Re: [Haskell-cafe] ordNub
On Oct 12, 2013, at 2:47 PM, Niklas Hambüchen m...@nh2.me wrote: I would like to come back to the original question: How can ordNub be added to base? I guess we agree that Data.List is the right module for a function of type Ord a = [a] - [a], but this introduces * a cyclic dependency between Data.List and Data.Set * a base dependency on containers. What is the right way to go with that? Should ordNub be introduced as part of Data.Set, as Conrad suggested? It does not really have anything to do with Set, apart from being implemented with it. I think nub's behavior is rather set-related, so I don't really understand the objection to putting it in Data.Set. Anthony On 14/07/13 14:12, Roman Cheplyaka wrote: Something like that should definitely be included in Data.List. Thanks for working on it. Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANN] New OpenCV Bindings
To be clear, I am not the maintainer of HOpenCV. I have used a fork of that library for experimenting with OpenCV interfaces over the past few years, and written quite a few kloc using it in several robotics oriented projects with computer vision needs. None of my experiments with HOpenCV are on hackage as they are experiments, but I have helped others get started with them over time. I am totally supportive of Arjun's new efforts: OpenCV has changed a lot, and there is reason to be optimistic that he will be able to provide a much better foundation for Haskell bindings than we have ever had. As the low level bindings come online, we will be able to introduce some of the extra type-driven code paths and static checks that have proven successful in the existing fragmented Haskell-OpenCV ecosystem. Anthony On Sep 28, 2013, at 2:31 PM, Arjun Comar nru...@gmail.com wrote: I've been talking to Anthony Cowley who I think is the current maintainer of HOpenCV and Ville Tirronen who has been developing the CV bindings. Basically the consensus is that these raw bindings provide a new base to work from, and it's worthwhile to rethink the API we provide with a fresh start. On Sat, Sep 28, 2013 at 2:23 PM, Ivan Perez ivanperezdoming...@gmail.com wrote: The people working on HOpenCV are very open to incorporating other's programmer's patches. Maybe you can incorporate your changes to cv-combinators? (Project's been halted since 2010, I'm sure they'll be very happy to see that sb is contributing). On 28 September 2013 19:13, Arjun Comar nru...@gmail.com wrote: Fair enough, it's been two or three years since I tried to play with them. Most of my work is in the raw bindings currently, which provide the C++ API in Haskell, so much lower level that cv-combinators. If HOpenCV were to incorporate parts of these bindings then cv-combinators would be able to benefit from this work. That said, my effort going forward is to provide something equivalent to cv-combinators in expressiveness. I'm definitely taking inspiration from the library though I'm not basing my work on their source code. On Sat, Sep 28, 2013 at 12:51 PM, Ivan Perez ivanperezdoming...@gmail.com wrote: I think they do work. cv-combinators depends on HOpenCV, which depends on OpenCV 2.0. On 28 September 2013 16:03, Arjun Comar nru...@gmail.com wrote: No, these are unrelated. Cv-combinators hasn't really worked since OpenCV 2.0 waa released I believe. On Sep 28, 2013 8:54 AM, Ivan Perez ivanperezdoming...@gmail.com wrote: Cool. Thanks a lot for uploading this. I have a question (and I confess that I haven't checked the link). How is this related to or overlaps with cv-combinators? Cheers Ivan On 28 September 2013 06:18, Arjun Comar nru...@gmail.com wrote: After receiving feedback, I went ahead and split out the raw C wrappers and Haskell bindings. You can find them at www.github.com/arjuncomar/opencv-raw. I'll upload it to hackage as opencv-raw once I have uploader privileges. Regards, Arjun On Fri, Sep 27, 2013 at 4:09 PM, Arjun Comar nru...@gmail.com wrote: Hi all, I've been hard at work on a new set of OpenCV bindings that will hopefully solve a lot of the shortcomings with previous attempts. An automatic header parser has been used to generate a full set of Haskell bindings for the C++ API, and I'm now working to create a pleasant Haskell API. The plan is to expose major functionality through pipes for two reasons: 1) OpenCV is not very referentially transparent, and so you're stuck in IO for anything non-trivial. Lazy IO is potentially problematic, and so immediate incorporation of a proper streaming library is probably best. 2) Computer vision algorithms are frequently expressed in terms of pipelines of functionality, and a pipes approach can provide a very natural API for expressing these algorithms. At this stage, I could very much use input from anyone who's interested in these bindings. I've got the basics of a library forming, but there's a ton to do and help in the form of pull requests are very very welcome. I could also use feedback on what's been done so far (especially criticisms) as well as feature requests. The current plan is to develop the pipes API for the core functionality. The plan is to provide the major functionality from core, highgui, imgproc, features2d, contrib, ml, flann, video, and objdetect as quickly as I can before trying to cover any of the more specialized parts of the API. The functions and types from these modules (baring a few major and important exceptions) are automatically translated into C wrappers and raw Haskell bindings. If there's sufficient interest in these raw bindings separately from the API I'm developing, I'll release them as a separate package on Hackage. I'm calling my project revelation for the moment because I'm bad at naming things
Re: [Haskell-cafe] OS X ghci problem
On Jul 13, 2013, at 8:04 PM, Jason Dagit dag...@gmail.com wrote: On Sat, Jul 13, 2013 at 4:39 PM, Mark Lentczner mark.lentcz...@gmail.com wrote: Bizarre - this just happened to me today, too. Anyone? Did you figure out a work around? For the record, I'm trying to bring Euterpea up. After some digging, experimenting, asking around, and head scratching my best guesses are: * GHCi's custom linker isn't doing the right thing (some versions of llvm/clang gave crashes like this and it was a linker bug for them, you can find reports on sites like StackOverflow). * We need to feed .m files to clang instead of ghc/gcc * GHCi needs to be built with Cocoa in mind (is it already?) * Some rts component of objective-c is not properly initialized (ARC vs. -fobjc-gc vs. -fnext-step, etc) My system is OS X 10.8.4, and I'm running HP 2013.2, so 7.6.3. And GLFW-0.5.1.0. In terms of experimentation, you can hand desugar the objective-c code in the GLFW init and when I do that I get segfaults. Also, the address mentioned in the objective-c exception has a suspicious value, which would further implicate the linker. Add to that, it works for a compile program (which uses the system linker, IIRC). Basically, I'm pretty sure it's GHCi's linker to blame here but I don't have a smoking gun. Jason I thought I'd had some success desugaring the Objective-C code, but I never went the whole way, so perhaps I just didn't get to the segfault. What I do for GLFW is use a dylib, then you don't rely on GHCi's static-ish linker. The only wrinkle is figuring out where you want the dylib. I think homebrew will put one in /usr/local/lib, which works out nicely, but they don't have GLFW 3 yet. Another option is to build the dylib yourself from the GLFW source bundled with the GLFW-b package, then tell cabal where to find it. It's worth the trouble, as having a GHCi-based workflow for graphics work is wonderful. A fancy Setup.hs that works out installation paths could generate the dylib, and I thought such code existed in the past. Was some problem found with that approach? Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What symbol / atom/ interned-string package is currently preferred?
