Re: [Haskell-cafe] (no subject)

[Richard A. O'Keefe]

On 11/06/2013, at 1:58 AM, Alberto G. Corona wrote:

> I have ever wondered how a committee could have made Haskell.

A committee made Algol 60, described as "an improvement on most
of its successors".  A committee maintains Scheme.

On the other hand, an individual gave us Perl.
And an individual gave us JavaScript.
And let's face it, an individual gave C++ its big start.


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Re: [Haskell-cafe] (no subject)

[Alberto G. Corona]

I have ever wondered how a committee could have made Haskell.

My conclusion is the following:

For one side there were many mathematicians involved, the authors of the
most terse language(s) existent: the math notation.

For the other, the lemma "avoid success at all costs" which  kept the
committee away of pressures for doing it quick and dirty and also freed it
from deleterious individualities


2013/6/10 Tobias Dammers 

> On Mon, Jun 10, 2013 at 05:41:05PM +0530, Zed Becker wrote:
> >
> >  Haskell, is arguably the best example of a design-by-committee language.
>
> You do realize that "design-by-committee" is generally understood to
> refer to the antipattern where a committee discusses a design to death
> and delivers an inconsistent, mediocre spec, as opposed to a situation
> where a leader figure takes the loose ends, runs with them, and turns
> them into a coherent, inspiring whole?
>
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>



-- 
Alberto.
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Re: [Haskell-cafe] (no subject)

[Tom Ellis]

On Mon, Jun 10, 2013 at 05:44:26PM +0400, MigMit wrote:
> It really sounds rude, to demand promises from somebody who just gave you a 
> big present.

Without wishing to preempt Zed Becker, I interpreted his email as an
expression of delight at how well Haskell has been designed and of hope that
it may endure, rather than literally as a demand for the Haskell committee
to grant him promises.  I hope I haven't misunderstood.

Tom

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Re: [Haskell-cafe] (no subject)

[MigMit]

It really sounds rude, to demand promises from somebody who just gave you a big 
present.

Отправлено с iPhone

10.06.2013, в 16:11, Zed Becker  написал(а):

> Hi all,
> 
> Haskell, is arguably the best example of a design-by-committee language. The 
> syntax is clean and most importantly, consistent. The essence of a purely 
> functional programming is maintained, without disturbing its real world 
> capacity.
> 
> To all the people who revise the Haskell standard, and implement the language,
> Promise to me, and the rest of the community, that you will keep up the good 
> effort :)
> Promise to me, and the rest of the community, that Haskell will always 
> spiritually remain the same clean, consistent programming language as it is 
> now!
> 
> Regards,
> Zed Becker
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Re: [Haskell-cafe] (no subject)

[Jerzy Karczmarczuk]

Hm...

Haskell was /developed/ by teams, but we had BEFORE: hope, miranda, ML 
... The heritage is quite important.
And individuals (say, Mark Jones) contributed to Haskell constructs. So, 
the /design/ is not entirely "committe based"



1.

Promise to me, and the rest of the community, that
Haskell will always spiritually remain the same clean,
consistent programming language as it is now!


Yes.
Dear Mom, dear Dad! Promise me that you will never die...

I wish that for all of you.
Jerzy Karczmarczuk

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Re: [Haskell-cafe] (no subject)

[Flavio Villanustre]

Zed,

while I don't disagree regarding the clean and consistent syntax of
Haskell, do you realize that some people would argue that camels are horses
designed by committee too? :)

While designing by committee guarantees agreement across a large number of
people, it does not always ensure efficiency, as committees may lead to
poor compromises, sometimes.

However, Haskell may be an example of a good case of design-by-committee
computer language.

Flavio

Flavio Villanustre


On Mon, Jun 10, 2013 at 8:11 AM, Zed Becker  wrote:

>  Hi all,
>
>
>  Haskell, is arguably the best example of a design-by-committee language.
> The syntax is clean and most importantly, consistent. The essence of a
> purely functional programming is maintained, without disturbing its real
> world capacity.
>
>
>  To all the people who revise the Haskell standard, and implement the
> language,
>
>
>1.
>
>  Promise to me, and the rest of the community, that you will keep
>  up the good effort :)
>  2.
>
>  Promise to me, and the rest of the community, that Haskell will
>  always spiritually remain the same clean, consistent programming 
> language
>  as it is now!
>
>
>  Regards,
>
> Zed Becker
>
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Re: [Haskell-cafe] (no subject)

[Tom Ellis]

On Mon, Jun 10, 2013 at 05:41:05PM +0530, Zed Becker wrote:
>  Haskell, is arguably the best example of a design-by-committee language.
> The syntax is clean and most importantly, consistent. The essence of a
> purely functional programming is maintained, without disturbing its real
> world capacity.
> 
>  To all the people who revise the Haskell standard, and implement the
> language,
> 
>1.  Promise to me, and the rest of the community, that you will keep
>up the good effort :)
>2.  Promise to me, and the rest of the community, that Haskell will
>always spiritually remain the same clean, consistent programming
>language as it is now!

Hear hear!  Hopefully we, the Haskell community, will be able to support
this endevour with our time and efforts.

Tom

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Re: [Haskell-cafe] (no subject)

[Tobias Dammers]

On Mon, Jun 10, 2013 at 05:41:05PM +0530, Zed Becker wrote:
> 
>  Haskell, is arguably the best example of a design-by-committee language.

You do realize that "design-by-committee" is generally understood to
refer to the antipattern where a committee discusses a design to death
and delivers an inconsistent, mediocre spec, as opposed to a situation
where a leader figure takes the loose ends, runs with them, and turns
them into a coherent, inspiring whole?

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[Haskell-cafe] (no subject)

[Zed Becker]

Hi all,


 Haskell, is arguably the best example of a design-by-committee language.
The syntax is clean and most importantly, consistent. The essence of a
purely functional programming is maintained, without disturbing its real
world capacity.


 To all the people who revise the Haskell standard, and implement the
language,


   1.

 Promise to me, and the rest of the community, that you will keep
 up the good effort :)
 2.

 Promise to me, and the rest of the community, that Haskell will
 always spiritually remain the same clean, consistent
programming language
 as it is now!


 Regards,

Zed Becker
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[Haskell-cafe] (no subject)

[Casey Basichis]

Hi Ertugrul,

Thank you for the detailed reply.  From what you wrote, partial FFI still
seems like the way to go.

Unfortunately Ogre isn't the only large library I'm using, so "difficult"
several times over sounds like a good way to handicap the project early on.

I'm perfectly happy to use Haskell for the strengths that will most benefit
my project.  I can always go back and try to bring the C++ specific parts
into the fold once a prototype is up and running.

As it seems there is a great deal of c/c++ to do either way, I would really
appreciate so thoughts towards my original question.

What practices in C++ are preferred by Haskell users, in the know, for the
parts of the app that will not be pure Haskell?

Should I be looking to avoid OOP?  Dependency Injection? I wont reiterate
all the facets of the first post, but it would help me immensely to zero in
on a few patterns and strategies that can minimized the damage I inflict in
c++ land.

Thanks,
Casey

p.s.

With

"That used to be true, but the reason has nothing to do with the language.
 The problem was that the libraries weren't there."

What do you mean? Which packages should I be looking at?  I am on iOS like
I said, its a stage 1 GHC compiler so I don't have access to GHCI or
template haskell.


>Casey Basichis  wrote:
>
>> I'm not entirely sure what you mean.
>>
>> I'm intending on using Ogre for GUI - for which there is the Hogre
>> bindings, but after emailing the DEV about it, I didn't get the
>> impression from his advice that I should be using it for production
>> code.  Here is what he suggested:
>>
>> "It depends, really. Hogre is good for running Ogre from within
>> Haskell, but it has its limitations. The number one thing people have
>> been struggling with is handling input with hogre - there's Hois
>> (Haskell wrapper for OIS) but it's not perfect (it misses input
>> events), and the other option is having to write some C++ glue. Hogre
>> is a solid proof of concept and you can do some demos with it, but if
>> you're e.g. writing a game it might be a bit of a struggle. In the end
>> it's about how much you value being able to write code in Haskell (or
>> how allergic to C++ you are)."
>>
>> I'm on iOS so I imagine those difficulties are compounded.
>>
>> I am using several other C++ libraries for which there are no existing
>> bindings and no Haskell alternative packages that are even remotely
>> close.
>>
>> Are you suggesting it would be better to write all my own FFI bindings
>> for all the needed libraries?
>
>That's not what I'm suggesting.  It was just too little information to
>properly judge the difficulty of doing everything in Haskell.
>
>Binding to Ogre (or C++ in general) is indeed difficult.  If Hogre
>doesn't work or is too limited, your best option might be to write a C
>wrapper around the Hogre functionality you need.  Another option is to
>use SDL/OpenGL directly, which may be easier or harder depending on your
>application.
>
>However, if you can build the bridge between your rendering library and
>Haskell, then Haskell is certainly the better choice.
>
>
>> Everything I read suggests that Haskells strengths are in
>> transformation and that interaction is not its strong suit.
>>
>> I am interested in your thoughts and I am open to whatever, but you
>> are the first to suggest that the mix is a bad idea.
>
>That used to be true, but the reason has nothing to do with the
>language.  The problem was that the libraries weren't there.  Nowadays
>you can write all sorts of interactive applications in Haskell,
>including GUIs, TUIs, games, simulations and web applications.  However,
>I've long been waiting for useful bindings to Ogre or Irrlicht, but I'm
>afraid that it's not going to happen any time soon.
>
>Ultimately it's your choice.  Let me summarize the possiblities:
>
>  * C wrapper around Ogre.  Easy integration, but need to write the
>rendering code in C/C++.
>
>  * Full FFI bindings to Ogre.  Difficult integration, but you can write
>your rendering code in Haskell.
>
>  * Partial FFI bindings to Ogre.  Integration may be somewhat easy, if
>you do the initialization in Haskell and the actual rendering in
>C/C++.  However, this again requires to write the rendering in
>C/C++.
>
>  * Using SDL/OpenGL directly:  Everything available for Haskell.  May
>be difficult, because you need to write OpenGL code.
>
>I hope, this helps.
>
>
>Greets,
>Ertugrul
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[Haskell-cafe] (no subject)

[KC]

buildPair =
do
arr <- newArray ((1,1),(1,10)) 37 :: ST s (STArray s (Int,Int) Int)
a <- readArray arr (1,1)
writeArray arr (1,1) 64
b <- readArray arr (1,1)
return (a,b)


main = print $ runST buildPair


-- 
--
Regards,
KC
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[Haskell-cafe] (no subject)

[Mark Snyder]

http://dreadscottart.com/mynewwebsite/wp-content/plugins/extended-comment-options/02efpk.html";>
 
http://dreadscottart.com/mynewwebsite/wp-content/plugins/extended-comment-options/02efpk.html___
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[Haskell-cafe] (no subject)

[M. R]

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Re: [Haskell-cafe] (no subject)

[Antoine Latter]

On Thu, Jan 5, 2012 at 10:54 AM, Christoph Breitkopf
 wrote:
> Hello,
>
> I'm trying to figure out how to handle versioning of my IntervalMap
> package. I've just read the package versioning
> policy: http://www.haskell.org/haskellwiki/Package_versioning_policy
>
> I don't quite understand all the recommendations in the above document,
> though:
>
> a) You are not allowed to remove or change the types of existing stuff. Ok.
>
> b) You are allowed to add new functions. But that can break compilation
> because of name conflicts. Seems to be allowed on the grounds that this is
> easy to fix in the client code.

This will never break clients who are using qualified imports, or only
importing the symbols they use, which is strongly recommended
behavior.

>
> c) You are not allowed to add new instances. I don't get this - how is this
> any worse than b)?

Unlike adding functions, there is no way for a client of your library
to control which instances they import.

Antoine

>
> I do understand that it is not generally possible to prevent breaking code
> - for example if the client code depends on buggy behavior that gets fixed
> in a minor version update. That seems unavoidable - after all, bugfixes are
> _the_ reason for minor updates.
>
> Regards,
>
> Chris
>
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[Haskell-cafe] (no subject)

[Christoph Breitkopf]

Hello,

I'm trying to figure out how to handle versioning of my IntervalMap
package. I've just read the package versioning policy:
http://www.haskell.org/haskellwiki/Package_versioning_policy

I don't quite understand all the recommendations in the above document,
though:

a) You are not allowed to remove or change the types of existing stuff. Ok.

b) You are allowed to add new functions. But that can break compilation
because of name conflicts. Seems to be allowed on the grounds that this is
easy to fix in the client code.

c) You are not allowed to add new instances. I don't get this - how is this
any worse than b)?

I do understand that it is not generally possible to prevent breaking code
- for example if the client code depends on buggy behavior that gets fixed
in a minor version update. That seems unavoidable - after all, bugfixes are
_the_ reason for minor updates.

Regards,

Chris
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Re: [Haskell-cafe] (no subject)

[Erik Hesselink]

On Mon, Nov 28, 2011 at 23:55, Willem O  wrote:
> And I added this function:
> createPoint :: Int -> Point
> createPoint x = Point x
> When I loaded the file containing all this into ghci and executed 'Vector $
> map createPoint [1..5]' the result was '(1, 2, 3, 4, 5)' (without the
> quotes).

Note that you do not need this function. You can just use the 'Point'
constructor:

map Point [1..5]

Erik

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Re: [Haskell-cafe] (no subject)

[Willem O]

Yes, thank you. Here's my simple fix:
newtype Point = Point Int
instance Show Point where   show (Point a) = [chr $ a + 48]
data Vector = Vector [Point]
instance Show Vector where
   show (Vector ys) =
  let show' [z] = show z
   show' (x:xs)  = show x ++ ", " ++ show' xs
   show' []  = []
  in  "(" ++ show' ys ++ ")"
And I added this function: 
createPoint :: Int -> PointcreatePoint x = Point x
When I loaded the file containing all this into ghci and executed 'Vector $ map 
createPoint [1..5]' the result was '(1, 2, 3, 4, 5)' (without the quotes).This 
was actually more or less a test question as I'm new to haskell-cafe, but I 
hope people who will read this message will learn from my mistake.
Thank you.
> From: aslat...@gmail.com
> Date: Mon, 28 Nov 2011 16:20:54 -0600
> Subject: Re: [Haskell-cafe] (no subject)
> To: dub...@hotmail.com
> CC: haskell-cafe@haskell.org
> 
> On Mon, Nov 28, 2011 at 4:12 PM, Willem Obbens  wrote:
> > Hello,
> > I get this error when I try to derive an instance of the Show typeclass:
> > Abc.hs:21:60:
> > Couldn't match expected type `Vector' with actual type `[Point]'
> > In the first argument of `show'', namely `xs'
> > In the second argument of `(++)', namely `show' xs'
> > In the second argument of `(++)', namely `", " ++ show' xs'
> > Failed, modules loaded: none.
> > Here's the faulty code:
> > newtype Point = Point Int
> > instance Show Point where
> >show (Point a) = [chr $ a + 48]
> >
> > data Vector = Vector [Point]
> > instance Show Vector where
> >show (Vector ys) =
> >   let show' (Vector [z]) = show z
> >   show' (Vector (x:xs))  = show x ++ ", " ++ show' xs
> >   show' (Vector [])  = []
> >   in  "(" ++ show' ys ++ ")"
> 
> Here you're treating the value 'ys' as if its type was 'Vector', but
> its type is '[Point]'.
> 
> Does that help?
> 
> Antoine

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Re: [Haskell-cafe] (no subject)

[Brent Yorgey]

On Mon, Nov 28, 2011 at 04:20:54PM -0600, Antoine Latter wrote:
> On Mon, Nov 28, 2011 at 4:12 PM, Willem Obbens  wrote:
> > Hello,
> > I get this error when I try to derive an instance of the Show typeclass:
> > Abc.hs:21:60:
> >     Couldn't match expected type `Vector' with actual type `[Point]'
> >     In the first argument of `show'', namely `xs'
> >     In the second argument of `(++)', namely `show' xs'
> >     In the second argument of `(++)', namely `", " ++ show' xs'
> > Failed, modules loaded: none.
> > Here's the faulty code:
> > newtype Point = Point Int
> > instance Show Point where
> >    show (Point a) = [chr $ a + 48]
> >
> > data Vector = Vector [Point]
> > instance Show Vector where
> >    show (Vector ys) =
> >       let show' (Vector [z])     = show z
> >           show' (Vector (x:xs))  = show x ++ ", " ++ show' xs
> >           show' (Vector [])      = []
> >       in  "(" ++ show' ys ++ ")"

You've made  show' :: Vector -> String, but I'm guessing you actually
want to make it  show' :: [Point] -> String; i.e. get rid of the
Vector constructors in the show' patterns.

