[Haskell-beginners] Reading input

[C.M.Brown]

Or, call median with your list of ints and forget about mainProg...:)

Chris.

On Wed, 20 Aug 2008, C.M.Brown wrote:

> Barry,
>
> On another note, you may want to avoid monads altogether for this. You can
> run this straight from ghci (replacing mainProg with main)
>
> mainProg :: [Int] -> Int
> mainProg arg = median lst
>
> and then call mainProg with your desired list of stings
>
> > mainProg [1,2,3,4]
>
> Chris.
>
>
> On Wed, 20 Aug 2008, Yitzchak Gale wrote:
>
> > Hi Barry,
> >
> > Barry Burd wrote:
> > > median :: [Int] -> Int
> > > median lst =
> > >  case medians lst of
> > >    -- All the values in the result are the same, we just pick the first one
> > >    x:xs -> x
> > >
> > > main = do
> > >    putStr "Enter a list: "
> > >    lst <- getLine
> > >    median lst
> >
> > > I'm sure this is because Haskell isn't automatically changing a String
> > > to a List of numbers. But how can I do this?
> >
> > Use the "read" function. Watch out, though - there is
> > no error checking there. So if the user enters a string
> > that does not have the right syntax for a Haskell list
> > of integers, your program will halt with an error message.
> >
> > You have another problem - you used the "median"
> > function as a step in a do block - but each step in a
> > do block must have type "IO a" for some type a.
> >
> > Here's how you could write your main function:
> >
> > main = do
> >    putStr "Enter a list: "
> >    lst <- getLine
> >    print $ median $ read lst
> >
> > Regards,
> > Yitz
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> >
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