[Haskell-cafe] runST readSTRef type error
I run into the following type error:
foo :: ST s (STRef s Int) - Int
foo p = (runST (p = readSTRef))
with ghc 6.12.1
st.hs:8:16:
Couldn't match expected type `s1' against inferred type `s'
`s1' is a rigid type variable bound by
the polymorphic type `forall s1. ST s1 a' at st.hs:8:9
`s' is a rigid type variable bound by
the type signature for `foo' at st.hs:7:10
Expected type: ST s1 (STRef s Int)
Inferred type: ST s (STRef s Int)
In the first argument of `(=)', namely `p'
In the first argument of `runST', namely `(p = readSTRef)'
However, if I add
{-# LANGUAGE RankNTypes #-}
and change the type signature to
foo :: (forall s.ST s (STRef s Int)) - Int
it works. I don't fully understand what's going on here.
Is this the right way to fix the problem? Are there other options?
My gut feeling is, for such a simple use case of the ST monad, I
shouldn't need such a big hammer as RankNTypes.
--ken
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Re: [Haskell-cafe] Crypto-api performance
On Tue, May 3, 2011 at 23:14, Daniel Fischer daniel.is.fisc...@googlemail.com wrote: did you notice that the comment says 128KB strings for ps and lps, but they are in fact 1MB strings: -- 128KB strings ps = B.replicate (2^20) 0 lps = L.replicate (2^20) 0 ? If not, the throughput would look much better, wouldn't it? Ah, I failed to mention this in my previous mail. I changed the test values from 128KB to 1MB to see if it would help the throughput (by lowering overhead in the framework). So I've already compensated for this in the MB/s calculations. Nice catch, though :-) -- Johan Brinch ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Crypto-api performance
Also, it appears that crypto-api needs vast amounts of memory when compiled with optimization enabled. The latest version 0.6.1 is effectively unbuildable on my EeePC, which has only 1GB RAM. That property is fairly undesirable for a library package. Take care, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] runST readSTRef type error
Hello Ken,
Strictly speaking, you only need Rank-2 types. This indeed the right
way to fix the problem.
Cheers,
Edward
Excerpts from Ken Takusagawa II's message of Wed May 04 02:00:49 -0400 2011:
I run into the following type error:
foo :: ST s (STRef s Int) - Int
foo p = (runST (p = readSTRef))
with ghc 6.12.1
st.hs:8:16:
Couldn't match expected type `s1' against inferred type `s'
`s1' is a rigid type variable bound by
the polymorphic type `forall s1. ST s1 a' at st.hs:8:9
`s' is a rigid type variable bound by
the type signature for `foo' at st.hs:7:10
Expected type: ST s1 (STRef s Int)
Inferred type: ST s (STRef s Int)
In the first argument of `(=)', namely `p'
In the first argument of `runST', namely `(p = readSTRef)'
However, if I add
{-# LANGUAGE RankNTypes #-}
and change the type signature to
foo :: (forall s.ST s (STRef s Int)) - Int
it works. I don't fully understand what's going on here.
Is this the right way to fix the problem? Are there other options?
My gut feeling is, for such a simple use case of the ST monad, I
shouldn't need such a big hammer as RankNTypes.
--ken
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Re: [Haskell-cafe] runST readSTRef type error
On Wed, 2011-05-04 at 02:00 -0400, Ken Takusagawa II wrote:
I run into the following type error:
foo :: ST s (STRef s Int) - Int
foo p = (runST (p = readSTRef))
with ghc 6.12.1
st.hs:8:16:
Couldn't match expected type `s1' against inferred type `s'
`s1' is a rigid type variable bound by
the polymorphic type `forall s1. ST s1 a' at st.hs:8:9
`s' is a rigid type variable bound by
the type signature for `foo' at st.hs:7:10
Expected type: ST s1 (STRef s Int)
Inferred type: ST s (STRef s Int)
In the first argument of `(=)', namely `p'
In the first argument of `runST', namely `(p = readSTRef)'
However, if I add
{-# LANGUAGE RankNTypes #-}
and change the type signature to
foo :: (forall s.ST s (STRef s Int)) - Int
it works. I don't fully understand what's going on here.
Is this the right way to fix the problem? Are there other options?
My gut feeling is, for such a simple use case of the ST monad, I
shouldn't need such a big hammer as RankNTypes.
