Yes, I wish Haskell had a 1-tuple. The obvious syntax is already taken, but I could accept something different, like 'One a'.
On Mon, Mar 10, 2008 at 11:17 PM, Dan Weston <[EMAIL PROTECTED]> wrote: > I understand the lack of distinction between a unit type and a 0-tuple, > since they are isomorphic. But it is strange that there is no 1-tuple, > since _|_ and the 1-tuple (_|_) would be different things entirely, no? > > Dan > > Rodrigo Queiro wrote: > > You're looking for mapM_ > > mapM_ :: (Monad m) => (a -> m b) -> [a] -> m () > > (see also sequence_ :: (Monad m) => [m a] -> m () ) > > > > I don't think that it is possible to have a 1-tuples, just 2 and up. () > > is a unit rather than a 0-tuple, apparently: > > http://www.haskell.org/onlinereport/basic.html#sect6.1.4 > > > > On 10/03/2008, *Paulo J. Matos* <[EMAIL PROTECTED] > > <mailto:[EMAIL PROTECTED]>> wrote: > > > > Hello all, > > > > I find it funny that IO () is different from IO [()]. > > For example, if I define a function to output some lines with mapT, > > I would do: > > outputLines :: Int -> IO () > > outputLines i = mapM (putStrLn . show) (take i $ iterate ((+) 1) 1) > > > > However, this is in fact > > outputLines :: Int -> IO [()] > > > > I would like to know if in fact there's any difference in practice > > between (), [()], i.e. if in practice the difference matters. > > My first guess is that this is just a consequence of the Haskell > type > > system and so that everything fits this really needs to be like > this. > > Because > > mapM :: (Monad m) => (a -> m b) -> [a] -> m [b] > > > > So I guess that it makes sense that you get IO [()] instead of IO > (), > > and adding an exception just to say that [()] == () isn't good. > > By the way, as a consequence can you possibly get IO (()) or IO > ([()]) > > and are these all different from each other? > > > > Cheers, > > > > -- > > Paulo Jorge Matos - pocm at soton.ac.uk <http://soton.ac.uk> > > http://www.personal.soton.ac.uk/pocm > > PhD Student @ ECS > > University of Southampton, UK > > Sponsor ECS runners - Action against Hunger: > > http://www.justgiving.com/ecsrunslikethewind > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe@haskell.org <mailto:Haskell-Cafe@haskell.org> > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > > > ------------------------------------------------------------------------ > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe@haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >
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