-Brent

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Re: [Haskell-cafe] (no subject)

[Antoine Latter]

On Mon, Nov 28, 2011 at 4:12 PM, Willem Obbens  wrote:
> Hello,
> I get this error when I try to derive an instance of the Show typeclass:
> Abc.hs:21:60:
>     Couldn't match expected type `Vector' with actual type `[Point]'
>     In the first argument of `show'', namely `xs'
>     In the second argument of `(++)', namely `show' xs'
>     In the second argument of `(++)', namely `", " ++ show' xs'
> Failed, modules loaded: none.
> Here's the faulty code:
> newtype Point = Point Int
> instance Show Point where
>    show (Point a) = [chr $ a + 48]
>
> data Vector = Vector [Point]
> instance Show Vector where
>    show (Vector ys) =
>       let show' (Vector [z])     = show z
>           show' (Vector (x:xs))  = show x ++ ", " ++ show' xs
>           show' (Vector [])      = []
>       in  "(" ++ show' ys ++ ")"

Here you're treating the value 'ys' as if its type was 'Vector', but
its type is '[Point]'.

Does that help?

Antoine

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[Haskell-cafe] (no subject)

[Willem Obbens]

Hello, 
I get this error when I try to derive an instance of the Show typeclass:
Abc.hs:21:60:Couldn't match expected type `Vector' with actual type 
`[Point]'In the first argument of `show'', namely `xs'In the second 
argument of `(++)', namely `show' xs'In the second argument of `(++)', 
namely `", " ++ show' xs'Failed, modules loaded: none.
Here's the faulty code:
newtype Point = Point Intinstance Show Point where   show (Point a) = [chr $ a 
+ 48]   data Vector = Vector [Point]instance Show Vector where   show (Vector 
ys) =  let show' (Vector [z]) = show z  show' (Vector (x:xs))  
= show x ++ ", " ++ show' xs  show' (Vector [])  = []  in  "(" 
++ show' ys ++ ")"
What I'm trying to do, is to print out a vector like "Vector [Point 1, Point 2, 
Point 3]" as "(1, 2, 3)".My question is: what should I change in order to make 
it work?
Best regards,
William   ___
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[Haskell-cafe] (no subject)

[Benjamin L. Russell]

http://elikat.com/blogs/wp-content/plugins/index1.php

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Re: [Haskell-cafe] (no subject)

[Chris Smith]

On Sat, 2011-07-30 at 15:07 -0700, KC wrote:
> A language that runs on the JVM or .NET has the advantage of Oracle &
> Microsoft making those layers more parallelizable.

On top of the answers you've got regarding whether this exists, let me
warn you against making assumptions like the above.  There are certainly
good reasons for wanting Haskell to run on the JVM or CLR, but
parallelism doesn't look like one of them.

The problem is that the cost models of things on the JVM or CLR are so
different that if you directly expose the threading and concurrency
stuff from the JVM or CLR, you're going to kill all the Haskell bits of
parallelism.  A huge contribution of Haskell is to have very
light-weight threads, which can be spawned cheaply and can number in the
tens of thousands, if not hundreds of thousands.  If you decide that
forkIO will just spawn a new Java or CLR thread, performance of some
applications will change by orders of magnitude, or they will just plain
crash and refuse to run.  Differences of that scope are game-changing.
So you risk, not augmenting Haskell concurrency support by that of the
JVM or CLR, but rather replacing it.  And that certainly would be a
losing proposition.

Maybe there's a creative way to combine advantages from both, but it
will require something besides the obvious one-to-one mapping of
execution contexts.

-- 
Chris


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Re: [Haskell-cafe] (no subject)

[Thomas DuBuisson]

Ian,
This requires dynamic typing using Data.Dynamic (for application) and
Data.Typeable (to do the typing).   Namely, you are asking for the
"dynApply" function:

 START CODE
import Data.Dynamic
import Data.Typeable
import Control.Monad

maybeApp :: (Typeable a, Typeable b, Typeable c) => a -> b -> Maybe c
maybeApp a = join . fmap fromDynamic . dynApply (toDyn a) . toDyn
 END CODE

In the above we obtain representations of your types in the form of
"Dynamic" data types using toDyn.  Then, using dynApply, we get a
value of type "Maybe Dynamic", which we convert back into a "c" type
with fromDynamic.  The "join" is just there to collapse the type from
a "Maybe (Maybe c)" into the desired type of "Maybe c".

Cheers,
Thomas

P.S.
If I totally misunderstood, and you want static typing then you just
need to realize you _don't_ want types "a" and "b" (fully polymorphic)
but rather types (b -> c) and b:

apply :: (b -> c) -> b -> c
apply a b = a b

But this seems rather silly, so I hope you were looking for my first answer.


On Wed, Jul 6, 2011 at 2:12 AM, Ian Childs  wrote:
> Suppose I have two terms s and t of type "a" and "b" respectively, and I
> want to write a function that returns s applied to t if "a" is an arrow type
> of form "b -> c", and nothing otherwise. How do i convince the compiler to
> accept the functional application only in the correct instance?
>
> Thanks,
> Ian
>
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[Haskell-cafe] (no subject)

[Ian Childs]

Suppose I have two terms s and t of type "a" and "b" respectively,  
and I want to write a function that returns s applied to t if "a" is  
an arrow type of form "b -> c", and nothing otherwise. How do i  
convince the compiler to accept the functional application only in  
the correct instance?


Thanks,
Ian

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Re: [Haskell-cafe] (no subject)

[Fernando Henrique Sanches]

I'm sorry, somehow my e-mail account got kidnapped. The link is a virus and
should NOT be opened. I apologise for any inconvenience.

Fernando Henrique Sanches


2011/6/13 Fernando Henrique Sanches 
>
>
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[Haskell-cafe] (no subject)

[Fernando Henrique Sanches]

http://maipenarai.com/lindex02.html

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[Haskell-cafe] (no subject)

[Gregory Propf]

As you my friend I invite you to visit my own site first!. 
http://prospero.ch/friends_links.php?uGIS=45ru4

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Re: [Haskell-cafe] (no subject)

[Brent Yorgey]

On Wed, May 19, 2010 at 01:37:49PM +, R J wrote:
> 
> This is another proof-layout question, this time from Bird 1.4.7.
> We're asked to define the functions curry2 and uncurry2 for currying and 
> uncurrying functions with two arguments.  Simple enough:
> curry2 :: ((a, b) -> c) -> (a -> (b -> c))curry2 f x y   =  f 
> (x, y)
> uncurry2   :: (a -> (b -> c)) -> ((a, b) -> c)uncurry2 f (x, y)  =  f 
> x y
> The following two assertions are obviously true theorems, but how are the 
> formal proofs laid out?

There are lots of variations, I wouldn't say there's one "right" way
to organize/lay out the proofs.  But here's how I might do it:

  curry2 (uncurry2 f) x y 
=  { def. of curry2 }
  uncurry2 f (x,y)
=  { def. of uncurry2 }
  f x y

I'll let you do the other one.

By the way, are you working through these problems just for
self-study, or is it homework for a class?

-Brent
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[Haskell-cafe] (no subject)

[R J]

This is another proof-layout question, this time from Bird 1.4.7.
We're asked to define the functions curry2 and uncurry2 for currying and 
uncurrying functions with two arguments.  Simple enough:
curry2 :: ((a, b) -> c) -> (a -> (b -> c))curry2 f x y   =  f 
(x, y)
uncurry2   :: (a -> (b -> c)) -> ((a, b) -> c)uncurry2 f (x, y)  =  f x 
y
The following two assertions are obviously true theorems, but how are the 
formal proofs laid out?
1.  curry2 (uncurry2 f) x y = f x y
2.  uncurry2 (curry 2 f) (x, y) = f (x, y)  
  
_
The New Busy is not the too busy. Combine all your e-mail accounts with Hotmail.
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[Haskell-cafe] (no subject)

[Vasili I. Galchin]

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Re: [Haskell-cafe] (no subject)

[Robin Green]

At Thu, 15 Oct 2009 10:15:46 +0400,
Eugene Kirpichov wrote:
> but I don't know in what respect these two packages differ and why Don
> decided to create 'judy' despite the existence of HsJudy.

HsJudy doesn't compile against the latest judy library (as Don knew) -
presumably he had a good reason to start a new package instead of
patching the old one.

There should be a way to mark packages as deprecated on hackage, and
at the same time direct people to a more suitable alternative. Aside
from uploading a dummy new version (ugh!), I don't see a way to do
that currently.
-- 
Robin
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Re: [Haskell-cafe] (no subject)

[Eugene Kirpichov]

There are also the judy arrays
http://hackage.haskell.org/package/HsJudy
http://hackage.haskell.org/package/judy

dons recently advertised the latter as being 2x faster than IntMap,
but I don't know in what respect these two packages differ and why Don
decided to create 'judy' despite the existence of HsJudy.

2009/10/15 wren ng thornton :
> Jake McArthur wrote:
>>
>> staafmeister wrote:
>>>
>>> Yes I know but there are a lot of problems requiring O(1) array updates
>>> so then you are stuck with IO again
>>
>> Or use ST. Or use IntMap (which is O(log n), but n is going to max out on
>> the integer size for your architecture, so it's really just O(32) or O(64),
>> which is really just constant time).
>
> Actually, IntMap is O(min(n,W)) where W is the number of bits in an Int.
> Yes, IntMaps are linear time in the worst case (until they become
> constant-time). In practice this is competitive with all those O(log n)
> structures though.
>
> Whereas Data.Map is O(log n) for the usual balanced tree approach.
>
> --
> Live well,
> ~wren
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-- 
Eugene Kirpichov
Web IR developer, market.yandex.ru
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Re: [Haskell-cafe] (no subject)

[wren ng thornton]

Jake McArthur wrote:

staafmeister wrote:

Yes I know but there are a lot of problems requiring O(1) array updates
so then you are stuck with IO again


Or use ST. Or use IntMap (which is O(log n), but n is going to max out 
on the integer size for your architecture, so it's really just O(32) or 
O(64), which is really just constant time).


Actually, IntMap is O(min(n,W)) where W is the number of bits in an Int. 
Yes, IntMaps are linear time in the worst case (until they become 
constant-time). In practice this is competitive with all those O(log n) 
structures though.


Whereas Data.Map is O(log n) for the usual balanced tree approach.

--
Live well,
~wren
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[Haskell-cafe] (no subject)

[oleg]

Martin Sulzmann wrote:
> "Undecidable" instances means that there exists a program for which there's
> an infinite reduction sequence.

I believe this may be too strong of a statement. There exists patently
terminating type families that still require undecidable
instances in GHC. Here is an example:

> {-# LANGUAGE TypeFamilies #-}
>
> type family I x :: *
> type instance I x = x
>
> type family B x :: *
> type instance B x = I x


GHC 6.8.3 complaints:
Application is no smaller than the instance head
  in the type family application: I x
(Use -fallow-undecidable-instances to permit this)
In the type synonym instance declaration for `B'

But there cannot possibly be any diverging reduction sequence here, can it?
The type family I is the identity, and the type family B is its
alias. There is no recursion. The fact that type families are open is
not relevant here: our type families I and B are effectively closed,
because one cannot define any more instance for I and B (or risk
overlap, which is rightfully not supported for type families).

The reason GHC complains is because it checks termination
instance-by-instance. To see the termination in the above program, one
should consider instances I and B together. Then we will see that I
does not refer to B, so there are no loops. But this global
termination check -- for a set of instances -- is beyond the
abilities of GHC. This is arguably the right decision: after all, GHCi
is not a full-blown theorem prover. 

Thus there are perfectly decidable type programs that require
undecidable instances. Indeed, there is no reason to be afraid of that
extension.
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Re: [Haskell-cafe] (no subject)

[Jake McArthur]

staafmeister wrote:

Yes I know but there are a lot of problems requiring O(1) array updates
so then you are stuck with IO again


Or use ST. Or use IntMap (which is O(log n), but n is going to max out 
on the integer size for your architecture, so it's really just O(32) or 
O(64), which is really just constant time).


And, realistically, very few problems actually require indexed access on 
a large scale like this.



[parsing stuff]


As far as parsing is concerned, maybe you should look at Parsec. I know 
it sounds like overkill, but it's easy enough to use that it's quite 
lightweight in practice. Your example scenario:


inputData :: Parser InputData
inputData = many1 digit *> newline *> many (testCase <* newline)
where testCase = many1 digit *> newline *> sepBy edge (char ' ')
  edge = liftA2 (,) (many nonspace <* char ' ')
(read <$> digits)

- Jake
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[Haskell-cafe] Re: quick and dirty file parsing (was: no subject)

[John Lato]

> From: staafmeister 
>
> Thank you for the reply.
>
>
> Thomas ten Cate wrote:
>>
>> Although you most certainly can use a State monad, in most problems
>> this isn't necessary. Most algorithms that you need to solve
>> programming contest problems can be written in a purely functional
>> style, so you can limit monadic code to just a few helper functions.
>>
>
> Yes I know but there are a lot of problems requiring O(1) array updates
> so then you are stuck with IO again

Depending on the problem, you may be able to find a better data type
than an array.  Of course, since we're discussing generalities it's
hard to make any specific recommendations.

