Hi,
I am using Data.Binary which defined instance Binary a = Binary
[a]. Now I need to define instance Binary [String] to make
something special for string list.
How to make it work? I looked into the chapter of
overlappinginstances, nothing works.
--
竹密岂妨流水过
山高哪阻野云飞
Am 05.01.2011 09:24, schrieb Magicloud Magiclouds:
Hi,
I am using Data.Binary which defined instance Binary a = Binary
[a]. Now I need to define instance Binary [String] to make
something special for string list.
How to make it work? I looked into the chapter of
overlappinginstances,
Hello,
{-# LANGUAGE OverlappingInstances, FlexibleInstances #-}
import Data.Binary
instance Binary [String] where
get = undefined
put = undefined
works fine here on GHC 6.12.3. That being said, it would be safer
perhaps to add a newtype around [String] so you can
You can't. If you have special semantics for [String], then it is not
really a [String], it is something else. So let the type system know
that:
newtype SomethingElse = SomethingElse [String]
instance Binary SomethingElse where
...
On Wed, Jan 5, 2011 at 1:24 AM, Magicloud Magiclouds
You have two choices (other people have enumerated the first while I
was typing):
First choice:
Wrap your Stringlist with a newtype:
newtype StringList = StringList [String]
The downside of this your code gets polluted with the newtype.
Second choice:
Write special putStringList and
Hi all,
I'm not able to find out how one can use Network.Curl with the
threaded runtime safely.
I have this simple example:
import Network.Curl
import Control.Concurrent
import Control.Concurrent.MVar
getUrl :: (Monad m) = String - IO (m String)
getUrl url = do
(code, body) - curlGetString
Cafe,
In every language I program in, I try to be as disciplined as possible
and use Test-Driven Development. That is, every language except
Haskell.
There are a few great benefits that come from having a comprehensive
test suite with your application:
1. Refactoring is safer/easier
2. You have
Jonathan Geddes wrote:
snip
So, am I missing the benefits of TDD in my Haskell code?
Probably. I work on a project which has 4+ lines of
haskell code (a compiler written in haskell) and has a huge
test suite that is a vital to continued development.
I've also written relatively small
Hi!
I am glad to announce a new version of Etage, a general data-flow
framework. Now it supports also GHC 7.0 and not just GHC head and
because of this also Hackage successfully generates documentation so
it is easier to understand the framework.
http://hackage.haskell.org/package/Etage
Feel
Steffen Schuldenzucker:
Sure. GHC would prompt that.
Jasper Van der Jeugt:
Not working with ghc7. But there sure are some threads about this
kind of things. I do not know if this is a bug of 6.* or 7, either.
Luke Palmer:
Sorry, by special, I meant, for example, [a, b] will be ab by
Erik de Castro Lopo wrote:
Jonathan Geddes wrote:
snip
So, am I missing the benefits of TDD in my Haskell code?
Probably. I work on a project which has 4+ lines of
haskell code (a compiler written in haskell) and has a huge
test suite that is a vital to continued development.
On 04/01/2011 21:20, Erik de Castro Lopo wrote:
Malcolm Wallace wrote:
The peaks I am guessing are largely attributable to parsing the source
files. Then, once the source has been converted to an AST, the DDC
compiler is presumably doing some analysis before moving on to the
next file? I
On 31/12/2010 09:19, Eric Stansifer wrote:
Hello,
I wish to use a mutable array in multiple threads. Can IO arrays be
used in any thread, or only the thread they are created in? (So if I
create an IO array in one thread, pass it to another via an MVar, can
I read / edit it in that other
Hi all,
I was reading:
http://www.haskell.org/haskellwiki/GHC/AdvancedOverlap
and I became curious. Playing with the code I started to find a way to say:
instance Show a = ShowPred a HTrue
instead of enumerating all the instances, mirroring those of the Show class:
instance ShowPred Int
On 01/05/2011 03:44 AM, Jonathan Geddes wrote:
When I write Haskell code, I write functions (and monadic actions)
that are either a) so trivial that writing any kind of unit/property
test seems silly, or are b) composed of other trivial functions using
equally-trivial combinators.
