Funny you should say that, I was just experimenting with generating one at a time using (StateT StdGen Maybe). If I get stuck (again) I'll check out ListT. Thanks! Chad On 8/15/07, Paul Johnson wrote:

Chad Scherrer wrote:

...

Thanks for your replies.

I actually starting out returning a single element instead. But a given lookup might return [], and the only way I could think of to handle it in (State StdGen a) would be to fail in the monad. But that's not really the effect I want - I'd rather have it ignore that element. Another option was to wrap with Maybe, but then since I really want a sequence of them anyway, I decided to just wrap in a List instead. Is there a way Maybe would work out better? Ahh. How about using ListT Gen then? That (if I've got it the right way round) works like the list monad (giving you non-determinism), but has your random number generator embedded as well. Take a look at "All About Monads" at http://www.haskell.org/all_about_monads/html/. Each action in the monad may use a random number and produce zero or more results.

Paul.

-- Chad Scherrer "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx