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Today's Topics:
1. index too large (Nathan M. Holden)
2. Re: index too large (Daniel Fischer)
3. Dynamic libraries not of required architecture when
installing via cabal (Snow Leopard) (Malthe J?rgensen)
4. Re: Dynamic libraries not of required architecture when
installing via cabal (Snow Leopard) (Brandon S. Allbery KF8NH)
5. Functor question. (Phillip Pirrip)
6. Re: Functor question. (Alexander Dunlap)
7. Re: Functor question. (Phillip Pirrip)
----------------------------------------------------------------------
Message: 1
Date: Thu, 12 Nov 2009 21:55:40 -0500
From: "Nathan M. Holden" <nathanmhol...@gmail.com>
Subject: [Haskell-beginners] index too large
To: beginners@haskell.org
Message-ID: <200911122155.40162.nathanmhol...@gmail.com>
Content-Type: Text/Plain; charset="us-ascii"
I've been working on a quick program that acts (vaguely) like a console, lets
me type notes and outputs them in a .tex file. I figure it's not that
complicated, but it uses a vaguely n-ary structure, so that I can have headers
and sub-notes, which loos like:
data Note = N {
nTitle :: {Char},
nBody :: {Char},
nFormat :: Format,
subs :: [Note]
| E [Char]
Format's just a collection of preset formats, so I don't have to dynamically
handle that (since I didn't need to for my uses).
Anyways, for whatever reason, sometimes while adding notes, it sends me an
error: Prelude.(!!): index too large
My only 2 uses of that are in
getFullName :: [Note] -> [Int] -> [Char]
getFullName d [] = "/"
getFullName d (x:xs) = "/" ++ getPartName (d!!x) ++ getFullName (subs (d!!x))
xs
and
moveIn :: [Note] -> [Int] -> [Char] -> Int -> [Int]
moveIn [] i m c = reverse i
moveIn ((N dt db df du):ds) [] m c = if matchNote (N dt db df du) m then c:[]
else moveIn ds [] m (c+1)
moveIn n i m c = last i : ((moveIn (subs (n!!(last i)))) (allButLast i) m 0)
where the [Int] is the variable I use to track where in the tree I am. Since
I'm not moving into a Note that doesn't exist, and the display shouldn't be
changing, what could be the problem?
This is probably too in-depth a question, now that I think about it...
------------------------------
Message: 2
Date: Fri, 13 Nov 2009 07:00:43 +0100
From: Daniel Fischer <daniel.is.fisc...@web.de>
Subject: Re: [Haskell-beginners] index too large
To: beginners@haskell.org
Message-ID: <200911130700.43557.daniel.is.fisc...@web.de>
Content-Type: text/plain; charset="iso-8859-1"
Am Freitag 13 November 2009 03:55:40 schrieb Nathan M. Holden:
> I've been working on a quick program that acts (vaguely) like a console,
> lets me type notes and outputs them in a .tex file. I figure it's not that
> complicated, but it uses a vaguely n-ary structure, so that I can have
> headers and sub-notes, which loos like:
>
> data Note = N {
> nTitle :: {Char},
> nBody :: {Char},
> nFormat :: Format,
> subs :: [Note]
>
> | E [Char]
>
> Format's just a collection of preset formats, so I don't have to
> dynamically handle that (since I didn't need to for my uses).
>
> Anyways, for whatever reason, sometimes while adding notes, it sends me an
> error: Prelude.(!!): index too large
Obviously, sometimes you call list!!index with index > (length list - 1).
Are you aware that the indices are 0-based?
If it's not that, one would have to analyse the code, but it would be better to
see more
of it for that.
------------------------------
Message: 3
Date: Sun, 15 Nov 2009 17:42:39 +0100
From: Malthe J?rgensen <malth...@hotmail.com>
Subject: [Haskell-beginners] Dynamic libraries not of required
architecture when installing via cabal (Snow Leopard)
To: beginners@haskell.org
Message-ID: <blu0-smtp480cb9db13aa710dd31191e3...@phx.gbl>
Content-Type: text/plain; charset="us-ascii"
I'm on Snow Leopard, so I've read numerous posts on the subject of GHC
and it's Snow Leopard (non-)compatibility. I've got most things
working - I can do a 'cabal update' - something that gave errors
before. GHC itself seems to be working fine.
