use strict;
use warnings;
use IO::Prompt;

$|++;

# Map:
#  foo <-> baz
#   |       ^
#   |       |
#   |       V
#   +----> bar
# You can get from foo to bar, but you have to return via baz. 
# You can also go from foo to baz to bar.
my %locations = (
  foo => [ qw(bar baz) ],
  bar => [ qw(baz)     ],
  baz => [ qw(foo bar) ],
);

my $current_location = 'foo';
while(1) {
  print_location($current_location);
  $current_location = read_destination($current_location);
  if ($current_location eq 'quit') {
    print "Bye!\n";
    exit;
  }
}

sub print_location {
  my ($where) = @_;
  if (-f "$where.txt") {
    if (open my $fh, "<", "$where.txt") {
      while(defined($_ = <$fh>)) {
        print;
      }
      close $fh;
    }
  }
  else {
    print "There's nothing interesting here.\n";
  }
}

sub read_destination {
  my ($where) = shift;
  my %next;
  @next{ @{$locations{$where}} } = ();
  print "You can go to: ", (join ', ', sort keys %next),"\n";
  my $next_place;
  while(! $next_place or !exists($locations{$next_place})) {
    prompt "Pick a place: ";
    $next_place = $_;
    last if $next_place eq 'quit';
  }
  return $next_place;
}