And then to
down = mconcat [downPar, downNew, downTrans]
Which is pretty cute considering that the original formulation is equivalent
to and a tiny tweak away from
down p = mconcat [downPar p, downNew p, downTrans p]
Hooray for Monoid!
- Conal
On Mon, Feb 9, 2009 at 6:31 AM, Wouter
Hi Peter,
I'm delighted to hear about your successes with Haskell programming!
I suspect that parametric polymorphism has a lot to do with phenomenon of
works-when-it-compiles. The more polymorphic a signature is, the fewer the
possible type-correct definitions. Luckily, the definition that "wo
On Fri, 2009-02-13 at 22:39 +1100, George Pollard wrote:
> RewriteRule "^packages/archive/[^/]+/[^/]+/(.+)$" - [env=pkgname:$1]
This should actually be more constrained since (as I've just noticed)
more than just packages are under this path :)
Perhaps:
> RewriteRule "^packages/archive/[^/]+/[^
(Omitted some useful information from original emails. Oops!)
Space partition data structures. Currently only a quadtree.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/spacepart
On Sun, Feb 15, 2009 at 7:28 PM, Corey O'Connor wrote:
> 0.1.0.0
>- Renamed Math.Geometry to Data.Sp
Okay, I tested it out and the arrow transformer has the same problem. I
realized this after I sent the last message -- the point is that at any
particular point, intuitively there should be exactly one copy of a State# s
for each state thread, and it should never get duplicated; allowing other
mon
0.1.0.0
- Renamed Math.Geometry to Data.SpacePart.AABB
- Renamed Data.QuadTree to Data.SpacePart.QuadTree
- Added Data.SpacePart.QuadTree.query. Returns all elements that
intersect a given boundary.
- The inclusive nature of the boundary's min extent should take
precedence of the ex
On Sunday 15 February 2009 9:44:42 pm Louis Wasserman wrote:
> Hello all,
>
> I just uploaded stateful-mtl and pqueue-mtl 1.0.1. The ST monad
> transformer and array transformer have been removed -- I've convinced
> myself that a heap transformer backed by an ST array cannot be
> referentially tra
On 2009 Feb 15, at 15:22, Colin Paul Adams wrote:
Can this be done with Haskell? In particular, I'm using ghc 6.10.1.
Can I get symbols for use with gdb, for instance
gdb would be extremely painful; the flow of execution in lazy
languages is unusual.
ghci from 6.8.1 on has an interactive de
Just for the record, here a few clarifications.
Expressiveness
~~
From a theoretical point of view, type families (TFs) and functional
dependencies (FDs) are equivalent in expressiveness. There is nothing
that you can do in one and that's fundamentally impossible in the
other.
Hello all,
I just uploaded stateful-mtl and pqueue-mtl 1.0.1. The ST monad transformer
and array transformer have been removed -- I've convinced myself that a heap
transformer backed by an ST array cannot be referentially transparent -- and
the heap monad is now available only as a basic monad an
On 15 Feb 2009, at 5:45 am, Wolfgang Jeltsch wrote:
So you mean a language which
* directly corresponds to a subset of MathML (and is therefore
easily
convertible into sensible MathML)
* is at the same time valid TeX source which can be processed by
TeX based
on a few macro
Louis Wasserman wrote:
I follow. The primary issue, I'm sort of wildly inferring, is that use of
STT -- despite being pretty much a State monad on the inside -- allows
access to things like mutable references?
That's exactly the problem. The essential reason for ST's existence are
STRefs whic
The module I put together already has everything I'd need to do it in terms
of an IntMap with much less work than that -- the generic MonadArray type
class has implementations both in terms of ST and in terms of an IntMap
already. Only three changes in the Heap implementation would be needed: two
Howdy y'all!
I was reading sigfpe's Beyond Monads post
(http://blog.sigfpe.com/2009/02/beyond-monads.html) about parameterized monads.
Great post, makes you go: this is so elegant and simple, why didn't I think of that?
