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Peyton Jones' "Beautiful Concurrency" .. i.e. Software Transactional Memory ...
by Galchin Vasili 24 Dec '07

24 Dec '07

Hello, My brain is a "out to lunch". I have read the paper "Beautiful Concurrency" (as well as a bunch of "gaming" papers regarding multi cores). I am playing with the "Account" example in the paper. In the paper, the alias "type Account = TVar Int" is used. I want to actually apply the function "withdraw" to an example "Account" parameter. I keep getting a type check error. Can someone give me a concrete example of > withdraw ...... ?? Kind regards, Vasya

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FW: Treating command-line arguments as a Haskell expression
by Simon Peyton-Jones 24 Dec '07

24 Dec '07

Would someone familiar with the command-line-parsing libraries care to help Krassimir? Thanks Simon -----Original Message----- From: Krassimir Krustev [mailto:krassimir.krustev@gmail.com] Sent: 23 December 2007 11:38 To: Simon Peyton-Jones Subject: Treating command-line arguments as a Haskell expression Dear Dr. Jones: I've been pulling my hair over the Christmas Holidays trying to figure the following: I want to call a function from within Haskell module so that the name of this function corresponds to my first command-line argument and the rest rest of the command-line arguments are would become themselves the argument to this function. Coundn't figure this out. It is my first week with Haskell. Yours, Krassimir

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Re: [Haskell-cafe] Functions are first class values in C
by Miguel Mitrofanov 24 Dec '07

24 Dec '07

> It is true, however, that preprocessing used to be (in pre-standard > days) separate from the language. This has not been true for decades. Well, I've seen cpp to be used as a preprocessor not for C sources but for something else.

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Fwd: Re: [Haskell-cafe] Functions are first class values in C
by Cristian Baboi 24 Dec '07

24 Dec '07

------- Forwarded message ------- From: "Cristian Baboi" <cristian.baboi(a)gmail.com> To: "Jules Bean" <jules(a)jellybean.co.uk> Cc: Subject: Re: [Haskell-cafe] Functions are first class values in C Date: Sat, 22 Dec 2007 15:58:50 +0200 On Sat, 22 Dec 2007 14:09:13 +0200, Jules Bean <jules(a)jellybean.co.uk> wrote: > Cristian Baboi wrote: >> Let me show you an example to prove it. > That's not C. > That's the C preprocessor, which is a textual substitution macro > language. Well, the preprocessor is part of the language in a way. These two come together. > Macros certainly aren't first class (you can't pass a macro to a > function, only its expansion). In Haskell I cannot pass a function to a function, only its expansion. > C does support function pointers, which are something like first class > functions. The main things C lacks which people associate with true > first-class function is: > The ability to construct anonymous/local functions. If you look at the example you will see I've done that. > The ability to capture local variables and return a function with some > variables bound. If I can construct "anonymous" functions and "constants", I can construct functions with some variables bound. > The ability to write type-safe functions with polymorphic arguments. I didn't know this must be a property of first-class functions. C is staticaly typed, so type errors will be detected. Haskell is just C with some syntactic sugar :-)

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Fwd: Re: [Haskell-cafe] more on the "Beautiful Concurrency" function "withdraw" application ...
by Dean Herington 24 Dec '07

24 Dec '07

>Date: Mon, 24 Dec 2007 01:44:16 -0500 >To: "Galchin Vasili" <vigalchin(a)gmail.com>, haskell-cafe(a)haskell.org >From: Dean Herington <heringtonlacey(a)mindspring.com> >Subject: Re: [Haskell-cafe] more on the "Beautiful Concurrency" >function "withdraw" application ... >Cc: >Bcc: >X-Attachments: > >At 12:19 AM -0600 12/24/07, Galchin Vasili wrote: >>module Main where >>import Control.Concurrent.STM >>import Control.Concurrent >>import System.Random >> >>type Account = TVar Int >> >>transfer :: Account -> Account -> Int -> IO () >>transfer from to amount >> = atomically (do {deposit to amount; >> withdraw from amount}) >> >>deposit :: Account -> Int -> STM () >>deposit acc amount = withdraw acc (- amount) >> >>withdraw :: Account -> Int -> STM () >>withdraw acc amount >> = do { bal <- readTVar acc; >> writeTVar acc (bal - amount) } >> >> >> >>When I try >> >>withdraw (TVar 10) .. >> >>I get "Not in scope: data constructor 'TVar'. OK .. "Tvar" is a >>class and not a Haskell data type ... so now what? > >You first need to create an account: > > > acct <- newTVar 100 Sorry, that would be: > acct <- atomically (newTVar 100) >Then you can withdraw from it: > > > atomically (withdraw acct 10) > >Dean

