YAML::Tiny sees sequences where there are none.

[perlpunk]

echo 'foo:
  -a
  -b' | ysh -MYAML::Tiny
$VAR1 = {
  'foo' => [
    'a',
    'b'
  ]
};

Correct would be:

$VAR1 = {
  'foo' => '-a -b'
};

(YAML::XS, YAML::Syck, YAML::PP)