[Haskell-beginners] Perfect numbers

wman 666wman at gmail.com
Thu Oct 2 01:25:17 EDT 2008

First step would probably be using Ints instead of Integers.

On Thu, Oct 2, 2008 at 6:45 AM, Matthew Williams <
Matthew_Williams at xyratex.com> wrote:

>  Hi Guys,
> I'm new to Haskell and I was wondering if you can help me:
> 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:
> --My First Perfect Number Generator
> factors :: Integer -> [Integer]
> factors x = [z | z <- [1..x-1], x `mod` z == 0]
> is_perfect :: Integer -> Bool
> is_perfect x = if sum(factors x) == x then True else False
> do_perfect :: [Integer] -> [Integer]
> do_perfect x = [z |z <- x, is_perfect z ]
> Then to run it:
> > do_perfect [1..9000]
> 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)
> Many thanks
> Matt
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