Re: [Haskell-cafe] Re: The instability of Haskell libraries

[Brandon S. Allbery KF8NH]

On Apr 27, 2010, at 00:55 , Aaron Denney wrote:

I despair that a better Numeric hierarchy will never make it into
Haskell.



I thought the main reason for that was that nobody could agree on a  
"better" hierarchy that was actually usable.  (Nobody wants to chain  
10 typeclasses together to get work done.)


--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com
system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu
electrical and computer engineering, carnegie mellon universityKF8NH




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Re: [Haskell-cafe] Re: The instability of Haskell libraries

[Ivan Miljenovic]

On 27 April 2010 14:55, Aaron Denney  wrote:
> I despair that a better Numeric hierarchy will never make it into
> Haskell.

I think the reason it hasn't is because I for one still haven't seen a
fully implemented such hierarchy that's worth using.

Then again, most of my numerical calculations are very basic; yay for
combinatorics! :p

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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[Haskell-cafe] Re: The instability of Haskell libraries

[Aaron Denney]

On 2010-04-24, John Goerzen  wrote:
> It is a funny thing, because our fundamental libraries *have* had time 
> to settle down, in a sense.  In another sense, I must say that the 
> innovations we have seen recently have been sorely needed and are 
> unquestionably a good thing.

Overall, agreed.  It still makes it a pain to write to the current
standard, because it is moving.

> Unicode support in IO,

This was "just" a bugfix in GHC, made more painful by people writing
code dependent on the old behaviour.

> I guess this is the price of failing to avoid 
> success, to borrow Simon's phrase.  And again, not entirely bad.

I despair that a better Numeric hierarchy will never make it into
Haskell.

-- 
Aaron Denney
-><-

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[Haskell-cafe] Re: Curl & UTF8

[Aaron Denney]

On 2010-04-23, Khudyakov Alexey  wrote:
> В сообщении от 23 апреля 2010 02:36:07 Rickard Karlsson написал:
>> Hi,
>> 
>> I'm trying to download a file in UTF-8 with libcurl(1.3.5) and GHC 6.12:
>> >import Network.Curl
>> >
>> >u = "http://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt";
>> >main = curlGetString u [] >>= putStrLn . snd
>> 
>> Which doesn't print the characters correctly. If i read the file from local
>> storage with getFile it is displayed properly.
>
> I think curl knows nothing about encoding and convert one byte to one Char 
> and 
> getFile uses new IO which uses system locale to choose encoding.

Then clearly curl should not return Strings, but byte arrays.  Of
course, curl can very well look at the headers which in this case do
specify UTF-8, and so perhaps it should do the translation itself.

-- 
Aaron Denney
-><-

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Re: [Haskell-cafe] Abstracted File Library?

[Marc Weber]

Hi Kazu,

I don't have a ghc Windows installation at the moment so I can't test.

filepath has functions such as normalise and equalFilePath.

Have a look at splitPath which is using pathSeparators which allows both
\\ and / on Windows.

filpath is using \\ to join pathes though.
So appling normalise on filepath on Windowsn will result in 
having paths containing \\ only.
This will still not help you writing your regex unless you replace / by
\\ on Windows.

It's easy to write [\\/] in regex to catch both.

So maybe a normalisePosix function should be added which always returns
/ ?

The fast way which would work for you only is making pathSeparator
return "/" only. Then you're done but your code will not be portable..

Including a local copy of filepath for exactly this reason could be an
option for you.

> isSymbolicLink, linkCounts, etc.

Don't know about them..

Marc Weber
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Re: [Haskell-cafe] Abstracted File Library?

[山本和彦]

Hello,

> Clarify this, please. Used by who?

It is by System.FilePath.
 Windows: combine "home" "bob" == "home\\bob"

> Both Cabal and filepath libraries do have functions operating on
> filepath strings. Eg filepath can split them.

I'm want to use regular expressions for results of 'combine', for
instance.

>> Are there any abstracted file library to solve these problems?
>> Or should I start to write such a library?
> 
> Which functions should this library have?

isSymbolicLink, linkCounts, etc.

> I'm pretty sure that filepath already has most functions you need.

Not really at least to me.

--Kazu
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Re: [Haskell-cafe] Abstracted File Library?

[Marc Weber]

Excerpts from Kazu Yamamoto (山本和彦)'s message of Tue Apr 27 04:59:46 +0200 2010:
> Hello,
> 
> I'm implementing a command which manipulates files both on Unix/Mac
> and Windows. I was very surprised because there is not
> "getStatusChangeTime" function. So, I wrote it with CPP.
> 
> http://github.com/kazu-yamamoto/Mew/blob/master/bin/hs/Stat.hs
> 
> Another problem is that since '\\' is used as the file separator of
> Windows, I cannot use regular expression naturally for file path. In

Clarify this, please. Used by who?
The user may enter \\ which is valid on Windows.

Both Cabal and filepath libraries do have functions operating on
filepath strings. Eg filepath can split them.

I agree that / is valid on Windows.

So before working on user input you have to sanitize paths
by replacing \\ by /

> Are there any abstracted file library to solve these problems?
> Or should I start to write such a library?

Which functions should this library have?

I'm pretty sure that filepath already has most functions you need.
You may want to patch it so that it's using / on Windows when assembling
paths form lists of directory names.

Marc Weber
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[Haskell-cafe] Abstracted File Library?

[山本和彦]

Hello,

I'm implementing a command which manipulates files both on Unix/Mac
and Windows. I was very surprised because there is not
"getStatusChangeTime" function. So, I wrote it with CPP.

http://github.com/kazu-yamamoto/Mew/blob/master/bin/hs/Stat.hs

Another problem is that since '\\' is used as the file separator of
Windows, I cannot use regular expression naturally for file path. In
many programming languages, '/' is only file separator for
programmers. And my friend, who is an expert of Windows API, says to me
that Windows API allows '/' as a file separator. Why don't we
use '/' on Windows, too?

Are there any abstracted file library to solve these problems?
Or should I start to write such a library?

--Kazu
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[Haskell-cafe] Re: Run haskell program in emacs without typing "main" in the ghci buffer.

[Jose A. Ortega Ruiz]

Zura_  writes:

> Hello,
>
> Is it possible to run haskell program in emacs without typing "main" in the
> ghci buffer? Assuming "main" function exists of course.
> Or, maybe automate sending "main\n" string to ghci buffer input.
> In other words, I want edit/run/see result style session.

Assuming you're using haskell-mode, does

  M-x inferior-haskell-load-and-run

do what you want? You can of course define a shortcut for it:

  (define-key haskell-mode-map "\C-l" 'inferior-haskell-load-and-run)

If you don't want to load the file, just run main:
  
   (defun haskell-main ()
  (interactive)
  (inferior-haskell-send-command (inferior-haskell-process)
 ":main"))

(This a very simple version; there're many possible variations; for
instance, adding (swith-to-haskell) at the end).

HTH,
jao

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Re: [Haskell-cafe] Proper Handling of Exceptional IEEE Floating Point Numbers

[Roman Leshchinskiy]

On 24/04/2010, at 22:42, Roman Leshchinskiy wrote:

> On 24/04/2010, at 22:06, Barak A. Pearlmutter wrote:
> 
>>> I was thinking of this:
>> 
>>> data T = T Double deriving ( Eq, Ord )
>> 
>>> ... GHC basically produces
>> 
>>> instance Ord T where
>>> compare (T x) (T y) = compare x y
>>> t < u = compare t u == LT
>> 
>> That is indeed what it does.  Which is a plain old bug, since it leads
>> to inconsistent behaviour between wrapped vs unwrapped values.
>> 
>> *Main> T (0/0) == T (0/0)
>> False
>> *Main> T (0/0) < T (0/0)
>> False
>> *Main> T (0/0) > T (0/0)
>> True
>> *Main> (0/0) > (0/0)
>> False
> 
> Urgh. You're right, I hadn't thought of this. Would you care to submit a bug 
> report?

I submitted one but on further reflection, this is not so simple. Let's look at 
pairs as an example. At the moment, (>) is implemented basically like this:

 (a,b) > (c,d) = case compare a c of
   LT -> False
   EQ -> compare b d
   GT -> True

Of course, this means that (0/0,'a') > (0/0,'a'). So we could change the 
implementation:

  (a,b) > (c,d) = a > c || (a == c && b > d)

But now we compare a to c twice which is very bad for, say, ([Int],Int). 
Clearly, we want to use the first definition but it leads to inconsistent 
results for Doubles. I don't see how to solve this while keeping IEEE semantics 
of silent NaNs.

Roman


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Re: [Haskell-cafe] Haskell Weekly News?

[Joe Fredette]

Most certainly, the HWN is easy to put together, it's just a little  
time consuming, the weekly schedule is just enough under a normal 40- 
hour courseload. When that number jumps into the high billions (as it  
did this last semester), it becomes someone more difficult to fit in.


HWN will always be HWN, at least as long as I can keep it that way. :D

/Joe


On Apr 26, 2010, at 8:17 PM, Ivan Miljenovic wrote:


On 27 April 2010 10:08, Joe Fredette  wrote:
 I hope to get HWN out shortly after it's all finished up. I shall  
return!


As long as you don't end up copying the Gentoo situation where the
Gentoo Weekly News died, was resurrected (not sure how many times),
was converted to the Gentoo Monthly News to make it simpler, and then
became the Gentoo Never News (hey, GNN sounds kinda catchy, though not
as good as C :p).

--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com


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Re: [Haskell-cafe] Haskell Weekly News?

[Ivan Miljenovic]

On 27 April 2010 10:08, Joe Fredette  wrote:
>  I hope to get HWN out shortly after it's all finished up. I shall return!

As long as you don't end up copying the Gentoo situation where the
Gentoo Weekly News died, was resurrected (not sure how many times),
was converted to the Gentoo Monthly News to make it simpler, and then
became the Gentoo Never News (hey, GNN sounds kinda catchy, though not
as good as C :p).

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Haskell Weekly News?

[Joe Fredette]

Hehe,

 Mostly, at the moment, as I mentioned to Deech, what is holding me  
up is trying to get HWN and 7 classes worth of finals and papers done.  
This is the last two weeks of my last semester, but it should be all  
done soon.


 I hope to get HWN out shortly after it's all finished up. I shall  
return!


/Joe

On Apr 26, 2010, at 7:54 PM, Ivan Miljenovic wrote:


On 27 April 2010 08:08, aditya siram  wrote:

Hi all,
I haven't seen a "Haskell Weekly News" in a while. Is there  
anything I

can do to help?


My guess is do John's marking, etc. for him so that he has some time
to do the HWN!

We also want him to avoid this situation: http://ro-che.info/ccc/06.html 
 :p


--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Haskell Weekly News?

[Ivan Miljenovic]

On 27 April 2010 08:08, aditya siram  wrote:
> Hi all,
> I haven't seen a "Haskell Weekly News" in a while. Is there anything I
> can do to help?

My guess is do John's marking, etc. for him so that he has some time
to do the HWN!

We also want him to avoid this situation: http://ro-che.info/ccc/06.html :p

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Haddock infix constructors in markup

[Ivan Miljenovic]

On 27 April 2010 02:15, Ozgur Akgun  wrote:
> data Expr = Num Int | Expr :+: Expr | Expr :-: Expr
>
> [snip]
>
> -- | If the input is 'Num' does magic, if it is ':+:' does even more magic!
> someFunc :: Expr -> Expr
>
> In the output of this markup, the 'Num' is hyperlinked but the ':+:' is not.

