On 12.09 15:28, Misha Aizatulin wrote:
I've been using existentially quantified data constructors like
data Box = forall a. Cxt a = Box a
If you can include Typeable into the mix then serializing works.
Serialize the value as name of type value.
When deserializing use a Map name of type
Daniel Fischer [EMAIL PROTECTED] writes:
Maybe I've misused the word segfault.
I think so. A segfault is the operating-system complaining about an
illegal memory access. If you get them from Haskell, it is likely a
bug in the compiler or run-time system (or you were using unsafeAt, or
FFI).
G'day all.
Quoting Jason Dagit [EMAIL PROTECTED]:
I was making an embedded domain specific language for excel
spreadsheet formulas recently and found that making my formula
datatype an instance of Num had huge pay offs.
Just so you know, what we're talking about here is a way to make that
Hello
Is there an elegant way of traversing a directed graph in STM?
type Node nt et = TVar (NodeT nt et)
type Edge et= TVar et
data NodeT nt et = NodeT nt [(Node nt et, Edge et)]
type MyGraph = Node String Int
When implementing a simple depth first search we need a way to
mark nodes (=
Einar Karttunen wrote:
Hello
Is there an elegant way of traversing a directed graph in STM?
type Node nt et = TVar (NodeT nt et)
type Edge et= TVar et
data NodeT nt et = NodeT nt [(Node nt et, Edge et)]
type MyGraph = Node String Int
When implementing a simple depth first search we
Michael Shulman wrote:
On 9/11/06, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote:
* (a `seq` return a) = evaluate a *right now*, then produce an IO
action
which, when executed, returns the result of evaluating a. Thus, if
a is undefined, throws an exception right now.
is a bit misleading
On 13.09 08:48, Chris Kuklewicz wrote:
And the concurrent searches are isolated from each other? Or are you
performing a single search using many threads?
Isolated from each other. Mainly dreaming of the per-transaction
variables attached to the nodes :-)
- Einar Karttunen
On Tue, Sep 12, 2006 at 08:59:30PM -0400, [EMAIL PROTECTED] wrote:
One of the proposals that comes up every so often is to allow the
declaration of a typeclass instance to automatically declare instances
for all superclasses. So, for example:
class (Functor m) = Monad m where
Daniel Fischer wrote:
Most certainly not. I'm pretty sure this is to a bug in your code.
Something retains a data structure which is actually unneeded. Probably
Apparently. And my money is on a load of lines from the file (of which I need
only the first and last Char).
Then you're
Lemmih wrote:
main = do
args - getArgs
flip mapM_ args $ \arg -
flip mapM_ [1..3] $ \n -
putStrLn $ show n ++ ) ++ arg
Or even:
main = do
args - getArgs
putStr $ unlines [ show n ++ ) ++ arg
| arg - args, n - [1..3] ]
I'm really at a loss
Ketil Malde wrote:
Daniel Fischer [EMAIL PROTECTED] writes:
Maybe I've misused the word segfault.
I think so. A segfault is the operating-system complaining about an
illegal memory access. If you get them from Haskell, it is likely a
bug in the compiler or run-time system (or you were
On Wed, 13 Sep 2006, Donald Bruce Stewart wrote:
lemmih:
On 9/13/06, Tim Newsham [EMAIL PROTECTED] wrote:
I was rewriting some non-haskell code in haskell and came up with this
construct:
foreach l f = mapM_ f l
main = do
args - getArgs
foreach args (\arg
On Tue, 12 Sep 2006, Aaron Denney wrote:
On 2006-09-12, Bryan Burgers [EMAIL PROTECTED] wrote:
And another problem I can see is that, for example, the Integers are a
group over addition, and also a group over multiplication;
Not over multiplication, no, because there is no inverse.
I
Hello Ketil,
Wednesday, September 13, 2006, 10:41:13 AM, you wrote:
But a String is something like 8 or 12 bytes per character, a
ByteString gets you down to 1.