On Tue, May 7, 2013 at 2:58 PM, Ryan Newton rrnew...@gmail.com wrote: Hi cafe, I use symbols all the time when manipulating code. I vacillate between using stringtable-atom, symbol, and simple-atom. Unfortunately: Stringtable-atom is has a broken build right now (GHC 7.6). (Also I've had some crashes with it in the past.) simple-atom has dependency upper bounds that restrict it to GHC = 7.0 symbol has a design flaw, which is that it exposes the constructor for Symbol, which reveals the (nondeterministic) unique Int IDs. I.e. it is not SafeHaskell. I submitted a pull request to relax simple-atom, but perhaps there are other packages people use with which I am not aware? Thanks, -Ryan This package is current and maintained: http://hackage.haskell.org/package/intern Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GPGPU
I wrote this some time ago. http://www.arcadianvisions.com/blog/?p=346 I know that soon after I wrote that, it worked with both OpenCL and gloss from hackage, but there may be some bitrot at this point. Anthony On May 4, 2013, at 6:00 AM, Christopher Howard christopher.how...@frigidcode.com wrote: Has anybody on the list been playing around with OpenCL at all? I'm just starting to look into it - need to get a newer Radeon card, I think - but I'm strongly interested in GPGPU programming. -- frigidcode.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GPGPU
On Sat, May 4, 2013 at 3:17 PM, Jason Dagit dag...@gmail.com wrote: On Sat, May 4, 2013 at 11:54 AM, Anthony Cowley acow...@seas.upenn.edu wrote: I wrote this some time ago. http://www.arcadianvisions.com/blog/?p=346 I know that soon after I wrote that, it worked with both OpenCL and gloss from hackage, but there may be some bitrot at this point. Some of the links in the blog seem to be broken as well. For instance, the link to the animation screen shot. Jason Thanks to the nudge from Jason, the bitrot has now been scraped off. The post is prettier, the code all works again, and the screenshot has been restored. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] data types with overlapping component names (in one module)?
On Tue, Apr 16, 2013 at 4:05 PM, Sturdy, Ian sturdy...@mail.wlu.edu wrote:
'vinyl' uses type-level literal strings and is very slick (although all
fields with the same name have the same type)
This is not entirely true, depending on what you mean by name. The
following is just fine. You only have naming issues if you want to
give @Field::baz:::Int@ a name, that name is, unsurprisingly, tied
to the field type of Int.
{-# LANGUAGE DataKinds, TypeOperators #-}
import Data.Vinyl
type Foo = '[baz ::: Int]
type Bar = '[baz ::: String]
x :: PlainRec Foo
x = Field =: 2
y :: PlainRec Bar
y = Field =: Two
Anthony
-IRS
From: haskell-cafe-boun...@haskell.org [haskell-cafe-boun...@haskell.org] on
behalf of Johannes Waldmann [waldm...@imn.htwk-leipzig.de]
Sent: Tuesday, April 16, 2013 8:17 AM
To: haskell-cafe@haskell.org
Subject: [Haskell-cafe] data types with overlapping component names (in one
module)?
What is the current situation: can we have two types
with overlapping component names in one module?
module M where
data T1 = C1 { foo :: Int }
data T2 = C2 { foo :: String }
It seems not (ghc says: Multiple declarations of 'foo'). This comes close:
http://www.haskell.org/ghc/docs/7.6.2/html/users_guide/syntax-extns.html#disambiguate-fields
but still requires the definitions to reside in different modules?
This is a major pain (it forces me to spread the source over several files),
and also a show-stopper when selling Haskell to OO folks, who naturally
assume that a class also denotes a scope. (And that you could nest them.)
Are/were there plans/proposals to address this?
- J.W.
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Re: [Haskell-cafe] Overloading
On Mar 9, 2013, at 3:33 PM, Peter Caspers pcaspers1...@gmail.com wrote: Hi, I just started playing around a bit with Haskell, so sorry in advance for very basic (and maybe stupid) questions. Coming from the C++ world one thing I would like to do is overloading operators. For example I want to write (Date 6 6 1973) + (Period 2 Months) for some self defined types Date and Period. Another example would be (Period 1 Years) + (Period 3 Months). So maybe make the types instances of typeclasses? This would be Num for (+) I guess. For the first example above it will not work however, alone for it is not of type a - a - a. Also the second example does not fit, because I would have to make Period an instance of Num, which does not make sense, because I can not multiply Periods (for example). Am I missing something or is that what I am trying here just impossible by the language design (and then probably for a good reason) ? Take a look at affine spaces and additive groups in the vector-space package. There may be other treatments of torsors on hackage, but vector-space has a fairly straightforward approach. A second question concerns the constructors in own datatypes like Date above. Is it possible to restrict the construction of objects to sensible inputs, i.e. reject something like Date 50 23 2013 ? My workaround would be to provide a function say date :: Int-Int-Int-Date checking the input and returning a Date object or throw an error if the input does not correspond to a real date. I could then hide the Date constructor itself (by not exporting it). However this seems not really elegant. Also again, taking this way I can not provide several constructors taking inputs of different types, can I ? This approach -- hiding data constructors and exporting functions that perform validation -- is called smart constructors, and is accepted practice. It isn't entirely satisfying due to interfering with pattern matching in client code, so you either need to work with projection functions for your data type, or use ViewPatterns to provide a more transparent record type at use sites. Anthony Thanks a lot Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Roshask
I know that it probably needs updating for Groovy. I don't think it has many users, which makes it more challenging to keep things running smoothly, but I'm willing to help any interested parties get it up and running. Anthony On Fri, Jan 11, 2013 at 4:37 PM, Tijn van der Zant robot...@gmail.com wrote: Hi, I want to use Haskell to program my robot using ros. I've found roshask https://github.com/acowley/roshask and I was wondering if someone on this list has experience with it and can tell me how good it is. Thanx! --Tijn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't prevent memoizing in simple code
On May 16, 2012, at 12:08 PM, Yves Parès wrote:
The buffer http://hpaste.org/68595 presents a simple code I tried to profile.
I spotted what I strongly think to be an abusive memoization. The problem is
that I don't see how to (simply) get rid of it.
Compiled with -O2, it consumes 130MB of memory, however lines A and B
executed separately consume each only 1MB.
The infinite list (l 1), whatever I do, keeps being shared between lines A
and B.
I tried to wrap it in a function, as you can see, I also tried to make it
explicitely polymorphic (bypassing monomorphic restriction), nothing solves
it, GHC is just to good at memoizing.
Adding a {-# NOINLINE l #-} annotation helps here. Syntactically, it must be
located somewhere a type signature for l would also be valid.
Anthony
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Re: [Haskell-cafe] Haskell integration with C/C++ (GSOC)
On Thursday, April 5, 2012 at 1:53 AM, Sutherland, Julian wrote:
Hey Guys,
I'm Julian, I am reaching the end of my second year as a JMC (Joint
Mathematics and Computer science) Student at Imperial College London
and I'd like to apply to GSOC for a project involving Haskell and I just
wanted to run my idea past the community.
[snip]
I found an example of such a bug, which I will test further before reporting
it.
