On Nov 30, 2007 5:39 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
> Hmm. Secret... library... How do you guys find out about all this stuff?
There's
http://www.haskell.org/haskellwiki/Arrays#Unsafe_indexing.2C_freezing.2Fthawing.2C_running_over_array_elements
.
Cheers,
--
Felipe.
_
On Nov 30, 2007 2:39 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
> Sebastian Sylvan wrote:
> > On Nov 29, 2007 9:10 PM, Andrew Coppin <[EMAIL PROTECTED]>
> wrote:
> >
> >> How do you avoid accidentally recomputing the list multiple times?
> >>
> >
> > What do you mean? It's exactly the same as yo
Bulat Ziganshin wrote:
Hello Andrew,
Friday, November 30, 2007, 12:10:16 AM, you wrote:
I don't understand the ST monad.
From what I can tell, it's not definable without using strange language
extensions. (I don't really like using things where it's unclear why it
works.)
Sebastian Sylvan wrote:
On Nov 29, 2007 9:10 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
How do you avoid accidentally recomputing the list multiple times?
What do you mean? It's exactly the same as your original program but
with ST instead of IO? Why would it get accidentally recompu
On Fri, 30 Nov 2007, Daniel Fischer wrote:
> Am Freitag, 30. November 2007 14:39 schrieb Henning Thielemann:
>
> > Is this thread still about the prime sieve? As I mentioned, I think one
> > can avoid the mutable array, because if there is only a small number of
> > array updates with much change
Am Freitag, 30. November 2007 14:39 schrieb Henning Thielemann:
> Is this thread still about the prime sieve? As I mentioned, I think one
> can avoid the mutable array, because if there is only a small number of
> array updates with much changes per update, it should be efficient enough
> to copy
On Fri, 30 Nov 2007, Bulat Ziganshin wrote:
> Hello Andrew,
>
> Thursday, November 29, 2007, 9:43:48 PM, you wrote:
>
> >> Fifth thing: better use an STUArray, don't drag IO in if it's not
> >> necessary.
> >>
>
> > I don't understand the ST monad.
>
> it's just a subset of IO monad, with rename
On Thu, 29 Nov 2007, Andrew Coppin wrote:
> Sebastian Sylvan wrote:
> > On Nov 29, 2007 6:43 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
> >
> >> I don't understand the ST monad.
> >
> > There's not a whole lot to understand if you just want to use it
> > (though it's all very cool from a theore
Hello Sebastian,
Friday, November 30, 2007, 11:31:22 AM, you wrote:
>> I don't see Data.Array.Base documented anywhere. (How did you know it
>> exists?)
i use library sources as reference. it allows to study implementation
and learn good programming style
--
Best regards,
Bulat
On Nov 29, 2007 9:10 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
> Sebastian Sylvan wrote:
> > On Nov 29, 2007 6:43 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
> >
> >> I don't understand the ST monad.
> >>
> >
> >
> > There's not a whole lot to understand if you just want to use it
> > (though i
Hello Andrew,
Thursday, November 29, 2007, 9:43:48 PM, you wrote:
>> Fifth thing: better use an STUArray, don't drag IO in if it's not necessary.
>>
> I don't understand the ST monad.
it's just a subset of IO monad, with renamed operations
the subset is selected in the way that guarantees r
Hello Andrew,
Friday, November 30, 2007, 12:10:16 AM, you wrote:
>>> I don't understand the ST monad.
> From what I can tell, it's not definable without using strange language
> extensions. (I don't really like using things where it's unclear why it
> works.)
this extension used only to guaran
On Nov 29, 2007, at 6:19 PM, Stefan O'Rear wrote:
On Thu, Nov 29, 2007 at 09:10:16PM +, Andrew Coppin wrote:
Sebastian Sylvan wrote:
On Nov 29, 2007 6:43 PM, Andrew Coppin <[EMAIL PROTECTED]>
wrote:
I don't understand the ST monad.
