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Re: [Haskell-cafe] Parallel interruptible computations
by Corentin Dupont 07 Sep '14

07 Sep '14

Nobody on those parallel interruptible computations/events? I believe this is related to FRP: we register on several events but only a part of them is enough to compute the result. But I don't see such operator in FRP frameworks such as reactive-banana... On Fri, Sep 5, 2014 at 12:59 PM, Corentin Dupont <corentin.dupont(a)gmail.com> wrote: > Hi guys! > I'm wondering if there is an abstraction (for example a typeclass) for > parallel interruptible computations. > I want several things to be computed in parallel. Those computations will > not finish at the same time, but as soon as enough result is gathered, the > remaining computations can be cancelled and the final result computed. > Clearly a Monad is not suited here: Monad are by definition for sequential > computation (since the result of the first computation is fed to the next). > > -> So the question is: is there an abstraction for parallel computations? > > Note that I'm not interrested with real implementations (such as with > threads) but with the abstraction. > For now I came up with: > > ShortcutEvents :: [Event a] -> ([a] -> Maybe b) -> Event b > > This takes a list of events and a function. The events can fire at > whatever moment, and as soon as one of the events fires, the function is > called with the results available so far. If the function returns Just, the > remaining events are cancelled and the final result is returned. > This is working fine, but I'd like a way to generalize this, especially to > generalize the list to any structure... > > The use case is a voting system: people can vote at whatever moment, but > sometime the result of the vote is known even if not everybody voted yet. > > Thanks! > Corentin >

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Fwd: an idea for improving 'shrink'
by Petr Pudlák 06 Sep '14

06 Sep '14

Hi, since I got no response from the QuickCheck mail address, so I'm resending it here, if someone wants to comment on the idea. Best regards, Petr ---------- Forwarded message ---------- From: Petr Pudlák <petr.mvd(a)gmail.com> Date: 2014-07-06 20:13 GMT+02:00 Subject: an idea for improving 'shrink' To: QuickCheck developers <quickcheck(a)projects.haskell.org> Hi, I was learning about 'shrink' lately and I was trying to create some instances. It felt quite awkward until I realized that the operation for producing shrunk tuples is an applicative functor. I was playing with the idea for a while and I'm sending an experimental patch against QuickCheck master that shows the basics of the idea and how it can help constructing 'shrink' instances. If you feel that this is a good idea, let me know, I'll work on a full patch. Best regards, Petr

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Functional dependency failure
by Alexander Pakhomov 06 Sep '14

06 Sep '14

Hi! I have following code: STRead.hs: import Control.Monad.Reader import Control.Monad.ST import qualified Data.Vector.Mutable as MV import qualified Data.Vector as V type ReadVecMonad s = ReaderT (MV.MVector s Int) (ST s) freezeV :: ReadVecMonad s (V.Vector Int) freezeV = ask >>= lift V.freeze Trying to compile this I have "Couldn't match type ... When using functional dependencies to combine" error following with kind mismatch and type with literaly the same type mismatch. How can I work this around? There's full error message: STRead.hs:9:11: Couldn't match type `V.MVector s Int' with `(->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int)' When using functional dependencies to combine MonadReader r (ReaderT r m), arising from the dependency `m -> r' in the instance declaration in `Control.Monad.Reader.Class' MonadReader ((->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int)) (ReaderT (V.MVector s Int) (ST s)), arising from a use of `ask' at STRead.hs:9:11-13 In the first argument of `(>>=)', namely `ask' In the expression: ask >>= lift V.freeze STRead.hs:9:19: Couldn't match kind `* -> *' with `*' Expected type: (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) -> ReaderT (V.MVector s Int) (ST s) (V.Vector Int) Actual type: (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) -> ReaderT (V.MVector s Int) (ST s) (V.Vector Int) Kind incompatibility when matching types: (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) :: * -> * (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) :: * In the return type of a call of `lift' In the second argument of `(>>=)', namely `lift V.freeze' STRead.hs:9:24: Couldn't match kind `*' with `* -> *' Expected type: V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int -> ReaderT (V.MVector s Int) (ST s) (V.Vector Int) Actual type: V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int -> ReaderT (V.MVector s Int) (ST s) (V.Vector Int) Kind incompatibility when matching types: (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) :: * (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) :: * -> * In the first argument of `lift', namely `V.freeze' In the second argument of `(>>=)', namely `lift V.freeze'