It seems to be the opposite of the following bug:
http://hackage.haskell.org/trac/ghc/ticket/5594
i.e. the stdout buffer isn't always correctly flushed when calling C/C++ in a
program whose main is written in Haskell.
For example, when running the code:
main.hs:
module Main where
import Foreign.C.Types
import System.IO
foreign import ccall inc c_inc :: CInt - CInt
main :: IO ()
main = do
putStr Enter n:
-- hFlush stdout
s -getLine
putStrLn . show . c_inc . read $ s
inc.c:
int inc(int i) __attribute__ ((const));
int inc(int i)
{
return i + 1;
}
Built with
Makefile:
all:
gcc -c -o inc.o inc.c
ghc --make -main-is Main main.hs inc.o -o test
rm *.hi *.o
The output comes out as:
[julek@cryptid inc]$ ./test
2
Enter n: 3
But when the hFlush stdout line is commented back in, the output is:
[julek@cryptid inc]$ ./test
Enter n: 2
3
which is correct, but the extra line shouldn't be necessary.
I am currently using ghc 7.4.1 which is the newest version, so this is a
current bug.
I think this is a consequence of line buffering rather than a bug. If you write
your own increment function in Haskell, you get the same behavior. If you
`hSetBuffering stdout NoBuffering` before your `putStr` call, you should get
the behavior you wanted. I've seen similar issues with programs written in many
languages; it's just one of those gotchas to be aware of when dealing with
console UI.
As to the rest of your proposal, when you started out talking about calling
Haskell from C or C++, I hoped you would focus on the pain of linking the final
executable. This seems to me a more fundamental -- and addressable -- stumbling
block than the richness of interaction with C++. As things stand, it is quite a
hassle to use a Haskell library of any complexity called from C. Improved
interaction with C++ could indeed be valuable, but, unless something has
changed recently, work is still needed to improve the more basic C - Haskell
FFI story.
Anthony
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Re: [Haskell-cafe] Trying to use more than one array in runSTUArray
On Thursday, March 15, 2012 at 2:27 PM, Juan Miguel Vilar wrote:
Hello, café:
I am trying to use more than one array with runSTUArray but I don't seem
to be able to understand how it works. My first try is this:
test1 n = runSTUArray $ do
a - newArray (1, n) (2::Int)
b - newArray (1, n) (3::Int)
forM_ [1..n] $ \i - do
v - readArray a i
writeArray b i (v+1)
return b
but it does not work. However, when I write
The problem is that GHC doesn't know what type of array a is. If you provide an
annotation, you can resolve the ambiguity:
a - newArray (1,n) (2::Int) :: ST s (STUArray s Int Int)
However, this is somewhat ugly, so we should look at your next example:
test2 n = runSTUArray $ do
let createArray v n = newArray (1, n) (v::Int)
a - createArray 2 n
b - createArray 0 n
forM_ [1..n] $ \i - do
v - readArray a i
writeArray b i (v+1)
return b
Note that the type of the b array was never in doubt thanks to runSTUArray.
What you've done here is said that the same function that creates b also
creates a, and since we know b's type, we now know a's type because GHC doesn't
make createArray's type as polymorphic as it might.
Another approach to resolving the types is to essentially do what you've done
in your second example, but give createArray a type that is as polymorphic as
you need:
{-# LANGUAGE FlexibleContexts #-}
newSTUArray :: (MArray (STUArray s) e (ST s), Ix i) =
(i,i) - e - ST s (STUArray s i e)
newSTUArray = newArray
test3 n = runSTUArray $ do
a - newSTUArray (1, n) False
b - newSTUArray (1, n) (3::Int)
forM_ [1..n] $ \i - do
v - readArray a i
writeArray b i (fromEnum v+1)
return b
I hope that helps clear things up. The issue to be aware of, particularly with
the Array types, is just how polymorphic the interfaces you rely upon are. The
best approach to figuring these problems out is to add type annotations to see
where your intuition diverged from the type checker's reality.
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Re: [Haskell-cafe] Understanding GC time
From that profiling data, I think you're just seeing a decrease in sharing. With one thread, you create the list structure in memory: the first fold could consume it in-place, but the second fold is still waiting for its turn. The list is built on the heap so the two folds can both refer to the same list. With two threads, GHC is being clever and inlining the definition you give for list, which is then optimized into two parallel loops. No list on the heap means there's not much for the GC to do. Sharing of index lists like this is a common source of problems. In particular, nested loops can make it even trickier to prevent sharing as there may not be an opportunity for parallel evaluation. Anthony On Mar 10, 2012, at 10:21 AM, Thiago Negri evoh...@gmail.com wrote: Hi all. I wrote a very simple program to try out parallel Haskel and check how it would look like to make use of more than one core in this language. When I tried the program with RTS option -N1, total time shows it took 2.48 seconds to complete and around 65% of that time was taken by GC. Then I tried the same program with RTS options -N2 and total time decreased to 1.15 seconds as I expected a gain here. But what I didn't expect is the GC time to drop to 0%. I guess I'm having trouble to understand the output of the RTS option -s. Can you enlighten me? The source for the testing program: module Main where import Data.List (foldl1') import Control.Parallel (par, pseq) import Control.Arrow (()) f `parApp` (a, b) = a `par` (b `pseq` (f a b)) seqApp = uncurry main = print result where result = (+) `parApp` minMax list minMax = minlist maxlist minlist = foldl1' min maxlist = foldl1' max list = [1..1999] The results on a Windows 7 64bits with an Intel Core 2 Duo, compiled with GHC from Haskell Platform: c:\tmp\hspar +RTS -s -N1 par +RTS -s -N1 2000 803,186,152 bytes allocated in the heap 859,916,960 bytes copied during GC 233,465,740 bytes maximum residency (10 sample(s)) 30,065,860 bytes maximum slop 483 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 1523 collections, 0 parallel, 0.80s, 0.75s elapsed Generation 1:10 collections, 0 parallel, 0.83s, 0.99s elapsed Parallel GC work balance: nan (0 / 0, ideal 1) MUT time (elapsed) GC time (elapsed) Task 0 (worker) :0.00s( 0.90s) 0.00s( 0.06s) Task 1 (worker) :0.00s( 0.90s) 0.00s( 0.00s) Task 2 (bound) :0.86s( 0.90s) 1.62s( 1.69s) SPARKS: 1 (0 converted, 0 pruned) INIT time0.00s ( 0.00s elapsed) MUT time0.86s ( 0.90s elapsed) GCtime1.62s ( 1.74s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time2.48s ( 2.65s elapsed) %GC time 65.4% (65.9% elapsed) Alloc rate936,110,032 bytes per MUT second Productivity 34.6% of total user, 32.4% of total elapsed gc_alloc_block_sync: 0 whitehole_spin: 0 gen[0].sync_large_objects: 0 gen[1].sync_large_objects: 0 c:\tmp\hspar +RTS -s -N2 par +RTS -s -N2 2000 1,606,279,644 bytes allocated in the heap 74,924 bytes copied during GC 28,340 bytes maximum residency (1 sample(s)) 29,004 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 1566 collections, 1565 parallel, 0.00s, 0.01s elapsed Generation 1: 1 collections, 1 parallel, 0.00s, 0.00s elapsed Parallel GC work balance: 1.78 (15495 / 8703, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) :0.00s( 0.59s) 0.00s( 0.00s) Task 1 (worker) :0.58s( 0.59s) 0.00s( 0.01s) Task 2 (bound) :0.58s( 0.59s) 0.00s( 0.00s) Task 3 (worker) :0.00s( 0.59s) 0.00s( 0.00s) SPARKS: 1 (1 converted, 0 pruned) INIT time0.00s ( 0.00s elapsed) MUT time1.15s ( 0.59s elapsed) GCtime0.00s ( 0.01s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time1.15s ( 0.61s elapsed) %GC time 0.0% (2.4% elapsed) Alloc rate1,391,432,695 bytes per MUT second Productivity 100.0% of total user, 190.3% of total elapsed gc_alloc_block_sync: 90 whitehole_spin: 0 gen[0].sync_large_objects: 0 gen[1].sync_large_objects: 0 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The (!) operation
On Thu, Mar 8, 2012 at 11:19 AM, Christopher Done chrisd...@googlemail.com wrote: ‘Ello. Is there a generalization of this operator? It's all over the place, it's basically (!) :: (Monad m, Indexed collection index value) = index - container - m value We have `(!!)` on lists, `(!)` on maps, vectors, json objects, … (doesn't seem there's one for bytestring) (Though I seem to recall the monadic return value being frowned upon but I don't recall why.) Thoughts? Perhaps Data.Key meets your needs? http://hackage.haskell.org/packages/archive/keys/2.1.2/doc/html/Data-Key.html Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Vector (or List) to CArray?
