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Today's Topics:
1. Re: type classes and multiple implementations (Chadda? Fouch?)
2. timer_create: Invalid argument (Thomas Friedrich)
3. Re: timer_create: Invalid argument (Daniel Fischer)
4. Re: timer_create: Invalid argument (Maur??cio)
5. Re: Re: timer_create: Invalid argument (Thomas Friedrich)
6. Re: timer_create: Invalid argument (Maur??cio)
7. exercise 3.10 in YAHT (George Huber)
8. Re: exercise 3.10 in YAHT (Fernando Henrique Sanches)
----------------------------------------------------------------------
Message: 1
Date: Sat, 6 Jun 2009 18:00:50 +0200
From: Chadda? Fouch? <chaddai.fou...@gmail.com>
Subject: Re: [Haskell-beginners] type classes and multiple
implementations
To: Sean Bartell <wingedtachik...@gmail.com>
Cc: beginners@haskell.org
Message-ID:
<e9350eaf0906060900l713faeabl47c8ef38d7e16...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Fri, Jun 5, 2009 at 7:09 PM, Sean Bartell<wingedtachik...@gmail.com> wrote:
> Â Â by_type :: Storage a => String -> String -> IO a
> This function must, for any Storage type, take any two strings and produce
> an IO value of that type. (by_type "disk" "xyz" :: Memory must be valid.) It
> doesn't really have the option of choosing which instance of Storage to use.
>
> In pure Haskell, you would probably have to do something like
> Â type Storage = Disk Handle | Memory String
> Â by_type :: String -> String -> Storage
> That way, by_type can return any Storage it wants.
>
> I'm sure there are also ways to do what you want with extensions.
I think the point is to be able to extend the storage methods in
another module ? If not, Sean's solution is what you want.
If you want to use the type class to allow anyone to add a new method
in his own module, you can use existential type, like :
> data Store = forall a . Storage a => Store a
and then your byType :
> byType "disk" x = Store (open x :: Disk)
> byType "memory" x = Store (open x :: Memory)
See XMonad and its Layout type for an example of this method.
--
Jedaï
------------------------------
Message: 2
Date: Mon, 08 Jun 2009 10:35:22 -0400
From: Thomas Friedrich <i...@suud.de>
Subject: [Haskell-beginners] timer_create: Invalid argument
To: beginners <beginners@haskell.org>
Message-ID: <4a2d21aa.2090...@suud.de>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi,
I need to check if a couple of files have the same number of lines in
them. So, I written a little Haskell program that counts the number of
lines in a file.
import System.Environment (getArgs)
main :: IO ()
main = do
[f] <- getArgs
cs <- readFile f
print $ length (lines cs)
Now, when I invoke the program on my computer, it does what it should do:
~ $ ./count count.hs
7
However, when I run the program on a different computer, I get the
following:
~ $ scp count count.hs thom...@...:~
tho...@...'s password:
count 100% 492KB 492.2KB/s 00:00
count.hs 100% 125 0.1KB/s 00:00
~ $ ssh tho...@...
[tho...@... ~] $ ./count count.hs
count: timer_create: Invalid argument
[tho...@... ~]$
What does this error message mean? And why does it occur? Other
programs that I written and compiled on my computer worked just fine on
the other. I run Arch Linux and I am using GHC 6.10.3, the other
computer is a RedHat 3.
Cheers,
Thomas
------------------------------
Message: 3
Date: Mon, 8 Jun 2009 17:17:33 +0200
From: Daniel Fischer <daniel.is.fisc...@web.de>
Subject: Re: [Haskell-beginners] timer_create: Invalid argument
To: beginners@haskell.org
Message-ID: <200906081717.33765.daniel.is.fisc...@web.de>
Content-Type: text/plain; charset="iso-8859-1"
Am Montag 08 Juni 2009 16:35:22 schrieb Thomas Friedrich:
> Hi,
>
> [tho...@... ~] $ ./count count.hs
> count: timer_create: Invalid argument
> [tho...@... ~]$
>
> What does this error message mean? And why does it occur? Other
> programs that I written and compiled on my computer worked just fine on
> the other. I run Arch Linux and I am using GHC 6.10.3, the other
> computer is a RedHat 3.
Do other Haskell programmes compiled with ghc-6.10.3 on Arch run on Red Hat 3?
I think the timer_create is called during initialisation of the run-time, for
+RTS -sstderr and such, probably RH3 has an older timer_create which doesn't
like the
passed argument.