...[and ST uses language extensions Andrew doesn't un
On Thu, Nov 29, 2007 at 09:10:16PM +, Andrew Coppin wrote:
> Sebastian Sylvan wrote:
>> On Nov 29, 2007 6:43 PM, Andrew Coppin <[EMAIL PROTECTED]>
>> wrote:
>>
>>> I don't understand the ST monad.
>>>
>>
>>
>> There's not a whole lot to understand if you just want to use it
>> (though
Am Donnerstag, 29. November 2007 19:43 schrieb Andrew Coppin:
> Daniel Fischer wrote:
> > One thing: since You check the array bounds, the system needn't check
> > them again, use unsafeWrite and unsafeRead. And use Int for the index,
> > that would be MUCH faster.
>
> I can't find the functions yo
Sebastian Sylvan wrote:
On Nov 29, 2007 6:43 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
I don't understand the ST monad.
There's not a whole lot to understand if you just want to use it
(though it's all very cool from a theoretical standpoint too).
From what I can tell, it's not d
On Nov 29, 2007 6:43 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
> Daniel Fischer wrote:
> > One thing: since You check the array bounds, the system needn't check them
> > again, use unsafeWrite and unsafeRead. And use Int for the index, that would
> > be MUCH faster.
> >
>
> I can't find the func
Daniel Fischer wrote:
One thing: since You check the array bounds, the system needn't check them
again, use unsafeWrite and unsafeRead. And use Int for the index, that would
be MUCH faster.
I can't find the functions you're talking about. I have however changed
the index type. (Make little
On Nov 28, 2007, at 16:28 , Andrew Coppin wrote:
Michaeljohn Clement wrote:
Andrew Coppin wrote:
First, somebody else wrote this in C:
int n = 2 , m , primesFound = 0;
for( n=0;n < MAX_NUMBERS;n++ )
if( prime[n] )
{
primesFound++;
if( primesFound == 10001 )
cout << n << " is the 10001st
On Nov 28, 2007 9:28 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
> Michaeljohn Clement wrote:
> > Andrew Coppin wrote:
> >
> >> First, somebody else wrote this in C:
> >>
> >> int n = 2 , m , primesFound = 0;
> >>
> >> for( n=0;n < MAX_NUMBERS;n++ )
> >> if( prime[n] )
> >> {
> >> primesFound++;
>
Am Mittwoch, 28. November 2007 22:31 schrieb Andrew Coppin:
> There are problems for which it's important to know how many times a
> given prime factor occurs. And there are other problems where it is
> merely necessary to know which primes are factors. I would say it's
> useful to have *both* func
Michaeljohn Clement wrote:
Andrew Coppin wrote:
First, somebody else wrote this in C:
int n = 2 , m , primesFound = 0;
for( n=0;n < MAX_NUMBERS;n++ )
if( prime[n] )
{
primesFound++;
if( primesFound == 10001 )
cout << n << " is the 10001st prime." << endl;
Um, I can't *believe* nob
Sebastian Sylvan wrote:
On Nov 28, 2007 12:12 PM, Kalman Noel <[EMAIL PROTECTED]> wrote:
Sebastian Sylvan:
primes :: [Integer]
primes = 2 : filter (null . primeFactors) [3,5..]
primeFactors :: Integer-> [Integer]
primeFactors n = factor n primes
where
factor m (p:ps) | p*p
On Nov 28, 2007 12:12 PM, Kalman Noel <[EMAIL PROTECTED]> wrote:
> Sebastian Sylvan:
> > primes :: [Integer]
> > primes = 2 : filter (null . primeFactors) [3,5..]
> >
> > primeFactors :: Integer-> [Integer]
> > primeFactors n = factor n primes
> > where
> > factor m (p:ps) | p*p > m
Sebastian Sylvan:
> primes :: [Integer]
> primes = 2 : filter (null . primeFactors) [3,5..]
>
> primeFactors :: Integer-> [Integer]
> primeFactors n = factor n primes
> where
> factor m (p:ps) | p*p > m= []
> | m `mod` p == 0 = p : factor (m `div` p) (p:
Don Stewart wrote:
This is an FAQ.