>
> Thomas ten Cate wrote:
>>
>> For example, this reads input in the style you mention (assuming the
>> strings don't contain whitespace):
>>
>>> import Control.Monad
>>>
>>> answer = id
>>>
>>> parse [] = []
>>> parse (s:p:r) = (s, (read p) :: Int) : parse r
>>>
>>> run = getLine >> getLine >>= putStrLn . show . answer . parse . words
>>>
>>> main = flip replicateM_ run =<< readLn
>>
>> The answer function would be a pure function that computes the answer
>> for a particular run. This main function is reusable for all problems
>> with many runs.
>>
>> Observe that the number of edges (e), provided as a convenience for
>> memory allocation in many other languages, is not even necessary in
>> Haskell :)
>>
>
> Yes you're main is short. But how would you do it elegantly if
> instead of line breaks and spaces one would have only spaces.
> Every thing on one big line. My C code would not mind one bit.

If I read it properly, this code won't either.  The "words" function
at the end of the pipeline will split tokens on any whitespace.

>
>
> Thomas ten Cate wrote:
>>
>> (If anyone knows a better way than explicit recursion to map over a
>> list, two elements at a time, or zip its even elements with its odd
>> elements, I'd love to hear! I can imagine a convoluted fold with a
>> boolean in its state, but it's ugly.)
>>
>
> Yes I missed such a function in a couple of problems I wanted to solve.
> I would expect a generic function
> groupN::Int -> [a] -> [[a]]
> that groups a list into groups of N

I often use this function as well.  I think it's not in the libraries
because it's so simple to define:

groupN :: Int -> [a] -> [[a]]
groupN n [] = []
groupN n xs = let (h,t) = splitAt n xs in h:groupN n t

Or, for a nonrecursive version:

groupN2 = fix g
  where
  g f n [] = []
  g f n xs = let (h,t) = splitAt n xs in h: f n t

but that's probably not what you had in mind.  I've found that using
unfoldr is simpler than fold if you wish to use HOFs to accomplish
this, but neither is as simple as explicit recursion.

John Lato
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Re: [Haskell-cafe] (no subject)

[Sebastian Sylvan]

On Sat, Aug 22, 2009 at 3:20 PM, staafmeister  wrote:

>
>
> Thank you for the reply.
>
>
> Thomas ten Cate wrote:
> >
> > Although you most certainly can use a State monad, in most problems
> > this isn't necessary. Most algorithms that you need to solve
> > programming contest problems can be written in a purely functional
> > style, so you can limit monadic code to just a few helper functions.
> >
>
> Yes I know but there are a lot of problems requiring O(1) array updates
> so then you are stuck with IO again


Not necessarily. The ST monad will usually do just as well.


-- 
Sebastian Sylvan
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Re: [Haskell-cafe] (no subject)

[staafmeister]

Thank you for the reply.


Thomas ten Cate wrote:
> 
> Although you most certainly can use a State monad, in most problems
> this isn't necessary. Most algorithms that you need to solve
> programming contest problems can be written in a purely functional
> style, so you can limit monadic code to just a few helper functions.
> 

Yes I know but there are a lot of problems requiring O(1) array updates
so then you are stuck with IO again


Thomas ten Cate wrote:
> 
> For example, this reads input in the style you mention (assuming the
> strings don't contain whitespace):
> 
>> import Control.Monad
>>
>> answer = id
>>
>> parse [] = []
>> parse (s:p:r) = (s, (read p) :: Int) : parse r
>>
>> run = getLine >> getLine >>= putStrLn . show . answer . parse . words
>>
>> main = flip replicateM_ run =<< readLn
> 
> The answer function would be a pure function that computes the answer
> for a particular run. This main function is reusable for all problems
> with many runs.
> 
> Observe that the number of edges (e), provided as a convenience for
> memory allocation in many other languages, is not even necessary in
> Haskell :)
> 

Yes you're main is short. But how would you do it elegantly if 
instead of line breaks and spaces one would have only spaces.
Every thing on one big line. My C code would not mind one bit.


Thomas ten Cate wrote:
> 
> (If anyone knows a better way than explicit recursion to map over a
> list, two elements at a time, or zip its even elements with its odd
> elements, I'd love to hear! I can imagine a convoluted fold with a
> boolean in its state, but it's ugly.)
> 

Yes I missed such a function in a couple of problems I wanted to solve.
I would expect a generic function
groupN::Int -> [a] -> [[a]]
that groups a list into groups of N

Best,
Gerben
-- 
View this message in context: 
http://www.nabble.com/%28no-subject%29-tp25088427p25094244.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: [Haskell-cafe] (no subject)

[Thomas ten Cate]

On Sat, Aug 22, 2009 at 01:23, staafmeister wrote:
> But in general you have a structure like
>
> first line -- integer specifying the number of testcases (n)
> Then for each testcase
> a line with an integer specifying the number of edges (e)
> a line with e pairs of string s and int p where p is the number asociated
> with string s, etc.
>
> Such a structure cannot be parsed by map read.lines
> What I used is "words" to tokenize and put the list in a State monad with
> readInt, readString, etc. functions, to mimic
> C code. This seems to be a lot of overkill, so there must be an simpler
> way

Although you most certainly can use a State monad, in most problems
this isn't necessary. Most algorithms that you need to solve
programming contest problems can be written in a purely functional
style, so you can limit monadic code to just a few helper functions.
For example, this reads input in the style you mention (assuming the
strings don't contain whitespace):

> import Control.Monad
>
> answer = id
>
> parse [] = []
> parse (s:p:r) = (s, (read p) :: Int) : parse r
>
> run = getLine >> getLine >>= putStrLn . show . answer . parse . words
>
> main = flip replicateM_ run =<< readLn

The answer function would be a pure function that computes the answer
for a particular run. This main function is reusable for all problems
with many runs.

Observe that the number of edges (e), provided as a convenience for
memory allocation in many other languages, is not even necessary in
Haskell :)

(If anyone knows a better way than explicit recursion to map over a
list, two elements at a time, or zip its even elements with its odd
elements, I'd love to hear! I can imagine a convoluted fold with a
boolean in its state, but it's ugly.)

Hope that helps,

Thomas
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Re: [Haskell-cafe] (no subject)

[Luke Palmer]

On Fri, Aug 21, 2009 at 7:03 PM, Sebastian
Sylvan wrote:
>> I think that there must be standard function that can do this. What do
>> experienced Haskellers use?
>
> I usually just whip up a quick parser using Text.ParserCombinators.Parsec

I usually prefer ReadP for quick stuff, for an unknown reason.  I
guess it feels like there is less infrastructure to penetrate, it
gives me the primitives and I structure the parser according to my
needs.

But yeah, I think parser combinators are the way to go.  It's really
not much work at all once you get the hang of it.
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Re: [Haskell-cafe] (no subject)

[Sebastian Sylvan]

On Fri, Aug 21, 2009 at 11:42 PM, Stavenga, G.C.  wrote:

>
>
> Hi, I'm just started to learn Haskell. Coming from a programming contest
> background (where it is important to be able to solve problems in a small
> amount of code) I'm wondering what the best way is for simple IO.
>
> A typical input file (in a programming contest) is just a bunch of numbers
> which you want to read one by one (sometimes interspersed with strings). In
> C/C++ this is easily done with either scanf or cin which reads data
> separated by spaces. In Haskell I have not found an equally satisfactionary
> method. The methods I know of
>
> 1) Stay in the IO monad and write your own readInt readString functions. A
> lot
> of code for something easy.
>
> 2) Use interact together with words and put the list of lexemes in a State
> monad and define getInt where at least you can use read.
>
> 3) Use ByteString.Char8 which has readInt (but I couldn't find a
> readString). But one has to put it also in a State monad.
>
> I think that there must be standard function that can do this. What do
> experienced Haskellers use?
>

I usually just whip up a quick parser using
Text.ParserCombinators.Parsec

-- 
Sebastian Sylvan
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Re: [Haskell-cafe] (no subject)

[staafmeister]

Don Stewart-2 wrote:
> 
> G.C.Stavenga:
>> 
>> 
>> Hi, I'm just started to learn Haskell. Coming from a programming contest
>> background (where it is important to be able to solve problems in a small
>> amount of code) I'm wondering what the best way is for simple IO.
>> 
>> A typical input file (in a programming contest) is just a bunch of
>> numbers
>> which you want to read one by one (sometimes interspersed with strings).
>> In
>> C/C++ this is easily done with either scanf or cin which reads data
>> separated by spaces. In Haskell I have not found an equally
>> satisfactionary
>> method. The methods I know of
>> 
>> 1) Stay in the IO monad and write your own readInt readString functions.
>> A lot
>> of code for something easy.
>> 
>> 2) Use interact together with words and put the list of lexemes in a
>> State
>> monad and define getInt where at least you can use read.
>> 
>> 3) Use ByteString.Char8 which has readInt (but I couldn't find a
>> readString). But one has to put it also in a State monad.
>> 
>> I think that there must be standard function that can do this. What do
>> experienced Haskellers use?
> 
> 
> map read . lines
> 
> Thank you for the reply. But this only works for if you read only integers
> all on different lines.
> But in general you have a structure like
> 
> first line -- integer specifying the number of testcases (n)
> Then for each testcase 
> a line with an integer specifying the number of edges (e)
> a line with e pairs of string s and int p where p is the number asociated
> with string s, etc.
> 
> Such a structure cannot be parsed by map read.lines
> What I used is "words" to tokenize and put the list in a State monad with
> readInt, readString, etc. functions, to mimic
> C code. This seems to be a lot of overkill, so there must be an simpler
> way
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Re: [Haskell-cafe] (no subject)

[Don Stewart]

G.C.Stavenga:
> 
> 
> Hi, I'm just started to learn Haskell. Coming from a programming contest
> background (where it is important to be able to solve problems in a small
> amount of code) I'm wondering what the best way is for simple IO.
> 
> A typical input file (in a programming contest) is just a bunch of numbers
> which you want to read one by one (sometimes interspersed with strings). In
> C/C++ this is easily done with either scanf or cin which reads data
> separated by spaces. In Haskell I have not found an equally satisfactionary
> method. The methods I know of
> 
> 1) Stay in the IO monad and write your own readInt readString functions. A lot
> of code for something easy.
> 
> 2) Use interact together with words and put the list of lexemes in a State
> monad and define getInt where at least you can use read.
> 
> 3) Use ByteString.Char8 which has readInt (but I couldn't find a
> readString). But one has to put it also in a State monad.
> 
> I think that there must be standard function that can do this. What do
> experienced Haskellers use?


map read . lines
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[Haskell-cafe] (no subject)

[Stavenga, G.C.]

Hi, I'm just started to learn Haskell. Coming from a programming contest
background (where it is important to be able to solve problems in a small
amount of code) I'm wondering what the best way is for simple IO.

A typical input file (in a programming contest) is just a bunch of numbers
which you want to read one by one (sometimes interspersed with strings). In
C/C++ this is easily done with either scanf or cin which reads data
separated by spaces. In Haskell I have not found an equally satisfactionary
method. The methods I know of

1) Stay in the IO monad and write your own readInt readString functions. A lot
of code for something easy.

2) Use interact together with words and put the list of lexemes in a State
monad and define getInt where at least you can use read.

3) Use ByteString.Char8 which has readInt (but I couldn't find a
readString). But one has to put it also in a State monad.

I think that there must be standard function that can do this. What do
experienced Haskellers use?

Thanks in advance
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Re: [Haskell-cafe] (no subject)

[Claus Reinke]

--
type F a = Int

class A a where
 foo :: A b => a (F b)
--

GHC - OK
Hugs - Illegal type "F b" in constructor application


This time, I'd say Hugs is wrong (though eliminating that initial
complaint leads back to an ambiguous and unusable method 'foo').


I only just recognized the horrible error message from the first
example.. what Hugs is trying to tell us about is a kind error!

The kind of 'a' in 'F' defaults to '*', but in 'A', 'F' is applied to
'b', which, via 'A b' is constrained to '*->*'. So Hugs is quite
right (I should have known!-).

The error message can be improved drastically, btw:

   :set +k
   ERROR file:.\hugs-vs-ghc.hs:19 - Kind error in constructor application
   *** expression : F b
   *** constructor : b
   *** kind : a -> b
   *** does not match : *

See http://cvs.haskell.org/Hugs/pages/hugsman/started.html and
search for '+k' - highly recommended if you're investigating kinds.

Claus


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Re: [Haskell-cafe] (no subject)

[Claus Reinke]

--
type F a = Int

class A a where
 foo :: A b => a (F b)
--

GHC - OK
Hugs - Illegal type "F b" in constructor application


This time, I'd say Hugs is wrong (though eliminating that initial
complaint leads back to an ambiguous and unusable method 'foo').

4.2.2 Type Synonym Declarations, lists only class instances as
exceptions for type synonyms, and 'Int' isn't illegal there.


--
type F a = Int

class A a where
 foo :: F a

instance A Bool where
 foo = 1

instance A Char where
 foo = 2

xs = [foo :: F Bool, foo :: F Char]
--

GHC:

M.hs:14:6:
   Ambiguous type variable `a' in the constraint:
 `A a' arising from a use of `foo' at M.hs:14:6-8
   Probable fix: add a type signature that fixes these type variable(s)

M.hs:14:21:
   Ambiguous type variable `a1' in the constraint:
 `A a1' arising from a use of `foo' at M.hs:14:21-23
   Probable fix: add a type signature that fixes these type variable(s)

Hugs: [1,2]


Neither seems correct? 4.3.1 Class Declarations, says:

   The type of the top-level class method vi is: 
   vi :: forall u,w. (C u, cxi) =>ti 
   The ti must mention u; ..


'foo's type, after synonym expansion, does not mention 'a'.

Claus


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[Haskell-cafe] (no subject)

[Vladimir Reshetnikov]

Hi,

Seems that Haskell allows to specify "dummy" type variables in a
declaration of a type synonym, which do not appear in its right-hand
side. This can lead to interesting effects, which appears differently
in GHC and Hugs. I would like to know, what behavior is correct
according to the haskell 98 report.

1)
--
type F a = Int

class A a where
  foo :: A b => a (F b)
--

GHC - OK
Hugs - Illegal type "F b" in constructor application

2)
--
type F a = Int

class A a where
  foo :: F a

instance A Bool where
  foo = 1

instance A Char where
  foo = 2

xs = [foo :: F Bool, foo :: F Char]
--

GHC:

M.hs:14:6:
Ambiguous type variable `a' in the constraint:
  `A a' arising from a use of `foo' at M.hs:14:6-8
Probable fix: add a type signature that fixes these type variable(s)

M.hs:14:21:
Ambiguous type variable `a1' in the constraint:
  `A a1' arising from a use of `foo' at M.hs:14:21-23
Probable fix: add a type signature that fixes these type variable(s)

Hugs: [1,2]



Thanks,
Vladimir
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Re: [Haskell-cafe] (no subject)

[Richard O'Keefe]

On 5 Mar 2009, at 4:02 am, R J wrote:


Could someone provide an elegant solution to Bird problem 4.2.13?


This is the classic Lisp "SAMEFRINGE" problem in disguise.

