#! /usr/bin/perl
use warnings;
use strict;
use feature qw{ say };


menu('Main Menu',
     [ 'Get date and time', sub { say scalar localtime } ],
     [ 'Go to submenu',     sub { $_[0] = submenu() } ],
     [ 'Quit',              sub { $_[0] = 1 } ],
);


sub menu {
    my ($title, @options) = @_;

    my $done;
    while (! $done) {
        say $title;
        say 1 + $_, ".  $options[$_][0]" for 0 .. $#options;

        chomp( my $reply = <> );
        next unless $reply =~ /^[1-9][0-9]*$/;
        next if $reply > @options;

        --$reply;
        $options[$reply][1]->($done, $reply);
    }
    return $done
}


sub submenu {
    my $result = menu('Submenu',
         [ 'Get username', sub { say scalar getpwuid $> } ],
         [ 'Back',         \&pass ],
         [ 'Quit',         \&pass ],
    );
    return $result == 2  # Propagate Quit.
}


sub pass { $_[0] = $_[1] }