Then no ghc-compiled programme from Arch should run on RH3, nor should C
programmes using
timer_create with like arguments.
>
> Cheers,
> Thomas
>
------------------------------
Message: 4
Date: Mon, 08 Jun 2009 12:26:48 -0300
From: Maur??cio <briqueabra...@yahoo.com>
Subject: [Haskell-beginners] Re: timer_create: Invalid argument
To: beginners@haskell.org
Message-ID: <h0jajo$u2...@ger.gmane.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> Now, when I invoke the program on my computer, it does what it should do:
> (...)
> However, when I run the program on a different computer, I get the
> following: (...)
> [tho...@... ~] $ ./count count.hs
> count: timer_create: Invalid argument
I don't know where time_create is exactly used here, however,
it seems like a linking problem. Have you tried rebuilding your
program in the remote machine? Actually, the fact that other
programs did succeed seems strange to me. You could show some
program that did work on both machines if you want to know why
it actually worked.
If you don't want to rebuild, why not to use it as a script? You
can do it by just adding this first line to your file:
#!/usr/bin/runhaskell
and allowing it to be used as a script:
chmod a+x count.hs
I usually add such scripts to ~/bin so I can run then anywhere
(but check if your distribution do add ~/bin to path).
Maurício
------------------------------
Message: 5
Date: Mon, 08 Jun 2009 13:46:56 -0400
From: Thomas Friedrich <i...@suud.de>
Subject: Re: [Haskell-beginners] Re: timer_create: Invalid argument
Cc: beginners <beginners@haskell.org>
Message-ID: <4a2d4e90.8050...@suud.de>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi Mauricio,
yes it is a linking problem. When I compile the program on my computer with
ghc --make A.hs -threaded
the program will run on the Red Hat 3. If I compile it with
ghc --make A.hs
it won't. I don't know why though, and I don't think this is an
expected behavior. Daniel suggested to file a bug report on this. I've
never done that before. Where would I do this? Is there something I
should know about filing a bug?
I cannot compile the program on the Red Hat machine, as GHC is not
installed there and I only have user rights.
Cheers,
Thomas
Maurício wrote:
>> Now, when I invoke the program on my computer, it does what it should
>> do:
> > (...)
>> However, when I run the program on a different computer, I get the
>> following: (...)
>> [tho...@... ~] $ ./count count.hs
>> count: timer_create: Invalid argument
>
> I don't know where time_create is exactly used here, however,
> it seems like a linking problem. Have you tried rebuilding your
> program in the remote machine? Actually, the fact that other
> programs did succeed seems strange to me. You could show some
> program that did work on both machines if you want to know why
> it actually worked.
>
> If you don't want to rebuild, why not to use it as a script? You
> can do it by just adding this first line to your file:
>
> #!/usr/bin/runhaskell
>
> and allowing it to be used as a script:
>
> chmod a+x count.hs
>
> I usually add such scripts to ~/bin so I can run then anywhere
> (but check if your distribution do add ~/bin to path).
>
> Maurício
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
------------------------------
Message: 6
Date: Mon, 08 Jun 2009 15:25:41 -0300
From: Maur??cio <briqueabra...@yahoo.com>
Subject: [Haskell-beginners] Re: timer_create: Invalid argument
To: beginners@haskell.org
Message-ID: <h0jl36$31...@ger.gmane.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
It seems it's a know question:
http://thread.gmane.org/gmane.comp.lang.haskell.cafe/49337
One of the problems discussed in that thread is the timer_create
issue, but it seems upgrading is the sugested solution.
Did Daniel mean to open a bug report on Red Hat or GHC? If you
ever want to report a bug on GHC:
http://haskell.org/ghc
The ReportABug link do have nice instructions. But maybe
this is worth discussing in haskell-cafe first, so I posted
a message there:
http://thread.gmane.org/gmane.comp.lang.haskell.cafe/59643
Best,
Maurício
> Hi Mauricio,
>
> yes it is a linking problem. When I compile the program on my computer
> with
>
> ghc --make A.hs -threaded
>
> the program will run on the Red Hat 3. If I compile it with
>
> ghc --make A.hs
>
> it won't. I don't know why though, and I don't think this is an
> expected behavior. Daniel suggested to file a bug report on this. I've
> never done that before. Where would I do this? Is there something I
> should know about filing a bug?
>
> I cannot compile the program on the Red Hat machine, as GHC is not
> installed there and I only have user rights.
>
> Cheers,
> Thomas
>
>
>
>
> Maurício wrote:
>>> Now, when I invoke the program on my computer, it does what it should
>>> do:
>> > (...)
