Creating generators from user defined data types in haskell

Question

I need some suggestions on how I can go about creating a random generator for the Foo data type such that the list of Boo is never empty?

data Boo = Boo Float Float Float
data Foo = Foo Float Float Float [Boo]

Answer 1

You can use the listOf1 function to get a generator which generates non-empty lists and use that for defining an appropriate Arbitrary instance, like:

import Test.QuickCheck
import Control.Applicative

instance Arbitrary Boo

instance Arbitrary Foo where
  arbitrary = Foo <$> arbitrary <*> arbitrary <*> arbitrary <*> listOf1 arbitrary