Easy. Change map_recursive() to not descend into recognized structures. That is probably the more sensible default behavior, agreed.

#!/usr/bin/perl -w

use strict;


sub map_recursive {
    my ($structure, $predicate) = @_;

    # don't descend into recognized structures

    if ($predicate->($structure)) {
        return $predicate->($structure);
    }

    # not recognized - pick apart

    my @result;
    if (UNIVERSAL::isa($structure, 'ARRAY')) {
        for (@{$structure}) {
            push @result, map_recursive($_, 
                                        $predicate);
        }
    } elsif (UNIVERSAL::isa($structure, 'HASH')) {
        for (keys %{$structure}) {
            push @result, map_recursive($structure->{$_}, 
                                        $predicate);
        }
    } else {
        push @result, $predicate->($structure);
    }
    return @result;
}

package Foo;
sub new { bless {}, shift }
sub get { $_[0]->{$_[1]} }
sub set { $_[0]->{$_[1]} = $_[2] }

package main;
my @list = (Foo->new, Foo->new, Foo->new);

$list[0]->set('a', 'b');
$list[1]->set('b', 'a');
$list[2]->set('x', 'y');

my $isa_foo = sub { UNIVERSAL::isa(shift, 'Foo') };

print "#1: ", join(',', map_recursive(\@list, $isa_foo)), "\n";

my @list2 = ( {a => 'm'}, { 1 => 55}, { Foo => 'Bar' });
my $h = sub { UNIVERSAL::isa(shift, 'HASH') };

print "#2: ", join(',', map_recursive (\@list2, $h)), "\n";
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Christian Lemburg
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