>>> However, when I run the program on a different computer, I get the
>>> following: (...)
>>> [tho...@... ~] $ ./count count.hs
>>> count: timer_create: Invalid argument
>>
>> I don't know where time_create is exactly used here, however,
>> it seems like a linking problem. Have you tried rebuilding your
>> program in the remote machine? Actually, the fact that other
>> programs did succeed seems strange to me. You could show some
>> program that did work on both machines if you want to know why
>> it actually worked.
>>
>> If you don't want to rebuild, why not to use it as a script? You
>> can do it by just adding this first line to your file:
>>
>> #!/usr/bin/runhaskell
>>
>> and allowing it to be used as a script:
>>
>> chmod a+x count.hs
>>
>> I usually add such scripts to ~/bin so I can run then anywhere
>> (but check if your distribution do add ~/bin to path).
>>
>> Maurício
>>
>> _______________________________________________
>> Beginners mailing list
>> Beginners@haskell.org
>> http://www.haskell.org/mailman/listinfo/beginners
------------------------------
Message: 7
Date: Tue, 09 Jun 2009 00:05:21 -0400
From: George Huber <geohu...@verizon.net>
Subject: [Haskell-beginners] exercise 3.10 in YAHT
To: beginn...@haskell.org.
Message-ID: <4a2ddf81.9060...@verizon.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I'm currently working through "Yet Another Haskell Tutorial" by H.
Daume and have a question on how to proceed with his exercise 3.10.
The exercise question is: Write a program that will repeatedly ask the
user for numbers until he types in zero, at which point it will tell him
the sum of all the numbers, the product of all the numbers, and, for
each number, its factorial.
The hint that is given is to write an IO action that reads a number and
either returns an empty list (if the number is zero) or recurses itself
making a list from the number and the result of the recursive call.
Daume presents and example of such a function:
askForWords = do
putStrLn "Please enter a word:"
word <- getLine
if word == ""
then return []
else do
rest <- askForWords
return (word : rest)
so, based on his example I created the function:
getNums = do
putStrLn "Enter a number (zero to stop):";
strNum <- getLine
let num = read strNum
if num == 0
then return []
else do
rest <- getNums
return (num:rest)
loading the file that contains the above function into GHCi (version
6.8.3) gives the following error "The last statement in a 'do' construct
must be an expression"
being a beginner, I'm at a loss at the cause of the error and how to fix
it -- any suggestions?
thanks,
george
------------------------------
Message: 8
Date: Tue, 9 Jun 2009 01:27:32 -0300
From: Fernando Henrique Sanches <fernandohsanc...@gmail.com>
Subject: Re: [Haskell-beginners] exercise 3.10 in YAHT
To: George Huber <geohu...@verizon.net>
Cc: beginners@haskell.org
Message-ID:
<174c72ef0906082127l2b9c9bbbkceb73a246c8d1...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
It compiles fine here with GHC 6.8.2:
*Main> getNums
Enter a number (zero to stop):
4
Enter a number (zero to stop):
3
Enter a number (zero to stop):
0
[4,3]
Are you sure the problem is in this function?
Fernando Henrique Sanches
On Tue, Jun 9, 2009 at 1:05 AM, George Huber <geohu...@verizon.net> wrote:
> I'm currently working through "Yet Another Haskell Tutorial" by H. Daume
> and have a question on how to proceed with his exercise 3.10.
>
> The exercise question is: Write a program that will repeatedly ask the
> user for numbers until he types in zero, at which point it will tell him the
> sum of all the numbers, the product of all the numbers, and, for each
> number, its factorial.
>
> The hint that is given is to write an IO action that reads a number and
> either returns an empty list (if the number is zero) or recurses itself
> making a list from the number and the result of the recursive call.
>
> Daume presents and example of such a function:
>
> askForWords = do
> putStrLn "Please enter a word:"
> word <- getLine
> if word == ""
> then return []
> else do
> rest <- askForWords
> return (word : rest)
>
> so, based on his example I created the function:
>
> getNums = do
> putStrLn "Enter a number (zero to stop):";
> strNum <- getLine
> let num = read strNum
> if num == 0
> then return []
> else do
> rest <- getNums
> return (num:rest)
>
> loading the file that contains the above function into GHCi (version 6.8.3)
> gives the following error "The last statement in a 'do' construct must be an
> expression"
>
> being a beginner, I'm at a loss at the cause of the error and how to fix it
> -- any suggestions?
>
> thanks,
> george
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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