There are
Mitar wrote:
Hi!
On Sat, Dec 25, 2010 at 11:58 AM, Edward Z. Yang ezy...@mit.edu wrote:
I think you're right. A further comment is that you don't really need
stringent timing conditions (which is the only thing I think of when
I hear race) to see another thread grab the mvar underneath
Hello,
does anyone have experiences (good/bad) or some good-to-know knowledge
about Intel's manycore lab, which supposedly has GHC 6.13
installed[1]?
Regards,
Michael
[1]
Use the text library instead?
On Jan 5, 2011 2:09 AM, Tony Morris tonymor...@gmail.com wrote:
I am reading files with System.IO.readFile. Some of these files start
with a UTF-8 Byte Order Marker (0xef 0xbb 0xbf). For some functions that
process this String, this causes choking so I drop the
Thanks that works, but I have packages that rely on mtl=2.0, so its
not the best solution. Perhaps the maintainer of FileManipCompat could
be contacted to update the package?
On 1/4/11, Daniel Fischer daniel.is.fisc...@googlemail.com wrote:
On Wednesday 05 January 2011 01:54:36, Tony Miller
On Wednesday 05 January 2011 19:43:53, Tony Miller wrote:
Thanks that works, but I have packages that rely on mtl=2.0, so its
not the best solution. Perhaps the maintainer of FileManipCompat could
be contacted to update the package?
Visiting http://hackage.haskell.org/package/FileManip reveals
Though its quite different to AdvancedOverlap, Conal Elliott has a
method of answering the title of your post - Choosing a type-class
instance based on the context.
See the CxMonoid (context monoid) in Section 3. Flexible Layout of the
paper Applicative Data-Driven Computation.
The Haskell type system is simply not rich enough to guarantee everything you
might need.
That's true, and after giving this a bit more thought, I realized it's
not JUST the type system that I'm talking about here. There are a few
other features that make it hard for me to want to use
[1]
http://software.intel.com/en-us/blogs/2010/10/14/prerelease-ghc-and-haskell-cnc-installed-on-intels-manycore-testing-lab-for-academic-use-2/
Very interesting. Had this been advertised here before?
Besides the technical issues - what kind of personal data does Intel collect?
I understand
On Wed, Jan 5, 2011 at 3:02 PM, Jonathan Geddes
geddes.jonat...@gmail.com wrote:
The Haskell type system is simply not rich enough to guarantee everything
you might need.
Despite all this, I suspect that since Haskell is at a higher level of
abstraction than other languages, the tests in
Haskell's type system makes large classes of traditional unit tests
irrelevant. Here are some examples:
- Tests that simply run code to make sure there are no syntax
errors or typos,
- Tests that exercise simple input validation that is handled by the
type system, i.e.
On Tue, Jan 4, 2011 at 5:16 PM, Joe Bruce bruce.jo...@gmail.com wrote:
I've had a bit of an adventure trying to build and run lambdabot on my box.
'cabal install lambdabot' does not work. It states it's not GHC 6.12 (and
certainly not 7.0) compatible, but I tried 6.12 anyway and got nowhere.
On Wed, Jan 5, 2011 at 12:53 PM, Rogan Creswick cresw...@gmail.com wrote:
State. I didn't have any trouble building lambdabot after setting an
upper version bound on the mtl dependency in lambdabot.cabal:
Library
build-depends: base, mtl = 2.0, bytestring, unix
My mistake, that should
On Wed, Jan 5, 2011 at 9:02 PM, Jonathan Geddes
geddes.jonat...@gmail.com wrote:
Despite all this, I suspect that since Haskell is at a higher level of
abstraction than other languages, the tests in Haskell must be at a
correspondingly higher level than the tests in other languages. I can
see
On Wed, Jan 05, 2011 at 10:27:29PM +0100, Gregory Collins wrote:
Once I had written the test harness, I spent literally less than a
half-hour setting this up. Highly recommended, even if it is a (blech)
Java program. Testing is one of the few areas where I think our
software engineering
Jonathan Geddes wrote:
I know that much of my code could benefit from a property test or two
on the more complex parts, but other than that I can't think that unit
testing will improve my Haskell code/programming practice.
