Am 09.12.2012 um 00:27 schrieb Holger Siegel:
> For deriving a monoid instance of w from monad (Writer w), you will need
> function execWriter:: Writer w a -> w, but in case of a general instance of
> (MonadWriter w m) you would have to use function listen :: m a -> m (a, w)
&
Am 08.12.2012 um 23:18 schrieb Edward Z. Yang:
> Excerpts from Roman Cheplyaka's message of Sat Dec 08 14:00:52 -0800 2012:
>> * Edward Z. Yang [2012-12-08 11:19:01-0800]
>>> The monoid instance is necessary to ensure adherence to the monad laws.
>>
>> This doesn't make any sense to me. Are you
Am 05.04.2012 um 08:42 schrieb Brandon Allbery:
> On Thu, Apr 5, 2012 at 01:53, Sutherland, Julian
> wrote:
> data Tree = Node Left Right | Leaf
>
> Could be converted to a struct in C/C++:
>
> struct Tree {
> struct Tree* left;
> struct Tree* right;
> };
>
> Shouldn't this actually
Am 13.03.2012 um 09:15 schrieb Morten Olsen Lysgaard:
> I'm running a project where i want to generate a map of a rather large data
> collection. The map is if the form: Data.Map.Map String a
> I'd like to be able to do inexact lookups on the map. Firstly, ignore the
> difference between upper
Am 28.02.2012 um 20:21 schrieb Johan Holmquist:
>>> inter :: (a -> a -> b) -> [a] -> [b]
>>> inter f [] = []
>>> inter f l = map (uncurry f) $ zip l (tail l)
>>
>> This is the same as
>>
>> inter :: (a -> a -> b) -> [a] -> [b]
>> inter f l = zipWith f l (tail l)
>
> Except when l == [], but t
Am 28.02.2012 um 18:06 schrieb Johan Holmquist:
> Two functions that I see useful are described here and I would like to
> know if they are defined in some more or less standard Haskell
> library. Hoogle (http://www.haskell.org/hoogle) did not reveal
> anything about that.
>
>
> Function 'inter
Am 18.02.2012 um 14:38 schrieb Roman Cheplyaka:
> * Holger Siegel [2012-02-18 12:52:08+0100]
>> You cannot. Common subexpression elimination is done by GHC very
>> conservatively, because it can not only affect impure programs: it can
>> also affects strictnes
Am 18.02.2012 um 11:56 schrieb Heinrich Hördegen:
> Hi,
>
> this is true. The optimization only works with -O2. I'd like to have more
> details about what's going on. How can I make sure, that this optimization
> triggers?
You cannot. Common subexpression elimination is done by GHC very
conse
Am 19.01.2012 um 22:24 schrieb Sean Leather:
> I have two types A and B, and I want to express that the composition of two
> functions f :: B -> A and g :: A -> B gives me the identity idA = f . g :: A
> -> A. I don't need g . f :: B -> B to be the identity on B, so I want a
> weaker statement
Am 08.12.2011 um 11:13 schrieb Asger Feldthaus:
> Haskell doesn't seem to support disjunctive patterns, and I'm having a
> difficult time writing good Haskell code in situations that would otherwise
> call for that type of pattern.
>
>
> In Haskell I can't find any equivalent to the disjunct
Am 29.11.2011 um 09:16 schrieb Martin DeMello:
> I have the following functions:
>
> makePair :: (String, String) -> IO PairBox
>
> parseFile :: String -> [(String, String)]
>
> importFile :: Editor -> String -> IO ()
> importFile ed path = do
> s <- readFile path
> ps <- mapM (\x -> makePai
Am 30.06.2011 um 22:57 schrieb Philipp Schneider:
> On 06/30/2011 09:49 PM, Holger Siegel wrote:
>> (...) But that won't work: After you have evaluated an entry of the
>> environment, you store the resulting value but you throw away its updated
>> environment. That m
Am 30.06.2011 um 20:23 schrieb Philipp Schneider:
> On 06/30/2011 02:36 PM, Holger Siegel wrote:
>> Am 29.06.2011 um 23:50 schrieb Philipp Schneider:
>>
>>> Hi cafe,
>>>
>>> in my program i use a monad of the following type
>>>
>>&
Am 29.06.2011 um 23:50 schrieb Philipp Schneider:
> Hi cafe,
>
> in my program i use a monad of the following type
>
> newtype M a = M (State -> (a, State))
>
> i use the monad in two different ways. The type variable "a" can be a
> pair as in
>
> interp :: Term -> Environment -> M (Value,Env
Am 03.05.2011 um 13:39 schrieb Stephen Tetley:
> Does it have an obvious default implementation, bearing in mind it we
> might really want a total function?