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Maintaining test-suite dependencies with cabal
by Bram Neijt 06 Sep '14

06 Sep '14

Dear reader, I have a single executable package in Cabal[1] and I have added a test for it using an example configuration from the ltc package[2]. With my test on my executable I can't depend on the main package, but I seem to have to repeat the dependencies of my executable, or split off functionality into a library. [3] Can I easily depend on the dependencies of another package or should I create a library and depend on that in my test and executable? All source is at: https://github.com/bneijt/after/ Greetings, Bram [1] https://github.com/bneijt/after/blob/master/after.cabal [2] https://github.com/scvalex/ltc/blob/master/ltc.cabal [3] A part of my cabal file added below executable after main-is: Main.hs build-depends: base >=4.7 && <4.8, options ==1.*, directory ==1.2.*, parallel-io ==0.3.*, filepath ==1.3.*, unix ==2.7.* hs-source-dirs: src ghc-options: -Wall default-language: Haskell2010 test-suite afterTests hs-source-dirs: test src main-is: AfterTest.hs type: exitcode-stdio-1.0 build-depends: base >=4.7 && <4.8, unix ==2.7.*, -- Here because of after depending on it directory ==1.2.*, -- Here because of after depending on it filepath ==1.3.*, -- Here because of after depending on it test-framework, test-framework-hunit, HUnit default-language: Haskell2010

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Elm-like IDE for Haste projects
by Alberto G. Corona 05 Sep '14

05 Sep '14

Following the thread on lightweight Web interfaces for Haskell: http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/112586 I finished an Elm-like IDE for Haste projects. The software is at: https://github.com/agocorona/tryhplay Running in a heroku instance: http://tryplayg.herokuapp.com Besides to edit-compile and run, it can also import , compile and run haste projects from git repositories (Although this, like the rest of the project is experimental). I use it for my hplayground framework but it can run any haste project. Using playground is easy to translate console programs to the browser and have reactive effects A simple example: http://tryplayg.herokuapp.com/try/console.hs/edit the hello-haste example: http://tryplayg.herokuapp.com/try/hello-haste.hs/edit Or something more complicated: the todo application, from todoMVC.com written in Haste and hplayground: http://tryplayg.herokuapp.com/try/todo.hs/edit rename the programs if you modify them. Follow the instructions to download the HTML generated, that include the Javascript generated. At this time there are no permission controls so it is more or less like a wiki, but heroku from time to time will reset the application. It is a free instance on heroku so expect delays and request timeouts when many people access to the application. I do not know what will happen. Feedback welcome My heroku instance is limited but It is easy to create your own instance in heroku. Follow the install instructions. Haste: https://github.com/valderman/haste-compiler http://haste-lang.org hplayground: https://github.com/agocorona/hplayground -- Alberto.

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Parallel evaluation of code dependencies
by felipe zapata 04 Sep '14

04 Sep '14

Hi Cafe, Suppose that I have a representation of a DSL in Haskell (a physical number crunching simulation using quasiquoting for instance) and I want to evaluate the resulting Haskell representation by splitting it into chunks and send these chunk to some cluster, a supercomputer, etc. It doesn't matter for the moment the distribution protocol. My advisor suggested me that the best way of doing such a thing, is through a call by value strategy. Where I simply evaluate in parallel all the arguments of the functions. The problem with this alternative is that I must manipulate the Haskell representation and use some library ( or write some code) to identify the dependencies and evaluate them in parallel. Can please someone suggest me the best way to tackle this problem? I really appreciate any help. Felipe Z.