I would hazard a guess that the Num hyperlink points to the Num
typeclass in the Prelude rather than your Num constructor.  As for
your infix constructor, I have no idea.

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Run haskell program in emacs without typing "main" in the ghci buffer.

[Ivan Miljenovic]

On 27 April 2010 05:43, Zura_  wrote:
> Is it possible to run haskell program in emacs without typing "main" in the
> ghci buffer? Assuming "main" function exists of course.
> Or, maybe automate sending "main\n" string to ghci buffer input.
> In other words, I want edit/run/see result style session.

This is probably possible if you have enough elisp-fu (which I don't,
but have a look at Flymake Haskell).

If so, it would be better to have this as a different emacs keybinding
rather than the default haskell-load-file one, as 1) you won't always
have a main action and 2) you won't always want to _run_ your main
action (e.g. it launches nuclear missiles and you don't want to run
that when you're just testing your countdown function...).

However, by using ":main" in the ghci session you have a bit more
control as it allows you to specify command-line flags and inputs,
which running just "main" doesn't.

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Re: What do _you_ want to see in FGL?

[Ivan Miljenovic]

On 27 April 2010 03:39, Louis Wasserman  wrote:
> I'm a fan of making FGL more record-based, but definitely keeping the
> inductive graph style.

Definitely.

> My own biggest gripe with previous versions of FGL was that the graph
> implementations were severely underoptimized.  In particular, PatriciaTree
> left open a lot of optimization.

Wouldn't know much about the optimisation side of things; when I've
used FGL graphs before they usually weren't the bottleneck in my
program.

> Ivan, would you like to set up a darcs repo for FGL-Prime or something at
> code.haskell.org, and start cracking?  I'm really excited for this project.

Sure, let's take these preliminary discussions off-list.


-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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[Haskell-cafe] Haskell statefull computations and co-algebras?

[Vasili I. Galchin]

Hello,

  I am fairly conversant in category. In any case, I am re-reading
Bart Jacobs co-algebra tutorial
citeseer.ist.psu.edu/jacobs97tutorial.html and draft book
www.cs.ru.nl/B.Jacobs/CLG/JacobsCoalgebraIntro.pdf.

  Have others read these?

  What role do co-algebras play in Haskell stateful computations
(as opposed to or complementing monads)?

Kind regards,

Vasili
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Re: [Haskell-cafe] and [] = True; or [] = False

[Richard O'Keefe]

On Apr 27, 2010, at 12:15 AM, Bjorn Buckwalter wrote:


Dear all,

Does it make good sense that 'and []' returns 'True' and 'or []'
returns 'False'?


YES!

There is no other behaviour that would make sense.

You wouldn't expect sum [] to return anything but 0, would you?


What got me thinking about this was the apparently incorrect intuition
that 'and xs' would imply 'or xs'.


Only if not (null xs).

See also Lisp and Scheme, where (AND) -> true, (OR) -> false,
and look up the behaviour of ∀ and ∃ in a logic book.
(∀x∈s)p(x) does NOT imply (∃x∈s)p(x) because s might be empty.
(This is where the modern ∀ and ∃ part company with Aristotelian
logic.  In syllogisms, "all unicorns are white" does not count as
true unless there is at least one unicorn.)

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[Haskell-cafe] Haskell Weekly News?

[aditya siram]

Hi all,
I haven't seen a "Haskell Weekly News" in a while. Is there anything I
can do to help?
-deech
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Re: [Haskell-cafe] Re: FRP for game programming / artifical life simulation

[Peter Verswyvelen]

2010/4/25 Patai Gergely :
>> (in my own FRP experiments I have an update thread and a render thread).
> I wonder how to nicely deal with state that requires communication with
> the outer world, even though it is functional at heart. For instance, if
> you want to change a vertex buffer or a texture or whatever during the
> update, how do you organise your code? Do you maintain separate pure and
> impure state information blocks?

I don't have a vertex buffers or texture in my update loop. These are
low level details, left to the render loop. Indeed I maintained a pure
information block in the update. If you really wanted to have
low-level access in the update loop, I wouldn't know how to do that,
although keeping two copies could work. Now my experiments were really
simple 2D games, so not really state of the art.

> Deciding between push and pull according to profiling results is a nice
> idea. :) It might be too expensive to do it adaptively during runtime
> (the overhead might easily distort the results and thus render them
> invalid), but treating it as just a flag could give us an interesting
> architecture to play with.

Yes, I see it more in the line of "profile based optimization", where
a compiler performs static optimization based on a previous profile.

I kind of abandoned the FRP thing because Haskell just feels a bit too
complicated/abstract for me. It might also be that for the average
person to learn Haskell really well, one needs a mentor. I would love
to follow courses about it actually :)
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Re: [Haskell-cafe] Haddock infix constructors in markup

[Daniel Fischer]

Am Montag 26 April 2010 22:18:53 schrieb Daniel Fischer:
> Am Montag 26 April 2010 22:05:48 schrieb Ozgur Akgun:
> > So, how can we make use of this fix?
>
> My guess:
>
> $ cabal install haddock-2.7.2

No, it's not yet in there :(
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Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)

[Daniel Fischer]

Am Montag 26 April 2010 22:23:42 schrieb Gregory Collins:
> Alexander Solla  writes:
> > On Apr 26, 2010, at 12:30 PM, Jeremy Shaw wrote:
> >> Does trying to install hsp-0.5.1 work any better?
> >
> > I hadn't tried it, since it forces hsx-0.7 to install.  But I gave it
> > a shot, and it fails the same way:
> >
> > [ a...@kizaru:~/ ]$ cabal install hsp-0.5.1
> > Resolving dependencies...
> > Configuring hsp-0.5.1...
> > Preprocessing library hsp-0.5.1...
> > Building hsp-0.5.1...
> > ghc: could not execute: trhsx
> > cabal: Error: some packages failed to install:
> > hsp-0.5.1 failed during the building phase. The exception was:
> > ExitFailure 1
>
> Is "$HOME/.cabal/bin" on your $PATH?
>
> G

He said it is. That would've been too easy.
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Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)

[Alexander Solla]

On Apr 26, 2010, at 1:23 PM, Gregory Collins wrote:


Is "$HOME/.cabal/bin" on your $PATH?



Argh.

I had "~/.cabal/bin" in my $PATH instead of "$HOME/.cabal/bin".  I'm  
still not sure what the semantic difference is in this use case, but  
one ($HOME) works and the other (~/) doesn't.


Thanks everybody
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Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)

[Gregory Collins]

Alexander Solla  writes:

> On Apr 26, 2010, at 12:30 PM, Jeremy Shaw wrote:
>
>>
>> Does trying to install hsp-0.5.1 work any better?
>
> I hadn't tried it, since it forces hsx-0.7 to install.  But I gave it a shot,
> and it fails the same way:
>
> [ a...@kizaru:~/ ]$ cabal install hsp-0.5.1
> Resolving dependencies...
> Configuring hsp-0.5.1...
> Preprocessing library hsp-0.5.1...
> Building hsp-0.5.1...
> ghc: could not execute: trhsx
> cabal: Error: some packages failed to install:
> hsp-0.5.1 failed during the building phase. The exception was:
> ExitFailure 1

Is "$HOME/.cabal/bin" on your $PATH?

G
-- 
Gregory Collins 
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Re: [Haskell-cafe] Haddock infix constructors in markup

[Daniel Fischer]

Am Montag 26 April 2010 22:05:48 schrieb Ozgur Akgun:
> So, how can we make use of this fix?
>

My guess:

$ cabal install haddock-2.7.2
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Re: [Haskell-cafe] Haddock infix constructors in markup

[Ozgur Akgun]

So, how can we make use of this fix?

On 26 April 2010 19:47, David Waern  wrote:

> 2010/4/26 Daniel Fischer :
> > Am Montag 26 April 2010 18:15:02 schrieb Ozgur Akgun:
> >> Hi all,
> >>
> >> If I have the following data type:
> >>
> >> data Expr = Num Int | Expr :+: Expr | Expr :-: Expr
> >>
> >> Haddock handles the infix constructors, and generates a very nice output
> >> (html in this case)
> >> However when I try to reference to one of the infix constructors in the
> >> markup of other functions it fails to hyperlink.
> >>
> >> -- | If the input is 'Num' does magic, if it is ':+:' does even more
> >> magic! someFunc :: Expr -> Expr
> >>
> >> In the output of this markup, the 'Num' is hyperlinked but the ':+:' is
> >> not. Is there a different syntax for infix constructors (and for infix
> >> functions presumably) or does haddock simple lack this feature?
> >
> > Infix functions work fine (try referring to e.g. '&&' in the haddock
> > comment), but infix constructors apparently not.
>
> Yes, I actually fixed this a few weeks ago in Haddock's lexer. Colon
> was just not included in the character set for identifiers.
>
> David
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-- 
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Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)

[Alexander Solla]

On Apr 26, 2010, at 12:30 PM, Jeremy Shaw wrote:



Does trying to install hsp-0.5.1 work any better?


I hadn't tried it, since it forces hsx-0.7 to install.  But I gave it  
a shot, and it fails the same way:


[ a...@kizaru:~/ ]$ cabal install hsp-0.5.1
Resolving dependencies...
Configuring hsp-0.5.1...
Preprocessing library hsp-0.5.1...
Building hsp-0.5.1...
ghc: could not execute: trhsx
cabal: Error: some packages failed to install:
hsp-0.5.1 failed during the building phase. The exception was:
ExitFailure 1

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[Haskell-cafe] Run haskell program in emacs without typing "main" in the ghci buffer.

[Zura_]

Hello,

Is it possible to run haskell program in emacs without typing "main" in the
ghci buffer? Assuming "main" function exists of course.
Or, maybe automate sending "main\n" string to ghci buffer input.
In other words, I want edit/run/see result style session.

Thanks in advance,
Zura
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View this message in context: 
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Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)

[Jeremy Shaw]

Hello,

Does trying to install hsp-0.5.1 work any better?

- jeremy

On Apr 26, 2010, at 12:27 PM, Alexander Solla wrote:



On Apr 23, 2010, at 2:59 PM, Thomas Hartman wrote:


So, you might need to
-- upgrade hsx
-- make sure that the upgraded trhsx executable is the one being
executed by cabal install hsx (maybe deleting/temporarily moving  
other

trhsx exes)


Unfortunately, this suggestion didn't work out for me.  I read  
through all the relevant GHC documentation I could find -- I didn't  
see a way to set a specific path for GHC to search through for  
binaries.  Whether I moved trhsx or not, the error was the same.   
But it's the only trhsx on my system.


I've upgraded through every version of hsx that is compatible with  
Happstack, and tried every hsp that is compatible with Happstack.   
I've built Cabal-install, removed it, used the Arch package; tried  
global/user installs for Happstack;  did a darcs get on the official  
Happstack repo, and tried to build using its build script, on a  
fresh GHC install; and other stuff that I guess didn't make much  
sense.


