The examples in the "error handling" chapter (19) of RWH don't run under
GHC 6.10.
For instance, an example might be
main = handle (\_ -> putStrLn "error") (print $ 5 `div` 0)
Trying to load this results in "amigous type variable 'e' in the
constraint: 'Exception e' arising from a use of 'han
On Wed, Oct 21, 2009 at 3:29 AM, Michael Mossey wrote:
> The examples in the "error handling" chapter (19) of RWH don't run under GHC
> 6.10.
>
> For instance, an example might be
>
> main = handle (\_ -> putStrLn "error") (print $ 5 `div` 0)
>
> Trying to load this results in "amigous type variab
Peter Verswyvelen wrote:
For learning, I would like to develop my own implementation of type
inference, based on the paper "Typing Haskell in Haskell".
At first sight, the source code of THIH contains a small number of
tests, but I was wandering if a large test set exist?
I'm pretty sure GHC m
Michael Mossey writes:
> The examples in the "error handling" chapter (19) of RWH don't run under GHC
> 6.10.
>
> For instance, an example might be
>
> main = handle (\_ -> putStrLn "error") (print $ 5 `div` 0)
I usually use:
main = handle (\(_ :: SomeException) -> putStrLn "error") (print
To deal with "amigous type variable 'e'", I often write the codes like:
handle (\...@someexception{} -> print e) (5 `div` 0)
and IIRC, the base-4.0 initially released with GHC 6.10.1, introduced
this exceptions. It enables us to specify which exception should be
caught and define types of exc
I was recently working on an type inference algorithm and to test it I did
the following:
Used the quickcheck Arbitrary typeclass to generate expressions
Inferred types of the expressions using my algorithm,
converted the expressions that passed inference to haskell and wrote them
to a file (
Hi,
Excerpts from Michael Mossey's message of Mi Okt 21 11:29:53 +0200 2009:
> how to get the RWH examples to run?
Changing the imports from Control.Exception to Control.OldException did it for
me. I am not sure whether this is what you were looking for, but it should at
least allow you to follow
update:
on haskell reddit, dons suggested simply patching time. reasonable
enough, but I hit a glitch where the Data.Fixed (in base lib) was
missing a Data instance, and gave up when I couldn't find the source
repo for base. Is this simply part of ghc?
Anyways, that instance seems to be added in
It's educational to port the examples yourself.
Dave
On Wed, Oct 21, 2009 at 8:56 AM, Benjamin Herr wrote:
> Hi,
>
> Excerpts from Michael Mossey's message of Mi Okt 21 11:29:53 +0200 2009:
> > how to get the RWH examples to run?
>
> Changing the imports from Control.Exception to Control.OldExce
Data.Fixed (in base) has been updated with Data instances in HEAD. When
that's released, I'll release time-extra that will contain Data
instances. I've got it all ready to go.
The reason Data instances are in time-extras is that the time library
must be Haskell 98, while Data instances require Ran
There's a thread on the plt-scheme list about creating a function of NO
arguments named NEXT that just returns the number of times it's been called, a
piece of cake in Scheme, but how would one do this in Haskell? Would the best
approach be to use a State monad?
Michael
On Wed, Oct 21, 2009 at 10:34:47AM -0700, michael rice wrote:
> There's a thread on the plt-scheme list about creating a function of NO
> arguments named NEXT that just returns the number of times it's been called,
> a piece of cake in Scheme, but how would one do this in Haskell? Would the
> be
2009/10/21 michael rice
>
> There's a thread on the plt-scheme list about creating a function of NO
> arguments named NEXT that just returns the number of times it's been called,
> a piece of cake in Scheme, but how would one do this in Haskell? Would the
> best approach be to use a State monad
I'm guessing the function looks something like this? (this is common lisp
not scheme)
(let ((counter 0))
(defun next ()
(incf counter)
counter))
So the first time you call (next), it returns 1, then 2, etc.
The function (next) is a closure over the variable 'counter' and acts by
increme
On Tue, Oct 20, 2009 at 10:07 AM, Peter Verswyvelen
wrote:
For learning, I would like to develop my own implementation of type
inference, based on the paper "Typing Haskell in Haskell".
At first sight, the source code of THIH contains a small number of
tests, but I was wandering if a large t
Here's an example in the IO monad:
import Data.IORef
import System.IO.Unsafe
counter = unsafePerformIO $ newIORef 0
next = do
modifyIORef counter (+1)
readIORef counter
Naturally, this uses unsafePerformIO, which as you know, is not kosher...
Cheers,
- Tim
On Wed, Oct 21, 2009 at 1:00 PM
2009/10/21 Tim Wawrzynczak
>
> Here's an example in the IO monad:
>
> import Data.IORef
> import System.IO.Unsafe
>
> counter = unsafePerformIO $ newIORef 0
>
> next = do
> modifyIORef counter (+1)
> readIORef counter
>
> Naturally, this uses unsafePerformIO, which as you know, is not kosher..