On Thu, Jan 19, 2012 at 1:15 PM, Dominic Espinosa dces...@fastmail.fm wrote: Hello, I'm trying to use the fftw binding, and its functions operate on CArrays of Complex. My data is coming from hsndfile, so it starts out as a Vector of Double. How do I convert this data to CArray? The API functions in the CArray module don't seem to indicate how. Thanks. I've not tried this, but I would expect to be able to use http://hackage.haskell.org/package/hsndfile-vector-0.4.0, and then use the ForeignPtr that lives inside the Vector the to build a CArray. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haxr standalone server?
On Thu, Jan 5, 2012 at 10:40 AM, Johannes Waldmann waldm...@imn.htwk-leipzig.de wrote: How could I use haxr (http://www.haskell.org/haskellwiki/HaXR) to build a stateful server? It should listen on some port, and fork threads (inside Haskell land) to handle incoming calls. Any of the Haskell web frameworks can do this? I use HaXR in conjunction with Snap. It basically boils down to using Network.XmlRpc.Server (handleCall, methods) in conjunction with Snap's getRequestBody and writeLBS. The good news is you don't need to worry about forking your own threads, the web server handles that. To make calls stateful, you just stash away a reference in the handler you give Snap (or whatever web server you use). Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alternative versus Monoid
On Dec 15, 2011, at 10:19 AM, Brent Yorgey wrote:
On Thu, Dec 15, 2011 at 06:49:13PM +1000, Gregory Crosswhite wrote:
So at the end of the day... what is the point of even making Maybe and []
instances of Alternative?
The Alternative and Monoid instances for [] are equivalent. However,
the Alternative and Monoid instances for Maybe are not. To wit:
(Just (Sum 4)) | (Just (Sum 3))
Just (Sum {getSum = 4})
(Just (Sum 4)) `mappend` (Just (Sum 3))
Just (Sum {getSum = 7})
We already have,
First (Just (Sum 4)) `mappend` First (Just (Sum 3))
First {getFirst = Just (Sum {getSum = 4})}
So the overlap of apparent Alternative and Monoid functionality remains. This
just represents an opportunity for the caller to select the monoid they want.
Anthony
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Re: [Haskell-cafe] I for one welcome our new Robotic Overlords
On Sep 27, 2011, at 2:01 PM, Jeremy Shaw jer...@n-heptane.com wrote: When the robots take over, do you want them to be developed using a sane language like Haskell or Agda? Or some dangerous untyped OO language? I think the answer is obvious. The question is, How?. The robots will not be developed by us, but by the children of today. So, we must reach their pure minds before they have been unsafely coerced by the evil unbelievers who do not worship the gods λ, Π, and ω. Timing: you have it. I presented the work behind https://github.com/acowley/roshask at IROS 2011 just this morning. ROS is possibly the most widely used robotics middleware today, and you can now use Haskell to work with existing ROS components. While FP isn't hugely popular among the robotics community (I've been pitching functional approaches here for several years), this time around I am optimistic that we've turned the corner, or at least started that process. There was a lot of support, and developers behind other large projects expressed eagerness to rely more heavily on the compositionally of good old functions. I am not aware of as good a story for Arduino-level development. Atom may be an appropriate foundation for such an effort, but I also hope that we can get GHC ARM support sorted out, and then use platforms like the forthcoming Raspberry Pi as the computational core of an inexpensive robotics platform. In short, you can just about achieve your vision today with a TurtleBot from Willow Garage and roshask. Anthony My long term vision is: A company which produces an extensible robotics platform for children and adults ages 8 and up. The platform would be very open, extensible, and hackable. The robotic programming languages would be based around concepts like functional reactive programming, dependent types, etc. Children would begin with a simple FRP language to control the robot. They would solve simple problems like go forward until an object is encountered. As the young masters grow, they can tackle more difficult problems such as maze solving. Even later they can delve into more advanced subjects like computer vision, speech recognition and synthesis, or mind control rays. The short term vision can be summarized in one word leverage. We need to find an existing robotic platform which can be easily targeted somehow using Haskell or Agda. Perhaps something that can be targeted using atom or lava? Maybe something Arduino based? I have created a wiki page here to record your suggestions and ideas: http://haskell.org/haskellwiki/RoboticOverlords The requirements now are something that is: - hackable/open - easily obtained - reasonable in price - can easily be targeted via Haskell The only candidate I know of so far is lego mindstorms via the NXT package on hackage, Though some could argue that lego mindstorms are not reasonably priced. http://hackage.haskell.org/package/NXT Let's here your ideas! - jeremy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Segfault in the libc malloc using FFI (occurs only in x86_64)
I reported a segfault in FFI calls a while back that should be fixed in 7.2. It turned out to be a stack alignment issue, which may or may not be related to what you are seeing. Here is the bug report: http://hackage.haskell.org/trac/ghc/ticket/5250 Anthony On Sat, Aug 20, 2011 at 12:51 PM, Vincent Gerard vinc...@xenbox.fr wrote: Hi cafe, I have been struggling with this issue for the past days. I have investigated at the Haskell, C and even at assembly level... Perhaps I'm missing something big ?? I hope someone familiar with FFI could help me on this Segfault. My env is: Linux Debian 3.0.0-1, SMP, GHC 7.0.4, x86_64, eglibc 2.13-10 (This issues occurs as well on others people with /= env, but only with x86_64 arch) The bug is in the hsmagick library (FFI bindings to GraphicsMagick), for which I am the maintainer. -- So here is a reproducer (Works fine in 32 bit, segfault in 64). You should have hsmagick + GraphicsMagick dev libs installed. import Graphics.Transform.Magick.Images main = do initializeMagick c - readImage image.jpg putStrLn End -- Executing this program, compiled with standard options, a Segfault occurs at runtime. If I compile this small program with -threaded option an assertion error is thrown at runtime: main: malloc.c:3096: sYSMALLOc: Assertion `(old_top == (((mbinptr) (((char *) ((av)-bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd old_size == 0) || ((unsigned long) (old_size) = (unsigned long)__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 * (sizeof(size_t))) - 1)) ~((2 * (sizeof(size_t))) - 1))) ((old_top)-size 0x1) ((unsigned long)old_end pagemask) == 0)' failed. This assertion error is cryptic for me... but it maybe could help someone here. However, having a C experience, investigating a Segfault is in my habits, so let's install debugs symbols on everything and dig with gdb. Here is the backtrace: Program received signal SIGSEGV, Segmentation fault. 