On Thu, Dec 22, 2005 at 02:02:56PM +0000, Daniel Carrera wrote:
I had never heard of mapM, or other -M functions. I can't imagine why those would be needed. It seems like pointless duplication.
(!!!) then you are missing out. the M functions (and monadic traversal functions in general) especially when combined with the mtl are some of the best swiss army knives haskell has to offer. and it is map that is redundant. map f xs = runIdentity $ mapM f xs sequence = mapM id I have come to think of the monadic forms of these functions as the 'true' versions and the others as just common special cases. though, not my most common function used from the prelude, it is up there. and the most commonly used non-trivial function other than return: 922 mapM 937 Nothing 1017 not 1061 error 1433 String 1456 Just 1544 IO 1777 map 1810 show 1972 text 2595 Int 5303 return John -- John Meacham - ⑆repetae.net⑆john⑈