On 09/13/2010 12:23 PM, Michael Lazarev wrote:
2010/9/13 Henning Thielemannlemm...@henning-thielemann.de:
It means that variables bound by let, may be instantiated to different types
later.
Can you give an example, please?
testOk = let f = id in (f 42, f True)
--testNotOk :: Monad m = m
On 09/13/2010 12:38 PM, Thomas Davie wrote:
On 13 Sep 2010, at 10:28, Gleb Alexeyev wrote:
On 09/13/2010 12:23 PM, Michael Lazarev wrote:
2010/9/13 Henning Thielemannlemm...@henning-thielemann.de:
It means that variables bound by let, may be instantiated to different types
later.
Can you
On 09/13/2010 12:45 PM, Gleb Alexeyev wrote:
is, pardon my pun, not ok, because f is let-bound and, therefore,
monomorphic
This line doesn't make sense, I was too hasty to hit the 'Send' button,
I meant to write 'lambda-bound', of course, apologies
Ozgur Akgun wrote:
In this case I think you should either make it a separate package, or don't
hide it in this module. It looks like an easy way to call Ubigraph from
Hhaskell, and there is no apparent alternative (in hackage) so why hide it?
I've contacted Kohei Ozaki, the author of
The new version (0.2.0.1) is on Hackage.
vacuum-ubigraph now depends on Hubigraph, basic customization is now
possible, e.g.:
import System.Vacuum.Ubigraph
import Graphics.Ubigraph
myNodeStyle n = map (setColor #ff) $ defaultNodeStyle n
where
setColor color (VColor _) =
Ozgur Akgun wrote:
Thanks for the answer.
I see your point, that Ubigraph does some magic* to place vertices and
edges.
This makes me wonder, how they generate the binary tree demo:
http://ubietylab.net/ubigraph/content/Demos/random_binary_tree.html
Is there a way to disable this optimal graph
Ozgur Akgun wrote:
A little bit of topic, but why is the module Graphics.Ubigraph hidden in
your package? I've been trying to use Ubigraph directly, and your module
helped me a lot. (I just patched the cabal file to expose Graphics.Ubigraph
as well)
Is there a specific reason for it to be
Ozgur Akgun wrote:
Hi all,
I am using vacuum-opengl and vacuum-ubigraph to visualise and analyse some
of my data structures. They are quite helpful most of the time, however
sometimes I feel the need to tweak the generated output -- such as removing
the auto-generted identifiers from
Yves Parès wrote:
Okay, well, apparently I have to rely on an external HTTP server. This is not
very simple, is there another more suitable way to get RPC working in
haskell?
Apparently it is possible to use Happstack as webserver, here's example
I came up with:
import
Ozgur Akgun wrote:
Is there any way to limit a functions type, not by a data type but by a
group of constructors of a data type? If not, what would be the *right*
thing to do to achieve this level of type safety?
data DT1 = X | Y | Z
data DT2 = A | B | C | D
func1 :: DT1 - DT2 -- instead of
Martijn van Steenbergen wrote:
Dear café,
I am deeply impressed with Vacuum[1][2], Ubigraph[3] and especially
their combination[4]. I can trivially and beautifully visualize the ASTs
that my parser produces. I can visualize zippers of the ASTs and confirm
that sharing is optimal.
Ubigraph
Brian Troutwine wrote:
Do you have any reason not to do the above?
Yes, the subset types that I wish to define are not clean partitions,
though my example does suggest this. Let's say that the definition of
Foo is now
data Foo = One | Two | Three | Four | Five | Six
while Odd and Even
Thomas Hartman wrote:
on haskell reddit today
powerSet = filterM (const [True, False])
Does it help if we inline the 'const' function and rewrite [True, False]
in monadic notation as (return True `mplus` return False)?
powerSet = filterM (\x - return True `mplus` return False).
You can
On Jul 17, 2009 1:40pm, Thomas Hartman wrote:
my question to all 3 (so far) respondants is, how does your
explanation explain that the result is the power set?
I guess you forgot to reply to the cafe.