--ken
To make the interface of ST works - i.e. to keeps it pure the signature
of runST is:
runST :: (forall s. ST s a) - a
Otherwise consider following code:
incST :: Num a = STRef s a - ST s a
incST r = readSTRef r = \v - writeSTRef r (v + 1) return v
add :: STRef s Int - Int - Int
add r x = runST (incST r = \v - return (v + x))
test :: [Int]
test = runST (newSTRef 0) = \r - map (add r) [1,2,3]
What is the result?
And what is the result of:
test2 :: [Int]
test2 = runST (newSTRef 0) = \r - map (add r) (map (add r) [1,2,3])
Regards
signature.asc
Description: This is a digitally signed message part
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Re: [Haskell-cafe] Please add a method for optimized concat to the Semigroup class
From: Edward Kmett ekm...@gmail.com On Tue, May 3, 2011 at 3:43 PM, Yitzchak Gale g...@sefer.org wrote: I'm sure there are countless other natural examples of semigroups in the wild, and that the typical non-trivial ones will benefit from an optimized sconcat. Sold! (modulo the semantic considerations above) Somewhat academic, but would there be a case for implementing sconcat in terms of Foldable (or similar)? John L ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Please add a method for optimized concat to the Semigroup class
On Wed, May 4, 2011 at 7:40 AM, John Lato jwl...@gmail.com wrote: From: Edward Kmett ekm...@gmail.com On Tue, May 3, 2011 at 3:43 PM, Yitzchak Gale g...@sefer.org wrote: I'm sure there are countless other natural examples of semigroups in the wild, and that the typical non-trivial ones will benefit from an optimized sconcat. Sold! (modulo the semantic considerations above) Somewhat academic, but would there be a case for implementing sconcat in terms of Foldable (or similar)? There is a Foldable1 in semigroupoids. I could move it into the semigroups package, but at the consequence that Data.Semigroup.Foldable wouldn't look like Data.Foldable API-wise, since the Semigroupoid package is what introduces Apply and Bind, giving you an Applicative sans pure and a Monad sans return, which are needed to make most of the analogues to the Foldable functions. So to do so, I'd need to move those into this package. This is not entirely implausible, if somewhat inconvenient from the perspective of keeping the semigroups package tiny. The default definition would wind up being something like: class Semigroup a where () :: a - a - a sconcat :: Foldable1 f = f a - a sconcat = fold1 class Foldable f = Foldable1 f where fold1 :: Semigroup a = f a - a fold1 = foldMap1 id foldMap1 :: Semigroup a = (b - a) - f b - a foldMap1 = ... foldr1 :: ... foldl1 :: ... choosing sconcat = fold1 by default seems pretty much optimal under those conditions, saying that if your Semigroup doesn't have an optimized fold, you might as well let the container figure out what to do instead. If we do that though, I'm hard pressed to find anything better to specialize to for most semigroups, which is what I was saying earlier to Yitzchak, and why I had omitted sconcat from the original API. I suppose you might exploit foldl, foldr, foldl' or foldr' instead to play a bit with how your traversal associates by default, or to use a different, more efficient intermediate state though. However, I am somewhat worried that with the type of the container abstracted that it probably won't receive the same love from the strictness analyzer though. One other annoying implementation consequence is that it would make the Data.Semigroup and Data.Semigroup.Foldable modules rather hopelessly entangled, so that I'd have to factor out the classes into a common Internals module, then re-export the appropriate fragments through separate modules. =/ -Edward ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fwd: Re: Binary and Serialize classes
On Tue, May 3, 2011 at 7:13 AM, Alberto G. Corona agocor...@gmail.com wrote: E1610With the exception of heavy serialization usage, for example, in very optimized RPC applications (and even there SOAP shows that this is not ever the case), text serialization is better. The unwritten rules of good design says that data representation and compression must be orthogonal. The binary formats were designed for performing both functionalities in the times when memory were measured in Kbytes. Actually, I'm using binary because it seems simpler. If it were text, I'd have to come up with some text format. I'd either have to invent some ad-hoc new language or figure out how to fit it into some generic format like JSON. There would be parsing, an intermediate format, conversion, typechecking, blah blah. All this complexity for what exactly? So people could edit the serialized output with a text editor? Why don't they edit it with my program, which is designed for that? At least just import the deserialize module and edit the typed data structure in the REPL. And say people do start editing it with text editors... now the format is inching toward public, and I can't change it without breaking someone's text editor habits. In fact, if I serialize the same data with Data.Serialize and with 'show', the binary version is slightly larger! I imagine it's because zeros in text format can fit in a few bytes, while in binary they always take the full 32 or 64 bits (or 128 for the default Double serialization!). So for me at least, it has nothing to do with compression. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] warning - Euler problem spoiler enclosed
Hi,
In the following solution to problem 24, why is nub ignored?
