#!/usr/bin/env perl
use strict;
use warnings;
use 5.010;

package snippets {

    my $ypp = YAML::PP->new;
    my $database = {
        42 => <<~'EOM',
            section_42:
                key1: val1
                key2: val2
            section_43:
                key1: val11
                key2: val22
            EOM
        52 => {
        },
    };

    sub load_snippet {
        my ($id) = @_;
        my $yaml = $database->{ $id };
    }

};

package main {
    use YAML::PP;
    my $ypp = YAML::PP->new;
    my $schema = $ypp->schema;
    my %sections;
    $schema->add_resolver(
        tag => "!load-snippets",
        match => [ all => => sub {
            my ($constructor, $event) = @_;
            # load YAML from "database"
            my $yaml = snippets::load_snippet($event->{value});
            my $ypp = YAML::PP->new;
            my $data = $ypp->load_string($yaml);
            %sections = (%sections, %$data);
            return 'placeholder';
        }],
        implicit => 0,
    );
    $schema->add_resolver(
        tag => "!section",
        match => [ all => sub {
            my ($constructor, $event) = @_;
            my $value = $event->{value};
            return $sections{ $value };
        }],
        implicit => 0,
    );

    my ($filename) = @ARGV;
    my $data = $ypp->load_file($filename);
    say $ypp->dump_string($data);
}

# snippets.yaml
---
snippets: !load-snippets 42
workflow:
- s1
- s2
sections:
  my_section: !section section_42

% perl snippets.pl snippets.yaml
---
sections:
  my_section:
    key1: val1
    key2: val2
snippets: placeholder
workflow:
- s1
- s2