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The future of purely functional user interfaces? (was "Why binding to existing widget toolkits doesn't make any sense")
by Peter Verswyvelen 29 Jan '09

29 Jan '09

Haskell desperately needs something like Windows Presentation Foundation or http://www.piccolo2d.org... (so no GUIs but ZUIs :) but then purely functional. I'm pretty sure when a good framework is made, the community would contribute all kinds of widgets. IMO currently no Haskell framework has made it into something of production quality for creating purely functional user interfaces. Some research papers have been written (Fudgets, Gadgets, Fruit, Yampa, Reactive, ...), and some attempts have been made, but I guess nobody has written a large UI application with any of these toolkits (maybe House [1] - on OS written in Haskell that uses an updated Gadgets library - is the exception, but I haven't looked at the details of it yet) Maybe Yampa could be usable for building UIs - but I believe it has scalability issues because it is fully pull based, although it seems work is being done here [2] Reactive should be more scalable, and maybe one day it will be stable enough to build large interactive UIs (maybe together with Fieldtrip), but it seems it will need some redesign [3] Grapefruit also looks promising, as it combines arrows with push based techniques. Other work [4] seems to indicate that arrows are too general for the dataflow programming and co-monads are more suitable and hence might be usable for interactive interfaces. It would be nice to hear opinions about "purely functional user interfaces" and its future. Isn't it a bit of a lost battle if people can't create *real* and complex user interfaces in Haskell without completely switching to an imperative style of programming (GTK2HS, wxHaskell, etc) Cheers, Peter Verswyvelen [1] http://web.cecs.pdx.edu/~kennyg/house/ [2] http://www.citeulike.org/user/msakai/article/3813058 [3] http://conal.net/blog/posts/why-classic-frp-does-not-fit-interactive-behavi… [4] http://lambda-the-ultimate.org/node/988 On Wed, Jan 28, 2009 at 10:01 PM, Achim Schneider <barsoap(a)web.de> wrote: > John Lato <jwlato(a)gmail.com> wrote: > > > Achim Schneider wrote: > > > > > > So what's left of those TK's if we don't use their abstractions and > > > replace them with Haskell? Drawing and layouting, that's what's > > > left[3]. Both, IMNSHO, do not justify carrying around bloaty > > > external dependencies, they're too trivial. They certainly don't > > > justify using unsafePerformIO to hide foreign side effects and the > > > headaches associated with it. > > > > > > > > > So, if you don't mind, I'm going to stop trying to fit cubes into > > > round holes and gonna use reactive and fieldtrip[4] to do things. > > > > > > > Does this mean you're volunteering to create a fieldtrip-based toolkit > > with widgets and layout? > > > Most likely, no. fieldtrip uses glut, which only supports one os-level > window and is therefore borked for a considerable amount of stuff one > wants a TK be able to do. It (currently) also doesn't support > orthographic projection, which you need to properly position 2d. In > the end, it's a small and great library for stuff you don't need for > a TK, and is thus quite unsuited as a platform for one. Fieldtrip > widgets are another thing, of course. > > > I'm not volunteering for anything. I'm just hacking away on stuff and > following some inspiration I had while I implemented a simplistic > widget UI under J2ME, limited to what the game needed. > > -- > (c) this sig last receiving data processing entity. Inspect headers > for copyright history. All rights reserved. Copying, hiring, renting, > performance and/or quoting of this signature prohibited. > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Dependencies conflict
by Martijn van Steenbergen 29 Jan '09

29 Jan '09

Hello, $ cabal install category-extras Resolving dependencies... cabal: dependencies conflict: ghc-6.10.1 requires process ==1.0.1.1 however process-1.0.1.1 was excluded because ghc-6.10.1 requires process ==1.0.1.0 What does this message mean? It makes little sense to me -- ghc-6.10.1 requires both process ==1.0.1.1 and process ==1.0.1.0? And, more importantly, how do I solve this? Below is my output of ghc-pkg list. Thanks much, Martijn. $ ghc-pkg list /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.1/./package.conf: Cabal-1.6.0.1, HUnit-1.2.0.3, QuickCheck-1.2.0.0, array-0.2.0.0, base-3.0.3.0, base-4.0.0.0, bytestring-0.9.1.4, containers-0.2.0.0, directory-1.0.0.2, (dph-base-0.3), (dph-par-0.3), (dph-prim-interface-0.3), (dph-prim-par-0.3), (dph-prim-seq-0.3), (dph-seq-0.3), editline-0.2.1.0, filepath-1.1.0.1, (ghc-6.10.1), ghc-prim-0.1.0.0, haddock-2.3.0, haskell-src-1.0.1.3, haskell98-1.0.1.0, hpc-0.5.0.2, html-1.0.1.2, integer-0.1.0.0, mtl-1.1.0.2, network-2.2.0.1, old-locale-1.0.0.1, old-time-1.0.0.1, packedstring-0.1.0.1, parallel-1.1.0.0, parsec-2.1.0.1, pretty-1.0.1.0, process-1.0.1.0, random-1.0.0.1, regex-base-0.72.0.2, regex-compat-0.71.0.1, regex-posix-0.72.0.3, rts-1.0, stm-2.1.1.2, syb-0.1.0.0, template-haskell-2.3.0.0, time-1.1.2.2, unix-2.3.1.0, xhtml-3000.2.0.1 /Users/Martijn/.ghc/i386-darwin-6.10.1/package.conf: HTTP-3001.1.5, binary-0.4.4, brainfuck-0.1, cpphs-1.6, data-accessor-0.1.4, data-accessor-template-0.1.4, extensible-exceptions-0.1.1.0, fgl-5.4.2.2, ghc-paths-0.1.0.5, haddock-2.4.1, haskeline-0.6.0.1, haskell-src-exts-0.3.12, haskell-src-exts-0.4.4, haskell-src-exts-0.4.6, haskell-src-exts-0.4.8, haskell98-1.0.1.0, hscurses-1.3.0.2, iconv-0.4.0.2, lambdabot-utils-4.2, oeis-0.2, parsec-3.0.0, process-1.0.1.1, readline-1.0.1.0, show-0.3.1, smallcheck-0.4, tagsoup-0.6, terminfo-0.3, uniplate-1.2.0.3, unlambda-0.1, utf8-string-0.3.3, zlib-0.5.0.0

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ANN: incremental-sat-solver
by Sebastian Fischer 29 Jan '09

29 Jan '09

Simple, Incremental SAT Solving as a Library ============================================ This Haskell library provides an implementation of the Davis-Putnam- Logemann-Loveland algorithm (cf. <http://en.wikipedia.org/wiki/DPLL_algorithm >) for the boolean satisfiability problem. It not only allows to solve boolean formulas in one go but also to add constraints and query bindings of variables incrementally. The implementation is not sophisticated at all but uses the basic DPLL algorithm with unit propagation. The package is available at: <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/incremental-sat-… > Unlike 'sat' and 'sat-micro-hs' it is a library, and unlike 'libsat' it provides an interface for incremental solving. On the other hand, the implementation is much simpler (and probably less efficient) than 'libsat's. You are invited to improve on that, if you like. The code is on github: <http://github.com/sebfisch/incremental-sat-solver> Cheers, Sebastian

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ANN: convertible (first release)
by John Goerzen 29 Jan '09

29 Jan '09

Hi folks, I have uploaded a new package to Haskell: convertible. At its heart, it's a very simple typeclass that's designed to enable a reasonable default conversion between two different types without having to remember a bunch of functions. The return type from this conversion is "Either ConvertError a", and conversions are expected to do sanity checking (such as bounds checking when converting to types like Int), so as to produce neither garbage nor exceptions as part of the conversion process. The package also includes instances of the Convertible typeclass for working with numeric types as well as dates and times. Notably, it has code to convert between System.Time types and their Data.Time siblings, and vice versa, a capability I found annoyingly lacking in the standard library. There is also a simple wrapper function called convert, that transforms a Left result into a call to error, and returns a Right result. For HDBC v2.0, the SqlValue/SqlType system has been completely rewritten in terms of Convertible, though I expect backwards compatibility will not be broken by this change (existing code will compile and run fine). I hope to release v2.0 of the HDBC API and backends in a few days. Convertible is not for everyone; if you care whether you use truncate or round to convert a Double to an Integer, this isn't for you. Note, though, that you can import the library without its default instances, so you can define your own if you prefer. API docs and downloads at: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/convertible -- John