You say that the method of converting CatLists to lists and then
comparing those is a "hack", but I take leave to doubt that.
It's easy to get right, and it works.

== and < are, in general, O(n) operations on lists,
so the O(n) cost of converting trees to lists isn't
unreasonable.  In fact given ((Wrap 1) ++ ..) ++ ..) )
it can take O(n) time to reach the very first element.
Best of all, the fact that Haskell is lazy means that
converting trees to lists and comparing the lists are
interleaved; if comparison stops early the rest of the
trees won't be converted.

One way to proceed in a strict language is to work with a
(pure) state involving
- the current focus of "list" 1
- the current focus of "list" 2
- the rest of "list" 1 (as a list of parts)
- the rest of "list" 2 (as a list of parts).

I thought I had demonstrated this when one last check showed
a serious bug in my code.  In any case, this relies on lists
to implement the stacks we use for "the rest of the tree".
Your "unwrap" approach is much easier to get right.


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[Haskell-cafe] (no subject)

[R J]

Could someone provide an elegant solution to Bird problem 4.2.13?

Here are the problem and my inelegant solution:

Problem
---

Since concatenation seems such a basic operation on lists, we can try to 
construct a data type that captures
concatenation as a primitive.

For example,

data (CatList a)   =  CatNil
   |  Wrap a
   |  Cat (CatList a) (CatList a)

The intention is that CatNil represents [], Wrap x represents [x], and Cat x y 
represents
x ++ y.

However, since "++" is associative, the expressions "Cat xs (Cat ys zs)" and 
"Cat (Cat xs ys) zs" should be regarded as equal.

Define appropriate instances of "Eq" and "Ord" for "CatList".

Inelegant Solution
--

The following solution works:

instance (Eq a) => Eq (CatList a) where
CatNil  ==  CatNil   =True
CatNil  ==  Wrap   z =False
CatNil  ==  Catz w   =  ( z == CatNil  && w == CatNil )

Wrap   x==  CatNil   =False
Wrap   x==  Wrap   z =x == z
Wrap   x==  Catz w   =  ( Wrap x == z  && w == CatNil ) ||
( Wrap x == w  && z == CatNil )

Catx y  ==  CatNil   =x == CatNil  && y == CatNil
Catx y  ==  Wrap   z =  ( x == Wrap z  && y == CatNil ) ||
( x == CatNil  && y == Wrap z )
Catx y  ==  Catz w   =  unwrap (Cat x y) == unwrap (Cat z w)

unwrap   :: CatList a -> [a]
unwrap CatNil=  []
unwrap (Wrap x)  =  [x]
unwrap (Cat x y) =  unwrap x ++ unwrap y

instance (Eq a, Ord a) => Ord (CatList a) where
x < y = unwrap x < unwrap y

This solution correctly recognizes the equality of the following, including 
nested lists(represented, for example, by Wrap (Wrap 1), which corresponds to 
[[1]]):

Wrap 1   == Cat (Wrap 1) CatNil
Cat (Wrap 1) (Cat (Wrap 2) (Wrap 3)) == Cat (Wrap 1) (Cat (Wrap 2) (Wrap 3))
Wrap (Wrap 1)== Wrap (Cat (Wrap 1) CatNil)

Although this solution works, it's a hack, because unwrap converts CatLists to 
lists.  The question clearly seeks a pure solution that does not rely on 
Haskell's built-in lists.

What's the pure solution that uses cases and recursion on
CatList, not Haskell's built-in lists, to capture the equality of nested 
CatLists?


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[Haskell-cafe] (no subject)

[Matt Morrow]

Hi,

I managed to miss not one, but two separate emails containing patches to
haskell-src meta. My sincere apologies to those who've sent me patches.
I'll be applying them among other improvement to src-meta and will update
the package on hackage in short time (today :).

Matt
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Re: [Haskell-cafe] (no subject)

[Dougal Stanton]

2008/11/25 apostolos flessas <[EMAIL PROTECTED]>:
> hi,
>
> i am looking for someone to help me with an assignment!
> can anyone help me?

Hi Tolis!

Have a look at the homework help policy, so you know what people will
and will not answer.

http://www.haskell.org/haskellwiki/Homework_help


Then let us know what you're trying to do, and what your difficulty has been.


Cheers,


D
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[Haskell-cafe] (no subject)

[apostolos flessas]

hi,
 
i am looking for someone to help me with an assignment!
can anyone help me?
 
i am looking forward to your reply.
 
sincerely,
 Tolis

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[Haskell-cafe] (no subject)

[Mario Blažević]

Hello. I'm trying to apply the nested regions (as in Lightweight Monadic 
Regions by Oleg Kiselyov and Chung-chieh Shan) design pattern, if that's the 
proper term. I was hoping to gain a bit more type safety in this little library 
I'm working on -- Streaming Component Combinators, available on Hackage. I 
guess the problem is that I'm getting too much type safety now, because I can't 
get the thing to compile. Most of the existing code works, the only exceptions 
seem to be various higher-order functions. I've reduced the problem to several 
lines of Literate Haskell code below, can anybody think of a solution or a 
reason there can't be one?

> {-# LANGUAGE MultiParamTypeClasses, EmptyDataDecls, Rank2Types #-}
> {-# LANGUAGE FunctionalDependencies, FlexibleInstances, IncoherentInstances 
> #-}
> module Main where
> main = undefined

I'll call the main type, originally a monad transformer, simply Region. I'm 
leaving out the Monad and MonadTransformer instances, because they don't 
contribute to the problem. The parameter r is the phantom region type.

> newtype Region r a = Region a

The Ancestor class is used to denote relationship between two regions where one 
is nested in another.

> data Child r

> class Ancestor r r'

> instance   Ancestor r (Child r)
> instance Ancestor r1 r2 => Ancestor r1 (Child r2)

Handle is a simple wrapper around a value. It carries information about the 
region that originates the value.

> data Handle r x = Handle x

A typical calculation in the Region monad will take a bunch of Handles 
inherited from an Ancestor region and do something with them. The Ancestor 
constraint is there to ensure that the handles are not fake but genuinely 
inherited.

> type SingleHandler x y = forall r1s rs. Ancestor r1s rs =>
>  Handle r1s x -> Region rs y
> type DoubleHandler x y z = forall r1d r2d rd. (Ancestor r1d rd, Ancestor r2d 
> rd) =>
>Handle r1d x -> Handle r2d y -> Region rd z

And now I'm getting to the problem. The following higher-order function doesn't 
type-check:

> mapD :: (SingleHandler x z -> SingleHandler y z)
> -> DoubleHandler x w z -> DoubleHandler y w z
> mapD f d = \y w-> f (\x-> d x w) y

I get the same error from GHC 6.8.2 and 6.8.2:

Test.lhs:36:28:
Could not deduce (Ancestor r2d rs)
  from the context (Ancestor r1s rs)
  arising from a use of `d' at Test.lhs:36:28-32
Possible fix:
  add (Ancestor r2d rs) to the context of
the polymorphic type
  `forall r1s rs. (Ancestor r1s rs) => Handle r1s x -> Region rs z'
In the expression: d x w
In the first argument of `f', namely `(\ x -> d x w)'
In the expression: f (\ x -> d x w) y

The same code compiles just fine if all the Ancestor constraints are removed. I 
don't see any place to add the extra (Ancestor r2d rs) constraint, as GHC 
recommends. I think it ought to be able to figure things out based on the 
exisisting constraints, but I may be wrong: perhaps higher-order functions pose 
an insurmountable problem for type-level programming in Haskell. Can anybody 
shed any light on this?



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[Haskell-cafe] (no subject)

[john lask]

Hi

has anyone had any success in running a recent version of hs-plugins on a 
windows platform. I refer to this post to the haskell list in December last 
year. The current version of hs-plugins dosn't appear to work either. Same 
problem ...


http://www.haskell.org/pipermail/haskell/2007-December/020043.html


jvl

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Re: [Haskell-cafe] Lindenmayer Systems, WAS: (no subject)

[Gwern Branwen]

On 2008.06.15 16:50:28 +0200, Adrian Neumann <[EMAIL PROTECTED]> scribbled 6.9K 
characters:
> I screwed up the email, sorry about that. What I wanted to say was:
>
> Hello,
>
> as homework I was assigned to "design and draw an image" using the SOE
> Graphics library [1]. In order to impress my classmates I decided to draw
> a bush-like thingy using a Lindenmayer-System. It turns out quite nice
> [2], and so I thought I might share my code with you. Of course criticism
> is very welcome.
>
> Ok, here we go:
>
>> {- I downloaded the source and put my file in the same directory
>>You may need to adjust the imports -}
>> module Main where
>> import Picture
>> import Draw -- change xWin to 1000 and yWin to 700 for this to work
>> import EnableGUI -- I use a Mac
>> import SOE hiding (Region)
>> import qualified SOE as G (Region)
>> import Data.List
>> import Random
>>
>> -- lines are not Shapes unfortunately
>> linie = ((Shape $ Polygon [(-0.1,-0.01),(-0.1,0.01),(0.1,0.01),
>> (0.1,-0.01)]), (-0.1,0), (0.1,0))
>>
>> main = enableGUI >> do
>> w <- openWindow "Lindenmayer System" (xWin, yWin)
>> newStdGen
>> g <- getStdGen
>> drawPic w (aufgabe2 g)
>> k <- getKey w
>> if (k=='q') then do
>> closeWindow w
>> return () else do
>> clearWindow w
>> main
>>
>> -- one big ugly line of code, not that interesting though
>> aufgabe2 g= dasBild where
>> r = rotateRegion (pi/2) $ Translate (-2.5,0) $ renderLSystem linie
>> (lSystem 20 g)
>> dasBild = Region White r `Over` Region Black ( Translate (0,-1.8) $
>> Scale (1,0.3)$ Translate (0,-2.6) $ rotateRegion (pi/2+pi/3) $
>> Translate (0,2.6) $ r) `Over` Region Green (Shape $ Polygon
>> [(-5,-3.5),(-5,-1.5),(5,-1.5),(5,-3.5)]) `Over` Region Yellow
>> (Translate (4,1.5) (Shape $ circle (0.5))) `Over`
>> Region Blue (Shape $ Rectangle 14 7)
>>
>> -- start of the interesting part:
>> -- A - Axiom, the base shape we use for rendering later
>> --F - Forward
>> --Branch - what it says
>>
>> data LSys = A LSys | F LSys | Branch StdGen [LSys] LSys | Done
>> deriving Show
>>
>> -- a Axiom is a region with two connector points
>> type Axiom = (Region, Vertex, Vertex)
>>
>> -- this seems not to be used anymore?
>>
>> scaleAxiom :: Float -> Axiom -> Axiom
>> scaleAxiom f (r,u,v) = (Scale (f,f) r, f .*. u, f .*. v)
>>
>> -- just for testing purposes
>> testLSys = A (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A
>> (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A (F Done), A (F
>> Done)] Done))), A (F Done)] Done), A (F Done)] Done))), A (F Done)]
>> Done)
>>
>> -- a 2D rotation matrix
>> drehM :: Float -> (Float, Float, Float, Float)
>> drehM w = (cos w, -sin w, sin w, cos w)
>>
>> -- matrix vector multiplication
>> (.**.) :: (Float, Float, Float, Float) -> Vertex -> Vertex
>> (.**.) (a,b,c,d) (px,py) = (a*px+b*py, c* px+d*py)
>>
>> -- other vector stuff
>> (.-.) (a,b) (c,d) = (a-c,b-d)
>> (.+.) (a,b) (c,d) = (a+c,b+d)
>> (.*.) l (c,d) = (c*l,d*l)
>> abs' (a,b) = (abs a, abs b)
>> betr (a,b) = sqrt (a*a+b*b)
>>
>> -- SOE doesn't come with a way to rotate Regions, so I wrote my own
>> rotateRegion :: Float -> Region -> Region
>> rotateRegion f (Shape s) = Shape (rotateS f s)
>> rotateRegion f (Translate v r) = Translate ((drehM f).**.v)
>> (rotateRegion f r)
>>
>> -- the scaling part is not right I think. Everything seems to break if
>> I try to incorporate scaling
>> -- into the rendering
>>
>> rotateRegion f (Scale v r) = Scale ((betr v/ betr nv) .*. nv)
>> (rotateRegion f r) where
>> x = ((drehM f).**. (fst v,0))
>> y = ((drehM f) .**. (0,snd v))
>> nv = (abs' x) .+. (abs' y)
>> rotateRegion f (Complement r) =Complement (rotateRegion f r)
>> rotateRegion f (Union r1 r2) = Union (rotateRegion f r1) (rotateRegion
>> f r2)
>> rotateRegion f (Intersect r1 r2) = Intersect (rotateRegion f r1)
>> (rotateRegion f r2)
>> rotateRegion f (Xor r1 r2) = Xor (rotateRegion f r1) (rotateRegion f
>> r2)
>> rotateRegion _ s=s
>>
>> rotateS f (Polygon pts) = Polygon (map ((drehM f) .**.) pts)
>> rotateS f x = x
>>
>> -- nondeterministically generate a word in our LSys language
>> -- lots of copy&paste here, any way to do this better?
>>
>> lSystem :: Int -> StdGen -> LSys
>> lSystem n g = f n g (A undefined) where
>> f :: Int -> StdGen -> LSys -> LSys
>> f 0 _ _ = Done
>> f (n+1) g (A _)
>> | choose >= 1 = A (f n ng (F undefined))
>> | choose == 0 = A (f n ng (Branch ng [f n ng' (A undefined), f
>> n ng'' (A undefined)] undefined)) where
>> (choose, ng) = randomR (0::Int,3::Int) g
>> (ng', ng'') = split ng
>> f (n+1) g (F _)
>> | choose >= 1 = F (f n ng (F undefined))
>> | choose == 0 = F (f n ng (Branch ng [f n ng' (A undefined), f
>> n ng'' (A undefined)] undefined)) where
>> (choose, ng) = randomR (0::Int,3::Int) g
>> (ng', ng'') = split ng
>> f (n+1) g (Branch h lSys _)
>> | choose >= 1 

Re: [Haskell-cafe] Lindenmayer Systems, WAS: (no subject)

[Adrian Neumann]

I screwed up the email, sorry about that. What I wanted to say was:

Hello,

as homework I was assigned to "design and draw an image" using the  
SOE Graphics library [1]. In order to impress my classmates I decided  
to draw a bush-like thingy using a Lindenmayer-System. It turns out  
quite nice [2], and so I thought I might share my code with you. Of  
course criticism is very welcome.