I.e. if you do lexOrder of 0012, you get twice as many permutations as with
012, even though I have used nub.
puzzled,
Bar
-- file Euler.hs
module Euler where
import Data.List
{-
problem 24
A permutation is an ordered arrangement of objects. For example, 3124
is one possible permutation of the digits 1, 2, 3 and 4. If all of the
permutations are listed numerically or alphabetically, we call it
lexicographic order. The lexicographic permutations of 0, 1 and 2 are:
012 021 102 120 201 210
What is the millionth lexicographic permutation of the digits 0, 1, 2,
3, 4, 5, 6, 7, 8 and 9?
-}
lexI :: Char - String - Int
lexI c s = maybe 1 (id) $ elemIndex c s
lexOrder :: [Char] - [[Char]]
lexOrder s
| length s == 1= [s]
| length s == 2= z : [reverse z]
| otherwise= concat $ map (\n - h n) [0..((length s) - 1)]
where z = sort $ nub s -- why is the nub ignored here?
h :: Int - [String]
h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c
z /= n) z
p24 = (lexOrder 1234567890)!!99
main :: IO()
main =
do
putStrLn $ show $ p24
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Re: [Haskell-cafe] warning - Euler problem spoiler enclosed
On Wed, 2011-05-04 at 07:13 -0600, Barbara Shirtcliff wrote: In the following solution to problem 24, why is nub ignored? I.e. if you do lexOrder of 0012, you get twice as many permutations as with 012, even though I have used nub. lexOrder :: [Char] - [[Char]] lexOrder s | length s == 1= [s] | length s == 2= z : [reverse z] | otherwise= concat $ map (\n - h n) [0..((length s) - 1)] where z = sort $ nub s -- why is the nub ignored here? h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z You are using (length s) in the otherwise case. If you want the results to be identical with duplicates, perhaps you meant to say (length z)? -- Chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Please add a method for optimized concat to the Semigroup class
On Wed, May 4, 2011 at 1:25 PM, Edward Kmett ekm...@gmail.com wrote: On Wed, May 4, 2011 at 7:40 AM, John Lato jwl...@gmail.com wrote: From: Edward Kmett ekm...@gmail.com On Tue, May 3, 2011 at 3:43 PM, Yitzchak Gale g...@sefer.org wrote: I'm sure there are countless other natural examples of semigroups in the wild, and that the typical non-trivial ones will benefit from an optimized sconcat. Sold! (modulo the semantic considerations above) Somewhat academic, but would there be a case for implementing sconcat in terms of Foldable (or similar)? There is a Foldable1 in semigroupoids. I could move it into the semigroups package, but at the consequence that Data.Semigroup.Foldable wouldn't look like Data.Foldable API-wise, since the Semigroupoid package is what introduces Apply and Bind, giving you an Applicative sans pure and a Monad sans return, which are needed to make most of the analogues to the Foldable functions. So to do so, I'd need to move those into this package. This is not entirely implausible, if somewhat inconvenient from the perspective of keeping the semigroups package tiny. The default definition would wind up being something like: class Semigroup a where () :: a - a - a sconcat :: Foldable1 f = f a - a sconcat = fold1 class Foldable f = Foldable1 f where fold1 :: Semigroup a = f a - a fold1 = foldMap1 id foldMap1 :: Semigroup a = (b - a) - f b - a foldMap1 = ... foldr1 :: ... foldl1 :: ... choosing sconcat = fold1 by default seems pretty much optimal under those conditions, saying that if your Semigroup doesn't have an optimized fold, you might as well let the container figure out what to do instead. If we do that though, I'm hard pressed to find anything better to specialize to for most semigroups, which is what I was saying earlier to Yitzchak, and why I had omitted sconcat from the original API. I suppose you might exploit foldl, foldr, foldl' or foldr' instead to play a bit with how your traversal associates by default, or to use a different, more efficient intermediate state though. However, I am somewhat worried that with the type of the container abstracted that it probably won't receive the same love from the strictness analyzer though. One other annoying implementation consequence is that it would make the Data.Semigroup and Data.Semigroup.Foldable modules rather hopelessly entangled, so that I'd have to factor out the classes into a common Internals module, then re-export the appropriate fragments through separate modules. =/ Good points. I was hoping for a reply like this, since I don't have a good intuition for how Foldable would fit into the semigroups package. I don't have a strong opinion in either direction. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] warning - Euler problem spoiler enclosed
