has_key_path.rb

def has_key_path?(h, path)
  !path.detect do |key|
    !(h.respond_to?(:has_key?) && h.has_key?(key) && true.tap { h = h[key] })
  end
end

h = {:a => {:b => 1, :c => nil}}

puts has_key_path?(h, [:a, :x])     # false
puts has_key_path?(h, [:a, :b])     # true
puts has_key_path?(h, [:a, :c])     # true
puts has_key_path?(h, [:a, :c, :d]) # false