Ivan Miljenovic wrote:
> On 20 May 2010 14:42, Tony Morris wrote:
>
>> We all know that "class (Functor f) => Monad f" is preferable but its
>> absence is a historical mistake. We've all probably tried once:
>>
>> instance (Functor f) => Monad f where
>>
>
> Do you mean the reverse of this
On 20 May 2010 14:42, Tony Morris wrote:
> We all know that "class (Functor f) => Monad f" is preferable but its
> absence is a historical mistake. We've all probably tried once:
>
> instance (Functor f) => Monad f where
Do you mean the reverse of this (instance (Monad m) => Functor m where) ?
>
We all know that "class (Functor f) => Monad f" is preferable but its
absence is a historical mistake. We've all probably tried once:
instance (Functor f) => Monad f where
...
However, is there a type system extension (even proposed but not
implemented) that allows me to retrospectively apply
You've been asking a lot of very tutorial-ish questions on this list.
Although this isn't necessarily a *bad* thing, you may receive
responses more appropriate to your skill level on the
haskell-beginners list <
http://www.haskell.org/mailman/listinfo/beginners >.
I don't own the Bird book, but wh
On May 20, 2010, at 3:18 AM, Brent Yorgey wrote:
On Wed, May 19, 2010 at 04:27:14AM +, R J wrote:
What are some simple functions that would naturally have the
following type signatures:
f :: (Integer -> Integer) -> Integer
Well, this means f is given a function from Integer to Intege
> (i) strange f g = g (f g)
>
> Assume g :: a -> b. Then f :: (a -> b) -> c. But since g :: a -> b,
> f g :: a, so c = a. Therefore, f :: (a -> b) -> a, and g (f g) :: a.
> Therefore, strange :: ((a -> b) -> a) -> (a -> b) -> a.
Almost. The return type of strange is the same as the return typ
On May 20, 2010, at 11:03 AM, R J wrote:
stranger f = f f
This doesn't have a type in Haskell.
Suppose f :: a -> b
Then if f f made sense, a = (a -> b) would be true,
and we'd have an infinite type.
Type the definition into a file, and try loading it
into ghci:
Occurs check: cannot con
Bird 1.6.3 requires deducing type signatures for the functions "strange" and
"stranger."
Are my solutions below correct?
(i) strange f g = g (f g)
Assume g :: a -> b. Then f :: (a -> b) -> c. But since g :: a -> b,f g :: a,
so c = a. Therefore, f :: (a -> b) -> a, and g (f g) :: a.Therefore,
Bird problem 1.6.2 is:
If f :: (a, b) -> c, then define a function "swap" such that:
flip (curry f) = curry (f . swap).
I'd very much appreciate if someone could tell me whether there's a rigorous
solution simpler than mine, which is:
Since (.) :: (q -> r) -> (p -> q) -> (p -> r), we have f :: q
aditya siram writes:
> Haskell has bindings to USB [1]. I don't know of any USB tutorials or
> any webcam specific libraries.
I don't know of any, but if using Linux then maybe writing a binding to
v4l (video for linux) might be the best/easiest approach.
--
Ivan Lazar Miljenovic
ivan.miljeno.
Haskell has bindings to USB [1]. I don't know of any USB tutorials or
any webcam specific libraries.
-deech
[1] http://hackage.haskell.org/package/usb
On 5/19/10, Eitan Goldshtrom wrote:
> Hi everyone,
>
> I would like to start working on a program that requires access to a
> camera attached to
Hi everyone,
I would like to start working on a program that requires access to a
camera attached to the computer probably via USB or otherwise
internally. Unfortunately I don't know anything about using devices in
haskell. I tried looking up how to access the microphone one too and had
littl
schlepptop:
> Don Stewart schrieb:
> > Or use things from the download-curl package, which provides a nice
> > openURL function.
>
> The openURL function from TagSoup is lazy, which the proposed
> replacement 'getResponseBody =<< simpleHTTP (getRequest x)' is not. Is
> the openURL function from do
Don Stewart schrieb:
> Or use things from the download-curl package, which provides a nice
> openURL function.