0x7510292c in malloc_consolidate (av=0x7540fe60) at malloc.c:5161 (this is inside the eglibc source) 5161 unlink(p, bck, fwd); (gdb) bt #0 0x7510292c in malloc_consolidate (av=0x7540fe60) at malloc.c:5161 #1 0x75104d64 in _int_malloc (av=0x7540fe60,bytes=8520) at malloc.c:4373 #2 0x75107420 in __libc_malloc (bytes=8520) at malloc.c:3660 #3 0x767bf311 in CloneImageInfo (image_info=0x0) at magick/image.c:1012 #4 0x00439dfa in hsmagickzm0zi5_GraphicsziTransformziMagickziFFIHelpers_mkNewImageInfo1_info () Yay, the Segfault is deep in the libc after a regular malloc (8520bytes) (I dug into the GraphicsMagick source starting from magick/image.c:1012) And this libc call is called by a call to CloneImageInfo(NULL) from Haskell, which is correct as it is graphicsMagick way to allocate an empty ImageInfo data structure. (http://www.graphicsmagick.org/api/image.html#cloneimageinfo) I tried in a C program to execute (after initializing ImageMagick) image_info=CloneImageInfo((ImageInfo *) NULL); And of course no Segfault... Let's look at the FFI call... This FFI call is the done by the mkNewImageInfo as shown in the trace. The Haskell FFI layer here has done the right job, calling the C function with the right args (NULL) Here is all the code related to mkNewImageInfo (the last Haskell part we see in the backtrace) --- mkNewImageInfo :: IO (ForeignPtr HImageInfo) mkNewImageInfo = mkFinalizedImageInfo = mkNewImageInfo_ mkFinalizedImageInfo :: Ptr HImageInfo - IO (ForeignPtr HImageInfo) mkFinalizedImageInfo = newForeignPtr imageInfoFinalizer mkNewImageInfo_ :: IO (Ptr HImageInfo) mkNewImageInfo_ = clone_image_info nullPtr -- CALL before the Segfault destroyImageInfo :: Ptr HImageInfo - IO () destroyImageInfo = destroy_image_info foreign import ccall static magick/api.h DestroyImageInfo imageInfoFinalizer :: FunPtr (Ptr HImageInfo - IO ()) foreign import ccall static magick/api.h CloneImageInfo clone_image_info :: Ptr HImageInfo - IO (Ptr HImageInfo) -- To me, this code is right (and works perfectly in 32 bit). Furthermore, as the call is made with a nullPtr arg, no data structure is used ... I tried this code without using ForeignPtr Finalizers (hsmagick = 0.4) and the Segfault occurs as well ... I even had a look at the generated assembly, which also looks right... It seems there is a real segmentation error, or an illegal access to a memory page... But I could not find the root cause of this error. And an additionnal piece to the puzzle, when running the program inside valgrind, there is no Segfault and the program works as expected. So if anyone have an idea on how only on 64bits arch an Haskell FFI call could led to a Segfault in the libc malloc, it would make my day, perhaps my week :) Thanks ! Vincent Gerard
Re: [Haskell-cafe] How to determine minimal dependency of package
On Fri, Jul 15, 2011 at 10:48 AM, yi huang yi.codepla...@gmail.com wrote: I'm writing my first haskell package, how do i determine the minimal dependency of it, for example, it use Data.Data, how do i know which version of base package first introduce Data.Data module, i can't find the answer with google. You should specify the minimum version you have tested with. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Lazy Evaluation in Monads
On Tue, May 31, 2011 at 3:49 PM, Scott Lawrence byt...@gmail.com wrote: I was under the impression that operations performed in monads (in this case, the IO monad) were lazy. (Certainly, every time I make the opposite assumption, my code fails :P .) Which doesn't explain why the following code fails to terminate: iRecurse :: (Num a) = IO a iRecurse = do recurse - iRecurse return 1 main = (putStrLn . show) = iRecurse Any pointers to a good explanation of when the IO monad is lazy? import System.IO.Unsafe iRecurse :: (Num a) = IO a iRecurse = do recurse - unsafeInterleaveIO iRecurse return 1 More interesting variations of this leave you with questions of whether or not the missles were launched, or, worse yet, was data actually read from the file handle? Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC 7, Platform 2011.2 vs OS X 10.5, Ubuntu 11.04
On Mon, May 23, 2011 at 5:17 AM, Jacek Generowicz jacek.generow...@cern.ch wrote: So, after this tale of agony, here are two concrete questions: a) Am I right in concluding that GHC 7.0.3 will not run on OS X 10.5 (without unreasonable effort)? This is a frustrating situation. Note that there is a binary for 7.0.1 that supports 10.5 http://www.haskell.org/ghc/download_ghc_7_0_1#macosxintel. From this, you should be able to build 7.0.3 yourself. One minor note: if you're interested in LLVM, stick to the 32-bit build.! If you encounter problems, #haskell will help. As for the platform, if it is giving you trouble, don't shy away from just using GHC and cabal as normal! After you've cabal installed a few big packages, you will find that you've acquired many of the most popular packages. b) On Ubuntu Natty I installed the generic linux GHC 7.0.3 binary. Downloaded Haskell Platform 2011.2.0.1 source distribution. ./configure worked happily. make fails as follows. Building transformers-0.2.2.0 /usr/local/haskell-platform-2011.2.0.1/bin/ghc --make Setup -o Setup -package Cabal-1.10.1.0 command line: cannot satisfy -package Cabal-1.10.1.0: Cabal-1.10.1.0-1fb2094e19492373b1a39284193e7984 is unusable due to missing or recursive dependencies: process-1.0.1.5-55dfaccf3a91c4cb8f6284a0bafef198 The Ubuntu HP story is a bit of a gotcha for the innocent user, too. But, again, you can happily install GHC 7.0.3, and then cabal install your way to happiness. The problem you encountered seems due to a conflict among packages that came with GHC. I think your strategy of nuking everything Haskell through your package manager (if available), then manually (not forgetting ~/.ghc and ~/.cabal) was prudent to get out of the hole you found yourself in. But don't let HP installation troubles keep you away from Haskell altogether! Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC 7, Platform 2011.2 vs OS X 10.5, Ubuntu 11.04
On Mon, May 23, 2011 at 8:16 AM, Jacek Generowicz jacek.generow...@cern.ch wrote: On 2011 May 23, at 13:45, Anthony Cowley wrote: As for the platform, if it is giving you trouble, don't shy away from just using GHC and cabal as normal! After you've cabal installed a few big packages, you will find that you've acquired many of the most popular packages. If by cabal install you mean use the command cabal ... yeah, that would be great, if only I could install cabal-install, which fails. Or do you mean manual install of Cabal packages? Either way, I'm not making much progress. What I do is get GHC installed, then download the cabal-install package from hackage and use the bootstrap.sh installer it comes with. Then you can use the cabal executable to install packages as you go. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Foreign function performance: monadic vs pure