One other thing I should mention that is that since a lot of
Haskell
These are some heuristics memories I have for myself, and you can feel
free to take whatever usefulness you can get out of it.
1. Don't confuse TDD with writing tests, in general.
2. Studies show that if you do TDD, you can write more tests than if you
write tests after you write the code.
On Wed, Jan 5, 2011 at 20:35, Stephen Tetley stephen.tet...@gmail.com wrote:
Though its quite different to AdvancedOverlap, Conal Elliott has a
method of answering the title of your post - Choosing a type-class
instance based on the context.
See the CxMonoid (context monoid) in Section 3.
On Wed, Jan 5, 2011 at 6:41 PM, John Zabroski johnzabro...@gmail.comwrote:
5. I have a hard time understanding statements like The difficulties in
unit testing OO code is coaxing objects into the correct state to test a
particular property. Difficulty in unit testing OO code is best
picoSec :: IO Integer
picoSec = do
t - ctPicosec `liftM` (getClockTime = toCalendarTime)
return t
rollDice :: Int - IO Int
rollDice n = do
ps - picoSec
return $ (take 1 $ randomRs (1,n) $ mkStdGen $ fromInteger ps) !! 0
The above code uses `ctPicosec` as seed. Is it better to
John Zabroski wrote:
5. I have a hard time understanding statements like The difficulties in
unit testing OO code is coaxing objects into the correct state to test a
particular property.
This is my direct experience of inheriting code written by others
without any tests and trying to add
Admittedly, I don't know much about this from the haskell end or about the
particular api.
If you want statistical randomness, your seed doesn't matter; just the PRNG.
I might even have seeded with a constant or taken the seed from the user.
Seeding from urandom will make your output more
It probably is, but definitly not portable. Try to find /dev/urandom
under Windows.
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On Wed, Jan 5, 2011 at 1:27 PM, Gregory Collins g...@gregorycollins.net wrote:
On Wed, Jan 5, 2011 at 9:02 PM, Jonathan Geddes
geddes.jonat...@gmail.com wrote:
Despite all this, I suspect that since Haskell is at a higher level of
abstraction than other languages, the tests in Haskell must be
Evan Laforge qdun...@gmail.com wrote in article
aanlktinfyp-bpbs1ga8_=o9wcrhe+duux-vfrmdl2...@mail.gmail.com in
gmane.comp.lang.haskell.cafe:
Incidentally, I've never been able to figure out how to use
QuickCheck. Maybe it has more to do with my particular app, but
QuickCheck seems to expect
You need both. A good static type system will tell you whether or not the
code is type-correct. It will not tell you whether or not it does what it's
supposed to do.
Consider:
sort :: [a] - [a]
If you change sort to be:
sort = id
It will still type check, but it obviously doesn't do what
On Jan 4, 2011, at 5:41 PM, Antoine Latter wrote:
Are you thinking that the BOM should be automatically stripped from
UTF8 text at some low level, if present?
It should not. Wether or not a U+FFEF can be stripped depends on context in
which it is found. There is no way that lower level code,
Simon Marlow wrote:
Or the C compiler, perhaps?
Thanks for the suggesion Simon. This one was actually easier
to test that Malcolm's suggestion.
To test it, I ran the same test under Oprofile [0], the Linux
kernel based profiler. OProfile is really cool because it
profiles the whole system,
Rogan,
Thanks for taking a look at it. No, mtl is not the problem, at least not
yet.
A detail that I've discovered is important: I'm on Mac OS X (10.6).
readline is my problem, and readline + mac + haskell seems to be a bad mix.
Macports installs readline in /opt/local/ by default, so I
I would supplement this excellent list of advices with an emphasis on
the first one: Test-Driven Development is *not* testing, TDD is a
*design* process. Like you said, it is a discipline of thought that
forces you first to express your intent with a test, second to write
the simplest thing that
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