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HDBC-ODBC, bindCol
by G?uenther Schmidt 29 Jan '09

29 Jan '09

Hi John, I've just been going through the HDBC-ODBC code wondering if I could find the spot that needs changing so that Doubles work properly with MS-Access. Could you please tell me, if I understand this correctly? The bindCol function does not actually look at the particular value type, ie. SqlDouble, SqlInteger ..., to determine the type but queries the database via sqlDescribeParam to get the type. Which might fail though and not leave a clue. In that case the SqlType still isn't used, but rather some default? If I was more literate in Haskell I would propably be able to answer this myself, sry, I'll catch up. And I had a hell of a time finding an SQL/ODBC for C Tutorial and never coded in C. Thanks upfront Günther

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Bugs in Hugs
by wren ng thornton 29 Jan '09

29 Jan '09

In testing some of my packages against Hugs, I've uncovered bugs[1]. Unfortunately the bug tracker at: http://hackage.haskell.org/trac/hugs/newticket?type=defect doesn't seem to allow normal users to submit tickets. Does anyone know how to submit bug reports to Hugs these days? [1] Namely, the Prelude.isNaN and Prelude.isInfinite functions don't work: Hugs> (0/0::Float) nan Hugs> isNaN (0/0::Float) False Hugs> (0/0::Double) nan Hugs> isNaN (0/0::Double) False Hugs> (1/0::Float) inf Hugs> isInfinite (1/0::Float) False Hugs> (1/0::Double) inf Hugs> isInfinite (1/0::Double) False -- Live well, ~wren

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Re: Why binding to existing widget toolkits doesn't make any sense
by John Lato 29 Jan '09

29 Jan '09

Achim Schneider wrote: > > So what's left of those TK's if we don't use their abstractions and > replace them with Haskell? Drawing and layouting, that's what's > left[3]. Both, IMNSHO, do not justify carrying around bloaty external > dependencies, they're too trivial. They certainly don't justify using > unsafePerformIO to hide foreign side effects and the headaches > associated with it. > > > So, if you don't mind, I'm going to stop trying to fit cubes into > round holes and gonna use reactive and fieldtrip[4] to do things. > Does this mean you're volunteering to create a fieldtrip-based toolkit with widgets and layout? John Lato

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GHC's -fwarn-unused-imports ignores function signatures
by Michael Snoyman 29 Jan '09

29 Jan '09

I was writing code similar to the following and compiling with "-Wall -Werror." Clearly I *am* using Data.ByteString for the function signatures. {-# OPTIONS_GHC -fwarn-unused-imports -Werror #-} import qualified Data.ByteString as B import qualified Data.ByteString.UTF8 as BU toString :: B.ByteString -> String toString = BU.toString fromString :: String -> B.ByteString fromString = BU.fromString main :: IO () main = putStrLn $ toString $ fromString "Hello World!" The warning I get is: Unused.hs:2:0: Warning: Module `Data.ByteString' is imported, but nothing from it is used, except perhaps instances visible in `Data.ByteString' To suppress this warning, use: import Data.ByteString() Am I doing something wrong or is this a bug in GHC? Thanks, Michael

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Re: [Haskell-cafe] hmatrix, Windows and GCC
by Patrick Perry 29 Jan '09

29 Jan '09

> Well, I guess I am not the only one! > > This blog show exactly what I am looking for! > > http://quantile95.com/2008/10/31/ann-blas-bindings-for-haskell-version-06/ If you're looking to implement other linear algebra algorithms in Haskell, there's enough at http://github.com/patperry/lapack to implement a QR decomposition with column pivoting with fairly minimal effort. Householder reflections and permutation matrices are already supported. You will also need the latest BLAS bindings, also available at github. Note that these libraries are not compatible with hmatrix. What would *really* be awesome would be an implementation of an SVD algorithm: take a bidiagonal matrix and produce a (lazy) list of Givens rotations that diagonalizes the matrix. That would probably be a 2-4 week project, but would be really useful. Take a look at the code and references at http://netlib.org/lapack/explore-html/zbdsqr.f.html if you're interested. The LAPACK version, zbdsqr, takes "B" and factors it as "B = Q S P^H". Optionally, it sets U := U Q VT := P^H VT C := Q^H C Annoyingly, there is no way to specify an input matrix "D" and set "D := D P". It'd be really cool to have a Haskell function of type svdBidiagonal :: (WriteBanded a m) => a (n,p) e -> m [(Givens,Givens)] The type signature means that "a" is a mutable banded matrix of shape "(n,p)" with elements of type "e" that can be modified in monad "m". I'm envisioning that the result is a lazy list, "gs", and that no computation gets done until the "gs" list is traversed. So, if someone just wants singular values, then they would do "liftM length . svdBidiagonal". If they want to update "U := U Q", then they would do something like: mapM_ (applyGivens u) $ liftM (fst . unzip) $ svdDidiagonal a The user has the option to update as many matrices they want in whatever way they want. This is only possible with laziness. It is a perfect example of the "glue" John Hughes talks about in "Why Functional Programming Matters". Patrick > > On Wed, Jan 28, 2009 at 08:21, Rafael Gustavo da Cunha Pereira Pinto < > RafaelGCPP.Linux at gmail.com> wrote: > > > I was planning to recompile everything (ATLAS, LAPACK and GHC > included) > > this weekend, so I can have a similar environment on Windows and > Linux... > > Having to "borrow" libraries > > > > Since I am married, this means it will actually happen on some > weekend till > > 2010. > > > > > > What I really would like to try is a (purely?) functional approach > to > > create a (P)LU decomposition of a matrix. I am not too much > worried (at > > first) with performance or memory constraints, since I only want > to see how > > beautiful it gets (or not!). (This one might happen somewhere in > this > > century...) > > > > > > Thanks anyway > > > > > > > > On Wed, Jan 28, 2009 at 07:57, allan <a.d.clark at ed.ac.uk> wrote: > > > >> Hi > >> > >> The INSTALL file in the hmatrix repository has some very clear > >> instructions for installation on Windows. > >> http://perception.inf.um.es/~aruiz/darcs/hmatrix/INSTALL<http://perception.inf.um.es/%7Earuiz/darcs/hmatrix/INSTALL > > > >> > >> However note this section at the bottom: > >> "Unfortunately the lapack dll supplied by the R system does not > include > >> zgels_, zgelss_, and zgees_, so the functions depending on them > >> (linearSolveLS, linearSolveSVD, and schur for complex data) > >> will produce a "non supported in this OS" runtime error." > >> > >> Of course linearSolve is exactly what you will be wanting so this > won't > >> work for you. > >> I ran into exactly this problem myself. I actually didn't get as > far as a > >> run-time error as I got a linker error. > >> > >> I don't have any solution for you though, sorry. > >> > >> regards > >> allan > >> > >> > >> > >> > >> Rafael Gustavo da Cunha Pereira Pinto wrote: > >> > >>> > >>> > >>> Hi all, > >>> > >>> I am writing a program that uses hmatrix for solving some linear > systems. > >>> The hmatrix package depends on BLAS, which, in turn, depend on > GCC 4.2 to be > >>> built (at least ATLAS does). > >>> > >>> GHC 6.10 for Windows is pre-packaged with GCC 3.4.5, and it > leaves me > >>> with the impression that I would have incompatible ABIs. > >>> > >>> My questions: > >>> > >>> 1) Why GHC 6.10 still uses GCC 3.4.5 in Windows? I know mingw > considers > >>> GCC 4.2 to be alpha, but, lets face it, 4.2 is almost obsolete! > >>> 2) Is it possible to rebuild GHC 6.10, using Windows and GCC > 4.2? Is > >>> there any guide for doing this? > >>> 3) Has any of you tried hmatrix on Windows? How did you do it? > >>> > >>> Thanks, > >>> > >>> Rafael > >>> > >>> -- > >>> Rafael Gustavo da Cunha Pereira Pinto > >>> Electronic Engineer, MSc. > >>> > >>> > >>> > ------------------------------------------------------------------------ > >>> > >>> _______________________________________________ > >>> Haskell-Cafe mailing list > >>> Haskell-Cafe at haskell.org > >>> http://www.haskell.org/mailman/listinfo/haskell-cafe > >>> > >> > >> > >> > >> -- > >> The University of Edinburgh is a charitable body, registered in > >> Scotland, with registration number SC005336. > >> > >> > > > > > > -- > > Rafael Gustavo da Cunha Pereira Pinto > > Electronic Engineer, MSc. > > > > > > -- > Rafael Gustavo da Cunha Pereira Pinto > Electronic Engineer, MSc. >