On 4 May 2011 13:13, Barbara Shirtcliff ba...@gmx.com wrote: Hi, In the following solution to problem 24, why is nub ignored? I.e. if you do lexOrder of 0012, you get twice as many permutations as with 012, even though I have used nub. [snip] lexOrder :: [Char] - [[Char]] lexOrder s | length s == 1 = [s] | length s == 2 = z : [reverse z] | otherwise = concat $ map (\n - h n) [0..((length s) - 1)] where z = sort $ nub s -- why is the nub ignored here? h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z As a guess, I think it's from the usage of length on the right-hand size. Also, note that lexOrder s@[_] = [s] is nicer than lexOrder s | length s == 1 = [s]. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] warning - Euler problem spoiler enclosed
Ah, thanks! On May 4, 2011, at 7:21 AM, Ivan Lazar Miljenovic wrote: On 4 May 2011 13:13, Barbara Shirtcliff ba...@gmx.com wrote: Hi, In the following solution to problem 24, why is nub ignored? I.e. if you do lexOrder of 0012, you get twice as many permutations as with 012, even though I have used nub. [snip] lexOrder :: [Char] - [[Char]] lexOrder s | length s == 1= [s] | length s == 2= z : [reverse z] | otherwise= concat $ map (\n - h n) [0..((length s) - 1)] where z = sort $ nub s -- why is the nub ignored here? h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z As a guess, I think it's from the usage of length on the right-hand size. Also, note that lexOrder s@[_] = [s] is nicer than lexOrder s | length s == 1 = [s]. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] warning - Euler problem spoiler enclosed
On Wednesday 04 May 2011 15:13:07, Barbara Shirtcliff wrote: Hi, In the following solution to problem 24, why is nub ignored? It isn't: *LexOrder lexOrder 00 [0,0] *LexOrder lexOrder 001 [01,10,*** Exception: Prelude.(!!): index too large lexI :: Char - String - Int lexI c s = maybe 1 (id) $ elemIndex c s lexOrder :: [Char] - [[Char]] lexOrder s | length s == 1= [s] | length s == 2= z : [reverse z] | otherwise= concat $ map (\n - h n) [0..((length s) - 1)] where z = sort $ nub s -- why is the nub ignored here? h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z Your problem is (well, the one I see immediately) that you check for the length of s, where you should check for the length of z. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] warning - Euler problem spoiler enclosed
On May 4, 2011, at 7:21 AM, Ivan Lazar Miljenovic wrote: On 4 May 2011 13:13, Barbara Shirtcliff ba...@gmx.com wrote: Hi, In the following solution to problem 24, why is nub ignored? I.e. if you do lexOrder of 0012, you get twice as many permutations as with 012, even though I have used nub. [snip] lexOrder :: [Char] - [[Char]] lexOrder s | length s == 1= [s] | length s == 2= z : [reverse z] | otherwise= concat $ map (\n - h n) [0..((length s) - 1)] where z = sort $ nub s -- why is the nub ignored here? h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z As a guess, I think it's from the usage of length on the right-hand size. Also, note that lexOrder s@[_] = [s] is nicer than lexOrder s | length s == 1 = [s]. I agree that that initial version was a little clumsy, but your suggestion doesn't really seem to work: lexOrder :: [Char] - [[Char]] lexOrder s@[_] = s lexOrder s = concat $ map (\n - h n) [0..((length z) - 1)] where z = sort $ nub s h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z Euler.hs:8:18: Couldn't match expected type `[Char]' with actual type `Char' Expected type: [[Char]] Actual type: [Char] In the expression: s In an equation for `lexOrder': lexOrder s@[_] = s ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] warning - Euler problem spoiler enclosed
Barbara Shirtcliff ba...@gmx.com писал(а) в своём письме Wed, 04 May 2011 16:41:07 +0300: Also, note that lexOrder s@[_] = [s] is nicer than lexOrder s | length s == 1 = [s]. I agree that that initial version was a little clumsy, but your suggestion doesn't really seem to work: lexOrder :: [Char] - [[Char]] lexOrder s@[_] = s lexOrder s = concat $ map (\n - h n) [0..((length z) - 1)] where z = sort $ nub s h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z Euler.hs:8:18: Couldn't match expected type `[Char]' with actual type `Char' Expected type: [[Char]] Actual type: [Char] In the expression: s In an equation for `lexOrder': lexOrder s@[_] = s It actually works, you have forgotten square brackets: lexOrder s@[_] = [s] --not s!. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] warning - Euler problem spoiler enclosed