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Re: [Haskell-cafe] diagrams fails to install
by Roger Mason 04 Sep '14

04 Sep '14

Hello Mike, Mike Meyer <mwm(a)mired.org> writes: > You should have a /usr/local/llvm32 directory. If so, try: > > PATH=/usr/local/llvm32/bin:$PATH cabal install diagrams. > > I have llvm34 installed, and it worked for me using > /usr/local/llvm34/bin:$PATH. > Thank you, that worked. best wishes, Roger

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diagrams fails to install
by Roger Mason 04 Sep '14

04 Sep '14

Hello, I'm trying to install Diagrams on FreeBSD 10. It fails thus: cabal install diagrams Resolving dependencies... Configuring arithmoi-0.4.1.1... Building arithmoi-0.4.1.1... Preprocessing library arithmoi-0.4.1.1... [ 1 of 34] Compiling Math.NumberTheory.Primes.Sieve.Indexing ( Math/NumberTheory/Primes/Sieve/Indexing.hs, dist/build/Math/NumberTheory/Primes/Sieve/Indexing.o ) <no location info>: Warning: Couldn't figure out LLVM version! Make sure you have installed LLVM ghc: could not execute: opt Failed to install arithmoi-0.4.1.1 cabal-install: Error: some packages failed to install: arithmoi-0.4.1.1 failed during the building phase. The exception was: ExitFailure 1 diagrams-1.2 depends on arithmoi-0.4.1.1 which failed to install. diagrams-contrib-1.1.2.1 depends on arithmoi-0.4.1.1 which failed to install. ghc --info reports: [("Project name","The Glorious Glasgow Haskell Compilation System") ,("GCC extra via C opts"," -fwrapv") ,("C compiler command","gcc47") ,("C compiler flags"," -fno-stack-protector -Wl,--hash-size=31 -Wl,--reduce-memory-overheads") ,("ar command","/usr/bin/ar") ,("ar flags","clqs") ,("ar supports at file","NO") ,("touch command","touch") ,("dllwrap command","/bin/false") ,("windres command","/bin/false") ,("perl command","/usr/bin/perl") ,("target os","OSFreeBSD") ,("target arch","ArchX86") ,("target word size","4") ,("target has GNU nonexec stack","True") ,("target has .ident directive","True") ,("target has subsections via symbols","False") ,("LLVM llc command","llc") ,("LLVM opt command","opt") ,("Project version","7.6.3") ,("Booter version","7.6.3") ,("Stage","2") ,("Build platform","i386-portbld-freebsd") ,("Host platform","i386-portbld-freebsd") ,("Target platform","i386-portbld-freebsd") ,("Have interpreter","YES") ,("Object splitting supported","YES") ,("Have native code generator","YES") ,("Support SMP","YES") ,("Unregisterised","NO") ,("Tables next to code","YES") ,("RTS ways","l debug thr thr_debug thr_l thr_p dyn debug_dyn thr_dyn thr_debug_dyn") ,("Leading underscore","NO") ,("Debug on","False") ,("LibDir","/usr/local/lib/ghc-7.6.3") ,("Global Package DB","/usr/local/lib/ghc-7.6.3/package.conf.d") ,("Gcc Linker flags","[\"-Wl,--hash-size=31\",\"-Wl,--reduce-memory-overheads\"]") ,("Ld Linker flags","[\"--hash-size=31\",\"--reduce-memory-overheads\"]") ] opt is installed as /usr/local/bin/opt32, so I tried symlinking /usr/local/bin/opt to it, but the error remains. Is there some workaround? Thanks, Roger

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Jobs at the University of Kent
by Simon Thompson 04 Sep '14

04 Sep '14

We've been doing functional programming at Kent for more than thirty years, and it would be great to recruit more people in FP, theory, type theory, programming languages, verification, concurrency ... Details of three positions here: https://jobs.kent.ac.uk/fe/tpl_kent01.asp?s=4A515F4E5A565B1A&jobid=38618,12… If you're interested in discussing, just send us an email. Simon Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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heroku-buildpack-haste
by Alberto G. Corona 04 Sep '14

04 Sep '14

Just to let you know that I created an heroku buildpack that install GHC and Haste in the running environment, so that web applications can invoke ghc, cabal, hastec haste-inst etc. I use it for the creation of an Haste IDE. But it may have other uses. https://github.com/agocorona/heroku-buildpack-haste -- Alberto.

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