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Problems running vectorised dph program
by Fabian Reck 29 Jan '09

29 Jan '09

Hi, I've just begun to play with Data Parallel Haskell but instantly ran into a problem. My very stupid but very simple example ought to sum the values of all Nodes in a Tree. The non-vectorised code behaves like I expected, the vectorised code doesn't terminate. I compiled and ran it the same way as the example in the tutorial: ghc -c -O -fdph-par Main.hs ghc -c -Odph -fcpr-off -fdph-par MinimalParTree.hs ghc -o MinimalParTree -fdph-par -threaded MinimalParTree.o Main.o ./MinimalParTree My question is: Is this a bug or is something wrong with the program? Thanks Fabian -------------------------------------------------------------------- module Main where import MinimalParTree main = do print $ sumTreeWrapper 20 -------------------------------------------------------------------- {-# LANGUAGE PArr, ParallelListComp #-} {-# OPTIONS -fvectorise #-} module MinimalParTree (sumTreeWrapper) where import qualified Prelude import Data.Array.Parallel.Prelude import Data.Array.Parallel.Prelude.Int data Tree a = Node a [: Tree a :] testTree :: Int -> Tree Int testTree elem = Node elem emptyP sumTree :: Tree Int -> Int sumTree (Node x ns) = x + sumP (mapP sumTree ns) {-# NOINLINE sumTreeWrapper #-} sumTreeWrapper :: Int -> Int sumTreeWrapper elem = sumTree (testTree elem) --------------------------------------------------------------------

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Haskell Web Frameworks
by John A. De Goes 29 Jan '09

29 Jan '09

On Jan 27, 2009, at 1:05 PM, Michaeljohn Clement wrote: > +1 > > This is the conclusion I have come to in building collaborative > Web applications. > > I agree that there seems to be a gap here in the Haskell Web > frameworks people are building. Yes. It's a dead end and it seems a shame to waste effort on it. > I do not believe compiling Haskell to ECMAScript/JavaScript is a > productive avenue. There is too much pain in trying to abstract > away the JavaScript model only to write everything in Haskell and > end up with worse performance as a reward. I believe GWT, among other projects, has shown that you can create faster executing JavaScript by compiling from a statically-typed language than you can by hand-coding JavaScript (for one, you can do a multitude of inlining and simplification transformations that are not easy in a dynamic language). There is much room for research and development, of course, especially in the context of functional languages. > There is very little wrong with ECMAScript if people would only > learn it properly and play to its strengths instead of trying to > turn it into things it is not. I like JavaScript, and I love ECMAScript 4 (which unfortunately won't see the light of day), but they are not functional languages. And for the foreseeable future, there is one and exactly one scripting language for the browser, and anyone who wants to use a different language will have to do so by compiling to JavaScript. Regards, John A. De Goes N-BRAIN, Inc. The Evolution of Collaboration http://www.n-brain.net | 877-376-2724 x 101

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Changing type of 'when'
by Maurício 28 Jan '09

28 Jan '09

Hi, Sugestion: 'when' in Control.Monad is typed as :: Bool -> IO () -> IO (). Why not type it as: :: forall a. => Bool -> IO a -> IO () ? It is easy for 'when' to ignore the result of the first computation, and this would not break existing code, and also save a lot of >> return ()s. Best, Mauríco

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hmatrix, Windows and GCC
by Rafael Gustavo da Cunha Pereira Pinto 28 Jan '09

28 Jan '09

Hi all, I am writing a program that uses hmatrix for solving some linear systems. The hmatrix package depends on BLAS, which, in turn, depend on GCC 4.2 to be built (at least ATLAS does). GHC 6.10 for Windows is pre-packaged with GCC 3.4.5, and it leaves me with the impression that I would have incompatible ABIs. My questions: 1) Why GHC 6.10 still uses GCC 3.4.5 in Windows? I know mingw considers GCC 4.2 to be alpha, but, lets face it, 4.2 is almost obsolete! 2) Is it possible to rebuild GHC 6.10, using Windows and GCC 4.2? Is there any guide for doing this? 3) Has any of you tried hmatrix on Windows? How did you do it? Thanks, Rafael -- Rafael Gustavo da Cunha Pereira Pinto Electronic Engineer, MSc.

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Monades - I've got it! (hopefully)
by Tobias Kräntzer 28 Jan '09

28 Jan '09

Hi, I think I now understand all the stuff about monades (not the mathematics). I have just one further question. Beside of the syntactic sugar of the "do" construct and the fact that the IO monade is an "internal type of haskell": Is haskell aware of the concept of monades? As I now understand it, it is "just" a programming model rather than a concept of the language. If not, I have to start new. One problem understanding monades could be, that everywhere is written, that it is so complicated and therefore I was a bit prestressed. . . . Tobias By the way: Merry Christmas! -- Tobias Kräntzer info(a)tobias-kraentzer.de

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ANN: data-spacepart - space partitioning data structure[s] (initial release)
by Corey O'Connor 28 Jan '09

28 Jan '09

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/data-spacepart The goal of this package is to be a collection of space partitioning data structures. Currently, however, there is only a simple quadtree implementation. The package neither has real documentation or tests I'd like for a quality release. However, if you need a quadtree implementation then hopefully this will help. Cheers, Corey O'Connor

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Text.Xhtml & output encoding
by akillah 28 Jan '09

28 Jan '09

Can Text.Xhtml output some specific encoding ? Only thing I'm able to get out of it is text literally filled with trigraphs, which strikes me as ugly and is longer than ie. UTF-8 formatted output. I've found that it had been recommended to sb. to use latin-1 as output encoding (question was concerning diacritical characters) so i'm guessing that the answer is no ... Am I mistaken ? Is there another lib (preferrably XHTML compliant) that can acomplish it ? Would using primHtml to incorporate properly encoded Strings be frowned upon ? Thanks, akillah.