On May 4, 2011, at 9:18 AM, Artyom Kazak wrote: Barbara Shirtcliff ba...@gmx.com писал(а) в своём письме Wed, 04 May 2011 16:41:07 +0300: Also, note that lexOrder s@[_] = [s] is nicer than lexOrder s | length s == 1 = [s]. I agree that that initial version was a little clumsy, but your suggestion doesn't really seem to work: lexOrder :: [Char] - [[Char]] lexOrder s@[_] = s lexOrder s = concat $ map (\n - h n) [0..((length z) - 1)] where z = sort $ nub s h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z Euler.hs:8:18: Couldn't match expected type `[Char]' with actual type `Char' Expected type: [[Char]] Actual type: [Char] In the expression: s In an equation for `lexOrder': lexOrder s@[_] = s It actually works, you have forgotten square brackets: lexOrder s@[_] = [s] --not s!. Прабда! Спасибо Б ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Another good video tutorial on monads
http://vimeo.com/20717301 I really liked how he starts off with the let statement. Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't install haskellnet with ghc7
I tried to install haskellnet with mime-mail-0.2.x and an older version of the text library but it still fails with the same error. Btw, what is the best way to uninstall a package that has been installed via cabal? (or to downgrade it, fwiw) -- Cp On Tue, Apr 26, 2011 at 23:31, Vincent Hanquez t...@snarc.org wrote: On 04/26/2011 10:17 PM, Charles-Pierre Astolfi wrote: Hi -cafe, Did anybody managed to install haskellnet from hackage with ghc7? I tried on windows and mac and I get the following type error: [ 4 of 11] Compiling Network.HaskellNet.SMTP ( Network/HaskellNet/SMTP.hs, dist/build/Network/HaskellNet/SMTP.o ) Network/HaskellNet/SMTP.hs:269:25: Couldn't match expected type `Data.Text.Internal.Text' with actual type `[Char]' Expected type: Data.Text.Internal.Text Actual type: String In the first argument of `simpleMail', namely `to' In a stmt of a 'do' expression: myMail- simpleMail to from subject plainBody htmlBody attachments Am I missing something? your mime-mail library is too recent. the upper version in the cabal file of haskellnet is not limited, so it's picking up the 0.3.0 version which is incompatible with the 0.2.x. Otherwise it was working for me with the previous version for both ghc6 and ghc7. -- Vincent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Advertisement: the Haskell Stack Overflow Q A site
One of the benefits of a site like SO as a forum is the ability to record and link to prior work, edit for technical errors, and easily search and categorize past answers. It is also less prone to noise, for those suffering from cafe overload. I would also recommend SO. My only experience of SO is that I asked a question once, and to this day it has still only been viewed a grand total of 6 times. (And I think that was just me looking to see if there were any replies yet.) OTOH, it wasn't Haskell-related. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Can't build Gtk2hs on Windows
Today I tried to install Gtk2hs. Big mistake! Last time I tried it, it was quite easy. Now that it uses Cabal, even on Windows you can compile this stuff from source fairly easily. It's just that you have to fiddle with environment variables to make it find stuff. However... 1. Since the move of haskell.org, the gtk2hs homepage has vanished off the face of the Earth. Is there any danger we might get this back some day? 2. http://hackage.haskell.org/trac/gtk2hs/ticket/1203 (In other words, every time you try to cabal install a GTK-related package, it fails during the register step, and you need to hand-edit Gtk2HsSetup.hs to fix the issue.) 3. http://hackage.haskell.org/trac/gtk2hs/ticket/1209 (In other words, certain GTK-related packages just plain fail to build due to undefined names or missing header files or...) In summary, it's just utterly broken. Which is very frustrating, given that not so long ago it was working really well. (I never did get Glade to work though... although it looks like that might be fixed now, if I could just get past all the other issues.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Advertisement: the Haskell Stack Overflow Q A site
