Re: Re[2]: a faster, accumulating mapM (was Re: [Haskell-cafe] mapM vs mapM_ performance)

On Thu, Apr 24, 2008 at 11:28 PM, Ben wrote:

2) Is there a reason to not use mapM3 above?

Yes, there certainly is. mapM3 is not equivalent to mapM; it is too strict: *Main> take 3 $ head $ mapM return [1,2,3,4,undefined] [1,2,3] *Main> take 3 $ head $ mapM3 return [1,2,3,4,undefined] [*** Exception: Prelude.undefined So, like foldl', mapM3 seems a viable alternative for mapM, but not a replacement. Luke