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Type families are awesome
by John Ky 28 Jan '09

28 Jan '09

Hi Haskell Cafe, I'm finding that I really like type families. For instance, the GHC.List.lookup and Data.Map.lookup functions annoy me because their names clash, yet their type are so similar. With type families, I could define a more generic lookup function like this: import Data.Map as MAP import GHC.List as LIST class MapType ma where type Key ma type Item ma lookup :: Key ma -> ma -> Maybe (Item ma) instance (Ord ka) => MapType (MAP.Map ka a) where type Key (MAP.Map ka a) = ka type Item (MAP.Map ka a) = a lookup ka ma = MAP.lookup ka ma instance (Eq ka) => MapType [(ka, a)] where type Key [(ka, a)] = ka type Item [(ka, a)] = a lookup ka ma = LIST.lookup ka ma This lookup function works on both "Map ka a" and "[(ka, a)]" types and I no longer need to qualify my lookup function with the module name. The downside I suppose is that lookup is no longer a function that can be manipulated freely: *Main> let x = lookup *Main> let y = Fx.Data.Map.lookup <interactive>:1:8: Ambiguous type variable `ma' in the constraint: `Fx.Data.Map.MapType ma' arising from a use of `Fx.Data.Map.lookup' at <interactive>:1:8-25 Probable fix: add a type signature that fixes these type variable(s) A shame that. I had been hoping it would be possible to have a generic lookup function that could be used in every way the current collection of various lookup functions can be used. So much nicer if 'y' above could be bound to the Fx.Data.Map.lookup with the same type: *Main> :t Fx.Data.Map.lookup Fx.Data.Map.lookup :: forall ma. (Fx.Data.Map.MapType ma) => Fx.Data.Map.Key ma -> ma -> Maybe (Fx.Data.Map.Item ma) And then have the ambiguity resolve later when 'y' is actually used. -John

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Fwd: [Haskell-cafe] Haskell Web Framework
by Alberto G. Corona 28 Jan '09

28 Jan '09

Sorry, I forgot to forward it to the list: ---------- Forwarded message ---------- From: Alberto G. Corona <agocorona(a)gmail.com> Date: 2009/1/25 Subject: Re: [Haskell-cafe] Haskell Web Framework To: Donnie Jones <donnie(a)darthik.com> hi, I´m working in a web application rather than a web framework. But I sometimes think about how a complete web application server should be. For my case, I don´t care about the presentation, because HSP is more than enough. However, I need active-active clustering, distributed transactions and workflows. I have created the module Workflow for the latter. For the former, I developped TCache, that is a transactional cache using STM, with configurable persistence. It´s like hibernate for Java and (the data part of) Rails for Rubi. Now I´m working in a extension of TCache with distributed transactions and remote clustering with some additonal interesting characteristics. My own view about haskell and Web applications is that something like " a web framework" is not in the philosophy of Haskell. What is in the philosophy of Haskell is the creation of modules that the people can combine to create their own web frameworks. 2009/1/25 Donnie Jones <donnie(a)darthik.com> Hello Michael, > > I am interested in contributing to a Haskell web framework. :) > > I have started an attempt to create my own Haskell web framework, but I got > busy working on my Master's thesis research, so I had to stop working on > it... I was a web developer at a start-up company for 1.5yrs with Ruby on > Rails, and I really really like the MVC design; however, I prefer a stricter > MVC implementation than Rails provides. More specifically, I don't think > code should appear in the view at all. I believe that using html tags, the > web framework can provide a function to "render" the view which would parse > the html tags and insert the content (whatever it may be). Functions can be > easily composed together to build more complex content in the views. For > example, > > <person id="name"></person> > <person id="age"></person> > > person_name = > renderView "person" "name" "John Doe" > > person_age = > renderView "person" "age" "40" > > I can show you my code which implements this parsing in a more structured > manner, but I think this stricter MVC implementation leads to more > maintenable projects and especially facilitates a graphic designer to work > independent of the web developer since the graphic designer won't be > confused by the code in the views. > > What do you think? > -- > Donnie Jones > > 2009/1/25 Michael Snoyman <michael(a)snoyman.com> > >> I'm interested on starting a project with others to create a powerful >> Haskell web framework in the same league as Rails or Django. I've enumerated >> (perhaps ad nauseum) my ideas for it in this blog post: >> http://blog.snoyman.com/2009/01/25/haskell-web-framework/. If people are >> interested in this, please respond to me either directly or on this mailing >> list. >> >> >> Just as a quick summary of the post, I would say the most salient points >> are that the framework should work in a shared hosting environment and >> should automatically abstract away most of the issues of writing an Ajax web >> application. It should also leverage the strengths of Haskell, eg type >> safety and speed. >> >> I welcome all comments and critiques as well. >> >> Michael >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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Gentle introduction questions / comments
by Matthijs Kooijman 28 Jan '09

28 Jan '09

Hi all, I've been reading the gentle introduction to Haskell a bit more closely today and there a few things which I can't quite understand (presumably because they are typo's). I've found two issues with the "Using monads" section [1]. Not sure if this is the right place to report this, but there's probably somewhere here who can fix it :-) The first one is in the state monad data type. It reads: data SM a = SM (S -> (a,S)) -- The monadic type I can't seem to find out what "S" is exactly here. It seems to be a universally quantified type variable, but then it should be lowercase. Considering that it is referred to later on as "s", I suspect this is a type? Further on, a resource monad is described. Here, a lift1 function is given to allow one to lift a normal computation into a resource aware computation, with the following type signature: lift1 :: (a -> b) -> (R a -> R b) A few lines down, the inc operation is defined as follows: inc i = lift1 (i+1) To me, this seems wrong. Even without going into the semantics, it seems that the (i+1) expression does not satisfy the type of the first argument to lift1. I suspect this should have been: inc = lift1 (+1) Gr. Matthijs [1]: http://www.haskell.org/tutorial/monads.html#sect9.3

3 4

Why monoids will abide...
by Don Stewart 28 Jan '09

28 Jan '09

http://apfelmus.nfshost.com/monoid-fingertree.html Thanks Apfelmus for this inspiring contribution!

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ANN: testpack (first release)
by John Goerzen 27 Jan '09

27 Jan '09

Hi, I've just uploaded testpack to Hackage. It's a collection of a few utilities for tests: some tools to convert QuickCheck properties into HUnit test cases, and various shortcuts and tools to increase verbosity while running tests in both QuickCheck and HUnit. It is pulled partly from MissingH (a few modules being split off), and partly from functions I find myself writing over and over again. API docs and downloads at: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/testpack Like convertible, it should be compatible with Hugs, GHC 6.8, and GHC 6.10. -- John

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Ann: Progress with IDE
by Jürgen Nicklisch-Franken 27 Jan '09

27 Jan '09

Leksah 0.4.0* pre-release is now available. This will become the first beta when it is stable enough. The current feature list: * Haskell customized editor with candy * Project management support based on Cabal * Visual editor for Cabal files * Location of compilation errors * Import helper, which writes the import statements * Navigation to definition * Module browser * Information about types and comments * Search for identifiers * Session support * Configurable visual appearance * Configurable keymaps Get more info at: http://www.leksah.org We now have a mailing list for Leksah: http://projects.haskell.org/cgi-bin/mailman/listinfo/leksah You need ghc 6.10 and gtk2hs 0.10 (which is not yet released, but you get it here: http://code.haskell.org/~pgavin/gtk2hs-0.10.0/ ) Please test Leksah and give me feedback. Contributors welcome. Jürgen --keksa leksa haksel--

4 4

foreign function types
by Eyal Lotem 27 Jan '09

27 Jan '09

I have encountered quite a bit of bugs in foreign bindings where "Int" was used in place of "Cint". As far as I know, no foreign function should ever take a Haskell Int, only CInts. Would it be possible to create an empty type-class of which various C-acceptable types are instances (e.g CInt, CString) but Haskell types aren't (Ints)? I am not sure this is the right solution, but I think the problem of accidentally using Int in place of CInt should be solved so that compile-time errors are received, as for x86-32 systems, no compile time or even runtime error will be issued. It will wait and crash when run on an x86-64 system. Eyal

2 1

ANN: Wired 0.2
by Emil Axelsson 27 Jan '09

27 Jan '09

There is now a new release of Wired available: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Wired The most important news in this release is that it now contains a 45nm cell library, which means that you can use Wired to create and analyze modern VLSI designs[*] today! However... Wired is still in the experimentation phase, but is slowly stabilizing. The current status is further explained in the package text. There's very little documentation (basically only a few examples), so I expect it to be quite hard to use if you haven't seen it before. I hope to improve the documentation in the future. Feel free to mail me questions meanwhile. / Emil [*] Unfortunately, while the 45nm library is "realistic", it's not based on any actual process that can be fabricated. Contact me if you have access to any real cell library and are interested in using it with Wired.