The openURL function from TagSoup is lazy, which the proposed
replacement 'getResponseBody =<< simpleHTTP (getRequest x)' is not. Is
the openURL function from download-curl lazy?
___
On Thu, May 13, 2010 at 7:16 PM, HASHIMOTO, Yusaku wrote:
> Sorry for spamming, what I wanted to write is I think `has' has better
> interface than other record packages in types.
>
> There are many libraries to write function "takes an record has Foo
> and Bar and returns something." But writing
Hi all,
I just read "Functional References are a cheap and cheerful technique
for working with the existing (non-extensible) record system, and may be
of interest to extensible record implementers. A good implementation can
be found on ..." on
http://hackage.haskell.org/trac/ghc/wik
David Leimbach wrote:
> I find it's often the most practical chapter that I hit a lot during
> writes and changes to my server process I have in Haskell in our control
> system code :-)
Are you actually saying that you use Haskell for a control system server?
Thta would be very interesting to me.
>>> I tried it and it didn't work. I don't know reason, though, maybe it
>>> was because my current password not entirely alphanumeric.
>> Shouldn't matter as long as you put it within quotes.
> I imagine things will go wrong if it includes an @... urlencoding is
> probably a smart idea.
Thank you
Hi Ralph,
> I was using TagSoup 0.8 with great success. On upgrading to 0.9 I have this
> error:
>
> TQ\TagSoup\TagSoupExtensions.lhs:29:17:
>`Tag' is not applied to enough type arguments
>Expected kind `*', but `Tag' has kind `* -> *'
>In the type synonym declaration for `Bundle'
> F
> I'm trying to build some haskell code as a .so/.dll so that it can
> ultimately be used by msvc. I have it working when I compile by hand
> (listed below) but I can't get the exact same thing built/linked with
> cabal. On linux everything builds fine, but when I try to link the
> resulting .so
Or use things from the download-curl package, which provides a nice
openURL function.
daniel.is.fischer:
> On Wednesday 19 May 2010 19:46:57, Ralph Hodgson wrote:
> > Forgot to add: I now need to understand the following warnings on this
> > line "> import Text.HTML.Download":
> >
> >
>
> In Text
On Wednesday 19 May 2010 19:46:57, Ralph Hodgson wrote:
> Forgot to add: I now need to understand the following warnings on this
> line "> import Text.HTML.Download":
>
>
In Text.HTML.Download, there's the following:
{-|
/DEPRECATED/: Use the HTTP package instead:
> import Network.HTTP
On May 19, 2010, at 04:49 , Ivan Lazar Miljenovic wrote:
Serguey Zefirov writes:
export http_proxy="http://${username}:${passwo...@${proxy_url}";
I tried it and it didn't work. I don't know reason, though, maybe it
was because my current password not entirely alphanumeric.
Shouldn't matter
Forgot to add: I now need to understand the following warnings on this line ">
import Text.HTML.Download":
TagSoupExtensions.lhs:24:2:
Warning: In the use of `openItem'
(imported from Text.HTML.Download):
Deprecated: "Use package HTTP, module Network.HTTP, getR
Thanks Malcolm,
Providing a 'String' type argument worked:
> type Bundle = [Tag String]
> extractTags :: Tag String -> Tag String -> Bundle -> Bundle
> extractTags fromTag toTag tags = takeWhile (~/= toTag ) $ dropWhile (~/=
> fromTag ) tags
From: Malcolm Wallace [mailto:mal
On Tue, 2010-05-18 at 17:31 -0400, Anthony LODI wrote:
> Hello,
>
> I'm trying to build some haskell code as a .so/.dll so that it can
> ultimately be used by msvc. I have it working when I compile by hand
> (listed below) but I can't get the exact same thing built/linked with
> cabal. On linux
On Wed, May 19, 2010 at 01:37:49PM +, R J wrote:
>
> This is another proof-layout question, this time from Bird 1.4.7.
