Many thanks to both Georg and Lemmih. Actually, I had considered laziness, but I didn't pursue it enough. I tried one version of runNReps in which I passed (f x) as an additional arg; when that didn't work, a little thought convinced me that laziness was doing me in. I also tried another approach, which was to "use" the function evaluation, but that didn't work either (note: I know (f x) can not be the empty list for values of x I'm interested in, but I don't think Haskell does, unless it's *really* smart :-) :
runNReps :: (Int -> [a]) -> Int -> Int -> IO () runNReps f x todo | todo > 0 = do let junk = (f x) if null junk then return (()) else runNReps f x (todo - 1) | otherwise = return (())
Ideas? Again, many thanks, -- Bill Wood bill.wood@acm.org