1 0

ANN: filestore 0.1
by Gwern Branwen 27 Jan '09

27 Jan '09

ANN filestore 0.1 We are pleased to announce the first release of a new library, filestore. What is it? filestore provides a uniform, abstract, generic interface for storing versioned files on disk. It allows calling programs to use generic commands to store strings or binary data and perform various queries, such as 'what files are in this repository?' or 'what were the contents of this file at revision XXXXXXX?' or 'give me a diff of this file between revision XXXXXXX and revision YYYYYYY.' Because the interface is abstract, the calling program is insulated from the messy details of the backend (which might be a VCS or a database). What backends are supported? Darcs and Git are fully supported. There are plans for a SQLite backend. What is this good for? Currently it is used by two wikis, Gitit and Orchid. We hope it will see use in other applications as well that need to version data and would like the various advantages of DVCSs (such as easy collaboration, advanced merging, etc.). Where can you get it? Your local cabal-install, Hackage at http://hackage.haskell.org/cgi-bin/hackage-scripts/package/filestore and of course you can do 'darcs get http://johnmacfarlane.net/repos/filestore' for the very latest. filestore was written by John MacFarlane, Gwern Branwen, and Sebastiaan Visser -- gwern

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bug in System.Mem.StableName
by Alberto G. Corona 27 Jan '09

27 Jan '09

Sometimes the StableName library gives different values for the samr function: Sometines gives two alternate values. I checked it in ghc-6.10.1 under windows and in ghc-6.8.2 under Linux: This is an example Prelude> System.Mem.StableName.hashStableName.System.IO.Unsafe.unsafePerformIO $ System.Mem.StableName.makeStableName (*) 15 Prelude> System.Mem.StableName.hashStableName.System.IO.Unsafe.unsafePerformIO $ System.Mem.StableName.makeStableName (*) 14 Prelude> System.Mem.StableName.hashStableName.System.IO.Unsafe.unsafePerformIO $ System.Mem.StableName.makeStableName (*) 15 Prelude> System.Mem.StableName.hashStableName.System.IO.Unsafe.unsafePerformIO $ System.Mem.StableName.makeStableName (*) 14

3 2

Haskell Web Framework
by Felix Martini 27 Jan '09

27 Jan '09

Hi Michael, May i suggest Johan Tibell's web application interface (see http://github.com/tibbe/hyena/tree/master) It is similar to WSGI. Hyena can then be used as an application server and frameworks won't have to create their own servers. Many people have different opinions about web frameworks but a single very robust Haskell server would be an asset for all frameworks. Felix

2 1

MySQL and HDBC?
by Galchin, Vasili 26 Jan '09

26 Jan '09

Hello, "Real World Haskell" seems to say that the abstraction layer HDBC doesn't support MySQL. If so, in what sense doesn't HDBC support MySQL?? Thanks, Vasili

7 10

Haskell Web Framework
by Michael Snoyman 26 Jan '09

26 Jan '09

I'm interested on starting a project with others to create a powerful Haskell web framework in the same league as Rails or Django. I've enumerated (perhaps ad nauseum) my ideas for it in this blog post: http://blog.snoyman.com/2009/01/25/haskell-web-framework/. If people are interested in this, please respond to me either directly or on this mailing list. Just as a quick summary of the post, I would say the most salient points are that the framework should work in a shared hosting environment and should automatically abstract away most of the issues of writing an Ajax web application. It should also leverage the strengths of Haskell, eg type safety and speed. I welcome all comments and critiques as well. Michael

3 3

Re: [Haskell-cafe] mapM_ -> Monoid.Monad.map
by George Pollard 26 Jan '09

26 Jan '09

On Fri, 2009-01-23 at 21:30 +0000, Joachim Breitner wrote: > Hi, > > Am Freitag, den 23.01.2009, 21:50 +0100 schrieb Henning Thielemann: > > However our recent Monoid discussion made me think about mapM_, > > sequence_, and friends. I think they could be useful for many monads if > > they would have the type: > > mapM_ :: (Monoid b) => (a -> m b) -> [a] -> m b > > I expect that the Monoid instance of () would yield the same efficiency > > as todays mapM_ > > will it? This is based on a naive, not well-founded understanding of > haskell evaluation, but looking at > > instance Monoid () where > > mempty = () > > _ `mappend` _ = () > > mconcat _ = () > I’d assume that evaluating > > mapM_ (putStrLn) lotsOfLargeStrings > with your proposed mapM_ will leave a thunk equivalent to > > () `mappend` () `mappend` () `mappend`... > in memory until the mapM_ has completely finished, where each () is > actually an unevalutated thunk that still has a reference to one of the > elements in the lotsOfLargeStrings list. Perhaps this is why the Monoid instance for () in GHC's source has the comment "should this be strict?" :)

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ANN: Hayoo! beta 0.3
by Timo B. Hübel 26 Jan '09

26 Jan '09

Hello! We are pleased to announce the next beta version 0.3 of Hayoo!, the Haskell API search engine with find-as-you-type and suggestions. Visit Hayoo! here: http://holumbus.fh-wedel.de/hayoo Basically, there is one new major feature available: Hayoo! now works even if your browser does not support JavaScript. Of course, this means that you won't have the find-as-you-type functionality, but everything else will be available. Hence everybody who has been scared away from Hayoo! because of all this crazy AJAX stuff now has no excuse anymore for not using Hayoo! ;-) Along the way we fixed several minor bugs and slightly improved the ranking algorithm as well as the help page. Since the last official announcement we were also able to bring back the source links. Still to come in the next weeks is a major index update to reflect the incredible package growth on Hackage. Please let us know about any problems, hints and suggestions. Happy hacking, Timo

1 0

wxHaskell and XP-Themes
by Günther Schmidt 26 Jan '09

26 Jan '09

Hi, my app is using wxHaskell for the gui part, how can I make it use XP-Themes? On XP it's using the Win2k themes. Günther

2 1

how to implement daemon start and stop directives?
by Belka 26 Jan '09

26 Jan '09

Hi! Could somebody please share some experience on how to implement daemon start and stop directives. In theory I need something like this: 1. "my_daemon start" - starts my app with an infinite loop of serving inside. 2. "my_daemon stop" - puts in some TVar a value signalizing, that stop is given - infinite loop brakes. 3. ...it on Linux platform. Thanks in advance! -- View this message in context: http://www.nabble.com/how-to-implement-daemon-start-and-stop-directives--tp… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

8 17

Fwd: [Haskell-cafe] Haskell Web Framework
by Artyom Shalkhakov 26 Jan '09

26 Jan '09

Sorry, forgot to forward to the ML. ---------- Forwarded message ---------- From: Artyom Shalkhakov <artyom.shalkhakov(a)gmail.com> Date: 2009/1/25 Subject: Re: [Haskell-cafe] Haskell Web Framework To: Michael Snoyman <michael(a)snoyman.com> Hello, 2009/1/25 Michael Snoyman <michael(a)snoyman.com>: > Just as a quick summary of the post, I would say the most salient points are > that the framework should work in a shared hosting environment and should > automatically abstract away most of the issues of writing an Ajax web > application. It should also leverage the strengths of Haskell, eg type > safety and speed. I'm doing some work on the same lines. I have a CGI test application running in a sandboxed environment that resembles shared hosting quite closely; nothing fancy ATM. I think more people will get interested in this over time. While HAppS is great, many people (I suppose :)) would like to use Haskell instead of PHP (well, at least I do). Regarding your blog post, let me comment it here. HStringTemplate can be used to handle templating in a principled fashion. There is however, some room for improvement (like, generating some structured data instead of plain strings, then enforcing constraints on that data, -- think (X)HTML validation at template "compile time"). User input validation is handled by formlets already. It is tempting to generate JS automagically, don't know if it will work out. WSGI-like abstraction would be great (I think of unifying FCGI/CGI apps, but AFAIK it's done already: there's a way to run Haskell FCGI applications as CGI applications, though it's not documented in tutorials). I prefer libraries to frameworks, because frameworks are just "preconfigured", "prewritten" bloated code bases (maybe, it's just me understanding it wrong...). Cheers, Artyom Shalkhakov.