It always broke in the same place:

[ a...@kizaru:~/ ]$ cabal install hsp-0.4.5
Resolving dependencies...
Configuring hsp-0.4.5...
Preprocessing library hsp-0.4.5...
Building hsp-0.4.5...
ghc: could not execute: trhsx
cabal: Error: some packages failed to install:
hsp-0.4.5 failed during the building phase. The exception was:
ExitFailure 1

The strange thing about it (that I noticed) is that GHC reports  
failing during the building phase instead of the preprocessing  
phase.  Maybe this is just an artifact of the logging system, but it  
seems like GHC is doing something strange.  If I increase the  
verbosity, (near the end) I get:


*** Haskell pre-processor:
trhsx src/HSP/HJScript.hs /tmp/ghc6345_0/ghc6345_6.hscpp /tmp/ 
ghc6345_0/ghc6345_0.hspp

*** Deleting temp files:
Deleting: /tmp/ghc6345_0/ghc6345_0.hspp /tmp/ghc6345_0/ 
ghc6345_6.hscpp /tmp/ghc6345_0/ghc6345_5.hscpp /tmp/ghc6345_0/ 
ghc6345_4.hscpp /tmp/ghc6345_0/ghc6345_3.hscpp /tmp/ghc6345_0/ 
ghc6345_2.hscpp /tmp/ghc6345_0/ghc6345_1.hscpp /tmp/ghc6345_0/ 
ghc6345_0.hscpp

Warning: deleting non-existent /tmp/ghc6345_0/ghc6345_0.hspp
*** Deleting temp dirs:
Deleting: /tmp/ghc6345_0
ghc: could not execute: trhsx
/usr/bin/ghc returned ExitFailure 1
cabal: Error: some packages failed to install:
hsp-0.4.5 failed during the building phase. The exception was:
ExitFailure 1


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Re: [Haskell-cafe] Rank-2 polymorphism and overloading

[Thomas van Noort]

On 26-4-2010 20:12, Daniel Fischer wrote:

Am Montag 26 April 2010 19:52:23 schrieb Thomas van Noort:

...


Yes, y's type is more general than the type required by f, hence y is an
acceptable argument for f - even z :: forall a b. a ->  b ->  Bool is.


That's what I thought. I've just never seen such a notion of a more 
general type involving overloading before.





However, it requires y to throw away the provided
dictionary under the hood, which seems counter intuitive to me.


Why? y doesn't need the dictionary, so it just ignores it.


Sure, but y's type explicitly mentions that it doesn't want a 
dictionary, so why would you provide one to it?






Regards,
Thomas




Regards,
Thomas

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Re: [Haskell-cafe] Rank-2 polymorphism and overloading

[Thomas van Noort]

On 26-4-2010 20:13, Jochem Berndsen wrote:

Thomas van Noort wrote:

...


f requires a function that is able to compute, for two values of type a
(which instantiates Eq), a Boolean.

y certainly fulfills that requirement: it does not even require that the
values are of a type instantiating Eq.

This is also well-typed and might or might not be enlightening:


z :: forall a. Eq a =>  a ->  a ->  Bool
z = y

g :: (Bool, Bool)
g = (f x, f z) -- note the use of z here instead of y


I find your example of z more intuitive as it is z that does not provide 
its dictionary to y, but throws it away explicitly. This in contrast to 
y that is provided a dictionary but throws it away implicitly.


Regards,
Thomas



Jochem


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Re: [Haskell-cafe] Haddock infix constructors in markup

[David Waern]

2010/4/26 Daniel Fischer :
> Am Montag 26 April 2010 18:15:02 schrieb Ozgur Akgun:
>> Hi all,
>>
>> If I have the following data type:
>>
>> data Expr = Num Int | Expr :+: Expr | Expr :-: Expr
>>
>> Haddock handles the infix constructors, and generates a very nice output
>> (html in this case)
>> However when I try to reference to one of the infix constructors in the
>> markup of other functions it fails to hyperlink.
>>
>> -- | If the input is 'Num' does magic, if it is ':+:' does even more
>> magic! someFunc :: Expr -> Expr
>>
>> In the output of this markup, the 'Num' is hyperlinked but the ':+:' is
>> not. Is there a different syntax for infix constructors (and for infix
>> functions presumably) or does haddock simple lack this feature?
>
> Infix functions work fine (try referring to e.g. '&&' in the haddock
> comment), but infix constructors apparently not.

Yes, I actually fixed this a few weeks ago in Haddock's lexer. Colon
was just not included in the character set for identifiers.

David
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[Haskell-cafe] The Poor Man's PVP-Checking Tool

[Neil Brown]

Hi,

The issue of a tool to help with checking packages against the Package 
Versioning Policy (PVP: 
http://www.haskell.org/haskellwiki/Package_versioning_policy) has come 
up several times on this list, and it seems to be a generally wanted 
tool.  One of the things desired in such a tool is the ability to check 
what has been added/changed/removed in the latest version of a package, 
to help see what kind of version bump is needed according to the PVP.  
This could also be used to check if past releases have obeyed the PVP.


A proper way to build this tool is to parse the types of everything 
involved (functions, data  types, and instances), and check them for 
being the same (given that the type parameters may have been renamed, or 
a definition substituted for a synonym and so on).  I have instead 
hacked together a tool in an hour or so that roughly does the job.  It 
uses Perl, which I haven't written for a long time, because that was 
quickest  -- if this bothers you, pretend its a crazy Haskell EDSL or 
something :-).  I've attached the Perl script.  It combines the 
command-line tools diff and sort with a tiny bit of manual processing 
along with the Haskell tool cabal-install, and brings them to bear on 
the output of "haddock --hoogle", which already nicely spits out the 
types of all functions, data types and instances in your library.


It looks for differences in the output between two package versions, and 
tells you what version bump it thinks you need.  It errs on the 
conservative side, I believe -- it should never miss a bump when it's 
needed, but you may sometimes get a false alarm if you've made a 
harmless change.


As an example, let's take the recent stm release.  You run the Perl 
script with the name and version of both package versions (if you omit 
the version, it should use the latest):



n...@beast ~: perl cmp.perl stm-2.1.2.0 stm-2.1.1.2
Warning: The documentation for the following packages are not installed. No
links will be generated to these packages: ffi-1.0, rts-1.0
Warning: The documentation for the following packages are not installed. No
links will be generated to these packages: ffi-1.0, rts-1.0
25a26
> Control.Concurrent.STM.TVar:readTVarIO :: TVar a -> IO a
39c40
< @version 2.1.1.2
---
> @version 2.1.2.0

Given previous version number A.B.C.D:
It seems you have added something.  You must increase C (or A or B)


For those who can read diff, you get the diff.  At the bottom, the tool 
works out the required bump; here something was added so C must be 
increased, and we can see that the package did just that.  Let's take 
another example from my latest development version of my CHP library; 
here I run the command with one argument (chp, which means the latest 
version on Hackage):



n...@banshee ~/work/chp: perl cmp.perl chp
Warning: The documentation for the following packages are not installed. No
links will be generated to these packages: rts-1.0

Control/Concurrent/CHP/Alt.hs:116:9:
   Warning: orphan instance: instance Alternative CHP
Warning: The documentation for the following packages are not installed. No
links will be generated to these packages: rts-1.0
6a7
> Control.Concurrent.CHP.Alt:instance Alternative CHP
82d82
< Control.Concurrent.CHP.Channels.Creation:class ChannelTuple t
88,92d87
< Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) => 
ChannelTuple (Chan r w a, Chan r w a)
< Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) => 
ChannelTuple (Chan r w a, Chan r w a, Chan r w a)
< Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) => 
ChannelTuple (Chan r w a, Chan r w a, Chan r w a, Chan r w a)
< Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) => 
ChannelTuple (Chan r w a, Chan r w a, Chan r w a, Chan r w a, Chan r w a)
< Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) => 
ChannelTuple (Chan r w a, Chan r w a, Chan r w a, Chan r w a, Chan r w 
a, Chan r w a)

102d96
< Control.Concurrent.CHP.Channels.Creation:newChannels :: (ChannelTuple 
t, MonadCHP m) => m t

149c143
< Control.Concurrent.CHP.Monad:class (MonadIO m) => MonadCHP m
---
> Control.Concurrent.CHP.Monad:class (Monad m) => MonadCHP m
155a150
> Control.Concurrent.CHP.Monad:foreverP :: CHP a -> CHP b
156a152
> Control.Concurrent.CHP.Monad:liftIO_CHP :: IO a -> CHP a
160a157
> Control.Concurrent.CHP.Monad:process :: String -> a -> a
164a162
> Control.Concurrent.CHP.Monad:subProcess :: String -> a -> a
169c167
< Control.Concurrent.CHP.Parallel:data (Monad m, MonadCHP m) => ForkingT m a
---
> Control.Concurrent.CHP.Parallel:data ForkingT m a
173d170
< Control.Concurrent.CHP.Parallel:instance (MonadIO m) => MonadIO 
(ForkingT m)

175c172
< Control.Concurrent.CHP.Parallel:instance MonadTrans ForkingT
---
> Control.Concurrent.CHP.Parallel:liftForking :: (Monad m) => m a -> 
ForkingT m a

239c236
< @version 2.1.0.1
---
> @version 2.2.0

Given previous version number A.B.C.D:
It seems you have added, removed o

Re: [Haskell-cafe] Rank-2 polymorphism and overloading

[Daniel Fischer]

Am Montag 26 April 2010 19:52:23 schrieb Thomas van Noort:
> Hello all,
>
> I'm having difficulties understanding rank-2 polymorphism in combination
> with overloading. Consider the following contrived definition:
>
> f :: (forall a . Eq a => a -> a -> Bool) -> Bool
> f eq = eq True True
>
> Then, we pass f both an overloaded function and a regular polymorphic
> function:
>
> x :: forall a . Eq => a -> a -> Bool
> x = \x y -> x == y
>
> y :: forall a . a -> a -> Bool
> y = \x y -> True
>
> g :: (Bool, Bool)
> g = (f x, f y)
>
> Could someone explain to me, or point me to some reading material, why g
> is correctly typed?
>
> I understand that x's type is what f expects, but why does y's
> polymorphic type fulfill the overloaded type of f's argument? I can
> imagine that it is justified since f's argument type is more restrictive
> than y's type.

Yes, y's type is more general than the type required by f, hence y is an 
acceptable argument for f - even z :: forall a b. a -> b -> Bool is.

> However, it requires y to throw away the provided
> dictionary under the hood, which seems counter intuitive to me.

Why? y doesn't need the dictionary, so it just ignores it.

>
> Regards,
> Thomas

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Re: [Haskell-cafe] Rank-2 polymorphism and overloading

[Jochem Berndsen]

Thomas van Noort wrote:
> Hello all,
> 
> I'm having difficulties understanding rank-2 polymorphism in combination
> with overloading. Consider the following contrived definition:
> 
> f :: (forall a . Eq a => a -> a -> Bool) -> Bool
> f eq = eq True True
> 
> Then, we pass f both an overloaded function and a regular polymorphic
> function:
> 
> x :: forall a . Eq => a -> a -> Bool
> x = \x y -> x == y
> 
> y :: forall a . a -> a -> Bool
> y = \x y -> True
> 
> g :: (Bool, Bool)
> g = (f x, f y)
> 
> Could someone explain to me, or point me to some reading material, why g
> is correctly typed?
> 
> I understand that x's type is what f expects, but why does y's
> polymorphic type fulfill the overloaded type of f's argument? I can
> imagine that it is justified since f's argument type is more restrictive
> than y's type. However, it requires y to throw away the provided
> dictionary under the hood, which seems counter intuitive to me.

f requires a function that is able to compute, for two values of type a
(which instantiates Eq), a Boolean.

y certainly fulfills that requirement: it does not even require that the
values are of a type instantiating Eq.