12-16. Char itself, pointer to the next list element, and two boxes
around them - this count for 16 bytes on 32-bit CPU. but cells
Hello Henning,
Wednesday, September 13, 2006, 1:12:35 PM, you wrote:
Adding sugar or using Template Haskell for such a simple task is a bit
unreasonable. I think Tim should use mapM a little bit and then he will
probably need no longer a special syntax.
i disagree. lack of good syntax makes
Hello Udo,
Wednesday, September 13, 2006, 12:53:38 PM, you wrote:
main = do
args - getArgs
flip mapM_ args $ \arg -
flip mapM_ [1..3] $ \n -
putStrLn $ show n ++ ) ++ arg
Or even:
main = do
args - getArgs
putStr $ unlines [ show n ++ ) ++ arg
On Wed, 13 Sep 2006, Bulat Ziganshin wrote:
Wednesday, September 13, 2006, 1:12:35 PM, you wrote:
Adding sugar or using Template Haskell for such a simple task is a bit
unreasonable. I think Tim should use mapM a little bit and then he will
probably need no longer a special syntax.
i
The sum function really only needs the argument list to be a monoid.
And the same is true for the product function, but with 1 and * as
the monoid operators. Sum and product are really the same function. :)
I don't think Haskell really has the mechanisms for setting up an
algebraic class
On Wed, 13 Sep 2006, Lennart Augustsson wrote:
The sum function really only needs the argument list to be a monoid.
And the same is true for the product function, but with 1 and * as the monoid
operators. Sum and product are really the same function. :)
... which got the same name, too,
G'day all.
Quoting Henning Thielemann [EMAIL PROTECTED]:
... which got the same name, too, namely 'foldl'.
You mean foldr. The place of foldl is a bit tricky, but in this case
it requires that the monoid be Abelian.
Cheers,
Andrew Bromage
___
On Sep 5, 2006, at 7:05 AM, Chris Kuklewicz wrote:
Bulat Ziganshin wrote:
Hello Bertram,
Tuesday, September 5, 2006, 12:24:57 PM, you wrote:
A quick hack up to use Data.ByteString uses a lot less ram, though
profiling still shows 95% of time spent in the building the Map.
Data.HashTable may
Am Mittwoch, 13. September 2006 11:07 schrieben Sie:
Daniel Fischer wrote:
Most certainly not. I'm pretty sure this is to a bug in your code.
Something retains a data structure which is actually unneeded.
Probably
Apparently. And my money is on a load of lines from the file (of
Sorry, this is a bit off-topic but I post here because:
* it is about a DSL and many Haskellers are fond of DSLs,
* the first implementation is written in Haskell.
http://www.cosmogol.fr/
describes a proposal to the IETF to standardize the language used for
finite state machines (which are
Einar Karttunen wrote:
I've been using existentially quantified data constructors like
data Box = forall a. Cxt a = Box a
If you can include Typeable into the mix then serializing works.
Serialize the value as name of type value.
When deserializing use a Map name of type
I start wondering, how OO languages solve the same problem.
Conceptually, what is needed is a mapping of the head of the input to a type.
This is indeed a recurring problem in OO languages; think of object
serialization or XML/Object mapping. One common way of accomplishing the
mapping is to
Tim Newsham wrote:
I was rewriting some non-haskell code in haskell and came up with this
construct:
foreach l f = mapM_ f l
main = do
args - getArgs
foreach args (\arg - do
foreach [1..3] (\n - do
putStrLn ((show n) ++ ) ++ arg)
)
)
which is reminiscent of foreach in other languages. Seems
Henning Thielemann wrote:
On Wed, 13 Sep 2006, Lennart Augustsson wrote:
I don't think Haskell really has the mechanisms for setting up an
algebraic class hierarchy the right way. Consider some classes we
might want to build: SemiGroup
Monoid
AbelianMonoid
Group
AbelianGroup
SemiRing
Ring
...
Hi, I have a question about ffi in Hugs98 (WinHugs-May2006.exe), the Hugs98 documentation says:"Only the ccall, stdcall and dotnet calling conventions are supported. All others are flagged as errors."But I can't get a dotnet import, the ffihugs returns me an error:ffihugs
Your solution would imply[1] that all Rational are multiplicatively
invertible -- which they are not.
The Rationals are not a multiplicative group -- although the _positive_
Rationals are. You can't express this in Haskell's type system AFAIK.
Your basic point is correct: if you are willing
foreach l f = mapM_ f l
... rename to forM_ as per previous emails ...