1 0

Re: list choices
by Yitzchak Gale 25 Jan '09

25 Jan '09

Both of the points raised by Malcolm are a matter of personal preference, in my opinion. In fact, my own preference is the opposite of Malcolm's in both cases. Both of Malcolm's suggestions would rob me of filtering capability. Malcolm Wallace wrote: > I would suggest that posting announcements *only* > to haskell@, but with followups set to haskell-cafe@, > is the ideal way to keep everyone informed... I am usually not interested in the posts to haskell - calls for papers and the like. So I receive it as a digest it and rarely look at it. Posts that interest me, such as announcements of new packages on hackage, tend to be cross-posted to haskell-cafe. That is ideal for me. > ...it would reduce _so_ much irritation > if all the haskell-related mailing lists could set the Reply-To header to > the list, instead of defaulting to the original poster. I filter haskell-cafe traffic into a place where I can browse it if I have time. But when I am participating in a thread, I want its messages to pop up in my inbox. Forcing active threads to the inbox would take work (given my setup), and the result would be far less accurate. I appreciate people's efforts to include me in a conversation by mentioning me as a recipient. Regards, Yitz

1 0

ANNOUNCE: DecisionTree 0.0
by Adrian Neumann 25 Jan '09

25 Jan '09

Hello, it is my pleasure to announce the DecisionTree package. It provides an implementation of the ID3 algorithm [1] and can be used to classify data with discrete valued attributes. You can get it from * hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ DecisionTree * my own webspace: http://page.mi.fu-berlin.de/aneumann/decisiontree/ DecisionTree-0.0.tar.gz At this stage it is very likely buggy and slow, as I don't have a sufficiently large dataset to test with. You are encouraged to have a look at the source, it is quite short and well commented. Please feel free to make suggestions, send in patches or point me to some dataset I could use for testing. Regards, Adrian

1 0

Fold that quits early?
by Andrew Wagner 25 Jan '09

25 Jan '09

This is almost a fold, but seemingly not quite? I know I've seem some talk of folds that potentially "quit" early. but not sure where I saw that, or if it fits. f xs [] = False f xs (y:ys) | any c ys' = True | otherwise = f (nub (y:xs)) (ys' ++ ys) where ys' = g y xs

4 9

Generic typeclass for converting between types
by John Goerzen 25 Jan '09

25 Jan '09

Hi folks, I've been thinking today that I frequently need to convert data beween types: * Between various numeric types * Between various calendar types (both within the new calendar system, and between the old and new) * Marshalling data back and forth to a database in HDBC It's hard to remember all the functions to use to do these. I often resort to a chart I made for numeric conversions. It occurs to me that it would be nice to be able to (convert (5.8::Double))::Int or (convert calendarTime)::ZonedTime So, the first question is: does something like this exist already? I'm not aware of it, but I'm not sure how to search either. I'm thinking of something like the below. With a little magic, it's quite possible to make errors easy to generate in the safe fashion (for instance, when converting from String to Integer using reads). {-# LANGUAGE MultiParamTypeClasses #-} import Control.Monad.Error type ConvertResult a = Either ConvertError a class Convertible a b where safeConvert :: a -> ConvertResult b instance Convertible Int Double where safeConvert = return . fromIntegral instance Convertible Double Int where safeConvert = return . truncate -- could do bounds checking here instance Convertible Integer Double where safeConvert = return . fromIntegral instance Convertible Double Integer where safeConvert = return . truncate convert :: Convertible a b => a -> b convert inp = case safeConvert inp of Left e -> error (show e) Right x -> x -- rudimentary error type for this example data ConvertError = ConvertError { sourceValue :: String, errorMessage :: String } deriving (Eq, Read, Show) instance Error ConvertError where strMsg x = ConvertError "(unknown)" x The other option is to use an approach more like I have in HDBC. In HDBC, there is a direct need to encapsulate data for transport, so I've got this: class (Show a) => SqlType a where toSql :: a -> SqlValue safeFromSql :: SqlValue -> FromSqlResult a data SqlValue = SqlString String | SqlByteString B.ByteString | SqlWord32 Word32 | SqlWord64 Word64 ... many more .... ... instance SqlType Int32 where sqlTypeName _ = "Int32" toSql = SqlInt32 safeFromSql (SqlString x) = read' x safeFromSql (SqlByteString x) = (read' . byteString2String) x safeFromSql (SqlInt32 x) = return x safeFromSql (SqlInt64 x) = return . fromIntegral $ x The advantage of this is that if you've got a whole slew of types and you're going to be converting between all of them (for instance, numeric types), if you turn on -Wall the compiler will help you know when your safeFromSql instance doesn't convert everything. The disadvantage is that the type system doesn't enforce whether or not it is even possible to convert certain things (for instance, a TimeOfDay to a Char), and so we have to return a Left for those. Any thoughts? -- John

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ANN: orchid-0.0.7
by Sebastiaan Visser 25 Jan '09

25 Jan '09

I am pleased to announce a new release of Orchid, just another Haskell Wiki. Some new features/fixes: * Attached wiki to FileStore package which means we now also have Git backend. * Orchid-demo now has a flag which allows user to choose Git or Darcs. * Searching document is now possible. * Deleting and renaming documents is now possible. * Better keyboard support in user interface. * Fixed the in-page HTML anchors. * Password are now saved in md5, not plain text. * Use extensible exceptions to be more compatible with older GHC. * Fixed bugs in directory listings. * Users now also have a email. Watch the demo at: http://funct.org/wiki/ Or get the demo from cabal: $ cabal install orchid-demo

1 0

ANN: gitit 0.5
by John MacFarlane 25 Jan '09

25 Jan '09

We are pleased to announce the latest release of Gitit, the multitalented distributed wiki written in Haskell. What's new in this release? * 'Gitit' is now something of a misnomer, as Gitit now makes use of the filestore library. The upshot is that Gitit can now work in Darcs repositories; if before you thought Gitit was cool but didn't like git, you now have no excuse! * Gitit has been optimized (thanks to the efforts of Gwern Branwen): - Pages are now gzipped whenever possible. - Expire headers are set so that CSS, images, and javascripts will be cached by the browser. - Those previously mentioned elements have been optimized for space, and rearranged in the generated pages for faster rendering. * A new configuration option allows reStructuredText to be used instead of markdown (thanks to a patch from Simon Michael). * Gitit now sports a 'Go' box. You can now either search through Search, or go to a specific page title via Go. * Search is smarter, and can also return page titles. * Revisions are better formatted: the author field now include the user's email as well. * Diffs are of much higher quality, thanks to filestore. * UTF8-related fixes. You can check out a running example at http://gitit.johnmacfarlane.net/. Or try it locally: cabal update cabal install -fhighlighting pandoc gitit gitit # note: this will create two subdirectories in the working directory # then browse to http://localhost:5001. The git repository for Gitit is at http://github.com/jgm/gitit/tree/master

2 1

Arch Haskell News: Jan 24 2009
by Don Stewart 25 Jan '09

25 Jan '09

A regular update of Haskell in Arch Linux http://archhaskell.wordpress.com/2009/01/24/arch-haskell-news-jan-24-2009/ * Arch now has 864 Haskell packages in AUR. That’s an increase of 37 new Haskell packages in the last 13 days, or 2.8 new Haskell apps and libraries a day packaged so far in January. Cheers, Don