On Mon, Apr 11, 2011 at 8:09 AM, Serguei Son serguei@gmail.com wrote: Consider two versions of sin wrapped: foreign import ccall math.h sin c_sin_m :: CDouble - IO CDouble Marking this call as unsafe (i.e. foreign import ccall unsafe math.h sin) can improve performance dramatically. If the FFI call is quick, then I believe this is the recommended approach. If you really need the imported function to be thread safe, then perhaps you should move more of the calculation into C to decrease the granularity of FFI calls. It is remarkably easy to get the meanings of safe and unsafe confused, and I can't even see the word unsafe in the current FFI user's guide! http://www.haskell.org/ghc/docs/7.0.3/html/users_guide/ffi-ghc.html Anthony and foreign import ccall math.h sin c_sin :: CDouble - CDouble One can invoke them so: mapM c_sin_m [1..n] mapM (return . c_sin) [1..n] On my computer with n = 10^7 the first version never finishes, whereas the second one calculates the result within seconds. To give you my context, I need to call a random variable generator multiple times, so that it must return IO a. Any explanation for this behavior? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Extending GHCi
On Sun, Feb 6, 2011 at 11:59 PM, C K Kashyap ckkash...@gmail.com wrote: $ ghci GHCi, version 6.12.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude :m +Data.IORef Control.Concurrent Control.Monad Prelude Data.IORef Control.Concurrent Control.Monad msg - newIORef Hello Prelude Data.IORef Control.Concurrent Control.Monad let echo = forever $ readIORef msg = putStrLn threadDelay 300 Prelude Data.IORef Control.Concurrent Control.Monad t - forkIO echo Hello Prelude Data.IORef Control.Concurrent Control.Monad Hello Hello writeIORefHello msg World Prelude Data.IORef Control.Concurrent Control.Monad World World Thanks ... this is the possibility I was looking for. Btw, I am thinking I'd need to use STM to synchronize right? Regards, Kashyap You need STM when you need groups of references to change simultaneously as perceived by concurrent processes. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding style vs. foreign interfaces
On Sun, Feb 6, 2011 at 10:10 PM, Donn Cave d...@avvanta.com wrote: Of the people who are apt to be interested, a sizeable percentage already will be familiar with ALARM_STUFF_WENT_WRONG, and as the nice Haskell spelling offers no practical advantage at all, it's purely a waste of their time to translate from one to the other. Is screenflicker_frequency() going to be screenFlickerFrequency, or screenflickerFrequency? gah! I don't think it's this simple. It is disheartening to innocently download a library from Hackage to find that it only supports a very non-Haskelly API. Why am I being punished by the history of a library? To support both kinds of users, we have designs like that used in the OpenGL library: a Foo-Raw library, with a friendlier API layered on top, perhaps in a separate package. If the friendly API turns out to be no friend of yours, you are free to turn to the raw wrappers. Perhaps we should aim for a more systematic application of this design pattern? I know that I appreciate a more idiomatic Haskell API when it is available, and certainly do not want library authors discouraged from providing such a service solely due to the provenance of the functionality. On the other hand, when I am porting, say, C coded against a particular API to Haskell, being able to use a more symmetric API is beneficial. One can keep both APIs in the same package until a legitimate desire to split them arises (e.g. to provide alternate high-level APIs). Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Extending GHCi
On Fri, Feb 4, 2011 at 9:41 AM, C K Kashyap ckkash...@gmail.com wrote: Thanks Steffen, Prelude :l MyModule.hs *MyModule conn - waitForAndAcceptConnection *MyModule someData - getSomeData conn *MyModule sendSomeAnswer conn $ processSomeData someData ... So this cycle of getting data from the connection and writing answer on the connection should happen concurrently with the ghci interaction ... so lets say that when the thread is forked that listens on socket behaves like an echo server ... as in, it reads data from the client till \n and echoes it back ... All this would happen without the intervention of the user using GHCI ... However, using GHCI, the user should be able to modify the code such that the server returns hello prepended to the input. .. startMyServer -- at this point the the echo server gets spawned -- echo server continues to run someFunction hello --- now onwards hello gets prepended --- echo server continues to run returning hello prepended someFunction world --- now onwards helloworld get I hope this is possible without having to modify ghci itself. Something like this, perhaps. Sorry that it is a bit hard to read. Anthony $ ghci GHCi, version 6.12.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude :m +Data.IORef Control.Concurrent Control.Monad Prelude Data.IORef Control.Concurrent Control.Monad msg - newIORef Hello Prelude Data.IORef Control.Concurrent Control.Monad let echo = forever $ readIORef msg = putStrLn threadDelay 300 Prelude Data.IORef Control.Concurrent Control.Monad t - forkIO echo Hello Prelude Data.IORef Control.Concurrent Control.Monad Hello Hello writeIORefHello msg World Prelude Data.IORef Control.Concurrent Control.Monad World World ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type System vs Test Driven Development
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 must be at a correspondingly higher level than the tests in other languages. I can see that such tests would give great benefits to the development process. I am convinced that I should try to write such tests. But I still think that Haskell makes a huge class of tests unnecessary. The way I think about this is that you want to write tests for things that can not be usefully represented in the type system. If you have a parametrically typed function, then the type system is doing a lot of useful testing for you. If you want to make sure that you properly parse documents in a given format, then having a bunch of examples that feed into unit tests is a smart move. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Confused about missing data constructor
On Tue, Nov 23, 2010 at 7:58 PM, Adam Miezianko a...@theorylounge.org wrote:
I'm working through Learn You a Haskell for Great Good [1] and getting
a compiler error while playing around with some of the code. I have
this:
Now, I'm not exactly sure how to read the documentation for
Control.Monad.State [2] but it seems that newtype State s a = State
{...} defines a constructor, or am I wrong on that point too? So,
what am I missing here? In case it matters, I am using mtl-2.0.1.0
and ghci 6.12.3.
[1] http://learnyouahaskell.com/for-a-few-monads-more
[2] http://cvs.haskell.org/Hugs/pages/libraries/mtl/Control-Monad-State.html
Wrong documentation page, the one you want is
http://hackage.haskell.org/packages/archive/mtl/2.0.1.0/doc/html/Control-Monad-State-Lazy.html
Anthony
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Re: [Haskell-cafe] date parsing and formatting
On Sat, Nov 13, 2010 at 4:35 PM, Alex Baranosky alexander.barano...@gmail.com wrote: I've been working with Haskell's Date.Time modules to parse a date like 12-4-1999 or 1-31-1999. I tried: parseDay :: String - Day parseDay s = readTime defaultTimeLocale %m%d%Y s And I think it wants my months and days to have exactly two digits instead of 1 or 2... What's the proper way to do this? Also, I'd like to print out my Day in this format: 12/4/1999 what's the Haskell way to? Something like this, perhaps, parseDate :: String - LocalTime parseDate = readTime defaultTimeLocale %m/%e/%Y printDate :: LocalTime - String printDate = formatTime defaultTimeLocale %m/%-e/%Y Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskellers.com skills list moderation?