On May 4, 2011, at 4:50 PM, Andrew Coppin wrote: One of the benefits of a site like SO as a forum is the ability to record and link to prior work, edit for technical errors, and easily search and categorize past answers. It is also less prone to noise, for those suffering from cafe overload. I would also recommend SO. My only experience of SO is that I asked a question once, and to this day it has still only been viewed a grand total of 6 times. (And I think that was just me looking to see if there were any replies yet.) OTOH, it wasn't Haskell-related. I think Haskell questions on SO tend to the opposite extreme; no matter how poorly thought-out the question, the Haskell community will descend on it like a swarm of helpful piranhas. Languages like Java and C# have such an overwhelmingly huge number of questions (the quality of which are, frankly, quite poor on average) that very few people are going to actually sit and look through even 1% of them. Haskell, on the other hand, has a small enough volume that people can at least skim the ones from the last past day or two in a fairly small amount of time. -- James ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Advertisement: the Haskell Stack Overflow Q A site
On Wednesday 04 May 2011 23:02:35, James Cook wrote: I think Haskell questions on SO tend to the opposite extreme; no matter how poorly thought-out the question, the Haskell community will descend on it like a swarm of helpful piranhas. That's a great picture. I like it. Haskell, where helpful piranhas swim :D ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Advertisement: the Haskell Stack Overflow Q A site
On Wed, May 4, 2011 at 5:02 PM, James Cook mo...@deepbondi.net wrote: Haskell, on the other hand, has a small enough volume that people can at least skim the ones from the last past day or two in a fairly small amount of time. They can and, in fact, do. Or at least I do, at any rate, even when I don't really have time to answer any. And I suspect Don Stewart does as well since by himself he's something like 20% of the answers by volume. Suffice it to say, questions with the [haskell] tag don't get overlooked. Overall, based on my experiences and glancing at the question lists, I'd estimate that most questions tagged [haskell] get at least 50 views and at least one useful answer within a few hours of being posted, depending on time of day and how many of the more prolific answerers are around. There're maybe 25 questions with no answers at all, which is less than 1% of the questions in the tag, and of the unanswered questions many are either very poorly thought out, very difficult to answer, or highly specific to some tool or library that not everyone may be familiar with. - C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't build Gtk2hs on Windows
On Wed, May 4, 2011 at 4:58 PM, Andrew Coppin andrewcop...@btinternet.com wrote: 2. http://hackage.haskell.org/trac/gtk2hs/ticket/1203 Another workaround for this is to install global: cabal install cairo --global Ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't build Gtk2hs on Windows
On Wednesday 04 May 2011 22:58:48, Andrew Coppin wrote: Today I tried to install Gtk2hs. Big mistake! Last time I tried it, it was quite easy. Now that it uses Cabal, even on Windows you can compile this stuff from source fairly easily. It's just that you have to fiddle with environment variables to make it find stuff. However... 1. Since the move of haskell.org, the gtk2hs homepage has vanished off the face of the Earth. Is there any danger we might get this back some day? 2. http://hackage.haskell.org/trac/gtk2hs/ticket/1203 (In other words, every time you try to cabal install a GTK-related package, it fails during the register step, and you need to hand-edit Gtk2HsSetup.hs to fix the issue.) Not here. 3. http://hackage.haskell.org/trac/gtk2hs/ticket/1209 (In other words, certain GTK-related packages just plain fail to build due to undefined names or missing header files or...) Not here. In summary, it's just utterly broken. Hmm, not so easy. It seems to work fine on linux (I only installed gtk* stuff for trying out leksah, so things might break with other stuff, but gtk, gio, glib, cairo, pango, gtksourceview2 went through without so much as a hiccough). So, by the looks of it, it seems to just work on linux, break on OS X and Windows, which might make it hard to pin down. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't install haskellnet with ghc7
