Here a meditation how to implement most of it in a pure functional and backwards compatible way:

NB:

• the choice of subnames is open to debate
• This is very beta and not heavily tested against all edge cases
• once this is stable for all edge cases it can be improved for performance

the basic ideas are:

• using for as a topicalizer
• a routine once {} like do {} but breaking out
• a routine check {} to explicitly define the criteria (in contrast to smartmatch)
• routines case() and break {} for syntactic sugar

use v5.12;
use warnings;
use subs qw/break/;

#use Data::Dump qw/pp dd/;
#use diagnostics;


say "========= IMPLEMENTATION";

{

    my $check;


    sub check(&) {
        $check = shift;
    }

    sub case {
        my $code;
        if (ref $_[-1] eq "my_break") {
            #warn "my break";
            $code = pop @_;
        }

        my $do;
        for my $val (@_) {
            $do ||= $check->($val);
        }

        if ($do){
            if ($code) {
                once($code) 
            } else {
                return $do
            }
        }
        return;
    }

    no warnings 'exiting';
    sub once (&) {
        (shift)->();
        next;
    }

    sub break(&) {
        return bless shift, "my_break"
    }
}


say "========= TESTS";


say "--- with basic logic";

for ( 0 .. 5 ) {
    $_< 1 and
      once { print "$_ smaller 1"};

    $_< 3 and
      once { print "$_ smaller 3"};

    $_ > 3  && $_ < 5 and
      once { print "$_ between 3 and 5"};

    print "$_ has no match";    # else

} continue {
    print "\n";
}


say "--- with some syntactic sugar";

for ( 0 .. 5 ) {
    check { $_ < shift };

    case 1
      and once { print "$_ smaller 1"};
    case 3
      and once { print "$_ smaller 3"};

    case 4,5
      and once { print "$_ smaller 4 or 5"};

    print "$_ has no match";            # else

} continue {
    print "\n";
}


say "--- with even MORE syntactic sugar";

for ( 0 .. 5 ) {
    check { $_ < shift };

    case 1
      => break { print "$_ smaller 1"};

    case 3
      => break { print "$_ smaller 3"};

    case 4,5
      => break { print "$_ smaller 4 or 5"};

    print "$_ has no match";

} continue {
    print "\n";
}
[download]

C:/Strawberry/perl/bin\perl.exe -w d:/tmp/pm/do_once.pl 
========= IMPLEMENTATION
========= TESTS
--- with basic logic
0 smaller 1
1 smaller 3
2 smaller 3
3 has no match
4 between 3 and 5
5 has no match
--- with some syntactic sugar
0 smaller 1
1 smaller 3
2 smaller 3
3 smaller 4 or 5
4 smaller 4 or 5
5 has no match
--- with even MORE syntactic sugar
0 smaller 1
1 smaller 3
2 smaller 3
3 smaller 4 or 5
4 smaller 4 or 5
5 has no match

Compilation finished at Sat Jul  3 18:15:36
[download]

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