[Haskell-beginners] [IO String] to IO [String]
byorgey at seas.upenn.edu
Sun Mar 31 12:29:22 CEST 2013
Unfortunately, with the definition
f = getLine : f
this will not work. 'sequence f' has to do *ALL* the IO before you
can process even the first String in the resulting list. Since it is
infinite, it will just sit there reading lines forever but never
letting you process them.
I think in this case using [IO String] is actually a good solution.
On Sun, Mar 31, 2013 at 12:24:33PM +0200, Nathan Hüsken wrote:
> sequence :: Monad m => [m a] -> m [a]
> I thinkg
> sequence f :: IO [String]
> should be what you want.
> On 03/31/2013 12:19 PM, Ovidiu D wrote:
> >I have the function f which reads lines form the stdin and looks like this:
> >f :: [IO String]
> >f = getLine : f
> >What I don't like is the fact that the line processing I'm doing will
> >have to be in the IO Monad
> >I would like to make this function to have the signature
> >f : IO [String]
> >...such that I can get rid of the IO monad and pass the pure string list
> >to the processing function.
> >Can I do this?
> >Beginners mailing list
> >Beginners at haskell.org
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