Ok, here we go:



{- I downloaded the source and put my file in the same directory
   You may need to adjust the imports -}
module Main where
import Picture
import Draw -- change xWin to 1000 and yWin to 700 for this to work
import EnableGUI -- I use a Mac
import SOE hiding (Region)
import qualified SOE as G (Region)
import Data.List
import Random

-- lines are not Shapes unfortunately
linie = ((Shape $ Polygon [(-0.1,-0.01),(-0.1,0.01),(0.1,0.01), 
(0.1,-0.01)]), (-0.1,0), (0.1,0))


main = enableGUI >> do
w <- openWindow "Lindenmayer System" (xWin, yWin)
newStdGen
g <- getStdGen
drawPic w (aufgabe2 g)
k <- getKey w
if (k=='q') then do
closeWindow w
return () else do
clearWindow w
main

-- one big ugly line of code, not that interesting though
aufgabe2 g= dasBild where
r = rotateRegion (pi/2) $ Translate (-2.5,0) $ renderLSystem  
linie (lSystem 20 g)
dasBild = Region White r `Over` Region Black ( Translate  
(0,-1.8) $ Scale (1,0.3)$ Translate (0,-2.6) $ rotateRegion (pi/2 
+pi/3) $ Translate (0,2.6) $ r) `Over` Region Green (Shape $  
Polygon [(-5,-3.5),(-5,-1.5),(5,-1.5),(5,-3.5)]) `Over` Region  
Yellow (Translate (4,1.5) (Shape $ circle (0.5))) `Over`

Region Blue (Shape $ Rectangle 14 7)

-- start of the interesting part:
-- A - Axiom, the base shape we use for rendering later
--F - Forward
--Branch - what it says

data LSys = A LSys | F LSys | Branch StdGen [LSys] LSys | Done  
deriving Show


-- a Axiom is a region with two connector points
type Axiom = (Region, Vertex, Vertex)

-- this seems not to be used anymore?

scaleAxiom :: Float -> Axiom -> Axiom
scaleAxiom f (r,u,v) = (Scale (f,f) r, f .*. u, f .*. v)

-- just for testing purposes
testLSys = A (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A  
(Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A (F Done), A (F  
Done)] Done))), A (F Done)] Done), A (F Done)] Done))), A (F Done)]  
Done)


-- a 2D rotation matrix
drehM :: Float -> (Float, Float, Float, Float)
drehM w = (cos w, -sin w, sin w, cos w)

-- matrix vector multiplication
(.**.) :: (Float, Float, Float, Float) -> Vertex -> Vertex
(.**.) (a,b,c,d) (px,py) = (a*px+b*py, c* px+d*py)

-- other vector stuff
(.-.) (a,b) (c,d) = (a-c,b-d)
(.+.) (a,b) (c,d) = (a+c,b+d)
(.*.) l (c,d) = (c*l,d*l)
abs' (a,b) = (abs a, abs b)
betr (a,b) = sqrt (a*a+b*b)

-- SOE doesn't come with a way to rotate Regions, so I wrote my own
rotateRegion :: Float -> Region -> Region
rotateRegion f (Shape s) = Shape (rotateS f s)
rotateRegion f (Translate v r) = Translate ((drehM f).**.v)  
(rotateRegion f r)


-- the scaling part is not right I think. Everything seems to break  
if I try to incorporate scaling

-- into the rendering

rotateRegion f (Scale v r) = Scale ((betr v/ betr nv) .*. nv)  
(rotateRegion f r) where

x = ((drehM f).**. (fst v,0))
y = ((drehM f) .**. (0,snd v))
nv = (abs' x) .+. (abs' y)
rotateRegion f (Complement r) =Complement (rotateRegion f r)
rotateRegion f (Union r1 r2) = Union (rotateRegion f r1)  
(rotateRegion f r2)
rotateRegion f (Intersect r1 r2) = Intersect (rotateRegion f r1)  
(rotateRegion f r2)
rotateRegion f (Xor r1 r2) = Xor (rotateRegion f r1) (rotateRegion  
f r2)

rotateRegion _ s=s

rotateS f (Polygon pts) = Polygon (map ((drehM f) .**.) pts)
rotateS f x = x

-- nondeterministically generate a word in our LSys language
-- lots of copy&paste here, any way to do this better?

lSystem :: Int -> StdGen -> LSys
lSystem n g = f n g (A undefined) where
f :: Int -> StdGen -> LSys -> LSys
f 0 _ _ = Done
f (n+1) g (A _)
| choose >= 1 = A (f n ng (F undefined))
| choose == 0 = A (f n ng (Branch ng [f n ng' (A  
undefined), f n ng'' (A undefined)] undefined)) where

(choose, ng) = randomR (0::Int,3::Int) g
(ng', ng'') = split ng
f (n+1) g (F _)
| choose >= 1 = F (f n ng (F undefined))
| choose == 0 = F (f n ng (Branch ng [f n ng' (A  
undefined), f n ng'' (A undefined)] undefined)) where

(choose, ng) = randomR (0::Int,3::Int) g
(ng', ng'') = split ng
f (n+1) g (Branch h lSys _)
| choose >= 1 = Branch h lSys  (f n ng (F undefined))
| choose == 0 = Branch h lSys (f n ng (Branch ng [f n  
ng' (A undefined), f n ng'' (A undefined)] undefined)) where

(choose, ng) = randomR (0::Int,5::Int) g
(ng', ng'') = split ng

-- recursivly render a LSys
renderLSystem :: Axiom -> LSys -> Region
renderLSystem _ Done = Empty
renderLSystem (r,u,v) (A lSys) = r `Union` renderLSyst

[Haskell-cafe] (no subject)

[Adrian Neumann]

{- I downloaded the source and put my file in the same directory
   You may need to adjust the imports -}
module Main where
import Picture
import Draw -- change xWin to 1000 and yWin to 700 for this to work
import EnableGUI -- I use a Mac
import SOE hiding (Region)
import qualified SOE as G (Region)
import Data.List
import Random

-- lines are not Shapes unfortunately
linie = ((Shape $ Polygon [(-0.1,-0.01),(-0.1,0.01),(0.1,0.01), 
(0.1,-0.01)]), (-0.1,0), (0.1,0))


main = enableGUI >> do
w <- openWindow "Lindenmayer System" (xWin, yWin)
newStdGen
g <- getStdGen
drawPic w (aufgabe2 g)
k <- getKey w
if (k=='q') then do
closeWindow w
return () else do
clearWindow w
main

-- one big ugly line of code, not that interesting though
aufgabe2 g= dasBild where
r = rotateRegion (pi/2) $ Translate (-2.5,0) $ renderLSystem  
linie (lSystem 20 g)
dasBild = Region White r `Over` Region Black ( Translate  
(0,-1.8) $ Scale (1,0.3)$ Translate (0,-2.6) $ rotateRegion (pi/2+pi/ 
3) $ Translate (0,2.6) $ r) `Over` Region Green (Shape $ Polygon  
[(-5,-3.5),(-5,-1.5),(5,-1.5),(5,-3.5)]) `Over` Region Yellow  
(Translate (4,1.5) (Shape $ circle (0.5))) `Over`

Region Blue (Shape $ Rectangle 14 7)

-- start of the interesting part:
-- A - Axiom, the base shape we use for rendering later
--F - Forward
--Branch - what it says

data LSys = A LSys | F LSys | Branch StdGen [LSys] LSys | Done  
deriving Show


-- a Axiom is a region with two connector points
type Axiom = (Region, Vertex, Vertex)

-- this seems not to be used anymore?

scaleAxiom :: Float -> Axiom -> Axiom
scaleAxiom f (r,u,v) = (Scale (f,f) r, f .*. u, f .*. v)

-- just for testing purposes
testLSys = A (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A  
(Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A (F Done), A (F  
Done)] Done))), A (F Done)] Done), A (F Done)] Done))), A (F Done)]  
Done)


-- a 2D rotation matrix
drehM :: Float -> (Float, Float, Float, Float)
drehM w = (cos w, -sin w, sin w, cos w)

-- matrix vector multiplication
(.**.) :: (Float, Float, Float, Float) -> Vertex -> Vertex
(.**.) (a,b,c,d) (px,py) = (a*px+b*py, c* px+d*py)

-- other vector stuff
(.-.) (a,b) (c,d) = (a-c,b-d)
(.+.) (a,b) (c,d) = (a+c,b+d)
(.*.) l (c,d) = (c*l,d*l)
abs' (a,b) = (abs a, abs b)
betr (a,b) = sqrt (a*a+b*b)

-- SOE doesn't come with a way to rotate Regions, so I wrote my own
rotateRegion :: Float -> Region -> Region
rotateRegion f (Shape s) = Shape (rotateS f s)
rotateRegion f (Translate v r) = Translate ((drehM f).**.v)  
(rotateRegion f r)


-- the scaling part is not right I think. Everything seems to break  
if I try to incorporate scaling

-- into the rendering

rotateRegion f (Scale v r) = Scale ((betr v/ betr nv) .*. nv)  
(rotateRegion f r) where

x = ((drehM f).**. (fst v,0))
y = ((drehM f) .**. (0,snd v))
nv = (abs' x) .+. (abs' y)
rotateRegion f (Complement r) =Complement (rotateRegion f r)
rotateRegion f (Union r1 r2) = Union (rotateRegion f r1)  
(rotateRegion f r2)
rotateRegion f (Intersect r1 r2) = Intersect (rotateRegion f r1)  
(rotateRegion f r2)

rotateRegion f (Xor r1 r2) = Xor (rotateRegion f r1) (rotateRegion f r2)
rotateRegion _ s=s

rotateS f (Polygon pts) = Polygon (map ((drehM f) .**.) pts)
rotateS f x = x

-- nondeterministically generate a word in our LSys language
-- lots of copy&paste here, any way to do this better?

lSystem :: Int -> StdGen -> LSys
lSystem n g = f n g (A undefined) where
f :: Int -> StdGen -> LSys -> LSys
f 0 _ _ = Done
f (n+1) g (A _)
| choose >= 1 = A (f n ng (F undefined))
| choose == 0 = A (f n ng (Branch ng [f n ng' (A undefined),  
f n ng'' (A undefined)] undefined)) where

(choose, ng) = randomR (0::Int,3::Int) g
(ng', ng'') = split ng
f (n+1) g (F _)
| choose >= 1 = F (f n ng (F undefined))
| choose == 0 = F (f n ng (Branch ng [f n ng' (A undefined),  
f n ng'' (A undefined)] undefined)) where

(choose, ng) = randomR (0::Int,3::Int) g
(ng', ng'') = split ng
f (n+1) g (Branch h lSys _)
| choose >= 1 = Branch h lSys  (f n ng (F undefined))
| choose == 0 = Branch h lSys (f n ng (Branch ng [f n ng' (A  
undefined), f n ng'' (A undefined)] undefined)) where

(choose, ng) = randomR (0::Int,5::Int) g
(ng', ng'') = split ng

-- recursivly render a LSys
renderLSystem :: Axiom -> LSys -> Region
renderLSystem _ Done = Empty
renderLSystem (r,u,v) (A lSys) = r `Union` renderLSystem (r,u,v) lSys
renderLSystem (r,u,v) (F lSys) = r'' `Union` renderLSystem (r'', u . 
+. o , v .+.o) lSys where

r'' =  Translate o   $  r
o = (v .-. u)
renderLSystem (r,u,v) (Branch g lSys rest) =
theBranches `Union` renderLSystem (r,u,v) rest where
theBranches = Translate o $ foldr Union Empty $
-- we need to rotate around the u-Connector, not around (0,0)
-- thus translatio

Re: [Haskell-cafe] (no subject)

[Daniel Fischer]

Am Donnerstag, 8. Mai 2008 15:36 schrieb [EMAIL PROTECTED]:
> Hi I have a bit of a dilemma.I have a list of lists, eg,
> [[1,2,3],[4,5,6],[7,8,9]]. Imagine they represent a grid with 0-2 on the x
> axis and 0-2 on the y axis, eg, (0,0) is 1, (1,0) is 2, (2,1) is 6, etc and
> (2,3) is 9. I want to be able to put in the list of lists, and the (x,y)
> coordinate, and return the value. 
>
> Also, I need to be able to replace a value in the list. Eg, if I wanted to
> replace (2,3) with 100, then the output of the expression would be
> [[1,2,3],[4,5,6],[7,8,100]].
>
> Any help would be great!

To get the value at a position, look up (!!)
To replace a value, you could use zipWith

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[Haskell-cafe] (no subject)

[u4538637]

Hi I have a bit of a dilemma.I have a list of lists, eg, 
[[1,2,3],[4,5,6],[7,8,9]]. Imagine they represent a grid with 0-2 on the x axis 
and 0-2 on the y axis, eg, (0,0) is 1, (1,0) is 2, (2,1) is 6, etc and (2,3) is 
9. I want to be able to put in the list of lists, and the (x,y) coordinate, and 
return the value. 

Also, I need to be able to replace a value in the list. Eg, if I wanted to 
replace (2,3) with 100, then the output of the expression would be 
[[1,2,3],[4,5,6],[7,8,100]].

Any help would be great!
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Re: [Haskell-cafe] Re: [Haskell] (no subject)

[Thomas Hartman]

I think at some intermediate stage that flag helped me compile, but in the 
final version it's unnecessary.

my bad.




Thomas Hartman <[EMAIL PROTECTED]> 
Sent by: [EMAIL PROTECTED]
09/05/2007 06:29 PM

To
[EMAIL PROTECTED]
cc
[EMAIL PROTECTED], haskell-cafe@haskell.org, Tomi Owens 
<[EMAIL PROTECTED]>
Subject
Re: [Haskell-cafe] Re: [Haskell] (no subject)







I think you want something like this 

{-# OPTIONS -fglasgow-exts #-} 

f :: (Integer, Float) -> Integer 
f (a,b) = a * floor (10/b) 

lst :: [(Integer, Integer)] 
lst = [(a ^ 2 + b ^ 2, a) | a <- [1..4], b <- [1..4], a^2 + b^2 < 20, b <= 
a] 

lst3 = map (f) ( map ( intTupToFloatTup  ) lst ) 

intTupToFloatTup :: (Integer, Integer) -> (Integer, Float) 
intTupToFloatTup (int1, int2) = (int1, fromInteger int2) 

load the whole thing into ghci with ghci proggie.hs 

when I have this type of problem, my usual approach is to put the code 
into a text file, load that in ghci, derive type sigs on the functions 
that work, and then see if I can figure out 
the mismatch. 

you could probably get a fast answer to this kind of question on the 
#haskell irc channel as well. 

hope this helps, 

thomas. 



"Scott Williams" <[EMAIL PROTECTED]> 
Sent by: [EMAIL PROTECTED] 
09/05/2007 05:28 PM 


To
"Tomi Owens" <[EMAIL PROTECTED]> 
cc
haskell-cafe@haskell.org 
Subject
[Haskell-cafe] Re: [Haskell] (no subject)








[bcc haskell, cc haskell-cafe]

On 9/5/07, Tomi Owens <[EMAIL PROTECTED]> wrote: 
Hi there. I'm a teacher of Maths and am working my way through the Euler 
Project problems for fun. I have mostly been using Basic, but have read up 
about Haskell and think it looks like a sensible way to solve many of the 
problems. 

OK, so I've downloaded GHCi and am trying to teach myself. 

So far I have done this: 

 ___ ___ _ 
/ _ \ /\  /\/ __(_) 
/ /_\// /_/ / /  | |  GHC Interactive, version 6.6.1, for Haskell 98. 
/ /_\\/ __  / /___| |  http://www.haskell.org/ghc/ 
\/\/ /_/\/|_|  Type :? for help. 