On Wed, Oct 20, 2010 at 9:02 AM, Ben Millwood hask...@benmachine.co.uk wrote: Robotics and Automation Would be tempted to drop Automation from here. That name was deliberately chosen, and is appropriate for people in the area, http://www.ieee-ras.org/ I have my own opinions on a lot of these tags, but haskell-cafe doesn't seem like the right forum for this polling. A difficulty is that while we may all be qualified to debate the merits of Mathematics as a discriminative label for programmers, some of these tags (such as the one above) are domain specific. We don't want people outside of an area of interest governing name choices that lessen the value of the tags. As a strawman for people to beat up on, what if each tag linked to a wiki description? Such a description could include a couple sentences of exposition, and perhaps links to relevant resources. Another alternate is that if a tag becomes *too* popular (i.e. more than x% of haskellers check it off), then perhaps there should be a poll to have it removed and its spirit embedded in the general site text. Tags like Algorithmic Problem Solving might fall into this category. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Eta-expansion destroys memoization?
On Thu, Oct 7, 2010 at 9:33 AM, Jan-Willem Maessen jmaes...@alum.mit.edu wrote: There's no evaluation magic here---all that's happening is GHC is executing the program exactly as written. It can't float the list out of the function, as that can lead to unexpected space leaks (if you didn't intend to keep the list of fibs around forever). To echo Jan-Willem a bit, the impact of let floating can be seen by compiling the eta expanded version (i.e. fib x = map fib' [0..] !! x) with different options. $ ghc --make -O -fforce-recomp FibMemo.hs [1 of 1] Compiling Main ( FibMemo.hs, FibMemo.o ) Linking FibMemo ... $ ./FibMemo 5 3 2 4 5 $ ghc --make -O -fforce-recomp FibMemo.hs -fno-full-laziness [1 of 1] Compiling Main ( FibMemo.hs, FibMemo.o ) Linking FibMemo ... $ ./FibMemo 5 3 2 4 2 3 2 5 My understanding is that this is just a case where GHCi is able to float a binding in the partial application formulation because the dependency analysis is trivial due to there being no name for the binding. Looking at the core for the optimized version of the eta expanded code, there is a a top-level function for building a list of fibonacci numbers, a top-level value of type [Type.Integer] set to an application of the builder function to zero, and finally the fib function that indexes into that list. The version with -fno-full-laziness leaves the let binding under the lambda as expected. So the optimizer is clever and can see through the lambda, but we make the interpreter's job easier by not putting a lambda over its eyes to begin with. Anthony On Thu, Oct 7, 2010 at 9:33 AM, Jan-Willem Maessen jmaes...@alum.mit.edu wrote: What people seem to be missing here is that the location of the where-binding with respect to the lambda changes in each case. As a result, I think the forgoing explanations were rather confusing; there's no magic going on here. On Thu, Oct 7, 2010 at 8:17 AM, Brent Yorgey byor...@seas.upenn.edu wrote: - Forwarded message from Yue Wang yulew...@gmail.com - From: Yue Wang yulew...@gmail.com Then there is a clever way to do that on haskell wiki: fib = ((map fib' [0 ..]) !!) where fib' 0 = 0 fib' 1 = 1 fib' n =trace(show(n)) fib (n - 1) + fib (n - 2) This is indeed equivalent to: fib = let fib' 0 = 0 fib' 1 = 1 fib' n = fib (n-1) + fib (n-2) in (map fib' [0..] !!) But adding the argument embeds the let inside the function call: fib x = let fib' 0 = 0 fib' 1 = 1 fib' n = fib (n-1) + fib (n-2) in (map fib' [0..] !!) Now we create a new fib' for each invocation of fib. Not efficient at all! (Much *less* efficient the the recursive fib). There's no evaluation magic here---all that's happening is GHC is executing the program exactly as written. It can't float the list out of the function, as that can lead to unexpected space leaks (if you didn't intend to keep the list of fibs around forever). -Jan-Willem Maessen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] interesting type families problem
2010/9/8 Gábor Lehel illiss...@gmail.com:
Oh. Hmm. That makes sense. So I gather there's absolutely no way to
specify which instance you mean, and hence to use `value` as any
concrete type?
Here's one way to indicate which value you are referring to.
Anthony
{-# LANGUAGE EmptyDataDecls, TypeFamilies #-}
data True
data False
class TypeValue a where
type ValueTypeOf a
value :: a - ValueTypeOf a
instance TypeValue True where
type ValueTypeOf True = Bool
value _ = True
instance TypeValue False where
type ValueTypeOf False = Bool
value _ = False
main = print (value (undefined::True))
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Re: [Haskell-cafe] bitmap examples
On Tue, Aug 24, 2010 at 11:02 AM, Raluca-Elena Podiuc ralucaelena1...@gmail.com wrote: Hi, I am trying to build a mini framework for image processing but I can find any examples about that (bitmap processing ). Does anybody know were can I find some tutorials or samples about that ? Noam Lewis's HOpenCV package on hackage http://hackage.haskell.org/package/HOpenCV is a great way to get started using OpenCV for image processing. My own fork of this project http://github.com/acowley/HOpenCV adds static checking of color and pixel depth, more OpenCV functionality, and interoperation with Data.Vector.Storable. However, it should definitely be classified as experimental as I'm still exploring how I want things to work. I am using it for real-time video processing in an active research project, though, so it is getting regularly exercised. An example program included in the repository is, import AI.CV.OpenCV.HighCV main = toFile closed.png . erode 8 . dilate 8 = fromFileGray input.png I've made some effort to provide reasonable haddock documentation, so I recommend building that (cabal haddock) and consulting it to find your way around. As I mentioned, it is all still very rough, but feel free to give it a try if it seems to do what you need. If you're looking to start your own effort from scratch, I think Data.Vector.Storable is nice way to mix Haskell and C. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Sifflet dependencies
On Tue, Aug 17, 2010 at 2:54 PM, Andrew Coppin andrewcop...@btinternet.com wrote: While we're on the subject... Suppose I have a package, which I know works with foo-8.7.2. What should the Cabal dependents field say? We have a choice of foo == 8.7.2 foo = 8.7.2 foo = 8.7 foo = 8.7 8.8 foo == 8.7.* I'd like to add another option since it's the one I use, foo = 8.7.2 8.8 Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Arrays and image processing
On Wed, Aug 4, 2010 at 12:49 AM, kirstin penelope rhys kirs...@speakeasy.net wrote: But now I need a fast multidimensional array which can handle a tuple of primitive types. My options, as far an I can see, are: 1) Add an instance for UArray (Int,Int) (Word16, Word16, Word16) and/or UArray (Int,Int) (Word8, Word8, Word8) 2) Add a multidimensional wrapper for Data.Vector What about something like, import qualified Data.Vector.Unboxed as V import Data.Word type Pixel = (Word8, Word8, Word8) type Image = (Int, Int, V.Vector Pixel) Since you may want interoperability with C, you could also consider using Data.Vector.Storable with flat data. Just put the multi-dimensional logic in your indexing operations. I do quite a bit of image processing with a mix of Haskell and C, and have found Unboxed and Storable Vectors effective. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] possible bug in default module lookup scheme / or invalid haskell?