On Wednesday 04 May 2011 21:57:51, Charles-Pierre Astolfi wrote: I tried to install haskellnet with mime-mail-0.2.x and an older version of the text library but it still fails with the same error. I just did $ cabal install --constraint=mime-mail 0.3 HaskellNet and it worked fine (ghc-7.0.3), text-0.11.0.7. Try the above with the --dry-run flag first, if it says it would install packages which you already have (except mime-mail), that may indicate problems, otherwise go ahead. Btw, what is the best way to uninstall a package that has been installed via cabal? (or to downgrade it, fwiw) $ ghc-pkg unregister mime-mail-0.3.0 perhaps? cabal has no uninstall command, so that job is for ghc-pkg unregister, unless you're willing to delete the whole ~/.ghc/i386- linux-7.0.3 and start from next to nothing. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] warning - Euler problem spoiler enclosed
The problem is lexOrder s@[_] = s where you just give back what you receive, i.e. [Char]. But you claim to give back [[Char]]. Try [s] on the right-hand side. On 05/04/2011 02:41 PM, Barbara Shirtcliff wrote: On May 4, 2011, at 7:21 AM, Ivan Lazar Miljenovic wrote: On 4 May 2011 13:13, Barbara Shirtcliffba...@gmx.com wrote: Hi, In the following solution to problem 24, why is nub ignored? I.e. if you do lexOrder of 0012, you get twice as many permutations as with 012, even though I have used nub. [snip] lexOrder :: [Char] - [[Char]] lexOrder s | length s == 1= [s] | length s == 2= z : [reverse z] | otherwise= concat $ map (\n - h n) [0..((length s) - 1)] where z = sort $ nub s -- why is the nub ignored here? h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z As a guess, I think it's from the usage of length on the right-hand size. Also, note that lexOrder s@[_] = [s] is nicer than lexOrder s | length s == 1 = [s]. I agree that that initial version was a little clumsy, but your suggestion doesn't really seem to work: lexOrder :: [Char] - [[Char]] lexOrder s@[_] = s lexOrder s = concat $ map (\n - h n) [0..((length z) - 1)] where z = sort $ nub s h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z Euler.hs:8:18: Couldn't match expected type `[Char]' with actual type `Char' Expected type: [[Char]] Actual type: [Char] In the expression: s In an equation for `lexOrder': lexOrder s@[_] = s ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't install haskellnet with ghc7
I just uploaded a new version of haskellnet that compiles with mime-mail-0.3.0. http://hackage.haskell.org/package/HaskellNet Hope that helps -- now for some sleep... http://hackage.haskell.org/package/HaskellNet-Rob On Wed, May 4, 2011 at 11:28 PM, Daniel Fischer daniel.is.fisc...@googlemail.com wrote: On Wednesday 04 May 2011 21:57:51, Charles-Pierre Astolfi wrote: I tried to install haskellnet with mime-mail-0.2.x and an older version of the text library but it still fails with the same error. I just did $ cabal install --constraint=mime-mail 0.3 HaskellNet and it worked fine (ghc-7.0.3), text-0.11.0.7. Try the above with the --dry-run flag first, if it says it would install packages which you already have (except mime-mail), that may indicate problems, otherwise go ahead. Btw, what is the best way to uninstall a package that has been installed via cabal? (or to downgrade it, fwiw) $ ghc-pkg unregister mime-mail-0.3.0 perhaps? cabal has no uninstall command, so that job is for ghc-pkg unregister, unless you're willing to delete the whole ~/.ghc/i386- linux-7.0.3 and start from next to nothing. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Crypto-api performance
While I haven't investigated myself, from seeing haskell build processes in the past this is almost certainly not crypto-api's fault and is in fact your linker's fault. If you are not using it already, try switching to gold over ld, it may help. --Matthew Maurer On 05/04/2011 04:27 AM, Peter Simons wrote: Also, it appears that crypto-api needs vast amounts of memory when compiled with optimization enabled. The latest version 0.6.1 is effectively unbuildable on my EeePC, which has only 1GB RAM. That property is fairly undesirable for a library package. Take care, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't build Gtk2hs on Windows
Just 5 weeks ago, http://thread.gmane.org/gmane.comp.lang.haskell.cafe/86738/focus=87456 Did anyone see it? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News - Issue 180