> We're asked to define the functions curry2 and uncurry2 for currying and
> uncurrying functions with two arguments. Simple enough:
> curry2 :: ((a, b) -> c) ->
On Wed, May 19, 2010 at 01:12:16PM +, R J wrote:
>
> Is this how a rigorous Haskeller would lay out the proofs of the following
> theorems? This is Bird 1.4.6.
> (i)
> Theorem: (*) x = (* x)
> Proof:
> (*) x ={definition of partial application} \y
On Wed, May 19, 2010 at 04:27:14AM +, R J wrote:
>
> What are some simple functions that would naturally have the following type
> signatures:
> f :: (Integer -> Integer) -> Integer
Well, this means f is given a function from Integer to Integer, and it
has to somehow return an Integer, (poss
On 19/05/2010, at 23:44, Ben Millwood wrote:
> On Wed, May 19, 2010 at 10:57 AM, Serguey Zefirov wrote:
>>
>> PS
>> Rationals:
>> Prelude> [1,1+2/3..10] :: [Rational]
>> [1 % 1,5 % 3,7 % 3,3 % 1,11 % 3,13 % 3,5 % 1,17 % 3,19 % 3,7 % 1,23 %
>> 3,25 % 3,9 % 1,29 % 3,31 % 3]
>>
>> Same result.
>
* Ben Millwood wrote:
>> Prelude> [1,1+2/3..10] :: [Rational]
>> [1 % 1,5 % 3,7 % 3,3 % 1,11 % 3,13 % 3,5 % 1,17 % 3,19 % 3,7 % 1,23 %
>> 3,25 % 3,9 % 1,29 % 3,31 % 3]
>>
>> Same result.
>
> This sounds like a bug to me. The section of the Haskell Report that
> deals with the Enum class mentions Fl
On Wed, May 19, 2010 at 10:57 AM, Serguey Zefirov wrote:
>
> PS
> Rationals:
> Prelude> [1,1+2/3..10] :: [Rational]
> [1 % 1,5 % 3,7 % 3,3 % 1,11 % 3,13 % 3,5 % 1,17 % 3,19 % 3,7 % 1,23 %
> 3,25 % 3,9 % 1,29 % 3,31 % 3]
>
> Same result.
This sounds like a bug to me. The section of the Haskell Rep
This is another proof-layout question, this time from Bird 1.4.7.
We're asked to define the functions curry2 and uncurry2 for currying and
uncurrying functions with two arguments. Simple enough:
curry2 :: ((a, b) -> c) -> (a -> (b -> c))curry2 f x y = f
(x, y)
uncurry2
Is this how a rigorous Haskeller would lay out the proofs of the following
theorems? This is Bird 1.4.6.
(i)
Theorem: (*) x = (* x)
Proof:
(*) x ={definition of partial application} \y -> x * y =
{commutativity of "*"} \y -> y * x ={defi
SAGE is the kind of thing that I dreamed to have available online a few
years ago.
To recode everithing in haskell perhaps does not worth the pain, but
perhapts it would be nice to do something similar to SAGE in an advanced
environment such is Google Wave, with all the collaborative facilities fo
On 19/05/2010, at 20:36, Ivan Lazar Miljenovic wrote:
> Roman Leshchinskiy writes:
>> Personally, I consider the Enum class itself to be broken.
>
> Oh? In what sense?
Firstly, the enumFrom* family of functions shouldn't be methods and the class
itself should provide enough facilities for imp
Roman Leshchinskiy writes:
> Personally, I consider the Enum class itself to be broken.
Oh? In what sense?
It seems to work fine for data types representing bounded enumerable
values with a proper mapping to/from Int (it's not bijective since
there's no proper mapping from Int -> Bool for examp
On 19/05/2010, at 19:24, Dmitry Olshansky wrote:
> Prelude> [1,1+2/3..10]
> [1.0,1.6665,2.333,2.9996,3.666,4.332,4.998,5.664,6.33,6.9964,7.6625,8.329,8.99
Thanks, it's clear now.