On Sun, Jul 18, 2010 at 3:59 AM, Carter Schonwald carter.schonw...@gmail.com wrote: I don't think that semantics creates the sort of ambiguity that Kevin is concerned about, and while yes there simple alternative approaches, they require whatever is starting up ghci to know what the correct directory to pass to the -i flag, and that seems a bit of a heavy weight expectation I usually use ghci's :cd command in this situation, and wouldn't want to think about changing source files depending on where they were on disk. While having to use fully hierarchical names might seem verbose, I have found it to be a very predictable mechanism that makes managing large-ish projects easier. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] possible bug in default module lookup scheme / or invalid haskell?
On Sun, Jul 18, 2010 at 1:55 PM, Carter Schonwald carter.schonw...@gmail.com wrote: I'm not sure I follow, because the toy example I'm asking about does in fact use hierarchical module names... are you proposing that a reasonable workaround in my use case is to do :cd .. :r this seems like a reasonableish approach, or was there a different example you had in mind? Yes, that is what I had in mind. The typical scenario for me is to be editing a file in emacs, C-c-C-l it, and have GHCi complain. I then issue a :cd .. in GHCi, and my subsequent loads are properly rooted at top of the project directory. What I was trying to describe as unwanted is for someone to take your toy example and, in the file A/B.hs have a line import B.C that is gets correctly resolved by GHC. I'm not sure that you were actually suggesting this, but this kind of leniency on the part of GHC (or GHCi) would make the file B.hs fragile with respect to moving it around on disk. Anthony On Sun, Jul 18, 2010 at 1:34 PM, Anthony Cowley acow...@seas.upenn.edu wrote: On Sun, Jul 18, 2010 at 3:59 AM, Carter Schonwald carter.schonw...@gmail.com wrote: I don't think that semantics creates the sort of ambiguity that Kevin is concerned about, and while yes there simple alternative approaches, they require whatever is starting up ghci to know what the correct directory to pass to the -i flag, and that seems a bit of a heavy weight expectation I usually use ghci's :cd command in this situation, and wouldn't want to think about changing source files depending on where they were on disk. While having to use fully hierarchical names might seem verbose, I have found it to be a very predictable mechanism that makes managing large-ish projects easier. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] design question/font metrics
On Tue, Jun 1, 2010 at 10:30 AM, Gery Debongnie gery.debong...@gmail.com wrote: 3. Perform a reading of the font metrics file in the main program, put the results into some FontMetrics object, and give that to stringWidth :: FontMetrics - Font - String - Double. Pros : allow me to avoid problems of solution 1 and 2, cons : it doesn't sound right for the main program to have to do this, it should be confined into a Font module. Ultimately all your IO is driven from main, so don't be afraid to add more IO dependencies to it. You can let IO infect a module for dealing with font files (e.g. a FontMetrics module with a function getMetrics :: [String] - Map String Double), then drive that module from main and feed its results into your pure code. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] dependent types
On Sun, Apr 11, 2010 at 5:54 PM, Jason Dagit da...@codersbase.com wrote:
On Sun, Apr 11, 2010 at 1:59 AM, Andrew U. Frank
fr...@geoinfo.tuwien.ac.at wrote:
in modeling real application we have often the case that the type of
some object depends on a value. e.g. small_boat is a vessel with size
less than a constant. big_boat is a vessel with a larger size. for
example, many legal classifications are expressed in this form (e.g. car
vs. truck)
depending on the type, operations are applicable or not (e.g. road with
restriction 'no trucks').
In the witness type version you may find that defining Vehicle as a GADT is
even better:
data Vehicle classification where
mkCar :: ... - Vehicle Car
mkTruck :: ... - Vehicle Truck
This is nice because it's direct and when you pattern match on the
constructor you recover the type of classification. For example, I believe
this would type check:
foo :: Vehicle c - c
foo (mkCar ...) = Car
foo (mkTruck ...) = Truck
You can combine GADTs with a mirror type for views of that data.
{-# LANGUAGE GADTs, EmptyDataDecls #-}
module GADTSmart (VehicleView(..), Vehicle, Car, Truck,
mkCar, mkTruck, view) where
data Car
data Truck
data Vehicle t where
VCar :: Int - Vehicle Car
VTruck :: Int - Vehicle Truck
data VehicleView t where
VVCar :: Int - VehicleView Car
VVTruck :: Int - VehicleView Truck
view :: Vehicle t - VehicleView t
view (VCar wt) = VVCar wt
view (VTruck wt) = VVTruck wt
mkCar :: Int - Maybe (Vehicle Car)
mkCar wt | wt 2000 = Just (VCar wt)
| otherwise = Nothing
mkTruck :: Int - Maybe (Vehicle Truck)
mkTruck wt | wt = 2000 = Just (VTruck wt)
| otherwise = Nothing
-- Client code that doesn't have access to the VCar or VTruck
-- constructors.
moveAcrossBridge :: Vehicle Car - IO ()
moveAcrossBridge c = case view c of
VVCar wt - putStrLn $ Car (++show wt++) on bridge
Now you can type your functions with the Vehicle GADT, but only
introduce values of that type using smart constructors. You could use
the VVCar or VVTruck data constructors to create invalid values, but
they won't work your functions.
Anthony
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Re: [Haskell-cafe] Re: Haskellers hate GUIs!!
On Fri, Apr 2, 2010 at 12:53 PM, Dominic Espinosa dces...@fastmail.fm wrote: Is there a general strategy for deploying Haskell apps, graphical or no, to MacOS X and/or Windows? I'm especially interested in cases where the application uses some heavyweight libraries like OpenGL. I have a GUI app that I deploy on Mac and Linux that uses OpenGL and wxHaskell. It has been a pretty good experience, but getting wx set up on every development machine is hairier than cabal install. The good news is that it was easy to set up a pure GLUT front end as well as a wx one that both use the same OpenGL code for rendering graphically intensive bits. I just have two build targets to switch between the two. For general cross-platform GUI apps that I need in a pinch, I turn to PLT Scheme. They have a really excellent system in this regard. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC RTS question
On Sun, Feb 21, 2010 at 1:58 PM, Artyom Kazak artyom.ka...@gmail.com wrote: So, if I type ./prog +RTS --RTS +RTS, the output will be +RTS. But I want the output to be equal to the input IN ALL CASES, without any quotes, additional options, etc. I want all the command line to go to my program. How can I do it? (The only way I know now - hacking the GHC. If there are no other ways, I'll do it.) How about a wrapper script? Something like, #! /usr/bin/env bash ./prog --RTS $* Just use that as the front-end to your Haskell program. Anthony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