Welcome to issue 180 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of April 24 to 30, 2011. Announcements Eric Kow suggested (http://goo.gl/bc4JM) the creation of a Haskell User Group starter kit. If you have ideas in this department, please see what Eric has started! Christopher Done wrote (http://goo.gl/2m7AJ) a response to a blog from Cedric entitled Why Scala's Option and Haskell's Maybe types won't save you from Null. A lively conversation followed. Henning Thielemann started an very interesting thread (http://goo.gl/FWyDE) with the title Python is lazier than Haskell. (See the quotes of the week for the full quote) Quotes of the Week These quotes are taken from the #haskell channel, and from the haskell/haskell-cafe mailing lists. * Henning Thielemann: If Haskell is great because of its laziness, then Python must be even greater, since it is lazy at the type level. * Ben Lippmeier: Laziness at the value level causes space leaks, and laziness at the type level causes mind leaks. Neither are much fun. When people start wanting laziness at the kind level we'll have to quarantine them before the virus spreads... * Gregg Reynolds: If the designers could find a way to support laziness at the programmer level, I for one would be very grateful. * Felipe Almeida Lessa: But I am sure that john-millikin-is-great.txt must be increasing like a memory leak ;) * James Cook: I think Haskell questions on SO tend to the opposite extreme; no matter how poorly thought-out the question, the Haskell community will descend on it like a swarm of helpful piranhas. * Philippa: C++ seeing a renaissance as a functional language, is this a bit like rusty nails seeing a renaissance as sex toys for masochists? * #haskell: aristid preflex: seen FunctorSalad * preflex_ is now known as preflex. * copumpkin is now known as postflex. * xplat is now known as circumflex. circumflex FunctorSalad was never seen on #haskell-world-conquest -4 years, 3 days, 7i minutes and 0 seconds ago, saying: RELEASE THE KRAKEN! * tolkad: Without a standard you are lost, adrift in a sea of unspecified semantics. Hold fast to the rules of the specification lest you be consumed by ambiguity. * Saizan: it's much easier via type theory, 1) prove bottom 2) 3) quodlibet * dons: Think of a monad as a spacesuit full of nuclear waste in the ocean next to a container of apples. Now, you can't put oranges in the space suite or the nuclear waste falls in the ocean, *but* the apples are carried around anyway, and you just take what you need. * tolkad: Perhaps by using it we could modernise haskell by applying the principles of the new kind of science Top Reddit Stories * The Irish Times: Functional programming is more than just esoteric; it's becoming somewhat cool. Domain: irishtimes.com, Score: 44, Comments: 6 On Reddit: http://goo.gl/cfUbb Original: http://goo.gl/1nHEY * Why Silkapp uses Haskell Domain: blog.silkapp.com, Score: 43, Comments: 0 On Reddit: http://goo.gl/IFREi Original: http://goo.gl/1SwNa * Harper again: The real point of laziness Domain: existentialtype.wordpress.com, Score: 38, Comments: 89 On Reddit: http://goo.gl/vA8oD Original: http://goo.gl/hqcpy * Patent 5,893,120 reduced to mathematical formulae (via Haskell) Domain: paulspontifications.blogspot.com, Score: 34, Comments: 13 On Reddit: http://goo.gl/PmB4K Original: http://goo.gl/QknmV * IO evaluates the Haskell heap Domain: blog.ezyang.com, Score: 33, Comments: 3 On Reddit: http://goo.gl/FzaGV Original: http://goo.gl/KNHku * Why Haskell? Domain: blog.mired.org, Score: 33, Comments: 19 On Reddit: http://goo.gl/t1r8I Original: http://goo.gl/cV6KL * Filter and Visualize Data in Seconds with Silk (Haskell-based startup) Domain: thenextweb.com, Score: 33, Comments: 18 On Reddit: http://goo.gl/hA9HF Original: http://goo.gl/NIR3U * Haskell libraries you should use Domain: blog.johantibell.com, Score: 29, Comments: 3 On Reddit: http://goo.gl/PPTWG Original: http://goo.gl/LmbT6 * Tying the Knot - a really mind bending Haskell technique Domain: haskell.org, Score: 27, Comments: 8 On Reddit: http://goo.gl/iEdSM Original: http://goo.gl/5Zg6f * haskell.org GSoC accepted projects are up. Domain: self.haskell, Score: 26, Comments: 32 On Reddit: http://goo.gl/mnrl9 Original: /r/haskell/comments/gxj1h/haskellorg_gsoc_accepted_projects_are_up/ Top StackOverflow Questions * What are the best Haskell libraries to operationalize a program? votes: 57, answers: 3 Read on SO: http://goo.gl/rYQiL * How do you design programs in Haskell or other