1 0

Factory methods in Haskell
by Jeremy Shaw 25 Jan '09

25 Jan '09

Hello, I was reading about the "Factory Method Pattern" on wikipedia, and noticed that the very first example was written in Haskell. Sweet! http://en.wikipedia.org/wiki/Factory_method_pattern#Haskell Unfortunately, it looks to me like it is missing the 'factory' part. I have attempted to implement something more factory like (see attached). I am wonder what other people think. Is the code on wikipedia really demoing a factory method? Is the code attached any better? Is there an even better what to write this in Haskell? Thanks! - j {-# LANGUAGE ExistentialQuantification #-} import Numeric (showFFloat) -- * A type which can hold different types of pizzas data Pizza = forall a. (PizzaMethods a) => Pizza a -- * A type class with functions common to different types of pizza class (Show a) => PizzaMethods a where price' :: a -> Double -- * Getter functions for the pizza type price :: Pizza -> Double price (Pizza p) = price' p pizzaType :: Pizza -> String pizzaType (Pizza p) = show p -- * Some types of pizza data HamAndMushroom = HamAndMushroom deriving (Read, Show) data Deluxe = Deluxe deriving (Read, Show) data Hawaiin = Hawaiin deriving (Read, Show) -- * Prices of various pizzas instance PizzaMethods HamAndMushroom where price' _ = 8.50 instance PizzaMethods Deluxe where price' _ = 10.50 instance PizzaMethods Hawaiin where price' _ = 11.50 -- * A pizza factory pizzaFactory :: String -> Pizza pizzaFactory pizzaType | pizzaType == "HamAndMushroom" = Pizza HamAndMushroom | pizzaType == "Deluxe" = Pizza Deluxe | pizzaType == "Hawaiin" = Pizza Hawaiin | otherwise = error "We don't serve your kind here." -- * An order at the pizza factory main = let pizza = pizzaFactory "HamAndMushroom" in putStrLn $ "You can get a " ++ pizzaType pizza ++ " for $" ++ showFFloat (Just 2) (price pizza) "."

2 1

ANNOUNCE: Scurry :: A cross platform (if you put your mind to it) P2P VPN
by John Van Enk 25 Jan '09

25 Jan '09

Hello All! I've finally brought Scurry, my P2P VPN application written in Haskell (and a little C), to a point where I'm comfortable letting the world more formally know that it's out there. Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Scurry SVN: http://code.google.com/p/scurry/ Reddit: http://www.reddit.com/r/haskell/comments/7s653/a_cross_platform_p2p_vpn_app… Patches, questions, and criticism are more than welcome! /jve

1 0

Re: [Haskell-cafe] How to define an operation in terms of itself (but of different type)?
by Olex P 25 Jan '09

25 Jan '09

But you know it doesn't make too much sense because I also have to define addition Scalar + Vector (that means construct vector from scalar and add a vector), Vector + Scalar and so on. And as we are not able to overload operations in C++ like way we have to create several different operations even if their meaning is pretty close. Probably it's possible with ad hoc overloading but I don't know is it good idea. On Sat, Jan 24, 2009 at 1:56 PM, Alberto G. Corona <agocorona(a)gmail.com>wrote: > What about making your Vector a instance of Num? you have + and * well > defined , although * is not commutative in this case > > 2009/1/24 Olex P <hoknamahn(a)gmail.com> > >> Yeah guys. I confused myself. I forgot why I had to implement several "+" >> operators (^+^, ^+, ^+. etc.) for Vector class. Now I've got an idea again. >> Different names make a perfect sense. >> >> Thanks a lot. >> >> >> On Sat, Jan 24, 2009 at 6:34 AM, Luke Palmer <lrpalmer(a)gmail.com> wrote: >> >>> 2009/1/23 Brandon S. Allbery KF8NH <allbery(a)ece.cmu.edu> >>> >>>> On 2009 Jan 23, at 17:58, Olex P wrote: >>>> >>>> class Vector v where >>>> (^+^) :: v -> v -> v >>>> >>>> class Matrix m where >>>> (^+^) :: m -> m -> m >>>> >>>> >>>> You can't reuse the same operator in different classes. Vector "owns" >>>> (^+^), so Matrix can't use it itself. You could say >>>> >>>> > instance Matrix m => Vector m where >>>> > (^+^) = ... >>>> >>> >>> No you can't! Stop thinking you can do that! >>> >>> It would be sane to do: >>> >>> class Vector m => Matrix m where >>> -- matrix ops that don't make sense on vector >>> >>> Thus anything that implements Matrix must first implement Vector. Which >>> is sane because matrices are square vectors with some additional structure, >>> in some sense. >>> >>> Luke >>> >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >

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unboxed, functional ATS language beats C++
by Alberto G. Corona 25 Jan '09

25 Jan '09

Language Shootout: ATS is the new top gunslinger. Beats C++<http://shootout.alioth.debian.org/u64q/benchmark.php?test=all&lang=all> http://www.reddit.com/r/programming/comments/72hmw/language_shootout_ats_is… ...Many people somehow think that ATS is fast because of its support for advanced types such as dependent types and linear types. Actually, types are primarily for enhancing safety rather than speed. The efficiency of ATS is largely rooted in its data representation (flat instead of boxed) and its support for tail-call optimization, which is vital for a functional language. What is interesting abut this ML derived language is the speed. The "theoriem proving" facilities seems like a language extensions for property checkings mainly for his non pure features. The type system seems to aid on the safety of pointer arithmetics and other dangerous operations.

2 1

Installing GHC with libedit in nonstandard location
by Grzegorz Chrupala 25 Jan '09

25 Jan '09

Hi all, I'm trying to install the GHC binary for Linux. The problem is my libedit is in $HOME/lib instead of /usr/lib So GHC installs but when I try to run it is fails with: error while loading shared libraries: libedit.so.0: cannot open shared object file: No such file ordirectory I tried setting LIBRARY_PATH and LD_RUN_PATH to $HOME/lib but it doesn't help Is there some way I can run GHC with libedit in a nonstandard location? Thanks -- Grzegorz -- View this message in context: http://www.nabble.com/Installing-GHC-with-libedit-in-nonstandard-location-t… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

2 2

"Enumerating" haskell types
by Maurício 25 Jan '09

25 Jan '09

Hi, I'm reading a book where the guy (Abraham Robinson, "Non-Standard Analysis") write a type system like following for his needs. First, he gets an initial type: 0 This is going to be the type of all individuals. Then, types of relations (sets, functions etc.) are built like this: given existing types, a n-uple of them is a new type. So, these are possible types: (0) ((0),0,0) (0,0,0) ( ((0),0,0) , 0 , 0 , (0,0,0) ) I think it's easy, and similar to above, to do that for Haskell kinds. Would it be possible to do something similar for haskell types? If possible, I think that it could be a great help in understanding Haskell type system, specially new things like GADTs and RankN types. Thanks, Maurício

1 0

re: Why monoids will abide...
by David F. Place 25 Jan '09

25 Jan '09

On Jan 20, 7:27 pm, Don Stewart <d...@galois.com> wrote: > http://apfelmus.nfshost.com/monoid-fingertree.html > > Thanks Apfelmus for this inspiring contribution! For additional reading material on a use of Monoids may I suggest my article in the Monad.Reader issue 11 "How to Refold a Map." http://haskell.org/sitewiki/images/6/6a/TMR-Issue11.pdf I also sketched an implementation of my incremental map data structure using Finger Trees. http://haskell.org/haskellwiki/The_Monad.Reader/Discuss_Issue11

