[Haskell-beginners] function defenition. Do I understand it right?

[Roelof Wobben]

Hello, 

 

I had a look at it but I don't think it will solve my problem.

What I try to achieve is this:

 

[1,2,3,4] will be [1,2] [3,4]

[1,2,3,4,5] will be [1,2,3] [3,4,5]

 

So the halfs have to be the same lenght.

 

So I use : 

 

length xs'div' 2 to figure out where the middle is.

lenght xs'mod'2 to look if it's a even or not even list.

 

So I can use splitat but then the lists will not be the same length if it's a not even list.

 

Roelof



----------------------------------------
> Subject: Re: [Haskell-beginners] function defenition. Do I understand it right?
> From: jhenahan at uvm.edu
> Date: Mon, 11 Jul 2011 15:55:13 -0400
> To: rwobben at hotmail.com
>
> You're overcomplicating things. Look at splitAt from Data.List:
>
> http://hackage.haskell.org/packages/archive/base/4.1.0.0/doc/html/Data-List.html#v%3AsplitAt
>
> On Jul 11, 2011, at 3:51 PM, Roelof Wobben wrote:
>
> > Hello,
> >
> > Thanks for the tip.
> > Im stuck now.
> >
> > I have this :
> >
> > halve (xs) | length xs'mod'2 == 0 = (take n xs drop n xs)
> > | otherwise = (take n+1 xs drop n+1 xs
> > where n= lenght xs'div'2
> >
> >
> > main = do
> > putStrLn $ show $ halve [1,2,3,4]
> > putStrLn $ show $ halve [1,2,3]
> >
> > But now I get this message :
> >
> > ERROR line 3 - Syntax error in expression (unexpected keyword "where")
> >
> > Appearently I can't use where here.
> >
> > How can I solve this ?
> >
> > Roelof
> >
> >
> >
> > > Date: Mon, 11 Jul 2011 11:44:28 -0400
> > > Subject: Re: [Haskell-beginners] function defenition. Do I understand it right?
> > > From: dmcbride at neondsl.com
> > > To: rwobben at hotmail.com
> > > CC: beginners at haskell.org
> > >
> > > For simple snippets like this, you can go to
> > > http://codepad.org/ddySVOPr and run your code to see if it works.
> > >
> > > And your first version (once corrected for syntax) works on any list
> > > length except for empty lists.
> > >
> > > On Mon, Jul 11, 2011 at 10:48 AM, Roelof Wobben <rwobben at hotmail.com> wrote:
> > > > Hello,
> > > >
> > > > I have made a exercise where I must split a even list.
> > > > The answer is :
> > > >
> > > > halve xs = (take n xs drop n xs)
> > > > where n = length xs 'div' 2
> > > >
> > > > Now I want to change it so i can split even and not even list,.
> > > > I thought this can be the answer
> > > >
> > > > halve xs =
> > > > lenght xs 'mod' 2 = 0 : (take n xs drop n xs)
> > > > otherwise : (take n+1 xs drop n+1 xs)
> > > > where
> > > > n = length xs 'div' 2
> > > >
> > > >
> > > > Can this be working ?
> > > > I did not check this on GCHI because Im re - installing my OS.
> > > >
> > > > Regards.
> > > >
> > > > Roelof
> > > >
> > > >
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