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Today's Topics:
1. Re: Exposing Ratio data constructor ( Chadda? Fouch? )
2. Perfect numbers (Matthew Williams)
3. Re: Perfect numbers (wman)
4. Re: Perfect numbers (Jason Dusek)
5. Re: Perfect numbers (wman)
----------------------------------------------------------------------
Message: 1
Date: Mon, 29 Sep 2008 21:03:50 +0200
From: " Chadda? Fouch? " <[EMAIL PROTECTED]>
Subject: Re: [Haskell-beginners] Exposing Ratio data constructor
To: "Casey Rodarmor" <[EMAIL PROTECTED]>
Cc: beginners@haskell.org
Message-ID:
<[EMAIL PROTECTED]>
Content-Type: text/plain; charset=ISO-8859-1
2008/9/29 Casey Rodarmor <[EMAIL PROTECTED]>:
>
> invertRatio r = denominator r % numerator
Ratio is an instance of Fractional, which means :
invertRation = recip
ou
invert f = 1 / f
(probably the default definition of recip anyway).
> Is there any way to avoid this, while still letting the user benefit
> from the nice pattern matching syntax that exposing the data
> constructor allows?
To this more general question : allow the convenience of pattern
matching while keeping a datatype abstract, the latest GHC (6.10)
bring a new extension called "view pattern", it may not be ideal but
it should be pretty useful in this direction.
http://hackage.haskell.org/trac/ghc/wiki/ViewPatterns
--
Jedaï
------------------------------
Message: 2
Date: Thu, 2 Oct 2008 05:45:01 +0100
From: "Matthew Williams" <[EMAIL PROTECTED]>
Subject: [Haskell-beginners] Perfect numbers
To: <beginners@haskell.org>
Message-ID:
<[EMAIL PROTECTED]>
Content-Type: text/plain; charset="us-ascii"
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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Message: 3
Date: Thu, 2 Oct 2008 07:25:17 +0200
From: wman <[EMAIL PROTECTED]>
Subject: Re: [Haskell-beginners] Perfect numbers
To: "Matthew Williams" <[EMAIL PROTECTED]>
Cc: beginners@haskell.org
Message-ID:
<[EMAIL PROTECTED]>
Content-Type: text/plain; charset="iso-8859-1"
First step would probably be using Ints instead of Integers.
On Thu, Oct 2, 2008 at 6:45 AM, Matthew Williams <
[EMAIL PROTECTED]> 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
>
> ______________________________________________________________________
> This email may contain privileged or confidential information, which should
> only be used for the purpose for which it was sent by Xyratex. No further
> rights or licenses are granted to use such information. If you are not the
> intended recipient of this message, please notify the sender by return and
> delete it. You may not use, copy, disclose or rely on the information
> contained in it.
>
> Internet email is susceptible to data corruption, interception and
> unauthorised amendment for which Xyratex does not accept liability. While we
> have taken reasonable precautions to ensure that this email is free of
> viruses, Xyratex does not accept liability for the presence of any computer
> viruses in this email, nor for any losses caused as a result of viruses.
>
> Xyratex Technology Limited (03134912), Registered in England & Wales,
> Registered Office, Langstone Road, Havant, Hampshire, PO9 1SA.
>
> The Xyratex group of companies also includes, Xyratex Ltd, registered in
> Bermuda, Xyratex International Inc, registered in California, Xyratex
> (Malaysia) Sdn Bhd registered in Malaysia, Xyratex Technology (Wuxi) Co Ltd
> registered in The People's Republic of China and Xyratex Japan Limited
> registered in Japan.
> ______________________________________________________________________
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Message: 4
Date: Wed, 1 Oct 2008 22:54:00 -0700
From: "Jason Dusek" <[EMAIL PROTECTED]>
Subject: Re: [Haskell-beginners] Perfect numbers
To: wman <[EMAIL PROTECTED]>
Cc: Matthew Williams <[EMAIL PROTECTED]>,
beginners@haskell.org
Message-ID:
<[EMAIL PROTECTED]>
Content-Type: text/plain; charset=UTF-8
On Wed, Oct 1, 2008 at 22:25, wman <[EMAIL PROTECTED]> wrote:
> First step would probably be using Ints instead of Integers.
Doesn't seem to make a real difference in GHCi.
--
_jsn
Prelude> do_perfect [1..2000] :: [Integer]
[6,28,496]
it :: [Integer]
(4.22 secs, 169352736 bytes)
Prelude> do_perfect [1..2000] :: [Int]
[6,28,496]
it :: [Int]
(4.23 secs, 153699692 bytes)
------------------------------
Message: 5
Date: Thu, 2 Oct 2008 07:54:47 +0200
From: wman <[EMAIL PROTECTED]>
Subject: Re: [Haskell-beginners] Perfect numbers
To: "Matthew Williams" <[EMAIL PROTECTED]>
Cc: beginners@haskell.org
Message-ID:
<[EMAIL PROTECTED]>
Content-Type: text/plain; charset="iso-8859-1"
factors :: Int -> [Int]
factors x = [z | z <- [1..(x `div` 2)], x `mod` z == 0]
is_perfect :: Int -> Bool
is_perfect x = sum(factors x) == x
do_perfect :: [Int] -> [Int]
do_perfect x = [z |z <- x, is_perfect z ]
main = print $ do_perfect [1..9000]
-- compile with ghc -O2, it's more than ten times faster for me
-- althought using 1..(x `div 2) instead of 1..x-1 is a bit of cheating ;-))
On Thu, Oct 2, 2008 at 6:45 AM, Matthew Williams <
[EMAIL PROTECTED]> 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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