This is also well-typed and might or might not be enlightening:

> z :: forall a. Eq a => a -> a -> Bool
> z = y
>
> g :: (Bool, Bool)
> g = (f x, f z) -- note the use of z here instead of y

Jochem
-- 
Jochem Berndsen | joc...@functor.nl

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[Haskell-cafe] Halp: wacky FFI problems

[Louis Wasserman]

Hey,

I'm trying to do some funky things with the FFI, and I'm clueless enough
with C that I could use some help.

In particular, I'm trying to bind to the glpk library in a multithreaded
style.  It's not normally thread-safe, but somebody suggested how to make it
safe here .

I have no idea how to integrate this with FFI-style bindings.  A
single-threaded set of bindings that I've written is here:
http://hackage.haskell.org/package/glpk-hs  I'm trying to figure out how to
integrate FFI bindings with pthreads, and yadda yadda, and I'm pretty
clueless.

Any suggestions?

Louis Wasserman
wasserman.lo...@gmail.com
http://profiles.google.com/wasserman.louis
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[Haskell-cafe] Rank-2 polymorphism and overloading

[Thomas van Noort]

Hello all,

I'm having difficulties understanding rank-2 polymorphism in combination 
with overloading. Consider the following contrived definition:


f :: (forall a . Eq a => a -> a -> Bool) -> Bool
f eq = eq True True

Then, we pass f both an overloaded function and a regular polymorphic 
function:


x :: forall a . Eq => a -> a -> Bool
x = \x y -> x == y

y :: forall a . a -> a -> Bool
y = \x y -> True

g :: (Bool, Bool)
g = (f x, f y)

Could someone explain to me, or point me to some reading material, why g 
is correctly typed?


I understand that x's type is what f expects, but why does y's 
polymorphic type fulfill the overloaded type of f's argument? I can 
imagine that it is justified since f's argument type is more restrictive 
than y's type. However, it requires y to throw away the provided 
dictionary under the hood, which seems counter intuitive to me.


Regards,
Thomas
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[Haskell-cafe] Re: What do _you_ want to see in FGL?

[Louis Wasserman]

I'm a fan of making FGL more record-based, but definitely keeping the
inductive graph style.

My own biggest gripe with previous versions of FGL was that the graph
implementations were severely underoptimized.  In particular, PatriciaTree
left open a *lot* of optimization.

Ivan, would you like to set up a darcs repo for FGL-Prime or something at
code.haskell.org, and start cracking?  I'm really excited for this project.

Louis Wasserman
wasserman.lo...@gmail.com
http://profiles.google.com/wasserman.louis
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Re: [Haskell-cafe] The instability of Haskell libraries

[Brandon S. Allbery KF8NH]

On Apr 26, 2010, at 09:33 , John Goerzen wrote:
It would, however, be nice if the language allowed you to override  
default instances with the code in your own package.



Many other languages refer to this kind of thing as "monkey patching"  
and warn against it because of the problems it causes.


--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com
system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu
electrical and computer engineering, carnegie mellon universityKF8NH




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Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)

[Alexander Solla]

On Apr 23, 2010, at 2:59 PM, Thomas Hartman wrote:


So, you might need to
-- upgrade hsx
-- make sure that the upgraded trhsx executable is the one being
executed by cabal install hsx (maybe deleting/temporarily moving other
trhsx exes)


Unfortunately, this suggestion didn't work out for me.  I read through  
all the relevant GHC documentation I could find -- I didn't see a way  
to set a specific path for GHC to search through for binaries.   
Whether I moved trhsx or not, the error was the same.  But it's the  
only trhsx on my system.


I've upgraded through every version of hsx that is compatible with  
Happstack, and tried every hsp that is compatible with Happstack.   
I've built Cabal-install, removed it, used the Arch package; tried  
global/user installs for Happstack;  did a darcs get on the official  
Happstack repo, and tried to build using its build script, on a fresh  
GHC install; and other stuff that I guess didn't make much sense.


It always broke in the same place:

[ a...@kizaru:~/ ]$ cabal install hsp-0.4.5
Resolving dependencies...
Configuring hsp-0.4.5...
Preprocessing library hsp-0.4.5...
Building hsp-0.4.5...
ghc: could not execute: trhsx
cabal: Error: some packages failed to install:
hsp-0.4.5 failed during the building phase. The exception was:
ExitFailure 1

The strange thing about it (that I noticed) is that GHC reports  
failing during the building phase instead of the preprocessing phase.   
Maybe this is just an artifact of the logging system, but it seems  
like GHC is doing something strange.  If I increase the verbosity,  
(near the end) I get:


*** Haskell pre-processor:
trhsx src/HSP/HJScript.hs /tmp/ghc6345_0/ghc6345_6.hscpp /tmp/ 
ghc6345_0/ghc6345_0.hspp

*** Deleting temp files:
Deleting: /tmp/ghc6345_0/ghc6345_0.hspp /tmp/ghc6345_0/ 
ghc6345_6.hscpp /tmp/ghc6345_0/ghc6345_5.hscpp /tmp/ghc6345_0/ 
ghc6345_4.hscpp /tmp/ghc6345_0/ghc6345_3.hscpp /tmp/ghc6345_0/ 
ghc6345_2.hscpp /tmp/ghc6345_0/ghc6345_1.hscpp /tmp/ghc6345_0/ 
ghc6345_0.hscpp

Warning: deleting non-existent /tmp/ghc6345_0/ghc6345_0.hspp
*** Deleting temp dirs:
Deleting: /tmp/ghc6345_0
ghc: could not execute: trhsx
/usr/bin/ghc returned ExitFailure 1
cabal: Error: some packages failed to install:
hsp-0.4.5 failed during the building phase. The exception was:
ExitFailure 1


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[Haskell-cafe] Fwd: Mancoosi International Solver Competition

[Johannes Waldmann]

This looks interesting: an international competition 
of solvers for package/component installation and upgrade problems.
http://www.mancoosi.org/misc-2010/  (deadline: June 10)

Is the underlying package dependency model the same as cabal's?
If (nearly) so, then cabal's solver could enter the competition -
if it wins, then fine; if not, then it could be replaced by the winner :-)


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Re: [Haskell-cafe] Haddock infix constructors in markup

[Daniel Fischer]

Am Montag 26 April 2010 18:15:02 schrieb Ozgur Akgun:
> Hi all,
>
> If I have the following data type:
>
> data Expr = Num Int | Expr :+: Expr | Expr :-: Expr
>
> Haddock handles the infix constructors, and generates a very nice output
> (html in this case)
> However when I try to reference to one of the infix constructors in the
> markup of other functions it fails to hyperlink.
>
> -- | If the input is 'Num' does magic, if it is ':+:' does even more
> magic! someFunc :: Expr -> Expr
>
> In the output of this markup, the 'Num' is hyperlinked but the ':+:' is
> not. Is there a different syntax for infix constructors (and for infix
> functions presumably) or does haddock simple lack this feature?

Infix functions work fine (try referring to e.g. '&&' in the haddock 
comment), but infix constructors apparently not.

>
> Best,

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[Haskell-cafe] Haddock infix constructors in markup

[Ozgur Akgun]

Hi all,

If I have the following data type:

data Expr = Num Int | Expr :+: Expr | Expr :-: Expr

Haddock handles the infix constructors, and generates a very nice output
(html in this case)
However when I try to reference to one of the infix constructors in the
markup of other functions it fails to hyperlink.

-- | If the input is 'Num' does magic, if it is ':+:' does even more magic!
someFunc :: Expr -> Expr

In the output of this markup, the 'Num' is hyperlinked but the ':+:' is not.
Is there a different syntax for infix constructors (and for infix functions
presumably) or does haddock simple lack this feature?

Best,

-- 
Ozgur Akgun
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Re: [Haskell-cafe] Bulk Synchronous Parallel

[Thomas Horstmeyer]

Hi Aaron,

On 21.04.2010 20:29, Aaron D. Ball wrote:
> Unfortunately, Eden is one of the examples I had in mind when
> referring to distributed Haskell projects as overly complicated and
> [for practical purposes] dead.  Their last release available for
> download was in 2006.  Their beta is "available upon request", which
> doesn't raise my confidence in the level of active development or
> openness of the project.
>
You're partly right. The development of the Eden system itself has been 
neglected for a time. Mostly because Jost Berthold (the main system 
programmer) finished his PhD and left Marburg (and has only limited 
spare time with his new job). The remaining members of the Eden group 
here were mostly language users and language developers, not system 
implementors. No one really opted to take over responsibility...
However, this is changing right now. We are actively merging the Eden 
runtime and that of the GpH language (as both need basically the same 
features) to get a new runtime based on GHC 6.12 (and GHC HEAD). This 
runtime, while still in beta state, is already usable. However, building 
it is currently still a bit too complicated to bother end users with it. 
So, if your "complicated" is referring to this, you are right. We hope 
to simplify this and to have a usable release in the near future. If 
your "complicated" was targetting the use of the Eden language itself, 
however, I object!



>
>> They just had a hackathon in St Andrews,
>>
>> http://hackage.haskell.org/trac/ghc/wiki/HackPar
>
> they don't seem to have even a source code repository yet, and they
> appear to be bogged down in that complexity I mentioned.
>
Of course, a source code repository for Eden always existed. The new 
repository was meant for the merged version of Eden/GpH. And that exists 
as well. The Eden webpage will be updated as soon as we have a 
pre-release of the 6.12 branch.



Best regards,
Thomas Horstmeyer (Eden group Marburg)

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[Haskell-cafe] Order of arguments to GCC when building SDL on Windows with Cabal

[JP Moresmau]

Hello, I've been trying for a while to build the SDL haskell library
on windows. People have told me it worked for them, but I can't get to
work for the life of me. I have the latest Haskell Platform, I think
more or less the latest MINGW and MSYS tools. I'm on Windows 7 64
bits. I installed the SDL library without hassle, and the samples
work. It's only the haskell library that's bothering me. I've modified
the .cabal file as indicated for Windows (extra-include-dirs,
extra-lib-dirs), and runhaskell Setup configure. But then runhaskell
Setup build fails with:

Preprocessing library SDL-0.5.9...
dist\build\Graphics\UI\SDL\General_hsc_make.o:General_hsc_make.c:(.text
+0x29): m
ultiple definition of `main'
d:/dev/mingw/bin/../lib/gcc/mingw32/4.5.0/../../../
libmingw32.a(main.o):main.c:(
.text+0x0): first defined here
D:\dev\SDL-1.2.14\lib/libSDLmain.a(SDL_win32_main.o): In function
`console_main'
:
/Users/hercules/trunk/SDL-1.2/./src/main/win32/SDL_win32_main.c:315:
undefined r
eference to `SDL_main'
collect2: ld returned 1 exit status
linking dist\build\Graphics\UI\SDL\General_hsc_make.o failed
command was: d:\dev\MinGW\bin\gcc.exe -LD:\dev\SDL-1.2.14\lib -L/usr/
lib -lmingw
32 -lSDLmain -lSDL -mwindows -LD:\dev\haskell\HaskellPlatform
\2010.1.0.0\base-4.
2.0.0 -lwsock32 -luser32 -lshell32 -LD:\dev\haskell\HaskellPlatform
\2010.1.0.0\i
nteger-gmp-0.2.0.0 -LD:\dev\haskell\HaskellPlatform\2010.1.0.0\ghc-
prim-0.2.0.0
-LD:\dev\haskell\HaskellPlatform\2010.1.0.0 -LD:\dev\haskell
\HaskellPlatform\201
0.1.0.0/gcc-lib -lm -lwsock32 -LD:\dev\haskell\HaskellPlatform
\2010.1.0.0 dist\b
uild\Graphics\UI\SDL\General_hsc_make.o -o dist\build\Graphics\UI\SDL
\General_hs
c_make.exe

(I have the same error with the gcc inside the Haskell Platform, the
same error running in a windows shell without MSYS on the path, in the
MSYS bash with MSYS on the path).