2010/5/19 Serguey Zefirov :
> 2010/5/19 Erik de Castro Lopo :
>> Dmitry Olshansky wrote:
>>
>>> It seems that I saw something like this in Cafe recevtly. But I am not
>>> sure...
>>> In GHC 6.12.1 (Platform 2010 on Windows Vista) I have
>>
>>
>>
>>
>>> Any comments?
>>
>>
But
Prelude Data.List> [1,1+2/3..4] :: [Double]
[1.0,1.6665,2.333,2.9996,3.666,4.332]
Prelude Data.List> unfoldr (\n -> let n'=n+2/3 in if n' <= 4 then Just
(n',n') else Nothing) 1 :: [Double]
[1.6665,2.333,2.
I started playing with type families. I wanted to achieve, for the
beginning, something like:
> import qualified Control.Monad.IO.Class as IOC
> import Control.Monad.Trans.Class
> import Control.Monad.Trans.Cont
> import Data.Functor.Identity
> class (Monad m, Monad (IO' m)) => MonadIO m where
>
Ivan Lazar Miljenovic writes:
> Dmitry Olshansky writes:
>
>> Hello all,
>>
>> It seems that I saw something like this in Cafe recevtly. But I am not
>> sure...
>> In GHC 6.12.1 (Platform 2010 on Windows Vista) I have
>>
>> Prelude> [1,1+2/3..10]
>> [1.0,1.6665,2.333,2.9
2010/5/19 Erik de Castro Lopo :
> Dmitry Olshansky wrote:
>
>> It seems that I saw something like this in Cafe recevtly. But I am not
>> sure...
>> In GHC 6.12.1 (Platform 2010 on Windows Vista) I have
>
>
>
>
>> Any comments?
>
> The problem you point out is not a problem with Haskell, but a pro
Dmitry Olshansky writes:
> Hello all,
>
> It seems that I saw something like this in Cafe recevtly. But I am not sure...
> In GHC 6.12.1 (Platform 2010 on Windows Vista) I have
>
> Prelude> [1,1+2/3..10]
> [1.0,1.6665,2.333,2.9996,3.666,4.33
Dmitry Olshansky wrote:
> It seems that I saw something like this in Cafe recevtly. But I am not sure...
> In GHC 6.12.1 (Platform 2010 on Windows Vista) I have
> Any comments?
The problem you point out is not a problem with Haskell, but a problem
with the whole concept of floating point arit
Hello all,
It seems that I saw something like this in Cafe recevtly. But I am not sure...
In GHC 6.12.1 (Platform 2010 on Windows Vista) I have
Prelude> [1,1+2/3..10]
[1.0,1.6665,2.333,2.9996,3.666,4.332,4.998,5.6
Neil says that the API of TagSoup changed in 0.9.
All usages of the type Tag should now take a type argument, e.g. Tag String.
Regards,
Malcolm
On Wednesday, May 19, 2010, at 08:05AM, "Ralph Hodgson"
wrote:
>___
>Haskell-Cafe mailing list
>Hask
Serguey Zefirov writes:
>> export http_proxy="http://${username}:${passwo...@${proxy_url}";
>
> I tried it and it didn't work. I don't know reason, though, maybe it
> was because my current password not entirely alphanumeric.
Shouldn't matter as long as you put it within quotes.
--
Ivan Lazar M
Ivan Lazar Miljenovic wrote:
> Heinrich Apfelmus writes:
>> Yes; what I mean is that you can retrofit a custom vertex type to any
>> graph implementation that uses a fixed vertex type. So, let's say that
>>
>>data Gr a b = .. -- graph with vertex type Vertex Gr = Int
>>
>> then
>>
>>type G
Hello Neil ,
I was using TagSoup 0.8 with great success. On upgrading to 0.9 I have this
error:
TQ\TagSoup\TagSoupExtensions.lhs:29:17:
`Tag' is not applied to enough type arguments
Expected kind `*', but `Tag' has kind `* -> *'
In the type synonym declaration for `Bundle'
F
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