Unless you use the same algorithm and data types in benchmarks, you're
not really benchmarking anything. And expecting one of the worst
possible algorithms to be good is hoping for a little too much :)
Well, if I was comparing my Haskell against some expe
Brent Yorgey wrote:
The algorithm you use to compute primes is actually quite inefficient,
and in particular, it is NOT the same algorithm that the C program is
using, despite first appearances! The call to 'filter' in the sieve
function works by checking *every* number for divisibility by p,
On 11/27/07, Sebastian Sylvan <[EMAIL PROTECTED]> wrote:
>
> That is indeed a nice and clear version that's pretty fast. It's
> basically the same as the C version except "backwards" (i.e. examine a
> number and work backwards through its divisors, rather than filling in
> a "map" of all multiples
Andrew Coppin wrote:
> On the other hand, I must relay to you how much fun I had with certain
> other problems.
You may want to look at:
http://haskell.org/haskellwiki/Euler_problems
and make some contributions. But be very careful
what you peek at, so don't spoil your own fun.
Regards,
Yitz
__
On the other hand, I must relay to you how much fun I had with certain
other problems.
For example, problem #12. I started with this:
triangles = scanl1 (+) [1..]
divisors n = length $ filter (\x -> n `mod` x == 0) [1..n]
answer = head $ dropWhile (\n -> divisors n < 500) triangles
Sadly,
On Nov 27, 2007 8:44 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
> Andrew Coppin wrote:
> > Also, I'm stuck with problem #10. (Find the sum of all primes less
> > than 1 million.) I've let the program run for well over 15 minutes,
> > and still no answer is forthcomming. It's implemented using the
On Nov 27, 2007 8:54 PM, Olivier Boudry <[EMAIL PROTECTED]> wrote:
>
> Hi Andrew,
>
> I don't remember who I stole this prime computation from, but it is very
> fast (10001's prime in 0.06 sec with Int and 0.2 with Integer on my machine)
> and not overly complex:
>
> primes :: [Integer]
> prime
Andrew Coppin wrote:
Also, I'm stuck with problem #10. (Find the sum of all primes less
than 1 million.) I've let the program run for well over 15 minutes,
and still no answer is forthcomming. It's implemented using the same
primes function as above, with a simple filter and sum. (The type has
Brent Yorgey wrote:
> For more information you might want to read this paper, which includes a
> much better primes implementation:
> www.cs.hmc.edu/~oneill /papers/Sieve-JFP.pdf
> In fact, this very same topic was discussed on the list a while back, you
> can read it here:
> http://thread.gmane.or
On Tue, 27 Nov 2007, Andrew Coppin wrote:
> So, now I have a Haskell version that's "only" several hundred times
> slower. Neither program is especially optimised, yet the C version is
> drastically faster. This makes me sad. :-(
I think the C version is so much faster because it does not need
a
andrewcoppin:
> Hi guys.
>
> Somebody just introduced me to a thing called "Project Euler". I gather
> it's well known around here...
>
> Anyway, I was a little bit concerned about problem #7. The problem is
> basically "figure out what the 10,001st prime number is". Consider the
> following t
On 11/27/07, Andrew Coppin <[EMAIL PROTECTED]> wrote:
>
> Hi guys.
>
> Somebody just introduced me to a thing called "Project Euler". I gather
> it's well known around here...
>
> Anyway, I was a little bit concerned about problem #7. The problem is
> basically "figure out what the 10,001st prime n
On Nov 27, 2007 2:34 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote:
> Hi guys.
>
> Somebody just introduced me to a thing called "Project Euler". I gather
> it's well known around here...
>
> Anyway, I was a little bit concerned about problem #7. The problem is
> basically "figure out what the 10,00
Hi guys.
Somebody just introduced me to a thing called "Project Euler". I gather
it's well known around here...
Anyway, I was a little bit concerned about problem #7. The problem is
basically "figure out what the 10,001st prime number is". Consider the
following two programs for solving this
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