And I figured out what's wrong with that line after thinking for a
while (as in, several days...): basically the line says something like
gcc sdl-flags file.o -o file.exe. If I revert the order of the
arguments and run gcc file.o -o file.exe sdl-flags, it works! The gcc
documentation explains that the libraries are searched in the order
they appear (http://gcc.gnu.org/onlinedocs/gcc/Link-Options.html), so
to put the libraries you depend on after the code that has the
dependencies. And I can see that building the SDL samples indeed puts
the .c file before the sdl linker flags. So this seems to be my
problem. What's the solution?
1. I've done something stupid or forgot some essential MINGW tool that
would make my system not dependent on the order of the arguments to
gcc? I've tried with gcc 3.4.5 and gcc 4.5.0, same result.
2. I can hack somewhere (where???) the command passed on to GCC when
building? Maybe some voodoo in the cabal file?
3. I can get runhaskell Setup build to only dump the commands it's
going to run, modify them in my favorite text editor and run them
manually (as said above, I've managed to create the first exe required
but build insists on rebuilding it even if present)
4. ...?

The fact that some people managed seem to point with a problem with my
config, but it's seems reasonnably clean to me, and I've even managed
to install wxWidgets and wxHaskell...

Any help appreciated!

-- 
JP Moresmau
http://jpmoresmau.blogspot.com/
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Re: [Haskell-cafe] Broken ghc documentation links

[Daniel Fischer]

Am Montag 26 April 2010 15:15:03 schrieb Ivan Lazar Miljenovic:
> Daniel Fischer  writes:
> > Am Montag 26 April 2010 13:36:22 schrieb Ivan Lazar Miljenovic:
> >> So, the problem is that there are broken links _in Hoogle_;
> >
> > No, hoogle just sends you to
> > http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Pre
> >lude.html#t%3AIO , which does exist. It's the 'Source' link in the
> > haddocks that sends you to the 404 Not Found.
> > It's the same with my local docs, I think it's haddock that got
> > confused by the move of the IO definition from base to ghc-prim.
>
> Yeah, as I've said I mis-read the initial problem (I've fielded a few
> queries recently regarding Hoogle not pointing to the 6.12.2 docs and
> initially thought this was another one).

Yes, I sent the reply before your second reply hit my inbox.
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[Haskell-cafe] maling-list manager in haskell?

[Günther Schmidt]

Hi,

is there a mailing-list manager written in haskell?

Best regards

Günther


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[Haskell-cafe] Re: ANNOUNCE: graphviz 2999.9.0.0

[Ivan Miljenovic]

A few things I forgot to mention in my haste to get this out:

1) I was planning on having a tutorial-style blog post where I'd use
graphviz to parse an manipulate the output "ghc-pkg dot"; however I've
been busier than I expected recently and figured it'd be better to get
this release out and do this later.

2) The website was developed with the help of John MacFarlane; at the
moment I'm using the CSS he uses for Pandoc's homepage, but I plan on
updating that during the week (again, better to get it out now and fix
it later).

And with that, I need to sleep.  Having a public holiday to get this
finished in was nice, but it didn't help with my sleep deprivation :s

On 26 April 2010 23:46, Ivan Lazar Miljenovic  wrote:
>
> I'm pleased to announce the latest version of my graphviz library that
> provides Haskell bindings to the Graphviz graph visualisation suite.
>
> There are numerous changes in this release, the most important of which
> are:
>
> * graphviz now has an FAQ and an improved README as well as its own
>  homepage: http://projects.haskell.org/graphviz/ (as prompted by Eric
>  Kow).
>
> * Add support for record labels; values are automatically
>  escaped/unescaped.  The `Record` and `MRecord` shapes have been
>  added for use with these labels.  Requested by Minh Thu and Eric
>  Kow.
>
> * Add support for HTML-like values (this replaces the wrong and
>  completely broken URL datatype).  Strings are automatically
>  escaped/unescaped.
>
> * Various parsing improvements (including a slight parsing speed
>  increase!).
>
> In particular, graphviz is now able to parse almost all Dot graphs found
> on my system (including samples shipped with Graphviz, Linux kernel
> documentation and various other package documentations).  A list of the
> breakages and why:
>
> * /usr/share/sgml/docbook/xsl-stylesheets/roundtrip/template.dot seems
>  to be a binary file and thus can't be read.
>
> * /usr/share/graphviz/graphs/directed/Latin1.gv uses Latin1 encoding; at
>  the moment graphviz uses the system's locale encoding (or whatever GHC
>  < 6.10 defaults to).
>
> * /usr/share/doc/boost-*/html/libs/graph/example/graphviz_test.dot
>  (various boost versions) has subgraphs in edges; graphviz currently
>  can't cope with these.
>
> * 
> /usr/src/linux-2.6.33-gentoo-r1/Documentation/blockdev/drbd/drbd-connection-state-overview.dot
>  uses incorrect syntax for the "minlen" attribute (it is meant to be an
>  integer but actually contains a floating point value).
>
> The plans for the next release (which I don't plan on even starting for
> a while) are to focus on improving printing and parsing performance,
> using a state-based printer and parser (as part of Dot syntax is
> state-based) and force usage of UTF-8 (via text or utf8-string).
>
> --
> Ivan Lazar Miljenovic
> ivan.miljeno...@gmail.com
> IvanMiljenovic.wordpress.com
>



-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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[Haskell-cafe] ANNOUNCE: graphviz 2999.9.0.0

[Ivan Lazar Miljenovic]

I'm pleased to announce the latest version of my graphviz library that
provides Haskell bindings to the Graphviz graph visualisation suite.

There are numerous changes in this release, the most important of which
are:

* graphviz now has an FAQ and an improved README as well as its own
  homepage: http://projects.haskell.org/graphviz/ (as prompted by Eric
  Kow).

* Add support for record labels; values are automatically
  escaped/unescaped.  The `Record` and `MRecord` shapes have been
  added for use with these labels.  Requested by Minh Thu and Eric
  Kow.

* Add support for HTML-like values (this replaces the wrong and
  completely broken URL datatype).  Strings are automatically
  escaped/unescaped.

* Various parsing improvements (including a slight parsing speed
  increase!).

In particular, graphviz is now able to parse almost all Dot graphs found
on my system (including samples shipped with Graphviz, Linux kernel
documentation and various other package documentations).  A list of the
breakages and why:

* /usr/share/sgml/docbook/xsl-stylesheets/roundtrip/template.dot seems
  to be a binary file and thus can't be read.

* /usr/share/graphviz/graphs/directed/Latin1.gv uses Latin1 encoding; at
  the moment graphviz uses the system's locale encoding (or whatever GHC
  < 6.10 defaults to).

* /usr/share/doc/boost-*/html/libs/graph/example/graphviz_test.dot
  (various boost versions) has subgraphs in edges; graphviz currently
  can't cope with these.

* 
/usr/src/linux-2.6.33-gentoo-r1/Documentation/blockdev/drbd/drbd-connection-state-overview.dot
 uses incorrect syntax for the "minlen" attribute (it is meant to be an
 integer but actually contains a floating point value).

The plans for the next release (which I don't plan on even starting for
a while) are to focus on improving printing and parsing performance,
using a state-based printer and parser (as part of Dot syntax is
state-based) and force usage of UTF-8 (via text or utf8-string).

--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] The instability of Haskell libraries

[John Goerzen]

On 04/25/2010 03:47 PM, Ivan Lazar Miljenovic wrote:

So you recommend having packages specifically for instances?

My main problem with this is if you want a custom variant of that
instance.  Let's take FGL graphs for example with instances for
QuickCheck's Arbitrary class.  Maybe you want arbitrary graphs that are
simple, or maybe multiple edges are fine.  Even when considering
Arbitrary instances for something like String you may wish to have a
custom variant that makes sense for what you're testing.

My conclusion: it is not possible to have hard-and-fast conclusions for
things like this :p


I'm inclined to agree.  As an example, there is the convertible library. 
 It grew out of the need to make an easy way to map Haskell to database 
types in HDBC, and these days is a more general way to convert from one 
type to another.  I provide a bunch of Convertible instances, but they 
are in separate modules, and thus can be omitted if a person doesn't 
want the instances.  As an example: what's the correct way to convert a 
Double to an Integer?  As an example, Prelude defines at least 4: 
ceiling, floor, truncate, and round.


Now, in a certain sense, Convertible is designed for people that don't 
care which is used.  (And yes, that is a perfectly valid answer in some 
cases.)  But if you want your own, you can simply not import the numeric 
Convertible instances.


It would, however, be nice if the language allowed you to override 
default instances with the code in your own package.


-- John
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[Haskell-cafe] Installing ghc in an OpenSolaris Zone

[Günther Schmidt]

Hello,

has anyone yet managed to install ghc (6.10.4) into an OpenSolaris zone?

Günther


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Re: [Haskell-cafe] Broken ghc documentation links

[Ivan Lazar Miljenovic]

Daniel Fischer  writes:

> Am Montag 26 April 2010 13:36:22 schrieb Ivan Lazar Miljenovic:
>> So, the problem is that there are broken links _in Hoogle_;
>
> No, hoogle just sends you to 
> http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Prelude.html#t%3AIO
> , which does exist. It's the 'Source' link in the haddocks that sends you 
> to the 404 Not Found.
> It's the same with my local docs, I think it's haddock that got confused by 
> the move of the IO definition from base to ghc-prim.

Yeah, as I've said I mis-read the initial problem (I've fielded a few
queries recently regarding Hoogle not pointing to the 6.12.2 docs and
initially thought this was another one).

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] and [] = True; or [] = False

[Bjorn Buckwalter]

Ok Guys, you've convinced me thrice within ten minutes of posing my
question. The quality of the mailing list is just ridiculous! ;)

And Miguel, thanks for the follow-up regarding "for all" and "exists"
– it's an excellent analogy and easy to remember!


On Mon, Apr 26, 2010 at 20:23, Jochem Berndsen  wrote:
> Bjorn Buckwalter wrote:
>> Dear all,
>>
>> Does it make good sense that 'and []' returns 'True' and 'or []'
>> returns 'False'? The Haskell Road to Logic, Maths and Programming says
>> so:
>>
>> "The function or takes a list of truth values and returns True if at
>> least one member of the list equals True, while and takes a list of
>> truth values and returns True if all members of the list equal True."
>>
>> "Should the conjunction of all elements of [] count as true or false?
>> As true, for it is indeed (trivially) the case that all elements of []
>> are true. So the identity element for conjunction is True. Should the
>> disjunction of all elements of [] count as true or false? As false,
>> for it is false that [] contains an element which is true. Therefore,
>> the identity element for disjunction is False."
>>
>> While the above reasoning is fine, and allows straight-forward
>> implementations, it isn't extremely convincing. In particular, it
>> isn't clear that, while simple, the definitions of the first paragraph
>> are the most sensible. Perhaps one of the more mathematically versed
>> readers on the Cafe could enlighten me?
>
> The empty sum is regarded to be zero. The empty product is equal to one.
> The empty conjunction is True. The empty disjunction is False.
>
> The reason for this is that these are the neutral elements, i.e.
>  0 + x = x
>  1 * x = x
>  True AND x = x
>  False OR x = x
>
> This allows some laws to hold also in degenerate cases, and it is quite
> useful in general to accept these conventions. An example of such a law is
> (∀ x : x ∈ A : P(x)) ∧ (∀ x : x ∈ B : P(x))
>  ==
> (∀ x : x ∈ A ∪ B : P(x)).
>
> This also works if A or B is empty, provided that we say that the empty
> conjunction is true.
>
> In Haskell, we now have that
>
> (and xs) && (and ys)
>  ==
> and (xs ++ ys),
>
> even if xs or ys is the empty list.
>
> Cheers, Jochem
> --
> Jochem Berndsen | joc...@functor.nl
>
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Re: [Haskell-cafe] and [] = True; or [] = False

[Neil Brown]

Bjorn Buckwalter wrote:

Dear all,

Does it make good sense that 'and []' returns 'True' and 'or []'
returns 'False'? 
It's certainly what I would expect it to do, based on several ways of 
thinking.


