=head1 Tutorial for MARC::MIR DSL

=head2 the DSL

to make things more readable and less error prone, we also add a DSL. Every keywords of this DSL works the same way. FIXME : explain. 

also, iso2709_records_of is an helper that stream the records of an ISO2709 formatted file.

=head2 some examples 

the perfect boilerplate

    use autodie;
    use Modern::Perl;
    use Perlude;
    use MARC::MIR;

print all the ids of the records (assuming the id is in 001, the common case)

    now    { say record_id from_iso2709 } iso2709_records_of "biblio.marc";

or

    marawk { say $ID } "biblio.marc";

remove every 9.. fields

    now {
	$_ = from_iso2709;
	with_fields { @$_ = grep { (tag) !~ /^9/ } @$_ };
	print to_iso2709;
    } iso2709_records_of "biblio.marc";

every 856$q must be jpeg

    now {
	$_ = from_iso2709;
	map_fields {
	    tag eq '856' and map_subfields {
		(tag) eq 'z' and with_value { $_ = 'jpeg' }
	    }
	}
	with_fields { @$_ = grep_fields { (tag) !~ /^9/ } @$_ };
    } iso2709_records_of "biblio.marc";

or 

    marawk { map_values { $_ = 'jpeg' } [qw< 856 z >] } "biblio.marc"

collect every 856$z by id

    use Modern::Perl;
    use YAML;
    use MARC::MIR;

    my %seen;
    marawk {
	map_values { push @{ $seen{$ID} }, $_ } [qw< 856 z >]
    } "data/*.RAW";
    say YAML::Dump \%seen;

=head2 marawk

# TODO: