Re: [Haskell-beginners] length problem

6 Feb 2015

      Oke,

I have solved it already.
The problem was that I did list.length but Haskell uses length list

Still too much Ruby in my system :(

Roelof

Francesco Ariis schreef op 6-2-2015 om 17:50:
...
(off-list) please consider not using html in your mails, it's quite difficult
to read them for us who plaintext-friendly client
On Fri, Feb 06, 2015 at 05:47:24PM +0100, Roelof Wobben wrote:
...
<html>
   <head>
<meta http-equiv="content-type" content="text/html; charset=windows-1252">
   </head>
   <body bgcolor="#FFFFFF" text="#000000">
     Hello, <br>
     <br>
     I have to double every second element from the right. <br>
     <br>
     So for a even length array that means : 1 , 3 , 5 and so on <br>
     and for a non even lenght that means the 2,4 and so on. <br>
     <br>
     So I thought I could solve that on this way : <br>
     <br>
     -- | Doubles every second number from the right.<br>
     doubleEveryOther :: [Integer] -> [Integer]<br>
     doubleEveryOther []         = []     <br>
     doubleEveryOther (x:[])     = [x]   <br>
     doubleEveryOther (x:(y:zs)) <br>
        | ((x:(y:zs)).length) `mod` 2 /= 0 = [x] ++ (y * 2) :
     doubleEveryOther zs<br>
        | otherwise = [x *2]  ++ y : doubleEveryOther zs<br>
     <br>
     <br>
     <br>
     but this does not work because I see this error message : <br>
     <br>
     <div class="ide-error-span">src/Main.hs@14:8-14:16 </div>
     <div class="ide-error-msg"><span>Couldn't match expected type ‘Int
         -> c0’ with actual type </span>
       <div class="CodeMirror cm-s-default" style="font-size: 14px;">[<span
           class="cm-variable-2">Integer</span>]</div>
       <span title="Click to show/hide extra information"
         class="ide-error-collapse-btn"> …</span><span style="display:
         inline;">
         In the first argument of ‘(.)’, namely ‘(x : (y : zs))’
         In the first argument of ‘mod’, namely ‘((x : (y : zs)) .
         length)’
         In the first argument of ‘(/=)’, namely ‘((x : (y : zs)) .
         length) `mod` 2’<br>
         <br>
         <br>
         Can anyone give me a better way to check if I have a even or odd
         length array ?<br>
         <br>
         Roelof<br>
         <br>
       </span></div>
     <br>
   </body>
</html>
_______________________________________________
Beginners mailing list
Beginners@haskell.org
http://www.haskell.org/mailman/listinfo/beginners