Hallo,
On 10/21/09, Tim Wawrzynczak wrote:
> Here's an example in the IO monad:
>
> import Data.IORef
> import System.IO.Unsafe
>
> counter = unsafePerformIO $ newIORef 0
>
> next = do
> modifyIORef counter (+1)
> readIORef counter
>
> Naturally, this uses unsafePerformIO, which as you know,
Thanks Job & Martijn for the feedback.
I would like to write a type inferrer that is mostly Haskell 98 with
Trex row polymorphism extensions (a bit like CAL I guess).
That will certainly take a while because I'm also studying the theory
in my spare time.
So as soon as (or if) I have something wo
michael rice wrote:
There's a thread on the plt-scheme list about creating a function of NO
arguments named NEXT that just returns the number of times it's been
called, a piece of cake in Scheme, but how would one do this in Haskell?
Would the best approach be to use a State monad?
Michael
True...here we go then:
import Data.IORef
import System.IO.Unsafe
mkNext :: (Num a) => IO (IO a)
mkNext = do
ref <- newIORef 0
return (do modifyIORef ref (+1)
readIORef ref)
next :: IO ()
next = do
foo <- mkNext
a <- sequence [foo,foo,foo]
putStrLn $ show a
running next
And just because this has not been explicitly stated: it's not just
for aesthetic reasons that you couldn't do this with a pure function,
but because it violates the semantics and gets you the wrong result.
So for example, if you modified Tim's code to be
import Data.IORef
import System.
2009/10/21 Tim Wawrzynczak :
> True...here we go then:
>
> import Data.IORef
> import System.IO.Unsafe
>
> mkNext :: (Num a) => IO (IO a)
> mkNext = do
> ref <- newIORef 0
> return (do modifyIORef ref (+1)
> readIORef ref)
>
> next :: IO ()
> next = do
> foo <- mkNext
> a <- se
satorisanitarium wrote:
>
> How to make a list of sublists out of a list, whether they be a list of
> numbers or a string.
>
Without recursion (with fold) starting from the tail of the input list:
foo n = foldr st [[]]
where
st x xss | x == n = [x]:xss
st x (xs:xss) = (x:x
I'm happy to announce a new release of the Data.Stream library.
http://hackage.haskell.org/package/Stream
The only change with the previous version has been to add irrefutable
patterns to several function definitions. This is rather delicate
design decision: too many irrefutable patterns c
Thanks everyone,
Hmm...I hadn't thought about it that way, but w/r/t Haskell you're absolutely
right.
People have said that Haskell is good to learn because it makes one think
differently about programming, and they're right.
Michael
--- On Wed, 10/21/09, Neal Alexander wrote:
From: Neal A
zaxis schrieb:
> winSSQ count noRed noBlue = do {
> yesRed <- [1..33] \\ noRed;
> yesBlue <- [1..16] \\ noBlue;
> bracket (openFile "ssqNum.txt" WriteMode) (hClose) (\hd1 -> pickSSQ
> count yesRed yesBlue hd1);
> return ()
You might prefer 'withFile' or even better and if possible
I've uploaded new versions of these two packages to hackage:
GPipe-1.0.2:
* Removed rasterize and made rasterizeFront work for other primitives than
triangles instead.
* Fixed notB Vertex and Fragment instances
Vec-Transform-1.0.1:
* Added rotationLookAt
Cheers
Tobias Bexelius
I'm on OS X Leopard 10.5.8, using ghc 6.10.4 from Haskell Platform.
I'm trying to get a static .a library, callable from C, that I can use in
an OS X Cocoa program. I've tried a very simple case (the one in Haskell
Wiki Tutorials,"calling haskell from C") I've managed to make a Mac Cocoa
applicat
It looks like both the THEN and the ELSE in an IF expression must each have an
expression. What's a graceful way to do nothing in either or both slots, kind
of like the Fortran CONTINUE statement.
--mr
[mich...@localhost ~]$ ghci
GHCi, version 6.10.3: http://www.haskell.org/
If its monadic code then use Control.Monad.when.
If its pure code then omitting the 'else' clause makes no sense
what-so-ever; to omit the else you must know the boolean is always true so
why have the if? See the "Common Misunderstandings" [1] page I put together
in response to seeing one too man
Yes, an if statement must have both 'then' and 'else' branches. As an
example, what if you had
let a = if b == 2 then True else False
and you were missing an else branch? What would 'a' get assigned to?
The if statement "returns" a value so must have both branches.
However, in a monadic const
Thanks guys,
I understand what you're telling me, but have some nested IFs and just want to
fall through on one of the ELSES but then I end up with two ELSES in a row and
nothing between them. Oh, well, on to restructuring.
Michael
--- On Wed, 10/21/09, Tim Wawrzynczak wrote:
From: Tim Wawr
If you have a long if/else if/else chain, you might consider a trivial
case statement with guards. Whether you think this is attractive is a
matter of taste, but it has the fall-through semantics you want and ghc
optimizes the _ pattern matching away:
f x = case () of
_| x == 2-> 22
_|
Those nested IF/THEN/ELSEs are real killers. I kind of use them to sort out my
thoughts, then end up with a nested mess. The restructuring to WHENs went
smoothly and looks a lot cleaner besides.