1 0

Haskell Weekly News: Issue 102 - January 24, 2009
by Brent Yorgey 25 Jan '09

25 Jan '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090124 Issue 102 - January 24, 2009 --------------------------------------------------------------------------- Welcome to issue 102 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements Monoids and fingertrees. Heinrich Apfelmus posted a [2]nice tutorial explaining the monoid magic behind 2-3 fingertrees. STM-IO-Hooks-0.0.1. Peter Robinson [3]announced the [4]stm-io-hooks library, which provides an STM monad with commit and retry IO hooks. A retry-action is run (once) in a separate thread if the transaction retries, while commit-actions are executed iff the transaction commits. The code is based on the [5]AdvSTM monad by Chris Kuklewicz, but in addition also ensures some atomicity guarantees for commit-actions. 1000 libraries. Don Stewart [6]announced that Hackage has now [7]reached 1000 packages! HTTP-4000.0.4 released. Sigbjorn Finne [8]announced that a new release of [9]HTTP, version 4000.0.4, is now available. The main change is the addition of registering a Browser event handler for capturing state changes to the request-response processing pipeline. Blog noise [10]Haskell news from the [11]blogosphere. * Luke Palmer: [12]Existential Memoization. * Luke Palmer: [13]The Third Virtue. Luke has a Grand Vision (TM)! * Darcs: [14]darcs weekly news #14. * Magnus Therning: [15]More sensible comments on cabal-debian. * GHC / OpenSPARC Project: [16]Wait and perform. * LHC Team: [17]Typeclasses are working, now we're missing a bunch of instances.... * Andy Gill: [18]Memoization in GHC. A cool tutorial on how to memoize a pure function with GHC, without changing the function's definition. * Magnus Therning: [19]Experience with cabal-debian. * Joachim Breitner: [20]darcswatch uploaded to hackage. * GHC / OpenSPARC Project: [21]The Strap. * Real-World Haskell: [22]Bryan O'Sullivan on the Power of Haskell. * Jeff Heard: [23]Visualizing groundwater nitrate concentration. * Don Stewart (dons): [24]Open source releases and growth. * Lennart Augustsson: [25]Performance update on LLVM. * Arch Haskell News: [26]Piet implementation for Arch. * Mark Jason Dominus: [27]Triples and Closure. Did you know that monads are like closure operators? If not, read on. * GHC / OpenSPARC Project: [28]The Grind. * LHC Team: [29]Functions in Haskell.. * Magnus Therning: [30]Building Debian packages of (cabalised) Haskell packages. * Xmonad: [31]xmonad cheatsheet. * Xmonad: [32]xmonad on twitter. * Jeff Heard: [33]A random note on programming with Gtk2Hs.. * Xmonad: [34]xmonad 0.8.1 : GHC 6.10 maintenance release. * Jonathan Tang: [35]Some observations on Kinds. * Martijn van Steenbergen: [36]Type Synonym Families. Quotes of the Week * Jonathan Cast: [on advertising for Haskell programmers and informing them that the codebase is actually in Perl at the interview] <Andrew Wagner> That's......evil. <Jonathan> I know. I'm evil too, though. So it's cool. * rwbarton: A type class is not a type just like a dog house is not a dog. * SPJ: [This is] clearly not a bug in GHC; but it would be more felicitous if it gave you a warning... * Gracenotes: > let o_o = 0.0 ;o' =(, ); ;o (*)=(*) ;( lol, xD :p )= o' o' $o.o$ (:[]) $o.o$ (:[]) o_o in (:[]) o_o :p * Cale: I plan on forming a symbiotic relationship with sandtrout, which, as they merge with my body, will sustain me as I slowly turn into a sandworm, and make use of my billions of other memories and prescience to rule over everyone and everything for millenia. * quicksilver: or in Java, we'd make it more generic by using a PolynomialDivisionOperatorFactory. * roconnor: I was going to read about laziness, but I decided to do it later, when I need to understand it. About the Haskell Weekly News New editions are posted to [37]the Haskell mailing list as well as to [38]the Haskell Sequence and [39]Planet Haskell. [40]RSS is also available, and headlines appear on [41]haskell.org. To help create new editions of this newsletter, please see the information on [42]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [43]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://apfelmus.nfshost.com/monoid-fingertree.html 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51249 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/stm-io-hooks 5. http://www.haskell.org/haskellwiki/New_monads/MonadAdvSTM 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51186 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/stats 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51165 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTTP 10. http://planet.haskell.org/ 11. http://haskell.org/haskellwiki/Blog_articles 12. http://lukepalmer.wordpress.com/2009/01/24/existential-memoization/ 13. http://lukepalmer.wordpress.com/2009/01/24/the-third-virtue/ 14. http://blog.darcs.net/2009/01/darcs-weekly-news-14.html 15. http://therning.org/magnus/archives/485 16. http://ghcsparc.blogspot.com/2009/01/wait-and-perform.html 17. http://lhc-compiler.blogspot.com/2009/01/typeclasses-are-working-now-were.h… 18. http://blog.unsafeperformio.com/?p=34 19. http://therning.org/magnus/archives/476 20. https://www.joachim-breitner.de/blog/archives/317-darcswatch-uploaded-to-ha… 21. http://ghcsparc.blogspot.com/2009/01/strap.html 22. http://www.realworldhaskell.org/blog/2009/01/21/bryan-osullivan-on-the-powe… 23. http://vis.renci.org/jeff/?p=63 24. http://donsbot.wordpress.com/2009/01/21/open-source-releases-and-growth/ 25. http://augustss.blogspot.com/2009/01/performance-update-ive-continued.html 26. http://archhaskell.wordpress.com/2009/01/20/piet-now-packaged/ 27. http://blog.plover.com/math/monad-closure.html 28. http://ghcsparc.blogspot.com/2009/01/grind.html 29. http://lhc-compiler.blogspot.com/2009/01/functions-in-haskell.html 30. http://therning.org/magnus/archives/458 31. http://xmonad.wordpress.com/2009/01/19/xmonad-cheatsheet/ 32. http://xmonad.wordpress.com/2009/01/19/xmonad-on-twitter/ 33. http://vis.renci.org/jeff/?p=24 34. http://xmonad.wordpress.com/2009/01/19/xmonad-081-ghc-610-maintainance-rele… 35. http://eve-language.blogspot.com/2009/01/some-observations-on-kinds.html 36. http://martijn.van.steenbergen.nl/journal/2009/01/11/type-synonym-families/ 37. http://www.haskell.org/mailman/listinfo/haskell 38. http://sequence.complete.org/ 39. http://planet.haskell.org/ 40. http://sequence.complete.org/node/feed 41. http://haskell.org/ 42. http://haskell.org/haskellwiki/HWN 43. http://code.haskell.org/~byorgey/code/hwn/

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Core questions
by Matthijs Kooijman 24 Jan '09

24 Jan '09

Hi all, for my Master's thesis, I'm looking into functional hardware descriptions, and in particular to translate haskell code into VHDL that can be programmed into an FPGA. For this, I'm using the GHC API to load the haskell source and give me (simplified) core representation. I then walk over the core tree and translate it to VHDL. On the whole the GHC API has been very useful to me. It took me some time to get used to all the (deeply) nested (algebraic) types (I didn't have any previous haskell experience when I started a month or so ago), but things are working out by now. However, there are two issues bothering me still. The first is that the Core types (in particular CoreExpr) are not instances of Show. They are instances of Outputable, which allows them to be pretty printed. However, this pretty printing is good to view the structure of the expression that the CoreExpr represents, but doesn't show the structure of the CoreExpr itself. For example, tuple construction is printed simply as (a, b), while the actual core expression is a nested application of two types, and a and b to the GHC.Tuple.(,) function (or datacon?). Also, the exact constructors used are not quite clear, which made it harder to work with the Core language for me. Instead of looking at the structure of the CoreExpr and write the appropriate patterns, I had to resort to a lot of trial and error. I tried deriving show for CoreExpr myself, but that required me to derive Show for a dozen other types and resulted in type errors beyond my understanding. Is there any compelling reason that CoreExprs are not instances of Show? My second question concerns typle construction. Since tuple types are not primitive types, but dependent types defined in various places (GHC.Tuple and Base IIRC), code working with tuples is not fundamentally different from code working with other (user defined) dependent types and thus not trivial to recognize. I've found that there are some predicate functions that can tell me if a type is a tuple type, but I've had no such luck for the actual tuple construction. In particular, when an expression creates a tuple of two Ints (a, b), this is represented in Core as the application of the element types and the element values to the (,) function (or data constructor? Not sure about this, in Core it's just a Var and the isDataConName [IIRC] predicate crashes when run on the Var). For now, I've manually matched the Var's name to GHC.Tuple.(,) and removed all type arguments to get at the actual values in the tuple. This is of course completely non-portable, to tuples with more than two elements, or unboxed tuples, etc. Is there some predicate function that can do this for me in a more portable way? Gr. Matthijs

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