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Today's Topics:
1. Re: type class question (Daniel Fischer)
2. Check out my photos on Facebook (Renick Bell)
3. Re: type class question (Ben)
4. Re: Re: Maybe, Either (Yusaku Hashimoto)
5. interface files (Luca Padovani)
6. Re: interface files (Daniel Fischer)
7. Re: interface files (Tim Sears)
8. Vaccum Cairo Errors (aditya siram)
----------------------------------------------------------------------
Message: 1
Date: Fri, 18 Sep 2009 17:28:06 +0200
From: Daniel Fischer <daniel.is.fisc...@web.de>
Subject: Re: [Haskell-beginners] type class question
To: beginners@haskell.org
Cc: Ben <midfi...@gmail.com>
Message-ID: <200909181728.07074.daniel.is.fisc...@web.de>
Content-Type: text/plain; charset="iso-8859-1"
Am Freitag 18 September 2009 16:38:19 schrieb Ben:
> > instance Summarizer RunningAverageState (State RunningAverageState) where
> > initialState = S 0 0
> > runOne = runningAverage
>
> but how would i use this, e.g.
>
> > --summarizeMany vs = last $ evalState (mapM runOne vs) initialState
>
> does not compile.
No, summarizeMany would have the type
(Summarizer m s) => [Double] -> Double
which is ambiguous. You would have to make m somehow accessible (dummy
argument?).
>
> 1) what am i doing wrong? what are the right type class and instance
> declarations?
>
> 2) is there a better way of expressing this kind of "on-line"
> calculation, perhaps in pure (non-monadic) functions?
Perhaps scanl ?
------------------------------
Message: 2
Date: Fri, 18 Sep 2009 08:49:59 -0700
From: Renick Bell <invite+ium~5...@facebookmail.com>
Subject: [Haskell-beginners] Check out my photos on Facebook
To: "Beginners@haskell.org" <beginners@haskell.org>
Message-ID: <2034a6f7f276b9d5acbb7f50b7f76...@localhost.localdomain>
Content-Type: text/plain; charset="utf-8"
Hi beginners@haskell.org,
I set up a Facebook profile where I can post my pictures, videos and events and
I want to add you as a friend so you can see it. First, you need to join
Facebook! Once you join, you can also create your own profile.
Thanks,
Renick
To sign up for Facebook, follow the link below:
http://www.facebook.com/p.php?i=100000244637353&k=Z6E3Y5U6QX413GGJPJ53RTSVZP&r
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Message: 3
Date: Fri, 18 Sep 2009 09:04:22 -0700
From: Ben <midfi...@gmail.com>
Subject: Re: [Haskell-beginners] type class question
To: Daniel Fischer <daniel.is.fisc...@web.de>
Cc: beginners@haskell.org
Message-ID:
<9157df230909180904g7109c82v28e8eab6ad1f6...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On Fri, Sep 18, 2009 at 8:28 AM, Daniel Fischer
<daniel.is.fisc...@web.de> wrote:
> No, summarizeMany would have the type
>
> (Summarizer m s) => [Double] -> Double
>
> which is ambiguous. You would have to make m somehow accessible (dummy
> argument?).
yes, i realize the type is ambiguous, ghc even says so in the error
message. but a dummy argument doesn't seem very elegant.
>> 2) is there a better way of expressing this kind of "on-line"
>> calculation, perhaps in pure (non-monadic) functions?
>
> Perhaps scanl ?
i originally was using mapAccumL (i need the final result of the
state) but it seemed like i was missing the point of the State monad.
i guess that is a matter of opinion?
b
------------------------------
Message: 4
Date: Sat, 19 Sep 2009 10:04:35 +0900
From: Yusaku Hashimoto <nonow...@gmail.com>
Subject: Re: [Haskell-beginners] Re: Maybe, Either
To: Heinrich Apfelmus <apfel...@quantentunnel.de>
Cc: beginners@haskell.org
Message-ID:
<d17c24b90909181804s70a18ca3lf4ac07b8f48ad...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Fri, Sep 18, 2009 at 6:05 PM, Heinrich Apfelmus
<apfel...@quantentunnel.de> wrote:
> Yusaku Hashimoto wrote:
>> - use Maybe as usual, we should use adapters as we need
>>
>> Conor, You have said this many times elsewhere, but unfortunately, I
>> heard it for the first time =) so please correct me if I'm wrong.
>>
>> I thought generalizing lookup is good example for usage of the
>> MonadPlus as I read in RWH[1], but you said it's not necessary.
>>
>> Now, I understood there are two positions for such classes. One is
>> using generalizing for it, another is not.
>>
>> So, I want to know that when such classes should be used from later position.
>>
>> Heinrich suggested that is for overloading.
>
> To elaborate on generality versus overloading: the function
>
> Â Â lookupM :: MonadPlus m => k -> Map k a -> m a
>
> is not more general than
>
> Â Â lookup :: k -> Map k a -> Maybe a
>
> because you can implement the former with the latter
>
> Â Â lookupM k = mop . lookup k
>
> Â Â mop = maybe mzero return
>
> In other words, Â lookupM Â doesn't introduce new functionality.
