require "yaml"

struct Good
  YAML.mapping(
    foo: { type: String, nilable: true }
  )
end

struct Bad1
  YAML.mapping(
    foo: String?
  )
end

alias Bad2 = Hash(String, String | Int32)?

yamls = [
  %q(foo: " x "),
  %q(foo: "x #{y} z"),
  %q(foo: "- oops")
]

yamls.each do |yaml|
  pp Good.from_yaml yaml
  begin
    pp Bad1.from_yaml yaml
  rescue ex
    pp ex.message
  end
  begin
    pp Bad2.from_yaml yaml
  rescue ex
    pp ex.message
  end
  puts "-----"
end