24 Apr
2008
24 Apr
'08
8:44 p.m.
niklas.broberg:
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.
Wow. A 10x slowdown for a very commonly used function that in 99.8% of all use cases has no need for the extra laziness at all. No wonder some people say Haskell is a toy language...
mapM_ is far more common, and optimised specially. -- Don