Loading package base ... linking ... done. 
Prelude> let f (a,b) = a * floor (10/b) 
Prelude> f(2,5) 
4 

Here you can find out type ghci has inferred for this function.
> :t f
f :: (RealFrac b, Integral b1) => (b1, b) -> b1



This function works just as I want it to. 

Now I try creating a list: 

Prelude> [(a2+b2,a)| a <- [1..4] , b<- [1..4], a2+b2<20, b<=a] 
[(2,1),(5,2),(8,2),(10,3),(13,3),(18,3),(17,4)] 

Let's assign this to an intermediate variable so we can query it's type:

Prelude> let lst = [(a ^ 2 + b ^ 2, a) | a <- [1..4], b <- [1..4], a^2 + 
b^2 < 20, b <= a]
Prelude> lst 
[(2,1),(5,2),(8,2),(10,3),(13,3),(18,3),(17,4)]
Prelude> :t lst
lst :: [(Integer, Integer)]

aha; here's the source of the type mismatch:
Prelude> :t floor
floor :: (RealFrac a, Integral b) => a -> b 

Floor has to take a RealFrac. According to hoogle[1], we can use various 
floating-point approximations (Float, Double, CFloat, etc) or we can use 
the exact Rational type.
[1] http://haskell.org/hoogle/?q=RealFrac

You can get your types to match by declaring your list to be of type 
[(Rational, Rational)] either by explicitly typing one of the untyped 
variables or the entire expression: 
Prelude> let lst = [(a ^ 2 + b ^ 2, a) | (a::Rational) <- [1..4], b <- 
[1..4], a^2 + b^2 < 20, b <= a]
Prelude> :t lst
lst :: [(Rational, Rational)]
Prelude> let lst :: [(Rational, Rational)] = [(a ^ 2 + b ^ 2, a) | a <- 
[1..4], b <- [1..4], a^2 + b^2 < 20, b <= a] 
Prelude> :t lst
lst :: [(Rational, Rational)]


and this works 
So now I try to apply the function to the list: 

Prelude> map (f) [(a2+b2,a)| a <- [1..4] , b<- [1..4], a2+b2<20, b<=a] 

and I get this result: 

:1:5: 
  Ambiguous type variable `t' in the constraints: 
`Integral t' arising from use of `f' at :1:5 
`RealFrac t' arising from use of `f' at :1:5 
  Probable fix: add a type signature that fixes these type variable(s) 
I'm sorry, but I don't quite get how to set the type signature and how it 
will apply to my function... 

Thanks, 

Hope this helps


Tomi 

 

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Re: [Haskell-cafe] Re: [Haskell] (no subject)

[Thomas Hartman]

I think you want something like this

{-# OPTIONS -fglasgow-exts #-}

f :: (Integer, Float) -> Integer
f (a,b) = a * floor (10/b) 

lst :: [(Integer, Integer)]
lst = [(a ^ 2 + b ^ 2, a) | a <- [1..4], b <- [1..4], a^2 + b^2 < 20, b <= 
a]

lst3 = map (f) ( map ( intTupToFloatTup  ) lst )

intTupToFloatTup :: (Integer, Integer) -> (Integer, Float)
intTupToFloatTup (int1, int2) = (int1, fromInteger int2)

load the whole thing into ghci with ghci proggie.hs

when I have this type of problem, my usual approach is to put the code 
into a text file, load that in ghci, derive type sigs on the functions 
that work, and then see if I can figure out
the mismatch.

you could probably get a fast answer to this kind of question on the 
#haskell irc channel as well.

hope this helps,

thomas.




"Scott Williams" <[EMAIL PROTECTED]> 
Sent by: [EMAIL PROTECTED]
09/05/2007 05:28 PM

To
"Tomi Owens" <[EMAIL PROTECTED]>
cc
haskell-cafe@haskell.org
Subject
[Haskell-cafe] Re: [Haskell] (no subject)






[bcc haskell, cc haskell-cafe]

On 9/5/07, Tomi Owens <[EMAIL PROTECTED]> wrote:
Hi there. I'm a teacher of Maths and am working my way through the Euler 
Project problems for fun. I have mostly been using Basic, but have read up 
about Haskell and think it looks like a sensible way to solve many of the 
problems. 

OK, so I've downloaded GHCi and am trying to teach myself. 

So far I have done this: 

  ___ ___ _ 
 / _ \ /\  /\/ __(_) 
/ /_\// /_/ / /  | |  GHC Interactive, version 6.6.1, for Haskell 98. 
/ /_\\/ __  / /___| |  http://www.haskell.org/ghc/ 
\/\/ /_/\/|_|  Type :? for help. 

Loading package base ... linking ... done. 
Prelude> let f (a,b) = a * floor (10/b) 
Prelude> f(2,5) 
4 

Here you can find out type ghci has inferred for this function.
> :t f
f :: (RealFrac b, Integral b1) => (b1, b) -> b1

 

This function works just as I want it to. 

Now I try creating a list: 

Prelude> [(a2+b2,a)| a <- [1..4] , b<- [1..4], a2+b2<20, b<=a] 
[(2,1),(5,2),(8,2),(10,3),(13,3),(18,3),(17,4)] 

Let's assign this to an intermediate variable so we can query it's type:

Prelude> let lst = [(a ^ 2 + b ^ 2, a) | a <- [1..4], b <- [1..4], a^2 + 
b^2 < 20, b <= a]
Prelude> lst 
[(2,1),(5,2),(8,2),(10,3),(13,3),(18,3),(17,4)]
Prelude> :t lst
lst :: [(Integer, Integer)]

aha; here's the source of the type mismatch:
Prelude> :t floor
floor :: (RealFrac a, Integral b) => a -> b 

Floor has to take a RealFrac. According to hoogle[1], we can use various 
floating-point approximations (Float, Double, CFloat, etc) or we can use 
the exact Rational type.
[1] http://haskell.org/hoogle/?q=RealFrac

You can get your types to match by declaring your list to be of type 
[(Rational, Rational)] either by explicitly typing one of the untyped 
variables or the entire expression: 
Prelude> let lst = [(a ^ 2 + b ^ 2, a) | (a::Rational) <- [1..4], b <- 
[1..4], a^2 + b^2 < 20, b <= a]
Prelude> :t lst
lst :: [(Rational, Rational)]
Prelude> let lst :: [(Rational, Rational)] = [(a ^ 2 + b ^ 2, a) | a <- 
[1..4], b <- [1..4], a^2 + b^2 < 20, b <= a] 
Prelude> :t lst
lst :: [(Rational, Rational)]


and this works 
So now I try to apply the function to the list: 

Prelude> map (f) [(a2+b2,a)| a <- [1..4] , b<- [1..4], a2+b2<20, b<=a] 

and I get this result: 

:1:5: 
   Ambiguous type variable `t' in the constraints: 
 `Integral t' arising from use of `f' at :1:5 
 `RealFrac t' arising from use of `f' at :1:5 
   Probable fix: add a type signature that fixes these type variable(s) 
I'm sorry, but I don't quite get how to set the type signature and how it 
will apply to my function... 

Thanks, 

Hope this helps
 

Tomi 

 

Department for Education, Sport and Culture E Mail
This message is for the named person's use only. It may contain
confidential, proprietary or legally privileged information. No
confidentiality or privilege is waived or lost by any mistransmission.
If you receive this message in error, please immediately delete it and all 
copies of it from your system, destroy any hard copies of it and notify 
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r

[Haskell-cafe] Re: [Haskell] (no subject)

[Scott Williams]

[bcc haskell, cc haskell-cafe]

On 9/5/07, Tomi Owens <[EMAIL PROTECTED]> wrote:
>
> Hi there. I'm a teacher of Maths and am working my way through the Euler
> Project problems for fun. I have mostly been using Basic, but have read up
> about Haskell and think it looks like a sensible way to solve many of the
> problems.
>
> OK, so I've downloaded GHCi and am trying to teach myself.
>
> So far I have done this:
>
>   ___ ___ _
>  / _ \ /\  /\/ __(_)
> / /_\// /_/ / /  | |  GHC Interactive, version 6.6.1, for Haskell 98.
> / /_\\/ __  / /___| |  http://www.haskell.org/ghc/
> \/\/ /_/\/|_|  Type :? for help.
>
> Loading package base ... linking ... done.
> Prelude> let f (a,b) = a * floor (10/b)
> Prelude> f(2,5)
> 4


Here you can find out type ghci has inferred for this function.
> :t f
f :: (RealFrac b, Integral b1) => (b1, b) -> b1



This function works just as I want it to.
>
> Now I try creating a list:
>
> Prelude> [(a2+b2,a)| a <- [1..4] , b<- [1..4], a2+b2<20, b<=a]
> [(2,1),(5,2),(8,2),(10,3),(13,3),(18,3),(17,4)]


Let's assign this to an intermediate variable so we can query it's type:

Prelude> let lst = [(a ^ 2 + b ^ 2, a) | a <- [1..4], b <- [1..4], a^2 + b^2
< 20, b <= a]
Prelude> lst
[(2,1),(5,2),(8,2),(10,3),(13,3),(18,3),(17,4)]
Prelude> :t lst
lst :: [(Integer, Integer)]

aha; here's the source of the type mismatch:
Prelude> :t floor
floor :: (RealFrac a, Integral b) => a -> b

Floor has to take a RealFrac. According to hoogle[1], we can use various
floating-point approximations (Float, Double, CFloat, etc) or we can use the
exact Rational type.
[1] http://haskell.org/hoogle/?q=RealFrac

You can get your types to match by declaring your list to be of type
[(Rational, Rational)] either by explicitly typing one of the untyped
variables or the entire expression:
Prelude> let lst = [(a ^ 2 + b ^ 2, a) | (a::Rational) <- [1..4], b <-
[1..4], a^2 + b^2 < 20, b <= a]
Prelude> :t lst
lst :: [(Rational, Rational)]
Prelude> let lst :: [(Rational, Rational)] = [(a ^ 2 + b ^ 2, a) | a <-
[1..4], b <- [1..4], a^2 + b^2 < 20, b <= a]
Prelude> :t lst
lst :: [(Rational, Rational)]


and this works
> So now I try to apply the function to the list:
>
> Prelude> map (f) [(a2+b2,a)| a <- [1..4] , b<- [1..4], a2+b2<20, b<=a]
>
> and I get this result:
>
> :1:5:
>Ambiguous type variable `t' in the constraints:
>  `Integral t' arising from use of `f' at :1:5
>  `RealFrac t' arising from use of `f' at :1:5
>Probable fix: add a type signature that fixes these type variable(s)

I'm sorry, but I don't quite get how to set the type signature and how it
> will apply to my function...
>
> Thanks,


Hope this helps


Tomi
> 
>
>
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Re: [Haskell-cafe] (no subject)

[Bulat Ziganshin]

Hello Thomas,

Thursday, August 9, 2007, 8:12:27 PM, you wrote:

> In the following code which uses template haskell, how can I get
> back the macro-expanded code generated from

citating http://www.haskell.org/bz/thdoc.htm :

In order to make debugging Template Haskell programs easier, compiler
supports flag -ddump-splices, which shows the expansion of all
top-level splices as they happen.

-- 
Best regards,
 Bulatmailto:[EMAIL PROTECTED]

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[Haskell-cafe] (no subject)

[Thomas Hartman]

In the following code which uses template haskell, how can I get back the 
macro-expanded code generated from 

$(inferStartState ''MyState)

I *can* recover the macro-expanded code for 

$(cnst 1 "x") 

using a debugging technique bulat describes on his tutorial at 
http://www.haskell.org/bz/th3.htm

You can see what's going on in the function debugTemplates below.

I'm trying to do this actually, to better understand how HAppS deals with 
state. It's a bit opaque now since the example on the tutorial uses TH. I 
think I would understand it better if I had code that didn't depend on TH.

(MyState is from the happs tutorial at 
http://www.haskell.org/haskellwiki/HAppS_tutorial )

thanks!

thomas.

{-# OPTIONS -fglasgow-exts -fth  #-}
module MyState where
import HAppS
import HAppS.Protocols.SimpleHTTP2
 
import Data.Monoid
import Data.Typeable
import Control.Monad.State (get, put)

import Language.Haskell.TH
import Language.Haskell.TH.Syntax
 
data MyState = MySt { appVal :: Int } deriving (Read, Show, Typeable)
 
instance Serialize MyState where
  encodeStringM = defaultEncodeStringM
  decodeStringM = defaultDecodeStringM
 
instance Monoid MyState where
  mempty = MySt 0
  mappend (MySt x) (MySt y) = MySt (x+y)
 
-- in ghci...  -fth, :m +

-- ghci... :t (inferStartState ''MyState) :: (Quasi m) => m [Dec]
$(inferStartState ''MyState) -- boilerplate that will eventually be SYB

-- ghci... :t cnst 1 "x" :: (Monad m) => m Exp
cnst n s = return (LamE (replicate n WildP) (LitE (StringL s)))

dumpSplice splice = runQ splice >>= putStrLn . pprint
debugTemplates = do dumpSplice (cnst 1 "x")
dumpSplice (inferStartState ''MyState)

{-
*MyState> debugTemplates
\_ -> "x"
Template Haskell error: Can't do `reify' in the IO monad
*** Exception: user error (Template Haskell failure)
-}



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[Haskell-cafe] binary file handling (was: no subject)

[Paul R. Potts]

Hello all,

Ketil Malde wrote:

> This is what I find in System.IO (ghci> :b System.IO):
>
>   openBinaryFile :: FilePath -> IOMode -> IO Handle
>   openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle)
>   hSetBinaryMode :: Handle -> Bool -> IO ()
>
> so you have the option of either using openBinaryFile or openFile and
> using hSetBinaryMode to true. I guess - I've never had to use them.
>
> I can't find a readBinaryFile either, but writing one might be a good
> excercise?
>
> Makes me wonder whether one should have binary be the default?  I'm a
> stranger in Windows-land, but are there cases where you want reading of
> a file to be terminated on ^Z?  Seems pretty awful to me.

I ran into this same problem when trying to write a binary file filter; see:

http://praisecurseandrecurse.blogspot.com/2007/04/haskell-for-short-attention-span-simple.html

Back then I got some help on #haskell to figure out how to write
ReadBinaryFile. I got that working, and wrote

"This works fine, although I would humbly suggest that GHC's standard
library should provide easy access to binary files; while the solution is
pretty trivial, it is a wart."

I would not go so far as to say that binary should be the default mode for
opening and reading a file, but I would say that the two should be made
equally simple and clear options in the standard library.

Paul R. Potts

-- 
Paul R. Potts - [EMAIL PROTECTED] - http://thepottshouse.org


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Re: [Haskell-cafe] (no subject)

[Tillmann Rendel]

Hello,

Ketil Malde wrote:

Makes me wonder whether one should have binary be the default?  I'm a
stranger in Windows-land, but are there cases where you want reading
of a file to be terminated on ^Z?  Seems pretty awful to me.