Anyway, I was wondering whether those monads have corresponding transform
You can roll your own pure STT monad, at the cost of performance:
-- Do not export any of these constructors, just the types STT and STTRef.
data W = forall a. W !a
data Heap s = Heap !Int !(IntMap W)
newtype STT s m a = STT (StateT (Heap s) m a) deriving (Monad,
MonadTrans, MonadIO, insert other
2009/2/15 Brandon S. Allbery KF8NH
> On 2009 Feb 15, at 11:50, Peter Verswyvelen wrote:
>
> I could try to read the article a couple of times again, but are there any
> other good readings about these existentially quantified types and how the
> ST monad works?
>
>
> You could think about it as p
Well, it makes me sad, I guess. pqueue-mtl provides an array-backed heap
monad transformer that is supposed to keep its own ST thread, if only for
the sake of retaining a purely functional interface without any externally
visible forall'd types, which is perfectly fine in most cases, but I'd have
On Sun, 15 Feb 2009, Louis Wasserman wrote:
I follow. The primary issue, I'm sort of wildly inferring, is that use of STT
-- despite being
pretty much a State monad on the inside -- allows access to things like mutable
references?
I assume that ST must always be the most inner monad, like
Peter Verswyvelen schrieb:
> I'm having trouble understanding the explanation of the meaning of the
> signature of runST at
>
> http://en.wikibooks.org/wiki/Haskell/Existentially_quantified_types
Is this one better
http://haskell.org/haskellwiki/Monad/ST ?
___
I follow. The primary issue, I'm sort of wildly inferring, is that use of
STT -- despite being pretty much a State monad on the inside -- allows
access to things like mutable references?
More serious question: The issue of nondeterministic branching and the State
monad is something that's occurre
It depends whether that's NaN ºC or NaN ºF.
2009/2/15 Fraser Wilson :
> Is that really cold or really hot?
>
> On Sun, Feb 15, 2009 at 11:27 PM, Henk-Jan van Tuyl
> wrote:
>>
>> The temperature is now NaN°:
>> http://traviswalters.net/?p=58
>>
>> --
>> Met vriendelijke groet,
>> Henk-Jan van Tuy
Hi,
I need to work with a web service that has a few thousand types in its
schema. I am trying to automate the generation of data types and
serializers from the schema. My first thought was to map each data
type to a Haskell record and generate pickle methods thereafter for
serialziation/deseriali
Is that really cold or really hot?
On Sun, Feb 15, 2009 at 11:27 PM, Henk-Jan van Tuyl wrote:
>
> The temperature is now NaN°:
> http://traviswalters.net/?p=58
>
> --
> Met vriendelijke groet,
> Henk-Jan van Tuyl
>
>
> --
> http://functor.bamikanarie.com
> http://Van.Tuyl.eu/
> --
>
>
>
The temperature is now NaN°:
http://traviswalters.net/?p=58
--
Met vriendelijke groet,
Henk-Jan van Tuyl
--
http://functor.bamikanarie.com
http://Van.Tuyl.eu/
--
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On Sun, Feb 15, 2009 at 11:50 AM, Kim-Ee Yeoh wrote:
> Having said that, I'm not sure about the statement on page 9
> that "readVar v simply does not have type forall s. ST s Bool."
> The variable v could be of type "forall s. MutVar s Bool",
> in which case all of "runST (readVar v)" typechecks.
It's true that you can do "program" the type checker even more if you
have dependent types, but first you should look into what you can do
in Haskell. You can do a lot with type classes.
-- Lennart
2009/2/15 Peter Verswyvelen :
> How practical is this dependent types thing? I hear a lot about
> OK, what did I do wrong here?
When making a request for help on a compiler issue, you failed to include key
information to make it possible to reproduce your problem, and what you did
include was broken or incorrect.
The three programs that submitted don't do even do the same thing.
Let's look
On Sun, Feb 15, 2009 at 09:59:28PM -, Sittampalam, Ganesh wrote:
> > Stateful-mtl provides an ST monad transformer,
>
> Is this safe? e.g. does it work correctly on [], Maybe etc?
>
> If not this should be flagged very prominently in the documentation.