>
> sconcat [] = error "Yikes - I wish this was total!"
> sconcat [a]= a
> sconcat (a:as) = a <> sconcat as
You have to provide th
Am 22.02.2011 um 22:03 schrieb Alberto G. Corona:
> Recently I had to navigatate trough data structures chained with mutable
> referenes in th STM monad. The problem is that their values are enveloped in
> Either or Maybe results.
>
> functional compositions in the Either of Maybe , or list
Am 25.09.2010 um 11:54 schrieb Tom Hawkins:
> Hi,
>
> Often I need to assemble a tree from things with unstructured
> hierarchical paths. I built a function [1] to do this for ImProve.
> But does a library already exist that does this? If not I may create
> one, as I need it for a few differen
Am 22.09.2010 um 17:10 schrieb David Sankel:
> The following code (full code available here[1], example taken from comments
> here[2]),
>
> const' = \a _ -> a
>
> test1 c = let a = const' (nthPrime 10)
> in (a c, a c)
>
> test2 c = let a = \_ -> (nthPrime 10)
> in (a
Am 01.07.2010 um 21:56 schrieb Mrwibbly:
>
> I'm having real trouble starting this project. Basically I have to create a
> record store that store information about artists and albums and also the
> number of sales that they have had. It also needs to generate a list of the
> top 5 sellers.
>
>
Hi Sebastian,
Am 15.06.2010 um 17:06 schrieb Sebastian Fischer:
> Dear Café,
>
> `MonadPlus` instances are usually required to satisfy certain laws, among
> them the monad laws and monoid laws for `mzero` and `mplus`. Additionally one
> may require that (>>=f) is a monoid morphism, that is:
Am 20.05.2010 um 14:16 schrieb Tony Morris:
> I've compared and clearly the former is significantly superior :)
>
> I'm rather interested if there are any sound suggestions to resolve the
> general issue of retrospective type-class extension.
>
I would like to have something like
parent class
Am 18.05.2010 um 00:24 schrieb David Matuszek:
> I'm trying to install Haskell Platform 2010.1.0.1 on my Mac,
> downloaded from http://hackage.haskell.org/platform/
>
> I have:
> Mac OS X 10.6.3
> 2 x 2.66 GHz Dual-Core Intel Xeon
> XCode 3.1.3
> Also, I am an admin on this machine.
>
> When
Am Samstag, den 20.02.2010, 10:47 + schrieb Andrew Coppin:
> I just discovered the highly useful function Data.Function.on. I vaguely
> recall a few people muttering a couple of years back that this would be
> a useful thing to have, but I had no idea it was in the standard
> libraries now.
Am Samstag, den 06.02.2010, 10:28 -0800 schrieb Ryan Ingram:
> As other people have mentioned, you are duplicating library
> functionality. But nobody has actually talked about the performance
> characteristics of your code.
>
> Fortunately for you, the calls to (++) in your recursion are
> right
Am Samstag, den 06.02.2010, 23:12 +1030 schrieb Mark Spezzano:
> Hi,
>
> Just wondering whether I can use ShowS or tupling or Difference Lists to
> speed up the following code?
>
> It's basic text processing. It takes in a list of Lines where each Line
> is a list of Words and intersperses " "
Am Donnerstag, den 28.01.2010, 19:37 + schrieb Maciej Piechotka:
> On Thu, 2010-01-28 at 14:07 -0500, Steve Schafer wrote:
> > I'm looking for some algorithmic suggestions:
> >
> > I have a set of several hundred key/value pairs. The keys are 32-bit
> > integers, and are all distinct. The valu
Am Mittwoch, den 27.01.2010, 21:19 +0300 schrieb Vladimir Matveev:
> Oh yeah, it seems I found it. Solution is to use getModuleFileName and
> getModuleHandle functions from System.Win32.DLL. Thanks for attention :)
You can also use the (portable) package 'directory' from Hackage
(http://hackage.ha
Am Dienstag, den 08.12.2009, 23:25 +0200 schrieb Vitaliy Akimov:
> Hi John,
>
> I don't know if this is useful for you, but these are instances of
> Cofunctor's comap. For example if we use TypeCompose package we have:
>
> rebox f = unFlip . cofmap f . Flip
>
> The rest are also Cofunctors. Ther
Am Donnerstag, den 03.12.2009, 16:23 +0100 schrieb Emmanuel CHANTREAU:
> Le Thu, 3 Dec 2009 13:20:31 +0100,
> David Virebayre a écrit :
>
> > It doesn't work this way : Strings are just lists of Chars. Comparison
> > is made recursively, Char by Char. You can have a look at the source
> > to make
d return
Dual [2, 1]
? Should it unwrap the lists beforehand and re-wrap them afterwards and
return
Dual [1, 2]
? Should it unwrap the resulting list afterwards and return [1, 2] or
even [2,1] ?
