Re: [Haskell-cafe] proper way to generate a random data in criterion

On Wed, 19 Oct 2011 21:21:48 +0200, Gregory Collins wrote:

On Wed, Oct 19, 2011 at 5:03 PM, Johan Tibell wrote:

...

It does. You need to use evaluate to have ensure actually be evaluated.

I'm almost certain you're wrong about this. The bang pattern on the return from ensure (!r1 <- ensure $ ...) forces r1 to WHNF, which goes through deepseq, and thus the whole list is forced. See https://gist.github.com/1299380 for a short counterexample.

G

You don't need the ensure function or the bang patterns if you do it like this: main = deepseq testList $ do putStrLn "we survived without evaluating testList" let x = foldl' (+) 0 $ take 50 testList putStrLn $ "x was " ++ show x Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html --