[Haskell-cafe] Re: Tutorial uploaded

[Tomasz Zielonka]

On Thu, Dec 22, 2005 at 02:02:56PM +0000, Daniel Carrera wrote:
> Paul Moore wrote:
> >As I say, I'm not trying to criticize anyone here, but it seems to be
> >quite hard to get across to people who have understood and assimilated
> >this sort of stuff, just how hard it feels to newcomers. We understand
> >the explanations (we do! really! :-)) but even understanding them, we
> >are still left with a lack of confidence. It's like being shown a full
> >set of carpentry tools, having every one explained, but still reaching
> >for the hammer every time and banging something no matter what we're
> >trying to do :-)
> 
> I had never heard of mapM, or other -M functions. I can't imagine why 
> those would be needed. It seems like pointless duplication.

The point of mapM is that you can use side-effects for each element
processed. For example, with mapM in IO monad you can turn a list
of filenames into a list of file contents.

Actually, it is map that is redundant, because it's equivalent to mapM
for the Identity monad.

Best regards
Tomasz

-- 
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