<div dir="ltr">How can i know when casting of types maked by compiler and when programmer must to do it?<br><br>
<div class="gmail_quote">On Tue, Apr 5, 2011 at 12:14 PM, Daniel Fischer <span dir="ltr"><<a href="mailto:daniel.is.fischer@googlemail.com">daniel.is.fischer@googlemail.com</a>></span> wrote:<br>
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<div class="im">On Tuesday 05 April 2011 10:38:37, Nadav Chernin wrote:<br>> Why only "length as" we must to cast? Why "sum as", that have type<br>> Integer can be used in (/).<br>><br>> :t (/)<br>
><br>> (/) :: (Fractional a) => a -> a -> a<br><br></div>No, sum as has the type of as's elements,<br><br>sum :: Num a => [a] -> a<br><br>So the use of (/) refines the constraint from (Num a) to (Fractional a).<br>
if you want it to work on Integers too,<br>you'd get<br><br>mean :: (Real a, Fractional b) => [a] -> b<br>mean xs = realToFrac (sum xs) / (fromIntegral $ length xs)<br></blockquote></div><br></div>