It is not safe: it has the same proble
OK, what did I do wrong here?
module Main () where
import Data.List
top = 10 ^ 8 :: Int
main = do
let numbers = [1 .. top]
print $ foldl' (+) 0 numbers
-- Runtime is 20 seconds.
#include
int main(void)
{
int total = 0;
int n;
for (n = 1, n < 1; n++)
total += n;
printf(
Hello,
I'm writing a small program to process Delicious [1] RSS feeds. I like
look at the recent feeds to see what others have bookmarked recently.
But, there are a lot of duplicates in the recent feeds as an entry is
shown for each person who bookmarks an individual URL. I decided to
write a sm
You might want to take a look at Timber
http://www.timber-lang.org
On Sun, Feb 15, 2009 at 6:22 PM, Maurício wrote:
> Hi,
>
> I've checked this 'BitC' language (www.bitc-lang.org). It
> uses some ideas we see in Haskell, although with different
> realization, and target mainly reliable low lev
How practical is this dependent types thing? I hear a lot about this from
really clever people who are usually 10 years ahead of their time :)
Actually, back in the eighties when I was an assembly language hacker, I
didn't want to switch to Pascal or C since I found the types in those
languages too
> Stateful-mtl provides an ST monad transformer,
Is this safe? e.g. does it work correctly on [], Maybe etc?
If not this should be flagged very prominently in the documentation.
Cheers,
Ganesh
==
Please access the att
This must be why there are no good compilers for dependently typed languages. :)
On Sun, Feb 15, 2009 at 9:40 PM, Stefan Monnier
wrote:
>> So IMO static typing is good, but it's only with functional programming that
>> it really shines.
>
> You can go one step further: if you start using dependen
> import Control.Applicative
>
> data Pair a = a :*: a
>
> instance Functor Pair where
> f `fmap` (x :*: y) = f x :*: f y
>
> instance Applicative Pair where
> (f :*: g) <*> (x :*: y) = f x :*: f y
The last f needs to be a g.
> pure x = x :*: x
>
> pointfree :: (a -> b -> c
> So IMO static typing is good, but it's only with functional programming that
> it really shines.
You can go one step further: if you start using dependent types, you'll
see that it gets yet harder to get your program to type-check, and once
it does, you don't even bother to run it since it's so
Hello all,
I just released two new packages on Hackage, stateful-mtl and pqueue-mtl.
Stateful-mtl provides an ST monad transformer, several useful operations on
generic monad transformers, and a monad transformer intended to cleanly
externally wrap operations on a mutable array (including resizin
Can this be done with Haskell? In particular, I'm using ghc 6.10.1.
Can I get symbols for use with gdb, for instance?
--
Colin Adams
Preston Lancashire
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On Sun, 2009-02-15 at 18:53 +0100, Tillmann Rendel wrote:
> Gregg Reynolds wrote:
> > BTW, I'm not talking about Haskell's Functor class, I guess I should
> > have made that clear. I'm talking about category theory, as the
> > semantic framework for thinking about Haskell.
>
> In that case, I eve
Peter Verswyvelen-2 wrote:
>
> I could try to read the article a couple of times again, but are there any
> other good readings about these existentially quantified types and how the
> ST monad works?
>
The primary source is if I'm not mistaken, the following
"State in Haskell" paper:
http:/
* Duncan Coutts [2009-02-13 12:19:29 +]:
> Can we do that just for one user agent? I don't think we want to use
> non-standard stuff in general. Apparently Content-Disposition is not in
> the official HTTP spec, but IE is known to follow it.
Well, it's mentioned in RFC 2616[1], and I'd expec
On Sun, Feb 15, 2009 at 7:54 PM, Svein Ove Aas wrote:
> 2009/2/15 Gregg Reynolds :
>>
>> The metaphor is action-at-a-distance. Quantum entanglement is a vivid way
>> of conveying it since it is so strange, but true. Obviously one is not
>> expected to understand quantum entanglement, only the id
2009/2/15 Gregg Reynolds :
>
> The metaphor is action-at-a-distance. Quantum entanglement is a vivid way
> of conveying it since it is so strange, but true. Obviously one is not
> expected to understand quantum entanglement, only the idea of two things
> linked "invisibly" across a boundary.
