simple symbolize_keys alternative without ActiveSupport

symbolize_keys.rb

# recursively symolizes keys in a Hash that are strings
# does not modify the original hash; returns a new hash
def symbolize_keys(hash)
  hash.to_a.reduce({}) do |acc, (key, val)|
    val = symbolize_keys(val) if val.is_a?(Hash)
    key = key.to_sym if key.is_a?(String)
    acc[key] = val
    acc
  end
end