That's not obvious to me.
> On Dec 3, 2009, at 1:25 AM, Holger Siegel wrote:
&
Am Donnerstag, den 03.12.2009, 01:16 +0100 schrieb Martijn van
Steenbergen:
> So here's a totally wild idea Sjoerd and I came up with.
>
> What if newtypes were unwrapped implicitly?
>
> What advantages and disadvantages would it have?
> In what cases would this lead to ambiguous code?
1)
instan
Am Mittwoch, den 16.09.2009, 03:23 -0700 schrieb Gregory Propf:
> I'm playing around with a little program that implements a simple
> virtual machine. I want to use a monad to represent machine state. I
> created a data type for the machine (VM) and a monadic type for the
> monadic computations u
Am Montag, den 23.03.2009, 12:55 + schrieb Jens Blanck:
> The above approach does not apply to my case. What I have is a
> monotone function f on a partial order satisfying f x >= x, for all x.
> Given that the partial order is in fact a cpo this is enough to
> guarantee that a least fixed poi
Am Donnerstag, den 26.02.2009, 20:54 + schrieb Colin Paul Adams:
> Hello Haskellers,
>
> I want to implement the negascout algorithm for the game I'm writing.
>
> Wikipedia gives the algorithm in imperative terms:
>
> http://en.wikipedia.org/wiki/Negascout
>
> I've tried to translate this i
Am Montag, den 19.01.2009, 14:47 +0100 schrieb Daniel Fischer:
> Am Montag, 19. Januar 2009 14:31 schrieb Antoine Latter:
> > 2009/1/19 Luke Palmer :
> > > As a side curiosity, I would love to see an example of any data structure
> > > which has more than one Functor instance. Especially those whi
On Sunday 11 January 2009 01:44:50 Andrew Wagner wrote:
> Nice Idea, though I don't know that I want something that extensive. I was
> more looking for whether there was a better way I could define the
> algebraic data type.
Let's have a look at your definitions from http://hpaste.org/13807#a1 :
On Thursday 18 December 2008 13:40:47 Ryan Ingram wrote:
> Actually, this is probably safer:
>
> import Foreign.Marshal.Alloc
> import Foreign.Ptr
> import Foreign.Storable
> import Data.Word
> import System.IO.Unsafe
>
> endianCheck = unsafePerformIO $ alloca $ \p -> poke p (0x01020304 ::
> Word32
On Saturday 06 December 2008 22:07:51 Paul Johnson wrote:
> So we could have
>
>fromListWithZero :: Ord k => (a -> b -> b) -> b -> [(k, a)] -> Map k b
>fromListWithZero combiner zero pairs = ...
>
> The first time a key is seen the combining function is called with
> "zero" as its second a
On Thursday 16 October 2008 02:01:57 Corey O'Connor wrote:
> I was just reminded of one of the joke definitions of recursion:
> "recursion: see recursion".
>
> Perhaps there is a similar one for fixed points?
> "To learn about fixed points find the fixed point of the process:
> Given somebody learn
On Saturday 11 October 2008 01:08:15 Justin Bailey wrote:
> This is a beta release (which is why I've limited the audience by
> using hackage) to get feedback before distributing the PDF to a wider
> audience. With that in mind, I welcome your comments or patches[2].
>
> Justin
>
> [1] http://hack
--- Adrian Neumann <[EMAIL PROTECTED]> schrieb am Mi, 16.7.2008:
> Von: Adrian Neumann <[EMAIL PROTECTED]>
> Betreff: [Haskell-cafe] Fixed-Point Combinators
> An: "Haskell Cafe mailing list"
> Datum: Mittwoch, 16. Juli 2008, 21:17
> Hello,
>
> while studying for a exam I came across this little
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