Re: [Haskell-cafe] Re: Generating repeatable arbitrary values with QuickCheck 2

Martijn, Ryan wrote:

...

Unfortunately, this makes things like

...

infinite_xs <- sequence (repeat arbitrary) no longer work, since the state never comes out the other side.

You replied:

You're asking to execute an infinite number of monadic actions. How can this ever terminate at all?

There is this thing called lazy evaluation, you know. ;-) Try for yourself: import System.Random import Test.QuickCheck foo :: Gen [Int] foo = do ns <- sequence (repeat arbitrary) return (take 5 ns) main :: IO () main = do stdGen <- newStdGen print (generate 42 stdGen foo) Cheers, Stefan