1: If we define the function using explicit recursion:
and (x:xs) = x && and xs
Therefore and [] has to be True.  Similar logic for or.

2: My instinct is to consider "and = all (== True)", while "or = any (== 
True)".  It's even clearer to me that "all [] = True" and "any [] = 
False" (similiar to Miguel's post).


Thanks,

Neil.
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Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?

[Ivan Lazar Miljenovic]

Bjorn Buckwalter  writes:
> So what would be the fix, to set an upper bound on base?

The fix is to have the maintainer check whether or not the package
builds with base-4 (you can do this the old manual way using runhaskell
Setup.hs).  If it does, then specify that it does so, e.g.:

  base < 5

The upper bound is needed (and Hackage now enforces this) because too
many packages have this same problem: the maintainers blindly assume
that the package will build for all time, and then it dies the next time
a new major version of the base package is released.  Note that some
people cheat by having dependencies like "base < 10" as Hackage will
accept this because there is indeed an upper bound, but this just causes
problems in the future (Don Stewart had "base < 5" for a release of
ghc-core which then failed to build with base-4).

> Is the general recommendation that all packages should specify upper
> bounds on all dependencies (if so why doesn't Cabal tell us?)?

This is the eventual goal and is why Duncan Coutts is pushing the
Package Versioning Policy
(http://www.haskell.org/haskellwiki/Package_versioning_policy) as you
can tell from the version (if it is followed correctly) when the API has
changed in a backwards-incompatible fashion.

At the moment, however, Hackage - not Cabal - enforces the requirement
on the base package for all new packages uploaded.  This isn't made
compulsory for all package dependencies as 1) it is base dependencies
that typically cause most of the breakages and 2) not all packages
follow the PVP and thus doing this doesn't always make sense (e.g. some
packages use a date-based versioning system for some reason).

> I can see that this would make some sense as a package might be broken
> by an API change in its dependencies. On the other hand I can also see
> it causing headaches occasionally...

Right, see the recent thread started by John Goerzon "The instability of
Haskell libraries" which is in part to do with this problem.  At the
moment when a dependency has a major version update but is still
buildable by your package you have to create a new release to let it use
that updated dependency, which is a pain and isn't always done promptly
by maintainers.  Possibly the best way towards fixing this is the
proposal to take the Cabal files outside of the tarballs and distribute
them separately; that way they can be edited without affecting the
tarball in question (thus making them even more like Gentoo's ebuild or
Arch's PKGBUILD files).

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?

[Daniel Fischer]

Am Montag 26 April 2010 14:32:03 schrieb Bjorn Buckwalter:
>
> So what would be the fix, to set an upper bound on base? Is the
> general recommendation that all packages should specify upper bounds
> on all dependencies (if so why doesn't Cabal tell us?)?

Yes, that's the general recommendation. (upper and lower bounds)

> I can see that
> this would make some sense as a package might be broken by an API
> change in its dependencies.

Exactly. That's why bounds on the versions of the dependencies are a good 
thing.

> On the other hand I can also see it
> causing headaches occasionally...

Yes, but probably less headaches than packages eternally breaking because 
of API changes in the dependencies.

>
> Thanks,
> Bjorn

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Re: [Haskell-cafe] and [] = True; or [] = False

[Miguel Mitrofanov]

Forgot about this one:

Bjorn Buckwalter wrote:

What got me thinking about this was the apparently incorrect intuition
that 'and xs' would imply 'or xs'.



No. See, "and" is very close to "for all", and "or" is similarly close to "exists". For example, the statement "all crows are black" means just "this crow is black AND this one too AND another one on 
the tree is also black AND..." etc.


Now, obviously, all real dragons can fly. But it doesn't mean there is such thing as a 
"real dragon".
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Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?

[Bjorn Buckwalter]

On Mon, Apr 26, 2010 at 20:07, Ivan Lazar Miljenovic
 wrote:
> Bjorn Buckwalter  writes:
>
>> On Mon, Apr 26, 2010 at 19:38, Ivan Lazar Miljenovic
>>  wrote:
>>> Bjorn Buckwalter  writes:
 Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when
 installing packages with an unqualified base requirement? Example:
>>>
>>> [snip]
>>>
>>> The reason that base-3 is chosen is because many of these old
>>> libraries won't build with base-4; as such, if no upper bound
>>> restriction is found on the base package then base-3 is chosen as it
>>> is more likely to work than base-4 (there were a _lot_ of breakages
>>> when base-4 first came out with 6.10.1).
>>
>> I see, I guess that's pragmatic although the deprecation warning is
>> unfortunate.
>
> The deprecation warning is due to GHC 6.12; this is a not-so-subtle hint
> to package maintainers to fix their code up, and to users to poke the
> maintainers of packages they use to do so!

Understood, but in this case the warning seems misdirected since fad
does not restrict itself to base-3.*...

So what would be the fix, to set an upper bound on base? Is the
general recommendation that all packages should specify upper bounds
on all dependencies (if so why doesn't Cabal tell us?)? I can see that
this would make some sense as a package might be broken by an API
change in its dependencies. On the other hand I can also see it
causing headaches occasionally...

Thanks,
Bjorn
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Re: [Haskell-cafe] and [] = True; or [] = False

[Daniel Fischer]

Am Montag 26 April 2010 14:15:40 schrieb Bjorn Buckwalter:
> Dear all,
>
> Does it make good sense that 'and []' returns 'True' and 'or []'
> returns 'False'? The Haskell Road to Logic, Maths and Programming says
> so:
>
> "The function or takes a list of truth values and returns True if at
> least one member of the list equals True, while and takes a list of
> truth values and returns True if all members of the list equal True."
>
> "Should the conjunction of all elements of [] count as true or false?
> As true, for it is indeed (trivially) the case that all elements of []
> are true. So the identity element for conjunction is True. Should the
> disjunction of all elements of [] count as true or false? As false,
> for it is false that [] contains an element which is true. Therefore,
> the identity element for disjunction is False."
>
> While the above reasoning is fine, and allows straight-forward
> implementations, it isn't extremely convincing. In particular, it
> isn't clear that, while simple, the definitions of the first paragraph
> are the most sensible. Perhaps one of the more mathematically versed
> readers on the Cafe could enlighten me?

It's necessary for

and (xs ++ ys) == and xs && and ys

and

or (xs ++ ys) == or xs || or ys

It's the same reason why sum [] == 0 and product [] == 1.

>
> What got me thinking about this was the apparently incorrect intuition
> that 'and xs' would imply 'or xs'.

Unless xs is empty

>
> Thanks,
> Bjorn

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Re: [Haskell-cafe] and [] = True; or [] = False

[Miguel Mitrofanov]

Well, what's the sum of an empty list? Seems naturally that it's 0, but why?

Let's say that sum [] = x.

If we take two lists, say, l1 = [1,2,3] and l2 = [4,5], then

sum l1 + sum l2 = 6 + 9 = 15 = sum [1,2,3,4,5] = sum (l1 ++ l2)

We expect it to be the case even if one of the lists is empty, so

x + 9 = sum [] + sum l2 =  = sum ([] ++ l2) = sum l2 = 9

Therefore, x = 0.

With "and" we have the same thing:

and [] = x

Let l1 = [True, True], l2 = [True, False]

and l1 && and l2 = True && False = False = and [True, True, True, False] = and 
(l1 ++ l2)

x && True = and [] && and l1 =  = and ([] ++ l1) = and l1 = True

Therefore, x = True.

Bjorn Buckwalter wrote:

Dear all,

Does it make good sense that 'and []' returns 'True' and 'or []'
returns 'False'? The Haskell Road to Logic, Maths and Programming says
so:

"The function or takes a list of truth values and returns True if at
least one member of the list equals True, while and takes a list of
truth values and returns True if all members of the list equal True."

"Should the conjunction of all elements of [] count as true or false?
As true, for it is indeed (trivially) the case that all elements of []
are true. So the identity element for conjunction is True. Should the
disjunction of all elements of [] count as true or false? As false,
for it is false that [] contains an element which is true. Therefore,
the identity element for disjunction is False."

While the above reasoning is fine, and allows straight-forward
implementations, it isn't extremely convincing. In particular, it
isn't clear that, while simple, the definitions of the first paragraph
are the most sensible. Perhaps one of the more mathematically versed
readers on the Cafe could enlighten me?

What got me thinking about this was the apparently incorrect intuition
that 'and xs' would imply 'or xs'.

Thanks,
Bjorn
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Re: [Haskell-cafe] and [] = True; or [] = False

[Jochem Berndsen]

Bjorn Buckwalter wrote:
> Dear all,
> 
> Does it make good sense that 'and []' returns 'True' and 'or []'
> returns 'False'? The Haskell Road to Logic, Maths and Programming says
> so:
> 
> "The function or takes a list of truth values and returns True if at
> least one member of the list equals True, while and takes a list of
> truth values and returns True if all members of the list equal True."
> 
> "Should the conjunction of all elements of [] count as true or false?
> As true, for it is indeed (trivially) the case that all elements of []
> are true. So the identity element for conjunction is True. Should the
> disjunction of all elements of [] count as true or false? As false,
> for it is false that [] contains an element which is true. Therefore,
> the identity element for disjunction is False."
> 
> While the above reasoning is fine, and allows straight-forward
> implementations, it isn't extremely convincing. In particular, it
> isn't clear that, while simple, the definitions of the first paragraph
> are the most sensible. Perhaps one of the more mathematically versed
> readers on the Cafe could enlighten me?

The empty sum is regarded to be zero. The empty product is equal to one.
The empty conjunction is True. The empty disjunction is False.

The reason for this is that these are the neutral elements, i.e.
  0 + x = x
  1 * x = x
  True AND x = x
  False OR x = x

This allows some laws to hold also in degenerate cases, and it is quite
useful in general to accept these conventions. An example of such a law is
(∀ x : x ∈ A : P(x)) ∧ (∀ x : x ∈ B : P(x))
 ==
(∀ x : x ∈ A ∪ B : P(x)).

This also works if A or B is empty, provided that we say that the empty
conjunction is true.

In Haskell, we now have that

(and xs) && (and ys)
 ==
and (xs ++ ys),

even if xs or ys is the empty list.