I want to install the SDL package from Hackage, which I first tried
doing like this:
'cabal install sdl'
which gives a bunch of warnings, all looking like this
'ld: warning: in /opt/local/lib/libSDL.dylib, file is not of required
architecture'
with 'libSDL.dylib' replaced with various *.a and *.dylib files
I then found this in a Usenet post about Snow Leopard breaking GHC:
-- Once cabal works, options --ld-option=-m32 (and also --gcc-option=-
m32) may be used. These options may also be passed to "./Setup
configure"
And tried this: (I think maybe my problem is that I'm not passing
these flags correctly to cabal)
'cabal install sdl --ld-options="-arch i386" --gcc-option=-m32 --
reinstall'
Well I get the same errors, well warnings actually.
Can I just ignore these warnings?
When compiling my small sample code:
import Prelude
import Graphics.UI.SDL as SDL
main = do
SDL.init [InitEverything]
setVideoMode 640 480 32 []
I again get the warnings:
ld: warning: in /opt/local/lib/libSDL.dylib, file is not of required
architecture
ld: warning: in /opt/local/lib/libSDLmain.a, file is not of required
architecture
and then a bunch of undefined symbols such as:
_SDL_Init
_SDL_SetClipRect
Well this post basically based on the assumption that the warnings are
breaking the SDL library and thereby keeping my code from compiling -
so how do I fix those warnings?
- Sorry for the long mail
Malthe
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Message: 4
Date: Sun, 15 Nov 2009 20:27:48 -0500
From: "Brandon S. Allbery KF8NH" <allb...@ece.cmu.edu>
Subject: Re: [Haskell-beginners] Dynamic libraries not of required
architecture when installing via cabal (Snow Leopard)
To: Malthe J?rgensen <malth...@hotmail.com>
Cc: beginners@haskell.org
Message-ID: <fd2da774-4257-46c7-a923-fe9ea1e11...@ece.cmu.edu>
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Message: 5
Date: Sun, 15 Nov 2009 22:50:05 -0500
From: Phillip Pirrip <ppir...@gmail.com>
Subject: [Haskell-beginners] Functor question.
To: beginners@haskell.org
Message-ID: <b3d87c85-fac0-48c8-b36c-e36aa2580...@gmail.com>
Content-Type: text/plain; charset=us-ascii
Hi,
When I define my data as fellow,
data Moo a = Moo a
deriving (Show)
instance Functor Moo where
fmap f (Moo a) = Moo (f a)
GHC gives me no problem. Then I add something,
data (Num a) => Moo a = Moo a
deriving (Show)
instance Functor Moo where
fmap f (Moo a) = Moo (f a)
Now GHC gives me the follow error - see bellow.
What is the reason behind this? What should I do to correct this?
thx,
//
matFun_v2.hs:16:12:
Could not deduce (Num a) from the context ()
arising from a use of `Moo' at matFun_v2.hs:16:12-14
Possible fix:
add (Num a) to the context of the type signature for `fmap'
In the pattern: Moo a
In the definition of `fmap': fmap f (Moo a) = Moo (f a)
In the instance declaration for `Functor Moo'
matFun_v2.hs:16:21:
Could not deduce (Num b) from the context ()
arising from a use of `Moo' at matFun_v2.hs:16:21-29
Possible fix:
add (Num b) to the context of the type signature for `fmap'
In the expression: Moo (f a)
In the definition of `fmap': fmap f (Moo a) = Moo (f a)
In the instance declaration for `Functor Moo'
------------------------------
Message: 6
Date: Sun, 15 Nov 2009 20:07:36 -0800
From: Alexander Dunlap <alexander.dun...@gmail.com>
Subject: Re: [Haskell-beginners] Functor question.
To: Phillip Pirrip <ppir...@gmail.com>
Cc: beginners@haskell.org
Message-ID:
<57526e770911152007y54165145veae92d4afd552...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Sun, Nov 15, 2009 at 7:50 PM, Phillip Pirrip <ppir...@gmail.com> wrote:
>
> Hi,
>
> When I define my data as fellow,
>
> data Moo a = Moo a
> Â Â Â Â Â Â deriving (Show)
>
> instance Functor Moo where
> Â fmap f (Moo a) = Moo (f a)
>
> GHC gives me no problem. Â Then I add something,
>
> data (Num a) => Moo a = Moo a
> Â Â Â Â Â Â deriving (Show)
>
> instance Functor Moo where
> Â fmap f (Moo a) = Moo (f a)
>
> Now GHC gives me the follow error - see bellow.
>
> What is the reason behind this? Â What should I do to correct this?