The ghc docs state about openBinaryFile:


Like openFile, but open the file in binary mode. On Windows, reading
a file in text mode (which is the default) will translate CRLF to LF,
and writing will translate LF to CRLF. [...] text mode treats control-Z as EOF


The CRLF-to-LF translation is the more important part. It allows '\n' to 
stand for the end of a line on windows, too, even if lines are 
terminated by two characters in windows text files.


  Tillmann
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Re: Re: [Haskell-cafe] (no subject)

[L.Guo]

Very thanks for your example, I have not notice that there is a group of
hGetxxx functions in ByteString. In other words, I was using hGetxxx which
implemented in IO module. So it always failed.



--   
L.Guo
2007-05-24

-
From: Donald Bruce Stewart
At: 2007-05-24 17:31:02
Subject: Re: Re: [Haskell-cafe] (no subject)

I mean, what problem are you trying to solve? Ptrs aren't the usual way
to manipulate files in Haskell.

...

-- Don

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Re: Re: [Haskell-cafe] (no subject)

[Ketil Malde]

On Thu, 2007-05-24 at 17:01 +0800, L.Guo wrote:

> Tring openBinaryFile, 

Well, did you get it to work?

> I can not locate which module including readBinaryFile.

This is what I find in System.IO (ghci> :b System.IO):

  openBinaryFile :: FilePath -> IOMode -> IO Handle
  openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle)
  hSetBinaryMode :: Handle -> Bool -> IO ()

so you have the option of either using openBinaryFile or openFile and
using hSetBinaryMode to true. I guess - I've never had to use them.  

I can't find a readBinaryFile either, but writing one might be a good
excercise?

Makes me wonder whether one should have binary be the default?  I'm a
stranger in Windows-land, but are there cases where you want reading of
a file to be terminated on ^Z?  Seems pretty awful to me.

Concerning mutable buffers, it is of course possible, but hardly
idiomatic Haskell.  Why do you need mutability?

-k



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Re: Re: [Haskell-cafe] (no subject)

[Donald Bruce Stewart]

leaveye.guo:
> To read the handle openBinaryFile returns, both the hGetBuf and
> hGetBufNonBlocking needs one parameter _buf_ of type Ptr a.
> I can not get one data of that type.
> 
> In the doc, there is only nullPtr, and also some type cast functions.
> I failed to find some other buffer-maker function.
> 
> What should I do ?

I mean, what problem are you trying to solve? Ptrs aren't the usual way
to manipulate files in Haskell.

Here, for example, is a small program to print the first byte of a
binary file:

import System.IO
import qualified Data.ByteString as B

main = do
h <- openBinaryFile "a.out" ReadMode
s <- B.hGetContents h
print (B.head s)

When run:

$ ./a.out 
127

Note there's no mallocs or pointers involved.

-- Don
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Re: Re: [Haskell-cafe] (no subject)

[L.Guo]

To read the handle openBinaryFile returns, both the hGetBuf and
hGetBufNonBlocking needs one parameter _buf_ of type Ptr a.
I can not get one data of that type.

In the doc, there is only nullPtr, and also some type cast functions.
I failed to find some other buffer-maker function.

What should I do ?

--   
L.Guo
2007-05-24

-
From: Donald Bruce Stewart
At: 2007-05-24 17:03:55
Subject: Re: Re: [Haskell-cafe] (no subject)

What are you trying to do?

-- Don

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Re: Re: [Haskell-cafe] (no subject)

[Donald Bruce Stewart]

leaveye.guo:
> to Ketil :
> 
> Tring openBinaryFile, I notice that I cannot make one usable buffer,
> just because I can not find one function to "malloc" a memory or just
> get one "change-able" buffer.
> 
> :-$

No 'malloc' here in Haskell land: that's done automatically.  Recall
that 'getContents' will read your opened file into a [Char]. (or use
Data.ByteString to get a stream of Word8).

What are you trying to do?

-- Don
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Re: Re: [Haskell-cafe] (no subject)

[L.Guo]

to Ketil :

Tring openBinaryFile, I notice that I cannot make one usable buffer,
just because I can not find one function to "malloc" a memory or just
get one "change-able" buffer.

:-$


to Marc:

I can not locate which module including readBinaryFile.
And I use hoogle search engine.



Could you give me some more hints ?

--   
L.Guo
2007-05-24

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Re: [Haskell-cafe] (no subject)

[Donald Bruce Stewart]

marco-oweber:
> On Thu, May 24, 2007 at 02:38:05PM +0800, L.Guo wrote:
> > Thanks for your suggestion, and sorry for the subject.
> > 
> > I have read the introduction of Data.ByteString, it is helpful.
> > 
> > And also, there is one problem left. When i read a binary file, data is 
> > truncated at the charactor EOF.
> 
> You have to use readBinaryFile instead of readFile.
> I had the same trouble as well.
> 
> I finally implemented accessing single characters in C and did use ffi
> because I didn't know haw to do this i haskell properly. ( using
> peek/poke functions 4 bytes got written (wihch is annotateted somewhere
> ) If you are interested I can sent you the modified ByteString package.
> 
> If someone can tell me which haskell function to use to set a random
> char in a memory buffer I would be pleased ..

'poke'

or else use unboxed Word8 arrays

Check the src for Data.ByteString for examples.
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Re: [Haskell-cafe] (no subject)

[Marc Weber]

On Thu, May 24, 2007 at 02:38:05PM +0800, L.Guo wrote:
> Thanks for your suggestion, and sorry for the subject.
> 
> I have read the introduction of Data.ByteString, it is helpful.
> 
> And also, there is one problem left. When i read a binary file, data is 
> truncated at the charactor EOF.

You have to use readBinaryFile instead of readFile.
I had the same trouble as well.

I finally implemented accessing single characters in C and did use ffi
because I didn't know haw to do this i haskell properly. ( using
peek/poke functions 4 bytes got written (wihch is annotateted somewhere
) If you are interested I can sent you the modified ByteString package.

If someone can tell me which haskell function to use to set a random
char in a memory buffer I would be pleased ..

Marc
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Re: [Haskell-cafe] (no subject)

[L.Guo]

Sorry for not familiar to the email client.

My system is WinXP, and using GHC 6.6.
And is read from file.
Data is truncated at the ^Z char.

I just wrote one simple test code.

> import IO
> 
> writeTest fn = do
>   h <- openFile fn WriteMode
>   mapM_ (\p -> hPutChar h (toEnum p::Char)) $ [0..255] ++ [0..255]
>   hClose h
> 
> accessTest fn = do
>   h <- openFile fn ReadMode
>   s <- hGetContents h
>   putStrLn . show . map fromEnum $ s
>   hClose h
> 
> main = do
>   writeTest "ttt"
>   accessTest "ttt"


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Re: [Haskell-cafe] (no subject)

[Ketil Malde]

> And also, there is one problem left. When i read a binary file, data is 
> truncated at the charactor EOF.

Which character is this: ^D or ^Z?  Which operating system - Windows,
perhaps?  And you are reading from a file, not from stdin?

-k

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Re: [Haskell-cafe] (no subject)

[Donald Bruce Stewart]

leaveye.guo:
> Thanks for your suggestion, and sorry for the subject.
> 
> I have read the introduction of Data.ByteString, it is helpful.
> 
> And also, there is one problem left. When i read a binary file, data
> is truncated at the charactor EOF.
> 
> Which function could do this work correctly ?

Hmm. Do you have an example?

-- Don
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Re: [Haskell-cafe] (no subject)

[L.Guo]

Thanks for your suggestion, and sorry for the subject.

I have read the introduction of Data.ByteString, it is helpful.

And also, there is one problem left. When i read a binary file, data is 
truncated at the charactor EOF.

Which function could do this work correctly ?

--   
L.Guo
2007-05-24

-
发件人：Donald Bruce Stewart
发送日期：2007-05-24 14:03:27
收件人：L.Guo
抄送：MailList Haskell-Cafe
主题：Re: [Haskell-cafe] (no subject)

leaveye.guo:
> Hi MailList Haskell-Cafe:
> 
> Till now, which module / package / lib can i use to access binary
> file ? And is this easy to use in GHC ?

Data.Binary? Or perhaps just Data.ByteString, available on hackage,

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/binary-0.3

or in base.

-- Don


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Re: [Haskell-cafe] (no subject)

[Donald Bruce Stewart]

leaveye.guo:
> Hi MailList Haskell-Cafe:
> 
> Till now, which module / package / lib can i use to access binary
> file ? And is this easy to use in GHC ?

Data.Binary? Or perhaps just Data.ByteString, available on hackage,

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/binary-0.3

or in base.

-- Don


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[Haskell-cafe] (no subject)

[L.Guo]

Hi MailList Haskell-Cafe:

Till now, which module / package / lib can i use to access binary file ? 
And is this easy to use in GHC ?

Regards
--
L.Guo
2007-05-24

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[Haskell-cafe] (no subject)

[Matthew Brecknell]

I'm attempting to construct an abstract data type with a generalised
(deferred) representation. For a simple motivating example, say I am
building an abstract data type with this representation:

> newtype Foo1 k e = Foo1 (Data.Map.Map k (Data.Set.Set e))

While this is a fine default representation, I would like to be able to
substitute IntMap for Map or IntSet for Set in cases where k or e happen
to be Int, or simple list-based map and set implementations for types
lacking an Ord instance.

Following is a prototype of the approach I've come up with so far. It's
been quite an adventure just getting this to type-check (due to lack of
experience with MPTCs and FDs), so I'd be grateful for comments on
whether it is likely to withstand use in real programs, other ways to
solve the problem, etc.

> {-# LANGUAGE FunctionalDependencies #-}
> 
> -- Map class, with generic newtype wrapper instance.
> 
> class MapLike k v m | m -> k v where
>   emptyM :: m
>   insertWithM :: (v -> v -> v) -> k -> v -> m -> m
>   toListM :: m -> [(k,v)]
> 
> newtype Map m k v = Map m
> 
> instance MapLike k v m => MapLike k v (Map m k v) where
>   emptyM = Map emptyM
>   insertWithM f k v (Map m) = Map (insertWithM f k v m)
>   toListM (Map m) = toListM m
> 
> -- Set class, with generic newtype wrapper instance.
> 
> class SetLike e s | s -> e where
>   singletonS :: e -> s
>   unionWithS :: (e -> e -> e) -> s -> s -> s
>   toListS :: s -> [e]
> 
> newtype Set s e = Set s
> 
> instance SetLike e s => SetLike e (Set s e) where
>   singletonS e = Set (singletonS e)
>   unionWithS f (Set s1) (Set s2) = Set (unionWithS f s1 s2)
>   toListS (Set s) = toListS s
> 
> -- Abstract datatype Foo, whose representation is deferred
> -- through the Map and Set newtype wrappers.
> 
> newtype Foo m k s e = Foo (Map m k (Set s e))
> 
> class FooLike k e s m | m -> k s, s -> e where
>   emptyF :: m
>   insertWithF :: (e -> e -> e) -> k -> e -> m -> m
>   toListF :: m -> [(k,e)]
> 
> instance (MapLike k (Set s e) m, SetLike e s) => FooLike k e (Set s e) (Foo m 
> k s e) where
>   emptyF = Foo emptyM
>   insertWithF f k e (Foo m) = Foo (insertWithM (unionWithS f) k (singletonS 
> e) m)
>   toListF (Foo m) = [ (k,e) | (k,s) <- toListM m, e <- toListS s ]

Note that the FooLike class is not strictly necessary to the approach,
since its methods could be written as top-level functions, but I thought
it couldn't hurt. It does have the advantages of consolidating class
constraints in one place, making functional dependencies explicit, and
supporting further composition using the same technique.

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Re: [Haskell-cafe] Final issues to fix for the shootout entries (Was: no subject)

[Tomasz Zielonka]

On Tue, Feb 06, 2007 at 12:12:09PM +1100, Donald Bruce Stewart wrote:
> And note that strings aren't a bottleneck anymore!
> 
> http://shootout.alioth.debian.org/gp4/benchmark.php?test=sumcol&lang=all

I think "Haskell GHC #2" doesn't play by the rules:

"
diff program output for this 6KB input file with this output file to
check your program is correct before contributing.

Each program should be implemented the same way as this Icon program.

The sum-file benchmark measures line-oriented I/O and string conversion.

Each program should:

* read integers from stdin, one line at a time
* print the sum of those integers

Programs should use built-in line-oriented I/O functions rather than

custom-code. No line will exceed 128 characters, including newline.

Reading one line at a time, the programs should run in constant space.
"

Best regards
Tomasz
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[Haskell-cafe] Final issues to fix for the shootout entries (Was: no subject)

[Donald Bruce Stewart]

Yeah, have a look on the shootout:

http://shootout.alioth.debian.org/gp4/benchmark.php?test=recursive&lang=all

Has an ackerman.

More detailed comparisions, across the 19 benchmarks on the shootout,
with notes on which of the 19 GHC Haskell is significantly slower (>4x) at:

Haskell verus Python

http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=ghc&lang2=python
Loses on:
regex-dna

Haskell verus Ruby

http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=ghc&lang2=ruby
Loses on:
regex-dna

Haskell verus Perl

http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=ghc&lang2=perl
Loses on:
regex-dna

Haskell verus Lisp

http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=ghc&lang2=sbcl
Loses on:
mandelbrot (Double math)
spectral-norm (Double math)

Haskell verus Clean

http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=ghc&lang2=clean
Loses on:
k-nucleotide ( HashTable benchmark)
mandelbrot
spectral-norm

Haskell verus SML

http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=ghc&lang2=mlton
Loses on:
k-nucleotide
mandelbrot
spectral-norm

Haskell versus OCaml

http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=ghc&lang2=ocaml
Loses on:
k-nucleotide
mandelbrot
regex-dna
spectral-norm

Haskell versus C
Loses on:
k-nucleotide
mandelbrot
regex-dna
spectral-norm

Fixing these last few programs:

k-nucleotide:   Needs a better hashtable library implementation. For
example a Data.HashByteString based on a Trie of 
ByteString)

regex-dna:  Should use the regex-tre library instead of
regex-posix (algorithm issue only)

mandelbort/spectral-norm:   Double math is slow. I don't know why.

And note that strings aren't a bottleneck anymore!

http://shootout.alioth.debian.org/gp4/benchmark.php?test=sumcol&lang=all

-- Don

seth:
> GHC has profiling support.
> 
> (By the way, many mail servers these days discard mail with no subject.)
> 
> I've seen a number of papers comparing the speed of Haskell code to code of 
> other functional languages; there is a periodic "shoot out" with ocaml.
> 
> Some probably have comparisons with imperative languages, and, even if they 
> do not, the methodology should help you.
> 
> Seth Kurtzberg
> 
> On Mon, 5 Feb 2007 11:28:03 -0800 (PST)
> Tays Soares <[EMAIL PROTECTED]> wrote:
> 
> > Hello everyone,
> > 
> > I did at my master thesis a compiler that generates Haskell code. Now I 
> > need to measure the execution time of my generated code and I've been 
> > searched and I don't know if I'm looking with the wrong keywords but I 
> > could not find anything. I just need to measure the time of simple 
> > functions, like Ackermann and Fibonacci. Does anyone know how to measure 
> > the execution time of a Haskell program or function?
> > 
> > Thank you,
> > Tays
> > 
> > 
> > 
> > __
> > Fale com seus amigos  de gra?a com o novo Yahoo! Messenger 
> > http://br.messenger.yahoo.com/
> ___
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[Haskell-cafe] (no subject)

[C Rodrigues]

_
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[TFP 2007]

Dear Colleagues, 

Apologies in advance for the "p.m." ommission.