Well, to me the modified definition I posted looks like the essence of
powerset, the set
Marcin Kosiba wrote:
Hi,
To illustrate what I meant I'm attaching two examples. In example_1.py I've
written code the way I think would be elegant (but it doesn't work). In
example_2.py I've written code so that it works, but it isn't elegant.
I know I'm abusing Python iterators here. Also,
Thomas Davie wrote:
No, I think it's extremely useful. It highlights that numbers can both
be lazy and strict, and that the so called useless lazy sum, is in
fact, useful.
But lazy sum should have beed defined in terms of foldr, not foldl. And
foldl is not strict enough for strict sum.
You may want to read the comments at
http://hackage.haskell.org/trac/ghc/ticket/1897.
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Don Stewart wrote:
Did you use hubigraph?
http://ooxo.org/hubigraph/
This cabalized project doesn't appear to be on hackage!
Oh, I wasn't aware of hubigraph until now.
Ubigraph has very simple XML-RPC-based API so I used it directly.
Hubigraph, of course, looks nicer with its custom
Daryoush Mehrtash wrote:
When I try to install the hubigraph I get the following error:
skip
Network/XmlRpc/Client.hs:113:23:
Not in scope: type constructor or class `ConnError'
Network/XmlRpc/Client.hs:113:51:
Not in scope: type constructor or class `ConnError'
cabal: Error: some
Don Stewart wrote:
Please upload!!
I've run into 2 problems while trying to do this.
The first one - haxr won't build with HTTP-4000, so I had to edit
haxr.cabal and add the upper version bound for HTTP.
The second one is puzzling me.
I've cabal-installed the package, but keep getting
Iavor Diatchki wrote:
Hi,
The linking problem might be due to a bug in the cabal file: if you
have modules that are not exposed, you still need to list them in the
other-modules section.
This was the problem, thanks!
___
Haskell-Cafe mailing list
Don Stewart wrote:
I am pleased to announce the release of vacuum-cairo, a Haskell library
for interactive rendering and display of values on the GHC heap using
Matt Morrow's vacuum library.
Awesome stuff, kudos to you and Matt Morrow!
I thought it'd be fun to visualize data structures in
Gleb Alexeyev wrote:
instance Eq a = Eq (CatList a) where
a == b = case (viewCL a, viewCL b) of
(Just (x, xs), Just (y, ys)) - x==y xs == ys
(Nothing, Nothing) - True
_- False
I just realized that my solution
Here's my attempt though it's not really different from using built-in
lists:
viewCL CatNil = Nothing
viewCL (Wrap a) = Just (a, CatNil)
viewCL (Cat a b) = case viewCL a of
Nothing - viewCL b
Just (x, xs) - Just (x, Cat xs b)
instance Eq a = Eq
Gregg Reynolds wrote:
However, consider:
getChar = \x - getChar
An optimizer can see that the result of the first getChar is discarded
and replace the entire expression with one getChar without changing the
formal semantics.
Let's imagine that IO datatype is defined thus:
{-#
Gregg Reynolds wrote:
I must be misunderstanding something. I don't know if it would be
optimized out, but I see no reason why it couldn't be. There's no data
dependency, right?
Of course there is data dependency. In my example, where IO is defined
as a (generalized) algebraic datatype,
Gregg Reynolds wrote:
Are you saying that using equations to add a level of indirection
prevents optimization? I still don't see it - discarding x doesn't
change the semantics, so a good compiler /should/ do this. How is
this different from optimizing out application of a constant function?
Duncan Coutts wrote:
Gleb Alexeyev did the majority of the work on this one. I'm most
grateful to him for heeding my recent calls for more volunteers for
Cabal hacking.
I guess you're overstating my contribution a little, but thanks :).
___
Haskell
Maurício wrote:
? It is easy for 'when' to ignore the result
of the first computation, and this would not
break existing code, and also save a lot of
return ()s.