Michael
--- On Wed, 10/21/09, Dan Weston wrote:
From: Dan Weston
Subject: Re: [Haskell-cafe] Is t
Busy night. I wanted the question and response to be on the same line (see
below), so I used putStr instead of putStrLn, but Haskell jumps the gun and
goes to the second line to get the response before the question ever gets
printed. Is this an example of needing strictness? How would I do that,
Hi Michael,
I believe stdout uses line buffering by default so you need to explicitly
flush the buffer to get the output
-- Johan
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Hey Johan,
And I can do that how?
Michael
--- On Wed, 10/21/09, Johan Tibell wrote:
From: Johan Tibell
Subject: Re: [Haskell-cafe] Needing strictness?
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Wednesday, October 21, 2009, 10:18 PM
Hi Michael,
I believe stdout uses line bufferin
Am Donnerstag 22 Oktober 2009 04:15:56 schrieb michael rice:
> Busy night. I wanted the question and response to be on the same line (see
> below), so I used putStr instead of putStrLn, but Haskell jumps the gun and
> goes to the second line to get the response before the question ever gets
> print
Am Donnerstag 22 Oktober 2009 04:15:56 schrieb michael rice:
> Busy night. I wanted the question and response to be on the same line (see
> below), so I used putStr instead of putStrLn, but Haskell jumps the gun and
> goes to the second line to get the response before the question ever gets
> print
Hi Daniel,
The first fix wouldn't work, but the second one (hFlush) did.
Thanks,
Michael
--- On Wed, 10/21/09, Daniel Fischer wrote:
From: Daniel Fischer
Subject: Re: [Haskell-cafe] Needing strictness?
To: haskell-cafe@haskell.org
Cc: "michael rice"
Date: Wednesday, October 21, 2009, 10:27
from my bash hints file:
thart...@ubuntu:~/haskellInstalls/gitit>thartman_ghci_with_data_files
Loading a package with data files in ghci
See
http://neilmitchell.blogspot.com/2008/02/adding-data-files-using-cabal.html
Snip:
The above method works well after a program has been ins
A few months ago, I started toying with a few alternative pump designs
to power our hydraulic hybrids. After not being able to secure a ProE
license, I searched for a free solid modeler to sketch out a few
ideas. To my surprise, their are practically no open source 3D CAD
packages available. So
> let aaa = unsafePerformIO $ newIORef []
> writeIORef aaa [1,2,3]
> readIORef aaa
[(),(),()]
sincerely!
--
View this message in context:
http://www.nabble.com/why-cannot-i-get-the-value-of-a-IORef-variable---tp26004111p26004111.html
Sent from the Haskell - Haskell-Cafe mailing list archive at
I assume you're trying this at the GHCi prompt, which is where you're
problem is coming from, specifically on the first line.
When you do:
> let aaa = unsafePerformIO $ newIORef []
GHCi takes a wild stab at the type of [] and comes up with the type [()], so
now you have a IORef [()] type, which is
Apparently the old exception library had convenience functions like
'arithExceptions' that could be used with 'handleJust'.
handleJust arithExceptions handler thing
With the new module you can write something like this (I determined this
from experimentation):
arithExceptionTester :: ArithEx
zaxis wrote:
>> let aaa = unsafePerformIO $ newIORef []
>> writeIORef aaa [1,2,3]
>> readIORef aaa
> [(),(),()]
What in Haskells name do you think you're doing? Don't use
unsafePerformIO like that! Its unnecessary and a bit concerning,
really.
Prelude> :m Data.IORef
Prelude Data.IORef> x <- n
Yes, it works now! thank you very much!
Kyle Murphy-2 wrote:
>
> I assume you're trying this at the GHCi prompt, which is where you're
> problem is coming from, specifically on the first line.
> When you do:
>> let aaa = unsafePerformIO $ newIORef []
> GHCi takes a wild stab at the type of []
thank you! In fact i really donot understand "unsafePerformIO" very much !
Thomas DuBuisson wrote:
>
> zaxis wrote:
>>> let aaa = unsafePerformIO $ newIORef []
>>> writeIORef aaa [1,2,3]
>>> readIORef aaa
>> [(),(),()]
>
> What in Haskells name do you think you're doing? Don't use
> unsafeP
zaxis> thank you! In fact i really donot understand
zaxis> "unsafePerformIO" very much !
Then all you have to understand is - never use it!
--
Colin Adams
Preston Lancashire
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For clarity, one trick that uses "unsafePerformIO" which you may have
seen posted on this list earlier today is the following way of
creating a globally visible IORef:
import Data.IORef
import System.IO.Unsafe
*** counter = unsafePerformIO $ newIORef 0 ***
next = do
modifyIORef counter (+
Hi John,
I just stumbled on this issue while trying to compile turbinado with
the haskell platform / ghc 6.10.4. I got past it by manually editing
back in the time definitions, but just wondering if there was an
official resolution. Thanks,
Warren
On Oct 13, 2009, at 6:48 AM, John Goerz
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