>
Th
On Sun, Feb 15, 2009 at 12:45 PM, Anton van Straaten wrote:
> Gregg Reynolds wrote:
>
>> Action-at-a-distance is a metaphor meant to enliven the concept.
>>
>
> Kind of like the container metaphor?
>
Yes, only, different. Non-pernicious. ;)
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Gregg Reynolds wrote:
Action-at-a-distance is a metaphor meant to enliven the concept.
Kind of like the container metaphor?
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On Sun, Feb 15, 2009 at 11:53 AM, Tillmann Rendel wrote:
> Gregg Reynolds wrote:
>
>> BTW, I'm not talking about Haskell's Functor class, I guess I should
>> have made that clear. I'm talking about category theory, as the
>> semantic framework for thinking about Haskell.
>
>
Don't forget the par
On 2009 Feb 15, at 11:50, Peter Verswyvelen wrote:
I could try to read the article a couple of times again, but are
there any other good readings about these existentially quantified
types and how the ST monad works?
You could think about it as playing a dirty trick on the typechecker.
Th
Quantum entanglement is related to a different kind of categorical
product. So, the metaphor is misleading.
But, that being said : I want to thank you for your blog. A bit
polemic but very interesting.
Christophe.
Came up with an alternative to the container metaphor for functors
that you
Gregg Reynolds wrote:
BTW, I'm not talking about Haskell's Functor class, I guess I should
have made that clear. I'm talking about category theory, as the
semantic framework for thinking about Haskell.
In that case, I even less see why you are not introducing category
theory proper. Certainly
Hi
>> > However the createProcess command structure has the close_fds flag,
>> > which seems like it should override that behaviour, and therefore this
>> > seems like a bug in createProcess.
>>
>> close_fds :: Bool
>>
>> Close all file descriptors except stdin, stdout and stderr i
On Sun, Feb 15, 2009 at 11:09 AM, Tillmann Rendel wrote:
> Gregg Reynolds wrote:
>
>> Came up with an alternative to the container metaphor for functors that
>> you
>> might find amusing: http://syntax.wikidot.com/blog:9
>>
>
> You seem to describe Bifunctors (two objects from one category are m
Hi,
I've checked this 'BitC' language (www.bitc-lang.org). It
uses some ideas we see in Haskell, although with different
realization, and target mainly reliable low level code,
like micro-kernels (although I think it could be used
anywhere C is also used, including writing libraries Haskell
could
Gregg Reynolds wrote:
Came up with an alternative to the container metaphor for functors that you
might find amusing: http://syntax.wikidot.com/blog:9
You seem to describe Bifunctors (two objects from one category are
mapped to one object in another category), but Haskell's Functor class
is
Peter Verswyvelen wrote:
> "Time on different cores does not progress monotonically"
Two cores executing the same code are not guaranteed to finish them in
the same time span, due to caching, temperature, voltage jaggies,
quantum-mechanic inference, ...
--
(c) this sig last receiving data pro
I'm having trouble understanding the explanation of the meaning of the
signature of runST at
http://en.wikibooks.org/wiki/Haskell/Existentially_quantified_types
I could try to read the article a couple of times again, but are there any
other good readings about these existentially quantified types
Came up with an alternative to the container metaphor for functors that you
might find amusing: http://syntax.wikidot.com/blog:9
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See http://okmij.org/ftp/Haskell/perfect-shuffle.txt
Paul.
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Krzysztof Skrzętnicki wrote:
On Sun, Feb 15, 2009 at 10:25, Martijn van Steenbergen
wrote:
Are there any Haskell libraries out there that implement telnet? Bare
sockets are a good approximation, but I'm looking for a library that
understands the escape sequences specific to telnet.
I think Yo
On Sun, 2009-02-15 at 11:06 +, Duncan Coutts wrote:
> On Sun, 2009-02-15 at 09:24 +, Neil Mitchell wrote:
> > Hi
> >
> > >> What have I done wrong? Did createProcess close the handle, and is
> > >> there a way round this?