I would like to add to this. The previous loop runs the code
once independantly for each item in the list. Sometimes you want
to carry state through the loop:
v = init
foreach x list do
code
v =
On 2006-09-13, Ross Paterson [EMAIL PROTECTED] wrote:
On Tue, Sep 12, 2006 at 08:59:30PM -0400, [EMAIL PROTECTED] wrote:
One of the proposals that comes up every so often is to allow the
declaration of a typeclass instance to automatically declare instances
for all superclasses. So, for
On 9/13/06, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote:
So `seq` forces its first argument. When we define
f x = x `seq` (Return x)
we thereby get
f _|_== _|_
f [] == Return []
f (x:xs) == Return (x:xs)
To compare, the semantics of (evaluate) is
evaluate _|_== ThrowException
Misha Aizatulin wrote:
This is indeed the only solution I see so far. It has a serious
problem though: as soon as I write the mapping, I limit once and for all
the set of all types that can be used with my box. And I do so in a
non-extensible way - if someone later would like to use my box
On 9/13/06, Henning Thielemann [EMAIL PROTECTED] wrote:
If you want more sugar, what about the list monad?
main = do
args - getArgs
sequence_ $
do arg - args
n - [1..3]
return (putStrLn $ show n ++ ) ++ arg)
Or, what about using ListT
At Wed, 13 Sep 2006 15:24:39 +0400,
Bulat Ziganshin wrote:
because REAL code is somewhat larger than examples. try to rewrite the
following:
directory_blocks - (`mapM` splitBy (opt_group_dir command)
files_to_archive)
( \filesInOneDirectory - do
datablocks - (`mapM`
On 9/13/06, Bertram Felgenhauer [EMAIL PROTECTED] wrote:
Michael Shulman wrote:
class MonadList m where
option :: [a] - m a
[...]
There's no need for an extra class, it can be done with MonadPlus:
option :: MonadPlus m = [a] - m a
option = msum . map return
But this doesn't always give
Aaron Denney wrote:
I know of no good way to express that a given data type obeys the
same interface two (or more) ways.
The best approach here is to use data structures instead of classes:
data Monoid a = MkMonoid
{
monoidNull :: a,
monoidFunc :: a - a - a
}
--
Ashley Yakeley
Michael Shulman wrote:
The frequent occurence of ListT $ return in my code when I use the ListT
monad transformer has made me wonder why there isn't a standard typeclass
`MonadList', like those for the other monad transformers, encapsulating
the essence of being a list-like monad -- in this
Brian Hulley wrote:
[EMAIL PROTECTED] wrote:
[...]
My reading of the semantics
(http://haskell.org/ghc/docs/latest/html/libraries/base/System-Mem-Weak.html#4)
is that you can be sure the proxy *object* is gone.
My problem is that I don't know what to make of the word
object in the
Dear Haskell Cafe,
When programming the other day I ran into this problem. What I want to do
is a function that would work like this:
splitStreams::Ord a=[(a,b)]-[(a,[b])]
splitStreams [(3,x),(1,y),(3,z),(2,w)]
[(3,[x,z]),(1,[y]),(2,[w])]
I don't care about the order that the pairs are
Magnus Jonsson wrote:
Dear Haskell Cafe,
When programming the other day I ran into this problem. What I want to
do is a function that would work like this:
splitStreams::Ord a=[(a,b)]-[(a,[b])]
splitStreams [(3,x),(1,y),(3,z),(2,w)]
[(3,[x,z]),(1,[y]),(2,[w])]
A O(n log(n)) algorithm
Nice try Twan but your example fails on infinite lists. I cleaned up
your example so that it compiles:
import qualified Data.Map as Map
splitStreamsMap :: Ord a = [(a,b)] - Map.Map a [b]
splitStreamsMap = foldl add Map.empty
where add m (a,b) = Map.insertWith (++) a [b] m
splitStreams ::
Magnus Jonsson wrote:
[...]
but your example fails on infinite lists
[...]
take 2 $ snd $ head $ splitStreams (map (\x - (0 ,x))
[1..])
Any approach, even sieving, will struggle with infinite
lists, won't it?
(take 2 . snd . head . splitStreams) [(i, i) | i -
[0..]]
Regards,
Tom
I'm having a problem with program execution in win32 which seems
to be tied to laziness. The function I'm using is:
runCmd cmd outdir dir base ext = do
let argv = words cmd
(i,o,e,p) - runInteractiveProcess (head argv) (drop 1 argv) Nothing
Nothing
hClose i
out - hGetContents
On Thu, 14 Sep 2006 [EMAIL PROTECTED] wrote:
Any approach, even sieving, will struggle with infinite
lists, won't it?
(take 2 . snd . head . splitStreams) [(i, i) | i -
[0..]]
Yes, if you expect two messages but only one comes then you'll
wait forever, true.
Regards,
Tom
Ross Paterson writes:
Such features would be useful, but are unlikely to be available for
Haskell'. If we concede that, is it still desirable to make these
changes to the class hierarchy?
I've collected some notes on these issues at
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