<div dir="ltr">First step would probably be using Ints instead of Integers.<br><br><div class="gmail_quote">On Thu, Oct 2, 2008 at 6:45 AM, Matthew Williams <span dir="ltr"><<a href="mailto:Matthew_Williams@xyratex.com">Matthew_Williams@xyratex.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div>
<div><span><font size="2" face="Arial">Hi
Guys,</font></span></div>
<div><span><font size="2" face="Arial"></font></span> </div>
<div><span><font size="2" face="Arial">I'm new to Haskell
and I was wondering if you can help me:</font></span></div>
<div><span><font size="2" face="Arial"></font></span> </div>
<div><span><font size="2" face="Arial">One of the first
program's I tend to write when I'm looking at a new language is a program to
generate a list of perfect numbers:</font></span></div>
<div><span><font size="2" face="Arial"></font></span> </div>
<div><span><font size="2" face="Arial">--My First Perfect
Number Generator<br>factors :: Integer -> [Integer]<br>factors x = [z | z
<- [1..x-1], x `mod` z == 0]</font></span></div>
<div> </div>
<div><span><font size="2" face="Arial">is_perfect ::
Integer -> Bool<br>is_perfect x = if sum(factors x) == x then True else
False</font></span></div>
<div> </div>
<div><span><font size="2" face="Arial">do_perfect ::
[Integer] -> [Integer]<br>do_perfect x = [z |z <- x, is_perfect z
]</font></span></div>
<div><span><font size="2" face="Arial"></font></span> </div>
<div><span><font size="2" face="Arial">Then to run
it:</font></span></div>
<div><span><font size="2" face="Arial">> do_perfect
[1..9000]</font></span></div>
<div><span><font size="2" face="Arial"></font></span> </div>
<div><font size="2" face="Arial"><span>I'm using GHC to run
it. My problem / question is this: It's running quite a lot slower than
equivalent programs in erlang and python. I suspect it's down to the way I've
written it. Any thoughts (or comments in general)</span></font></div>
<div><font size="2" face="Arial"><span></span></font> </div>
<div><font size="2" face="Arial"><span>Many
thanks</span></font></div>
<div><font size="2" face="Arial"><span></span></font> </div>
<div><font size="2" face="Arial"><span>Matt</span></font></div>
<br>
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<br></blockquote></div><br></div>