intridea/grape — pull request #510 by myitcv (2013-11-19 15:48:35+00:00)
Title: Support lambda-based default values for params

The test gives an example of what we're looking for here:

```ruby
params do
optional :random, default: -> { Random.rand }
optional :not_random, default: Random.rand
end
get '/numbers' do
{ random_number: params[:random], non_random_number: params[:non_random_number] }
end
```