>
> thx,
>
> //
>
> matFun_v2.hs:16:12:
> Â Could not deduce (Num a) from the context ()
> Â Â arising from a use of `Moo' at matFun_v2.hs:16:12-14
> Â Possible fix:
> Â Â add (Num a) to the context of the type signature for `fmap'
> Â In the pattern: Moo a
> Â In the definition of `fmap': fmap f (Moo a) = Moo (f a)
> Â In the instance declaration for `Functor Moo'
>
> matFun_v2.hs:16:21:
> Â Could not deduce (Num b) from the context ()
> Â Â arising from a use of `Moo' at matFun_v2.hs:16:21-29
> Â Possible fix:
> Â Â add (Num b) to the context of the type signature for `fmap'
> Â In the expression: Moo (f a)
> Â In the definition of `fmap': fmap f (Moo a) = Moo (f a)
> Â In the instance declaration for `Functor Moo'
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
Your datatype Moo cannot be an instance of Functor because Moo cannot
contain all types. fmap takes a function of type (a -> b), which means
that the function can be from *any* type a to *any* type b, and
produces a function of type (f a -> f b), which in your case means Moo
a -> Moo b. But the function fmap f (Moo x) = Moo (f x) does not have
type "a -> b"; it has type "(Num a, Num b) => a -> b", since if you
can have a type Moo a, a must be an instance of Num.
In general, people recommend against using constriants on datatypes,
recommending instead to put those constraints on the functions that
operate on the datatypes. I'm not quite sure why that is, though.
Alex
------------------------------
Message: 7
Date: Sun, 15 Nov 2009 23:34:39 -0500
From: Phillip Pirrip <ppir...@gmail.com>
Subject: Re: [Haskell-beginners] Functor question.
To: Alexander Dunlap <alexander.dun...@gmail.com>
Cc: beginners@haskell.org
Message-ID: <9b0f47a5-1d25-4144-800d-b91a94d6b...@gmail.com>
Content-Type: text/plain; charset=us-ascii
On 2009-11-15, at 11:07 PM, Alexander Dunlap wrote:
> On Sun, Nov 15, 2009 at 7:50 PM, Phillip Pirrip <ppir...@gmail.com> wrote:
>>
>> Hi,
>>
>> When I define my data as fellow,
>>
>> data Moo a = Moo a
>> deriving (Show)
>>
>> instance Functor Moo where
>> fmap f (Moo a) = Moo (f a)
>>
>> GHC gives me no problem. Then I add something,
>>
>> data (Num a) => Moo a = Moo a
>> deriving (Show)
>>
>> instance Functor Moo where
>> fmap f (Moo a) = Moo (f a)
>>
>> Now GHC gives me the follow error - see bellow.
>>
>> What is the reason behind this? What should I do to correct this?
>>
>> thx,
>>
>> //
>>
>> matFun_v2.hs:16:12:
>> Could not deduce (Num a) from the context ()
>> arising from a use of `Moo' at matFun_v2.hs:16:12-14
>> Possible fix:
>> add (Num a) to the context of the type signature for `fmap'
>> In the pattern: Moo a
>> In the definition of `fmap': fmap f (Moo a) = Moo (f a)
>> In the instance declaration for `Functor Moo'
>>
>> matFun_v2.hs:16:21:
>> Could not deduce (Num b) from the context ()
>> arising from a use of `Moo' at matFun_v2.hs:16:21-29
>> Possible fix:
>> add (Num b) to the context of the type signature for `fmap'
>> In the expression: Moo (f a)
>> In the definition of `fmap': fmap f (Moo a) = Moo (f a)
>> In the instance declaration for `Functor Moo'
>> _______________________________________________
>> Beginners mailing list
>> Beginners@haskell.org
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>
> Your datatype Moo cannot be an instance of Functor because Moo cannot
> contain all types. fmap takes a function of type (a -> b), which means
> that the function can be from *any* type a to *any* type b, and
> produces a function of type (f a -> f b), which in your case means Moo
> a -> Moo b. But the function fmap f (Moo x) = Moo (f x) does not have
> type "a -> b"; it has type "(Num a, Num b) => a -> b", since if you
> can have a type Moo a, a must be an instance of Num.
>
> In general, people recommend against using constriants on datatypes,
> recommending instead to put those constraints on the functions that
> operate on the datatypes. I'm not quite sure why that is, though.
>
> Alex
Thanks Alex. That is very clear. I didn't expect that (Num a, Num b)=>a->b is
actually different than a->b from the compiler point of view. I was under the
assumption that the more constraint I put there the better for the compiler.
//pip
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