[Haskell-beginners] length problem

Fri Feb 6 16:55:55 UTC 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 at 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>
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