>
> Rather, it gives you the syntactic convenience of not having to mention
>  mop  by overloading the result type. In other words, you can write
>
>   lookup  = lookupM
>
> or
>
> Â Â lookupE :: k -> Map k a -> Either e a
> Â Â lookupE = lookupM
I got it. Thank you for explanation.
>> But do any other usages are exist?
>
> I'm not quite sure I understand what you mean here?
I had misread the Conor's post like the raison d'etre of type classes
was denied, so I asked how type class should be used. Thanks again.
Cheers
-nwn
------------------------------
Message: 5
Date: Mon, 21 Sep 2009 15:12:45 +0200
From: Luca Padovani <luca.padov...@uniurb.it>
Subject: [Haskell-beginners] interface files
To: beginners@haskell.org
Message-ID:
<cd5d3a640909210612p1796e934g6549d0e08e446...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
I'd like to be able to extract the "interface" of a Haskell module,
where the interface should basically contain the list of values
defined within the module along with their type, as well as the types
defined in the module.
It seems to me like the only way of doing this is with GHC and the
option --show-iface, which dumps the .hi file into some readable
format. However, the dumped interface seems to contain far more
information than the one I'm looking for (like annotations to the data
types explaining whether they are recursive, etc.), and am not sure
whether the grammar of this format is documented anywhere (other than
the actual source of GHC, I mean).
Is there any other convenient utility to automatically extract this
kind of "interfaces"? [*]
Thanks in advance.
Luca
------------------------------
Message: 6
Date: Mon, 21 Sep 2009 15:25:53 +0200
From: Daniel Fischer <daniel.is.fisc...@web.de>
Subject: Re: [Haskell-beginners] interface files
To: beginners@haskell.org
Cc: Luca Padovani <luca.padov...@uniurb.it>
Message-ID: <200909211525.54006.daniel.is.fisc...@web.de>
Content-Type: text/plain; charset="iso-8859-1"
Am Montag 21 September 2009 15:12:45 schrieb Luca Padovani:
> I'd like to be able to extract the "interface" of a Haskell module,
> where the interface should basically contain the list of values
> defined within the module along with their type, as well as the types
> defined in the module.
>
> It seems to me like the only way of doing this is with GHC and the
> option --show-iface, which dumps the .hi file into some readable
> format. However, the dumped interface seems to contain far more
> information than the one I'm looking for (like annotations to the data
> types explaining whether they are recursive, etc.), and am not sure
> whether the grammar of this format is documented anywhere (other than
> the actual source of GHC, I mean).
>
> Is there any other convenient utility to automatically extract this
> kind of "interfaces"? [*]
haddock ?
>
> Thanks in advance.
>
> Luca
------------------------------
Message: 7
Date: Mon, 21 Sep 2009 09:47:23 -0400
From: Tim Sears <t...@timsears.com>
Subject: Re: [Haskell-beginners] interface files
To: Luca Padovani <luca.padov...@uniurb.it>
Cc: beginners@haskell.org
Message-ID: <44c98e6c-a7b2-4c90-8f4a-9d951fc82...@timsears.com>
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
I have been trying out leksah over the past few days and it displays
the interface information for all the packages on my system.
I have found if *very* helpful for reading code. Thanks leksah devs!
The leksah IDE extracts this information from cabal files in order to
display it to the developer.
Depending on what you are doing, you could either use leksah, or
examine the code to see how it extracts the information.
-Tim
On Sep 21, 2009, at 9:12 AM, Luca Padovani wrote:
> I'd like to be able to extract the "interface" of a Haskell module,
> where the interface should basically contain the list of values
> defined within the module along with their type, as well as the types
> defined in the module.
>
> It seems to me like the only way of doing this is with GHC and the
> option --show-iface, which dumps the .hi file into some readable
> format. However, the dumped interface seems to contain far more
> information than the one I'm looking for (like annotations to the data
> types explaining whether they are recursive, etc.), and am not sure
> whether the grammar of this format is documented anywhere (other than
> the actual source of GHC, I mean).
>
> Is there any other convenient utility to automatically extract this
> kind of "interfaces"? [*]
>
> Thanks in advance.
>
> Luca
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
------------------------------
Message: 8
Date: Mon, 21 Sep 2009 09:21:10 -0500
From: aditya siram <aditya.si...@gmail.com>
Subject: [Haskell-beginners] Vaccum Cairo Errors
To: beginners <beginners@haskell.org>
Message-ID:
<594f78210909210721u4ae0148k41deff7855a6...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
Hi all,
I am trying out the awesome Vacuum Cairo package on GHC 6.10.3 but I am
getting some interesting errors. The following works in GHCI:
> view [1 .. 3]
But the following does not work in GHCI:
> let x = [1 .. 3]
> view x
or,
> x <- return [1 .. 3]
> view x
For the last two I get:
context: "(:)|0" -> >>> {"1|1", <<< "(:)|2"}
ghc: ../../src/xcb_lock.c:77: _XGetXCBBuffer: Assertion `((int) ((xcb_req) -
(dpy->request)) >= 0)' failed.
Aborted
and GHCI quits.
Any ideas?
thanks ...
deech
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