As Neil Mitchell pointed out[1], ignoring results implicitly may
indicate an error. Perhaps it's cleaner to define
ignore m =
Ertugrul Soeylemez wrote:
And to prove that IORefs do lead to a pointer race condition and hence
are insecure, try the following code:
main :: IO ()
main = do
ref - newIORef False
forkIO $ forever $ modifyIORef ref not
forever $ readIORef ref = print
It crashes for me. I'm
Sjoerd Visscher wrote:
When I try this bit of code:
class C1 a where
type F a :: *
x :: F a
y :: F a
x = y
I get this error:
Couldn't match expected type `F a1' against inferred type `F a'
In the expression: y
In the definition of `x': x = y
I can't figure out
Mauricio wrote:
But how is this:
data SomeNum = forall a. SN a
different from:
data SomeNum = SN (forall a. a)
In the first case the constructor SN can be applied to the monomorphic
value of any type, it effectively hides the type of the argument. For
example, you can have a list like
I just thought that the shorter explanation could do better: the
difference is in the types of the constructor functions.
Code:
{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE RankNTypes #-}
data SomeNum1 = forall a. SN1 a
data SomeNum2 = SN2 (forall a. a)
ghci session:
*Main :t
Mauricio wrote:
After you pointed my dumb mistake, I was able to build
the first example -- without any of the extensions! Haskell
can be misterious some times.
Strange enough, I can't get the original (and, to my eyes,
equal) problem to work.
Indeed Haskell can be misterious sometimes. Now
Manlio Perillo wrote:
import System.Posix.Files as PF
Try this:
import qualified System.Posix.Files as PF
The problem you described should go away.
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
Mauricio wrote:
Hi,
I have this problem trying to define a function
inside a do expression. I tried this small code
to help me check. This works well:
---
import Data.Ratio ;
main = do {
printNumber - let {
print :: (Num n,Show n) = n - IO () ;
print n = do { putStrLn $ show n}
Jacques Carette wrote:
-- This does not however help at all! The only way I have found of
'fixing' this requires annotating the code itself, which I most
definitely do not want to do because I specifically want the code to be
polymorphic in that way. But GHC 6.8.2 does not want to let me do
Derek Elkins wrote:
As Derek Elkins has written, one of the options is to use delimited
continuations, see
http://research.microsoft.com/~simonpj/papers/control/ for Haskell
implementation.
I made no such suggestion.
I didn't mean that you suggested using implementation referenced
Dimitry Golubovsky wrote:
If I have
callCC $ \exit - do
foo
...
I cannot jump to `exit' from within foo unless `exit' is given to foo
as an argument.
As Derek Elkins has written, one of the options is to use delimited
continuations, see
Bryan O'Sullivan wrote:
ChrisK wrote:
That is almost certainly because the algorithm expects the source
string to have
a unique character at its end.
Chris is correct. I'll ensure that the docs make this clear.
Apologies, I should have thought of this myself.
Thanks.
Bryan O'Sullivan wrote:
I just posted a library named suffixtree to Hackage.
http://www.serpentine.com/software/suffixtree/
It implements Giegerich and Kurtz's lazy construction algorithm, with a
few tweaks for better performance and resource usage.
API docs:
Dimitrios Vytiniotis wrote:
I hope this helps more than confuses,
It really does, thank you. To understand your explanation completely I
have to study 'Boxy types' paper thoroughly, but from the user's point
of view everything is clear - GHC currently cannot correctly instantiate
type
Hello Cafe!
I asked about this problem on IRC channel but with little luck.
The problem boils down to the following: readline crashes on any input
if the calling program runs in the Emacs buffer. To reproduce this bug,
load the code below into ghci using haskell-mode and run main.
import
Dmitry Antonyuk (lomeo) came up with a piece of code that hung GHC 6.6:
newtype Foo a = Foo (Foo a - a)
bar x@(Foo f) = f x
baz = bar (Foo bar)
See the original discussion (in Russian) at:
http://lomeo.livejournal.com/35674.html
___
Haskell-Cafe
Neil Mitchell wrote:
It's a documented bug in GHC:
http://www.haskell.org/ghc/docs/latest/html/users_guide/bugs.html#bugs-ghc
GHC's inliner can be persuaded into non-termination using the
standard way to encode recursion via a data type
Thanks Neil!
Sorry for the noise, I should have
45 matches
Mail list logo