Cheers, Jochem
-- 
Jochem Berndsen | joc...@functor.nl
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[Haskell-cafe] and [] = True; or [] = False

[Bjorn Buckwalter]

Dear all,

Does it make good sense that 'and []' returns 'True' and 'or []'
returns 'False'? The Haskell Road to Logic, Maths and Programming says
so:

"The function or takes a list of truth values and returns True if at
least one member of the list equals True, while and takes a list of
truth values and returns True if all members of the list equal True."

"Should the conjunction of all elements of [] count as true or false?
As true, for it is indeed (trivially) the case that all elements of []
are true. So the identity element for conjunction is True. Should the
disjunction of all elements of [] count as true or false? As false,
for it is false that [] contains an element which is true. Therefore,
the identity element for disjunction is False."

While the above reasoning is fine, and allows straight-forward
implementations, it isn't extremely convincing. In particular, it
isn't clear that, while simple, the definitions of the first paragraph
are the most sensible. Perhaps one of the more mathematically versed
readers on the Cafe could enlighten me?

What got me thinking about this was the apparently incorrect intuition
that 'and xs' would imply 'or xs'.

Thanks,
Bjorn
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Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?

[Ivan Lazar Miljenovic]

Bjorn Buckwalter  writes:

> On Mon, Apr 26, 2010 at 19:38, Ivan Lazar Miljenovic
>  wrote:
>> Bjorn Buckwalter  writes:
>>> Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when
>>> installing packages with an unqualified base requirement? Example:
>>
>> [snip]
>>
>> The reason that base-3 is chosen is because many of these old
>> libraries won't build with base-4; as such, if no upper bound
>> restriction is found on the base package then base-3 is chosen as it
>> is more likely to work than base-4 (there were a _lot_ of breakages
>> when base-4 first came out with 6.10.1).
>
> I see, I guess that's pragmatic although the deprecation warning is
> unfortunate.

The deprecation warning is due to GHC 6.12; this is a not-so-subtle hint
to package maintainers to fix their code up, and to users to poke the
maintainers of packages they use to do so!

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Broken ghc documentation links

[Daniel Fischer]

Am Montag 26 April 2010 13:36:22 schrieb Ivan Lazar Miljenovic:
> So, the problem is that there are broken links _in Hoogle_;

No, hoogle just sends you to 
http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Prelude.html#t%3AIO
, which does exist. It's the 'Source' link in the haddocks that sends you 
to the 404 Not Found.
It's the same with my local docs, I think it's haddock that got confused by 
the move of the IO definition from base to ghc-prim.

> have you
> thought about contacting the author Neil Mitchell directly?
>
> "hask...@kudling.de"  writes:
> > To reproduce:
> >
> > 1) Look for "data IO" on Hoogle, e.g.
> > http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude
> >.html#t%3AIO
> >
> > 2) Click "source", which redirects to
> > http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/GHC
> >-Types.html#IO
> >
> > 3) Observe a "Not Found" page
> >
> > Is there anyone interested in fixing this?

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Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?

[Bjorn Buckwalter]

On Mon, Apr 26, 2010 at 19:38, Ivan Lazar Miljenovic
 wrote:
> Bjorn Buckwalter  writes:
>> Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when
>> installing packages with an unqualified base requirement? Example:
>
> You mean cabal-install rather than Cabal.  The reason that base-3 is
> chosen is because many of these old libraries won't build with base-4;
> as such, if no upper bound restriction is found on the base package then
> base-3 is chosen as it is more likely to work than base-4 (there were a
> _lot_ of breakages when base-4 first came out with 6.10.1).

I see, I guess that's pragmatic although the deprecation warning is unfortunate.

(I'm aware of the cabal-install versus Cabal distinction, but I
understand that cabal-install uses Cabal to resolve dependencies; thus
I assumed Cabal was the culprit.)

Thanks,
Bjorn


>> $ cabal install -v fad --reinstall
>> [snip]
>> Resolving dependencies...
>> selecting fad-1.0 (hackage)
>> selecting base-3.0.3.2 (installed) and 4.2.0.0 (installed) and discarding
>> syb-0.1.0.0, 0.1.0.1, 0.1.0.2, 0.1.0.3, 0.2 and 0.2.1
>> [snip]
>> Configuring fad-1.0...
>> Dependency base ==3.0.3.2: using base-3.0.3.2
>> [snip]
>> [1 of 1] Compiling Numeric.FAD      ( Numeric/FAD.hs, 
>> dist/build/Numeric/FAD.o )
>>
>> Numeric/FAD.hs:1:0:
>>     Warning: Module `Prelude' is deprecated:
>>                You are using the old package `base' version 3.x.
>>                Future GHC versions will not support base version 3.x. You
>>                should update your code to use the new base version 4.x.
>> [snip]
>>
>
> --
> Ivan Lazar Miljenovic
> ivan.miljeno...@gmail.com
> IvanMiljenovic.wordpress.com
>
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Re: [Haskell-cafe] Broken ghc documentation links

[Ivan Lazar Miljenovic]

"hask...@kudling.de"  writes:
> While the URL http://www.haskell.org/hoogle/ contains the word "Hoogle", the 
> URL
> http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude.html#t%3AIO
> does not and it does no mention "Hoogle" on the page either.
> 
> How did you determine that the latter is related to Hoogle?

Oh, sorry, I misunderstood what you were doing; I thought the actual
link you got from Hoogle was wrong (since a lot of people recently have
been complaining that Hoogle should now point to the 6.12.2
documentation).

In this case, you should talk to GHC maintainers.

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Fwd: Re: [Haskell-cafe] Broken ghc documentation links

[hask...@kudling.de]

FYI
 

-- Ursprüngliche Nachricht --
Von: "hask...@kudling.de" 
An: Ivan Lazar Miljenovic 
Cc: Neil Mitchell 
Datum: 26. April 2010 um 13:45
Betreff: Re: [Haskell-cafe] Broken ghc documentation links

Hi,
 
> So, the problem is that there are broken links _in Hoogle_; have you
> thought about contacting the author Neil Mitchell directly?
 
While the URL http://www.haskell.org/hoogle/ contains the word "Hoogle", the URL
http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude.html#t%3AIO
does not and it does no mention "Hoogle" on the page either.
 
How did you determine that the latter is related to Hoogle?
 
Bye,
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Re: [Haskell-cafe] Ada-style ranges

[Steffen Schuldenzucker]

On 04/26/2010 12:50 PM, hask...@kudling.de wrote:
> 
> 
> Hi list,
> 
>  
> 
> how would you describe Ada's ranges in Haskell's typesystem?
> 
> http://en.wikibooks.org/wiki/Ada_Programming/Types/range

Hi Lenny,

can non-constant expressions be given as arguments to 'range'? If not, then
what about a opaque wrapper type?

{-# LANGUAGE GeneralizedNewtypeDeriving #-}

module Range1 (Range1, fromRange1, mkBounded, mkRange1) where

newtype Range1 = Range1 { fromRange1 :: Integer }
deriving (Eq, Num, Ord, Show)

instance Bounded Range1 where
minBound = Range1 $ -5
maxBound = Range1 $ 10

mkBounded :: (Bounded a, Ord a) => (b -> a) -> b -> Maybe a
mkBounded f x = case f x of
y | minBound <= y && y <= maxBound -> Just y
  | otherwise  -> Nothing

mkRange1 ::  Integer -> Maybe Range1
mkRange1 = mkBounded Range1

-- Steffen
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Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?

[Ivan Lazar Miljenovic]

Bjorn Buckwalter  writes:
> Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when
> installing packages with an unqualified base requirement? Example:

You mean cabal-install rather than Cabal.  The reason that base-3 is
chosen is because many of these old libraries won't build with base-4;
as such, if no upper bound restriction is found on the base package then
base-3 is chosen as it is more likely to work than base-4 (there were a
_lot_ of breakages when base-4 first came out with 6.10.1).

>
>
> $ cabal install -v fad --reinstall
> [snip]
> Resolving dependencies...
> selecting fad-1.0 (hackage)
> selecting base-3.0.3.2 (installed) and 4.2.0.0 (installed) and discarding
> syb-0.1.0.0, 0.1.0.1, 0.1.0.2, 0.1.0.3, 0.2 and 0.2.1
> [snip]
> Configuring fad-1.0...
> Dependency base ==3.0.3.2: using base-3.0.3.2
> [snip]
> [1 of 1] Compiling Numeric.FAD  ( Numeric/FAD.hs, 
> dist/build/Numeric/FAD.o )
>
> Numeric/FAD.hs:1:0:
> Warning: Module `Prelude' is deprecated:
>You are using the old package `base' version 3.x.
>Future GHC versions will not support base version 3.x. You
>should update your code to use the new base version 4.x.
> [snip]
>

-- 
Ivan Lazar Miljenovic
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IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Broken ghc documentation links

[Ivan Lazar Miljenovic]

So, the problem is that there are broken links _in Hoogle_; have you
thought about contacting the author Neil Mitchell directly?

"hask...@kudling.de"  writes:

> To reproduce:
> 
> 1) Look for "data IO" on Hoogle, e.g.
> http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude.html#t%3AIO
>
> 2) Click "source", which redirects to
> http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/GHC-Types.html#IO
> 
> 3) Observe a "Not Found" page
> 
> Is there anyone interested in fixing this?


-- 
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ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] What do _you_ want to see in FGL?

[Ivan Lazar Miljenovic]

Stephen Tetley  writes:
> What would your thoughts be on freezing FGL as it is and putting
> changes into a new package "FGL2" or "NewFGL"?

That's another possibility.  However, I was planning on keeping the
fundamental layout and design of FGL.  I quite like and have used the
inductive approach of graph construction/deconstruction in my own code;
I just plan on updating/modernising the layout and design (after all,
large all-in-one packages are _so_ pre-Hackage :p).

Whilst freezing it is an option, I feel that this will lead to the same
problems that we already face with mtl: most people agree/know that the
approach/design is bad, but we keep using it because there's no (one)
viable alternative to be used (and thus mtl stays in the Platform, which
means more people use it, and thus we have this vicious cycle).  By
using the same name we can break this cycle: there is no implicit
"loyalty" to an old package that people still use because its familiar
(of course, this leaves it open to the problems with QuickCheck and
Parsec, yet they are being resolved and more and more people are moving
to QuickCheck-2 and Parsec-3).

> The implementation technique for FGL is independently interesting;
> Martin Erwig expanded on it in other papers ('Metamorphic
> Programming') but no one else seems to have picked up on it. As I
> think there is more mileage in the idiom and hopefully someone will
> pick up on it at some point, it would be nice if it survives in the
> code.

Hmmm I haven't come across "Metamorphic Programming" before, will
have to have a read through it (which isn't that appealing at the
moment, since I'm in the middle of the literature review section of my
PhD :s).

-- 
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[Haskell-cafe] Re: Unicode strings and runCommand / runProcess

[S. Astanin]

> > >> Actually, the behavior of openFile when given a String with characters >
> > >> 0xFF is also completely undocumented.  I am not sure what it does with
> > >> that.  It should probably be the same as runCommand, whatever it is.

Actually, the behaviour of openFile is known to be platform-dependent.
According to Simon Marlow,

> Be careful with FilePaths. On Windows they are interpreted as Unicode,
> on Unix they are interpreted as [Word8], by taking the low 8 bits of
> each Char. So if you always encode FilePaths to UTF-8, that will break
> on Windows. Fixing FilePaths is a high priority.

