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use 5.010; use strict; use warnings FATAL => 'all'; { package Tree; use MooseX::Role::Parameterized; use Moose::Util::TypeConstraints qw(union role_type); use Scalar::Does; use List::Util qw(max); parameter child_names => (isa => 'ArrayRef[Str]', required => 1); role { my @child_names = @{ shift->child_names }; # We allow each child to be undef, a string, or another Tree # Strings are arguably a bad idea. Instead we should create # Tree objects with a "payload". (See below.) has $_ => ( is => 'rw', trigger => sub { my ($self, $new, $old) = @_; $old->_clear_parent if does $old, 'Tree'; $new->_set_parent($self) if does $new, 'Tree'; }, isa => union(qw( Undef Str ), role_type('Tree')), ) for @child_names; has parent => ( does => 'Tree', reader => 'parent', writer => '_set_parent', clearer => '_clear_parent', predicate => 'has_parent', ); method mk_balanced => sub { my ($class, $depth) = @_; my $self = $class->new; return $self unless $depth; $self->children( map { $class->mk_balanced($depth - 1) } @child_names ); return $self; }; method is_orphan => sub { not shift->has_parent; }; method child_depth => sub { my $self = shift; return 1 + max map { does($_, 'Tree') ? $_->child_depth : (defined $_ + ? 0 : -1) } $self->children; }; method parent_height => sub { my $self = shift; return 0 if $self->is_orphan; return 1 + $self->parent->parent_height; }; method children => sub { my $self = shift; if (@_) { for (@child_names) { $self->$_(shift); } } return map { $self->$_ } @child_names; }; method has_children => sub { grep defined, shift->children; }; method to_string => sub { my $self = shift; return "(leaf node)" unless $self->has_children; my @child = map { does($_, 'Tree') ? $_->to_string : (defined $_ ? + qq("$_") : '(undef)') } $self->children; # indent by three spaces s/^/ /mg for @child; return join "\n", "(node)", @child; }; } } { package Tree::Binary; use Moose; with Tree => { child_names => [qw( a b )] }; } say "Make a balanced binary tree, 3 layers deep"; my $tree = Tree::Binary->mk_balanced(3); say "Tree depth is ", $tree->child_depth; say $tree->to_string; say "----"; say "Extend one of the leaf nodes"; $tree->b->a->a( Tree::Binary->mk_balanced(2) ); say "Tree depth is ", $tree->child_depth; say $tree->to_string; say "----"; say "Now let's try a ternary tree"; { package Tree::Ternary; use Moose; with Tree => { child_names => [qw( a b c )] }; } my $ternary = Tree::Ternary->mk_balanced(2); say "Tree depth is ", $ternary->child_depth; say $ternary->to_string; say "----"; say "Trees where each node has a payload."; { package Tree::Binary::WithString; use Moose; extends 'Tree::Binary'; has payload => (is => 'rw', isa => 'Str', required => 1); around to_string => sub { my ($orig, $self) = @_; my $string = $self->$orig; $string =~ s/\((.*node)\)/"($1 \"".$self->payload."\")"/e; return $string; }; } my $people = Tree::Binary::WithString->new(payload => 'People'); $people->children( Tree::Binary::WithString->new(payload => 'Men'), Tree::Binary::WithString->new(payload => 'Women'), ); say $people->to_string; say "----";

updated to add example with payloads

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re: recursive creation of attached objects? by tobyink
in thread recursive creation of attached objects? by Anonymous Monk

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