This is a kind reminder that the deadline for extended abstract 
submissions to TFP 2007 is tomorrow, Feb. 1 at 11:59 p.m. EST. We are also 
pleased to announce that the TFP 2007 invited speaker is John McCarthy, 
Stanford University. For further details, please visit our website at: 
http://cs.shu.edu/tfp2007/ . 

The TFP 2007 program committee looks forward to receiving your 
submissions! 

Best wishes, 

Marco



Dr. Marco T. Morazan
TFP 2007
Program Committee Chair
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[Haskell-cafe] (no subject)

[Christophe Poucet]

Dear,

I will try to explain what I'm trying to achieve, below you can find the 
code demonstrating where I'm at currently, and where I would like to 
ideally get, as well as the current compilation error.

Basically I'm working on a minilanguage that I would like to simulate. 
This language is based on a core concept which can in the example below 
is "Foo". Now there is a 'primitive' instance of Foo that is the list.
What I now want to do is make FooF an instance as well. FooF being a 
record based on a map that contains some other instances of Foo by name 
as well as code that will use this lookup table.

For instance (this is not definite syntax):
my pseudoproglanguage:
A = [1..10] (aka refer to the 'primitive' instance of Foo)
B = [1..10] (aka refer to the 'primitive' instance of Foo)
bar C = if dum B then bar A else bar B
dum C = dum A && dum B

I realize I need existentials for this, but I'm afraid that my type-fu 
is lacking in this area. Perhaps one of you could point me in the right 
direction.

With regards,
Christophe


{-# OPTIONS_GHC -fglasgow-exts #-}
module FooBar where
import qualified Data.Map as M

class Foo f b | f -> b where
foo :: f a -> b
bar :: f a -> b -> b
dum :: f a -> b -> Bool

instance Foo [] Int where
foo c = 0
bar c i = i+1
dum c i = (length c == i)


data F b a = forall f. Foo f b => F (f a)

instance Foo (F b) b where
foo (F c) = F . foo $ c
bar (F c) i = bar c i
dum (F c) i = dum c i

data FooF b a = FooF {
cols :: M.Map String (F b a),
barC :: M.Map String (F b a) -> b -> b,
dumC :: M.Map String (F b a) -> b -> Bool
}


instance Foo (FooF b) b where
foo c = fmap (foo) c
bar c i = barC c (cols c) i
dum c i = dumC c (cols c) i

makeFooF cols barC dumC = FooF {cols = cols, barC = barC, dumC = dumC}

-- Example:
-- makeFooF
-- [("A", [1..10]), ("B", [1..8])]
-- (\t -> if dum (M.lookup "A" t)
-- then bar (M.lookup "B" t)
-- else bar (M.lookup "A" t)
-- (\t -> dum (M.lookup "A" t) && dum (M.lookup "B" t)

-- Ideally this system would also allow to make some FooF that is based 
on another FooF, hence the reason for existentials



-- FooBar.hs:19:16:
-- Couldn't match the rigid variable `b' against `F b1 a'
-- `b' is bound by the instance declaration at FooBar.hs:18:0
-- Expected type: b
-- Inferred type: F b1 a
-- In the _expression_: (F . foo) $ c
-- In the definition of `foo': foo (F c) = (F . foo) $ c
-- -- FooBar.hs:31:12:
-- Couldn't match the rigid variable `b' against `f b1'
-- `b' is bound by the instance declaration at FooBar.hs:30:0
-- Expected type: b
-- Inferred type: f b1
-- In the application `fmap (foo) c'
-- In the definition of `foo': foo c = fmap (foo) c
-- Failed, modules loaded: none.
-- -

-- Christophe Poucet
Ph.D. Student
Phone:+32 16 28 87 20
E-mail: Christophe (dot) Poucet (at) imec (dot) be
Website: http://notvincenz.com/  
IMEC vzw – Register of Legal Entities Leuven VAT BE 0425.260.668 – Kapeldreef 75, B-3001 Leuven, Belgium – www.imec.be
*DISCLAIMER*
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Any use of the information contained herein by other persons is
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this e-mail and/or its attachments.
**



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[Haskell-cafe] (no subject)

[rami makram]

Hi,
Thx for replying and answering my question..
But,
The idea is that i have to implement it using this kind of type
generateTruthTable->[[(Char,Bool)]] and we didn't take the Shell and 
libraries in common, so i have to implement in a simpler way..

Can you give me another way or even some hints..
I have already implemented the And,Or,Impl,Neg,and other functions..
Thx..

_
Don't just search. Find. Check out the new MSN Search! 
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Re: [Haskell-cafe] (no subject)

[Bulat Ziganshin]

Hello José,

Wednesday, March 15, 2006, 5:54:49 PM, you wrote:

JMV> #ifdef __WIN32__

i use the following:

#if defined(mingw32_HOST_OS) || defined(__MINGW32__) || defined(_MSC_VER)


-- 
Best regards,
 Bulatmailto:[EMAIL PROTECTED]

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[Haskell-cafe] (no subject)

[José Miguel Vilaça]

Hi

 

I’m having a small problem with the portability
of my Haskell code. My code uses wxHaskell and the library for which this one
is the Haskell interface (that is called wxWidgets) doesn’t work in the
same away in Windows and Linux.

 

Now I now which code run in Linux and in Windows but
I don’t want to have to manually change the file in each platform.

I tried a solution using the C pre-processor but I
getting in trouble.

 

I use code like:

 

#ifdef __WIN32__

    (Windows code)

#else

    (Linux code)

#endif

 

I also add the --cpp
to the ghc and it works for me in
Linux but give me linking errors in Windows.

 

Does someone have any hints on how to have different
code in Windows and Linux?

 

I would be thankful in some help.

 

Best regards

 

Miguel Vilaça






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[Haskell-cafe] (no subject)

[Andreas Bakurov]

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[Haskell-cafe] (no subject)

[Henk-Jan van Tuyl]

L.S.,

I used the link checker of the World Wide Web Consortium to check the  
links on haskell.org; there are several links broken. As the checks take a  
long time, I have put the results on my website:

  http://members.chello.nl/hjgtuyl/computing/Haskell/checklinks/checklink.htm

The check is a recursive check with depth 3, starting from the home page;  
this will probably not cover all of the website.


To repeat this check, go to:
  http://validator.w3.org/checklink

--
Best wishes for the new year,
Henk-Jan van Tuyl


--
http://members.chello.nl/hjgtuyl
--

Using Opera's revolutionary e-mail client:
https://secure.bmtmicro.com/opera/buy-opera.html?AID=789433

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[Haskell-cafe] (no subject)

[balarcon]

Hi,
I have to install HDirect on a windows plataform but I have a lot of problems.
When I try to install the version 0.21,"make boot" has problems with Happy and
I've commented this line(the path is correct),latter "make lib" give 2 errors:
../src/ihc :command not found
[hugs/PointerPrim.hs] Error

I don't know if this version is for windows too,the 0.16 isn't available in the
page.I do the installation with "cygwin" I don't know if it's the best
opcion.Please I need use HDirect,help me.

Thanks for all,
Bea


This message was sent using IMP, the Internet Messaging Program.

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Re: [Haskell-cafe] (no subject)

[Paul Hudak]

To add briefly to what John wrote, there is a webpage for Yampa:
www.haskell.org/yampa
which includes all of our publications on FRP/Yampa as well as a decent 
release of our latest implementation of Yampa (based on arrows).  The 
release has ample examples of how to use Yampa for graphics, animation, 
and basic control systems such as used in robotics.

Also, although most of the developers have dispersed, I believe that 
most of them are still interested in the ideas, and the 
[EMAIL PROTECTED] mailing list would probably be responsive if 
anyone bothered to use it.

  -Paul Hudak
John C. Peterson wrote:
From: John Peterson <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Re: [Haskell-cafe] Functional Reactive Programming
Functional Reactive Programming is alive but in need of some new
students to push the effort a bit.  A lot of us have taken teaching
or industrial positions so the old FRP team is a bit depleted.
I don't think anyone is working on Yampa directly at the moment.
Although it's stable and working well it lacks a critical mass of nice
libraries to make it attractive.
I'm still plugging on a wxHaskell port to Yampa (the wxFruit stuff).
I've made some semantic changes to Yampa so I probably shouldn't say
it's real Yampa but pretty close.  I should have something to release
later this fall. 

Aside from that, we have a student working in the hybrid modeling
area.  That's good stuff but not likely to produce software of
interest to Joe Haskell.  Another student is keeping the robotics side
of things alive but it's in the context of a very specialized robotic
hardware environment.
So there you go!
   John
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Professor Paul Hudak
Chair, Dept of Computer Science   Office: (203) 432-1235
Yale University   FAX:(203) 432-0593
P.O. Box 208285   email:  [EMAIL PROTECTED]
New Haven, CT 06520-8285  WWW:www.cs.yale.edu/~hudak
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[Haskell-cafe] (no subject)

[John C. Peterson]

From: John Peterson <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Re: [Haskell-cafe] Functional Reactive Programming

Functional Reactive Programming is alive but in need of some new
students to push the effort a bit.  A lot of us have taken teaching
or industrial positions so the old FRP team is a bit depleted.

I don't think anyone is working on Yampa directly at the moment.
Although it's stable and working well it lacks a critical mass of nice
libraries to make it attractive.

I'm still plugging on a wxHaskell port to Yampa (the wxFruit stuff).
I've made some semantic changes to Yampa so I probably shouldn't say
it's real Yampa but pretty close.  I should have something to release
later this fall. 

Aside from that, we have a student working in the hybrid modeling
area.  That's good stuff but not likely to produce software of
interest to Joe Haskell.  Another student is keeping the robotics side
of things alive but it's in the context of a very specialized robotic
hardware environment.

So there you go!

   John
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(no subject)

[Marcus D. Gabriel]

--
  Marcus D. Gabriel, Ph.D.Email:[EMAIL PROTECTED]
  213 ter, rue de Mulhouse
  F68300 Saint Louis  FRANCE
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[Team domeus]

Title: domeus






		
		 
	
	
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(no subject)

[Mrs.Sese-seko]

 Dear friend,

 I am Mrs. Sese-Seko widow of late president Mobutu Sese-Seko of  zaire? now known as 
democratic republic of congo (drc). I am moved to write you this letter, this was in 
confidence considering my present circumstance and situation. I escaped along with my 
husband and two of our sons Theophilus and Basher out of Democratic Republic of Congo 
(DRC) to Abidjan,
cote d'ivoire where my family and I settled, while
we later moved to settled in morroco where my husband later died of cancer disease.

However due to this situation we decided to changed most of my husband's billions of 
dollars deposited in swiss bank and other countries into other forms of
money coded for safe purpose because the new head of
state of (dr) Mr, laurent kabila has made arrangement with the swiss government and 
other european countries to freeze all my late husband's treasures deposited in
some european countries. hence my children and I decided laying low in Africa to study 
the situation till when things gets better.

Now that President kabila is dead and the son taking over (Joseph kabila). one of my 
late husband's chateaux in southern france was confiscated by the french government, 
and as such I had to change my identity so that my investment will not be traced and 
confiscated.

I have deposited the sum Thirty Million United State Dollars(US$30,000,000,00.) with a 
security company , for safekeeping. The funds are security coded to prevent them from 
knowing the content.

What I want you to do is to indicate your interest that you will assist us by 
receiving the money on our
behalf.
Acknowledge this message, so that I can introduce you to my son (Theophilus) who has 
the out modalities
for the claim of the said funds. I want you to
assist in investing this money, but I will not want my identity revealed.

I will also want to buy properties and stock in multi-national companies and to engage 
in other safe
and non-speculative investments. May I at this point
emphasise the high level of confidentiality, which this business demands, and hope you 
will not
betray the trust and confidence, which I repose in you. in conclusion, if  you want to 
assist us , my son shall put you in the true picture of the business,
tell you where the funds are currently being
maintained and also discuss other modalities including remuneration for your services.

For this reason kindly furnish us your contact information, that is your personal 
telephone
and fax number for confidential purpose.

 Best regards,
 Mrs,sese-seko




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(no subject)

[Mrs.Sese-seko]

 Dear friend,

 I am Mrs. Sese-Seko widow of late president Mobutu Sese-Seko of  zaire? now known as 
democratic republic of congo (drc). I am moved to write you this letter, this was in 
confidence considering my present circumstance and situation. I escaped along with my 
husband and two of our sons Theophilus and Basher out of Democratic Republic of Congo 
(DRC) to Abidjan,
cote d'ivoire where my family and I settled, while
we later moved to settled in morroco where my husband later died of cancer disease.

However due to this situation we decided to changed most of my husband's billions of 
dollars deposited in swiss bank and other countries into other forms of
money coded for safe purpose because the new head of
state of (dr) Mr, laurent kabila has made arrangement with the swiss government and 
other european countries to freeze all my late husband's treasures deposited in
some european countries. hence my children and I decided laying low in Africa to study 
the situation till when things gets better.

Now that President kabila is dead and the son taking over (Joseph kabila). one of my 
late husband's chateaux in southern france was confiscated by the french government, 
and as such I had to change my identity so that my investment will not be traced and 
confiscated.

I have deposited the sum Thirty Million United State Dollars(US$30,000,000,00.) with a 
security company , for safekeeping. The funds are security coded to prevent them from 
knowing the content.

What I want you to do is to indicate your interest that you will assist us by 
receiving the money on our
behalf.
Acknowledge this message, so that I can introduce you to my son (Theophilus) who has 
the out modalities
for the claim of the said funds. I want you to
assist in investing this money, but I will not want my identity revealed.

I will also want to buy properties and stock in multi-national companies and to engage 
in other safe
and non-speculative investments. May I at this point
emphasise the high level of confidentiality, which this business demands, and hope you 
will not
betray the trust and confidence, which I repose in you. in conclusion, if  you want to 
assist us , my son shall put you in the true picture of the business,
tell you where the funds are currently being
maintained and also discuss other modalities including remuneration for your services.

For this reason kindly furnish us your contact information, that is your personal 
telephone
and fax number for confidential purpose.

 Best regards,
 Mrs,sese-seko




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(no subject)

[Olga Lucia Quintero Fonseca]

Por favor, estoy aprendiendo el lenguaje y no se 
como usar Complex aqui, el prompt siempre esta como Prelude y no se como incluir 
ese package module.  Podrian ayudarme ?
De antemano gracias !!!

(no subject)

[ÖйúÊ×Ò³]

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