> > >
> > > The docs for runProcess says:
> > >
> > >Any Han
On Sun, 2009-02-15 at 16:48 +0530, Lakshmi Narasimhan wrote:
> I designed a basic GUI with Menu bar and menu items in glade. I use the
> glade bindings in haskell to get the menu item using xmlGetWidget and
> castToMenuItem function. I set a *onActivateItem* handler for this
> menuitem. However
Felipe Lessa wrote:
> Heinrich Apfelmus wrote:
>>
>> It's fair, but may duplicate elements, i.e. it doesn't necessarily
>> create a permutation. For example, rs could be something like
>>
>> rs = [5,3,3,3,2,4]
>>
>
> But our sort doesn't discard values when the keys are the same. For example,
On Sun, Feb 15, 2009 at 10:25, Martijn van Steenbergen
wrote:
> Are there any Haskell libraries out there that implement telnet? Bare
> sockets are a good approximation, but I'm looking for a library that
> understands the escape sequences specific to telnet.
I think Yogurt
http://hackage.haskell
I'm not sure what you mean with "Time on different cores does not progress
monotonically". Time could come from a dedicated clock device. E.g. in the
broadcast television sector a time signal is distributed across all hardware
components to keep them all in sync within some margin, or you could use
On Sun, Feb 15, 2009 at 9:47 AM, Heinrich Apfelmus
wrote:
> It's fair, but may duplicate elements, i.e. it doesn't necessarily
> create a permutation. For example, rs could be something like
>
> rs = [5,3,3,3,2,4]
>
But our sort doesn't discard values when the keys are the same. For example,
Heinrich Apfelmus wrote:
Jon Fairbairn wrote:
Heinrich Apfelmus writes:
The answer is a resounding "yes" and the main idea is that shuffling a
list is *essentially the same* as sorting a list; the minor difference
being that the former chooses a permutation at random while the latter
chooses a
Jon Fairbairn wrote:
> Heinrich Apfelmus writes:
>
>> The answer is a resounding "yes" and the main idea is that shuffling a
>> list is *essentially the same* as sorting a list; the minor difference
>> being that the former chooses a permutation at random while the latter
>> chooses a very particu
I designed a basic GUI with Menu bar and menu items in glade. I use the
glade bindings in haskell to get the menu item using xmlGetWidget and
castToMenuItem function. I set a *onActivateItem* handler for this
menuitem. However this is not working. I saw the glade file and it has a
signal functi
Heinrich Apfelmus writes:
> The answer is a resounding "yes" and the main idea is that shuffling a
> list is *essentially the same* as sorting a list; the minor difference
> being that the former chooses a permutation at random while the latter
> chooses a very particular permutation, namely the
On Sun, 2009-02-15 at 09:24 +, Neil Mitchell wrote:
> Hi
>
> >> What have I done wrong? Did createProcess close the handle, and is
> >> there a way round this?
> >
> > The docs for runProcess says:
> >
> >Any Handles passed to runProcess are placed immediately in the
> >closed
On Sat, Feb 14, 2009 at 2:04 AM, Brandon S. Allbery KF8NH
wrote:
>
> liftIO is defined there, I believe. Many of the monad modules re-export it
> with their MonadTrans definitions, but apparently Control.Monad.CC doesn't
> so you need to go to the source.
Yeah, I knew the answer :D It was sort o
Just came across this 6 part video of Feynman lecture on relationship of
mathematics and physics.
http://www.youtube.com/watch?v=W1jIPzjFU_U&e
Enjoy,
Daryoush
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I have blogged my experience of trying out xmonad with Fedora 10 at
http://colina.demon.co.uk/?q=node/534 .
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Preston Lancashire
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Hello,
Are there any Haskell libraries out there that implement telnet? Bare
sockets are a good approximation, but I'm looking for a library that
understands the escape sequences specific to telnet.
Thanks,
Martijn.
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Ha
Hi
>> What have I done wrong? Did createProcess close the handle, and is
>> there a way round this?
>
> The docs for runProcess says:
>
>Any Handles passed to runProcess are placed immediately in the
>closed state.
>
> but the equivalent seems to be missing from the documentation f
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