(/) operates on a Fractional instance... but length returns an Int, which is not a Fractional.<div><br></div><div>You can convert the Int to a Fractional instance:</div><div>mean xs = sum xs / fromIntegral (length xs)</div>
<div><br></div><div>or try an integer division:</div><div><div>mean xs = sum xs `div` length xs</div><div><br></div><div>-n</div><br><div class="gmail_quote">On Thu, Jun 30, 2011 at 10:55 PM, Ruohao Li <span dir="ltr">&lt;<a href="mailto:liruohao@gmail.com">liruohao@gmail.com</a>&gt;</span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">Hi guys,<div><br></div><div>I just started learning some Haskell. I want to implement a mean function to compute the mean of a list. The signature of the function is:</div>
<div><font face="&#39;courier new&#39;, monospace">mean :: (Num a, Fractional b) =&gt; [a] -&gt; b</font></div>
<div>But when I implement this simple function, the compiler keep whining at me on type errors. I know this is wrong:</div><div><font face="&#39;courier new&#39;, monospace">mean xs = sum xs / length xs</font></div>
<div>But how to get it right? Thanks.</div>
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