stands for a single parameter, which is taken as a list, and unpacked into the two variables. But @list1 Z @list2 returns a list of lists which flattens the sublists when you iterate over it. To stop that flattening, you can write

      for (@male Z @female).tree ->[$m,$f] { # .... }

      which indeed works in current Rakudo.

      Also, how would you push a stringified concatenation onto a new array?

      Several ways:

      my @array; for @male Z @female -> $m, $f { push @array, "$m $f; # or @array.push: "$m $f"; # or @array.push: $m ~ ' ' ~ $f } # or my @array = (@male Z @female).map("$^a $^b");

      Since Z can also be used as a meta operator, you can also get zip and concatenation in one go, using Z~:

      my @array = @male Z~ @female; # without joining space

      To get the space between the two operands, you can use one of these tricks:

      # with the list repetition operator: @array = @male Z~ ' ' xx @male Z~ @female; # with cross instead of zip: @array = @male X~ ' ' Z~ @female;

      All of these solutions work with current Rakudo.