The last sentence gives me some hope.

http://ghcmutterings.wordpress.com/2009/09/30/heads-up-what-you-need-to-know-about-unicode-io-in-ghc-6-12-1/#comment-61

> But truncation makes impossible to pass non ASCII strings portably. They
> should be encoded there is no easy way to do so.
>
> Actually problem is use of strings. String is sequence of _characters_ and
> program talk to outside world using sequence of bytes. I think that right (but
> impossible) way to solve this problem is to use separate data types for file
> path, command line arguments.

I think that Strings should be used _only_ for characters (code
points).
Using the same data type for encoded/truncated data is dangerous. Most
of the
current problems with Unicode is due to the fact that Strings could
turn
out to be anything (are not strictly typed from this point of view).
Hence, the runtime checks and hacks like isUTF8Encoded :: String ->
Bool,
encodeString :: String -> String and decodeString :: String ->
String...

So I absolutely support that truncating is wrong. Expecting encoded
data
in Strings is wrong too. So the only option (except changing the
standard library and introducing a new type for FilePath), is to do
all
necessary conversions inside openFile and similar functions.

> I think there are two alternatives. One is to encode/decode strings using
> current locale and provide [Word8] based variants. Main problem is that
> seeming innocent actions like getting directory content could crash program
> (exception )

Actually, any IO action is unpredictible. So trying to get directory
contents can produce an error (for various reasons, e.g. permission
denied). If it reports an error when there are filenames not
presentable
in the current locale (e.g. contain invalid UTF-8 sequences in UTF-8
locale), the problem is likely to be the wrong locale settings. What's
the
problem with an exception?

I think [Word8] variants for those who wants to deal with such cases
(guess file system encoding etc.) is enough.

> Another options is to provide function to encode/decode strings. This is ugly
> and mix strings which hold characters and string which hold bytes and
> completely unhaskellish but it seems there is no good solution.

This is ugly, because it's impossible to know if a String is already
encoded or not. This is ugly because application code will be polluted
with conditional compilation to be cross-platform (or worse, people
will
forget to write cross-platform code in _some_ cases).

> Also truncation could have security implications. It makes almost impossible
> to escape dangerous characters robustly. Consider following code. This is more
> matter of speculations than real threat but nevertheless:

Nice example. It shows that escaping should be the last step.

S.
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[Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?

[Bjorn Buckwalter]

Dear all,

Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when
installing packages with an unqualified base requirement? Example:


$ cabal install -v fad --reinstall
[snip]
Resolving dependencies...
selecting fad-1.0 (hackage)
selecting base-3.0.3.2 (installed) and 4.2.0.0 (installed) and discarding
syb-0.1.0.0, 0.1.0.1, 0.1.0.2, 0.1.0.3, 0.2 and 0.2.1
[snip]
Configuring fad-1.0...
Dependency base ==3.0.3.2: using base-3.0.3.2
[snip]
[1 of 1] Compiling Numeric.FAD  ( Numeric/FAD.hs, dist/build/Numeric/FAD.o )

Numeric/FAD.hs:1:0:
Warning: Module `Prelude' is deprecated:
   You are using the old package `base' version 3.x.
   Future GHC versions will not support base version 3.x. You
   should update your code to use the new base version 4.x.
[snip]


Thanks,
Bjorn
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[Haskell-cafe] Ada-style ranges

[hask...@kudling.de]

Hi list,
 
how would you describe Ada's ranges in Haskell's typesystem?
http://en.wikibooks.org/wiki/Ada_Programming/Types/range
 
I feel, you can not because this is a runtime property.
 
Bye,
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[Haskell-cafe] Broken ghc documentation links

[hask...@kudling.de]

To reproduce:
 
1) Look for "data IO" on Hoogle, e.g.
http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude.html#t%3AIO

2) Click "source", which redirects to
http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/GHC-Types.html#IO
 
3) Observe a "Not Found" page
 
Is there anyone interested in fixing this?
 
Bye,
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RE: [Haskell-cafe] London HUG domain expired

[Bayley, Alistair]

> From: sefer@gmail.com [mailto:sefer@gmail.com] On 
> Behalf Of Yitzchak Gale
> 
> On Fri, Apr 23, 2010 at 1:24 PM, Bayley, Alistair wrote:
> > Looks like the London HUG domain (londonhug.net) registration has
> > expired. Neil Bartlett was the registrant.
> > Neil: do you plan to renew?
> 
> The whois database reports:
> > Domain name: LONDONHUG.NET
> > This domain name is up for auction for a limited time.
> > To place a bid, visit: http://www.namejet.com
> 
> And it appears that someone has already placed a $75 bid.
> 
> The domain should be renewed promptly, before the grace
> period expires.

Probably the best option, but can anyone other than Neil do this?

If not, does anyone know if Neil is reachable? (could try his phone
number listed in the whois record, but that seems a little invasive).

Alistair
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Re: [Haskell-cafe] What do _you_ want to see in FGL?

[Stephen Tetley]

Hello Ivan

What would your thoughts be on freezing FGL as it is and putting
changes into a new package "FGL2" or "NewFGL"?

The implementation technique for FGL is independently interesting;
Martin Erwig expanded on it in other papers ('Metamorphic
Programming') but no one else seems to have picked up on it. As I
think there is more mileage in the idiom and hopefully someone will
pick up on it at some point, it would be nice if it survives in the
code.

Best wishes

Stephen
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[Haskell-cafe] happstack/SOAP

[Johannes Waldmann]

Hi - I'm looking for an example/demo happstack server 
that handles SOAP requests. - Thanks, J.W.



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[Haskell-cafe] Re: What do _you_ want to see in FGL?

[Christian Maeder]

Ivan Lazar Miljenovic schrieb:
>> I would vote against these experimental features like associated types
>> or MPTC and FD.  I prefer plain type parameters for data types, but
>> that does not fit well together with type classes.
> 
> Why don't you like extensions?  I used to feel the same way, but then
> someone pointed out to me that just because Haskell98 doesn't have them
> doesn't mean they aren't good/useful, and we should be coding for
> _modern_ Haskell.

My feeling is, that the last words about fancy type class extension are
not spoken yet. Already the simple classes have disadvantages (wrt
multiple instances), that i.e. parameterized modules solve differently
(but maybe also not good enough, yet).

Parametrized data types, hofs, purity, etc. are proven concepts also
found in other functional languages that I prefer to stick to.

Cheers Christian
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Re: [Haskell-cafe] What do _you_ want to see in FGL?

[Neil Brown]

Hi,

Primarily I want to see in FGL: documentation, documentation and more 
documentation.  The library has lots of undocumented functions 
(especially the queries, e.g. 
http://hackage.haskell.org/packages/archive/fgl/5.4.2.2/doc/html/Data-Graph-Inductive-Query-DFS.html 
has no documentation at all), and the only reference is the original 
paper.  I've seen several people who didn't read the paper (or didn't 
read the right bits) get confused by the inductive way the graph is 
constructed, when they try to de-construct it.


I would also like to see the library reduced in size/scope if possible; 
there's a lot of modules in FGL, but all I've ever used are D.G.I.Graph, 
D.G.I.Tree, D.G.I.Graphviz and D.G.I.Query.DFS.  I consider this to 
probably be the most common usage of the library by others too (if you 
throw in D.G.I.Query.BFS).  So by the sounds of it, if you split 
Graphviz and Query off to separate libraries, I probably only use the 
core module.


Ivan Lazar Miljenovic wrote:

Here are some ideas that I have regarding FGL:

* Better fundamental data structures: one of the things that has always
  annoyed me about FGL is how much it uses tuples; I propose re-defining
  the Context type to be a record-based data structure.  Also, usage of
  Sets, Maps, etc. where applicable.
  
I think this is worth doing, even if it does break code.  If you're 
doing Context, you may as well do LNode and LEdge too.



* Data.Graph.Inductive.Monad: does anyone actually use this?
  
No, now that I look at it, it's not what I would expect.  It seems to be 
a lot of operations that could be constructed by sticking liftM before 
the normal operations.  For example:


nodesM :: GraphM m gr => m (gr a b) -> m [Node]

I would have thought the useful operations for graphs and monads would 
have been something more like:


nodesM :: GraphM m gr => gr (m a) (m b) -> m [Node]

On that node, I would like to see some instances for the graph types: 
particularly Functor, Foldable and Traversable, for both (Gr a) and 
(Flip Gr b) -- where Flip is 
http://hackage.haskell.org/packages/archive/TypeCompose/latest/doc/html/Control-Compose.html#t:Flip 
or 
http://hackage.haskell.org/packages/archive/category-extras/latest/doc/html/Control-Functor-Combinators-Flip.html


If you put FGL in a repository somewhere, I might be able to find some 
time to write those instances and perhaps contribute a bit of 
documentation (no promises, though!).


Thanks,

Neil.

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[Haskell-cafe] Re: What do _you_ want to see in FGL?

[Ivan Lazar Miljenovic]

Christian Maeder  writes:

> Ivan Lazar Miljenovic schrieb:
>> - Having a separate parameter (using associated types?) for the node
>>   type rather than just using Int.
>
> "Just Int" for nodes was disappointing. It should have been at least a
> "newtype". 

This then loses you all of the advantages of using Int (pre-defined data
type with known space usage, ordering, etc. and the ability to use
IntMap and IntSet which out-perform the normal ones).

> I would vote against these experimental features like associated types
> or MPTC and FD.  I prefer plain type parameters for data types, but
> that does not fit well together with type classes.

Why don't you like extensions?  I used to feel the same way, but then
someone pointed out to me that just because Haskell98 doesn't have them
doesn't mean they aren't good/useful, and we should be coding for
_modern_ Haskell.

>> * Better fundamental data structures: one of the things that has always
>>   annoyed me about FGL is how much it uses tuples; I propose re-defining
>>   the Context type to be a record-based data structure.  Also, usage of
>>   Sets, Maps, etc. where applicable.
>
> Right, these tuples annoyed me, too. (If this changes, it will break a
> lot of our existing code, though.)

All of my proposals will break existing code though, but I believe for
the better.  We can't be afraid to innovate/change our libraries,
otherwise they can't improve.

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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[Haskell-cafe] Re: What do _you_ want to see in FGL?

[Christian Maeder]

Ivan Lazar Miljenovic schrieb:
> - Having a separate parameter (using associated types?) for the node
>   type rather than just using Int.

"Just Int" for nodes was disappointing. It should have been at least a
"newtype". I would vote against these experimental features like
associated types or MPTC and FD.
I prefer plain type parameters for data types, but that does not fit
well together with type classes.

> * Better fundamental data structures: one of the things that has always
>   annoyed me about FGL is how much it uses tuples; I propose re-defining
>   the Context type to be a record-based data structure.  Also, usage of
>   Sets, Maps, etc. where applicable.

Right, these tuples annoyed me, too. (If this changes, it will break a
lot of our existing code, though.)

I also did not like the list of links, that let me redefine the context
data type (although it does not fit well into the current class):

newtype Gr a b = Gr { convertToMap :: Map.IntMap (GrContext a b) }

data GrContext a b = GrContext
{ nodeLabel :: a
, nodeSuccs :: Map.IntMap [b]
, loops :: [b]
, nodePreds :: Map.IntMap [b] }
 
http://trac.informatik.uni-bremen.de:8080/hets/browser/trunk/Common/Lib/Graph.hs

Maybe "Ord b" should be required for edge labels "b" (in order to use
sets), although it may make sense to have many edges with the same label
between the same two nodes. However, for this special case the user
could provide an additional index or a counter.

> * Data.Graph.Inductive.Monad: does anyone actually use this?

I did not use it. (I've got no opinion about the other points you made.)

Cheers Christian
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