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more on the "Beautiful Concurrency" function "withdraw" application ...
by Galchin Vasili 24 Dec '07

24 Dec '07

module Main where import Control.Concurrent.STM import Control.Concurrent import System.Random type Account = TVar Int transfer :: Account -> Account -> Int -> IO () transfer from to amount = atomically (do {deposit to amount; withdraw from amount}) deposit :: Account -> Int -> STM () deposit acc amount = withdraw acc (- amount) withdraw :: Account -> Int -> STM () withdraw acc amount = do { bal <- readTVar acc; writeTVar acc (bal - amount) } When I try withdraw (TVar 10) .. I get "Not in scope: data constructor 'TVar'. OK .. "Tvar" is a class and not a Haskell data type ... so now what? Vasya

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Re: ANNOUNCE: GHC version 6.8.2
by Judah Jacobson 24 Dec '07

24 Dec '07

I neglected to CC the below email to haskell-cafe; apologies if anyone gets this twice. ---------- Forwarded message ---------- From: Judah Jacobson <judah.jacobson(a)gmail.com> Date: Dec 21, 2007 2:12 PM Subject: Re: [Haskell-cafe] Re: ANNOUNCE: GHC version 6.8.2 To: John Dorsey <haskell(a)colquitt.org> On Dec 21, 2007 12:48 PM, John Dorsey <haskell(a)colquitt.org> wrote: > On a related topic, I've been trying to build 6.8.2 on Leopard lately. > I've been running up against the infamous OS X readline issues. I know > some builders here have hacked past it, but I'm looking for a good > workaround... ideally one that works without changes outside the GHC > build area (besides installing a real readline). > > Here's what I noticed before I started drowning in the build platform. > (I'm no gnu-configure expert nor GHC insider.) > > I can get gnu-readline installed from Macports, no problem. > > The top-level configure in GHC doesn't respond to my various attempts: > > o using --with-readline-libraries and --with-readline-includes > (Although it looks like the libraries/readline/configure script > might recognize these, I can't get an option to pass through.) Actually, this is supposed to work. When running the top-level ghc configure, you should be able to just say ./configure --with-readline-libraries=/opt/local/lib --with-readline-includes=/opt/local/include and have those arguments automatically passed to the readline configure script. I just checked that this works on my machine (Tiger x86) when building 6.8.2 against MacPorts' readline. If it doesn't work for you, what errors are you getting? Also, a couple of other generic questions: - Are you on x86 or PPC? (The latter is not working right yet with Leopard.) - How are you bootstrapping the build of 6.8.2: are you using a pre-built binary of ghc-6.8.1, or some other way? Best, -Judah

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Gtk2Hs installation problem with ghc 6.8.2 on Ubuntu 7.10
by Yin Wang 23 Dec '07

23 Dec '07

Hi, I'm installing Gtk2Hs on my Ubuntu 7.10. I have ghc 6.8.2 compiled with the extra libs in my home directory with the configuration "./configure --prefix=/home/wy/Programs" and it worked well. Then I configured gtk2hs in the same way and it compiled and installed with no problem. But when I tried to compile the demo program with any of the following command line: # ghc --make World.hs # ghc --make World.hs `pkg-config --cflags --libs gtk+-2.0` # ghc --make World.hs `pkg-config --cflags --libs gtk+-2.0` -L/home/wy/Programs/lib/gtk2hs It give some linking errors: Linking World ... World.o: In function `r2JR_info': (.text+0x46): undefined reference to `gtkzm0zi9zi12zi1_GraphicsziUIziGtkziAbstractziWidget_widgetShowAll_closure' World.o: In function `r2JR_info': (.text+0x4d): undefined reference to `gtkzm0zi9zi12zi1_GraphicsziUIziGtkziTypes_zdf550_closure' World.o: In function `r2JT_info': (.text+0xaa): undefined reference to `gtkzm0zi9zi12zi1_GraphicsziUIziGtkziAbstractziContainer_containerChild_closure' World.o: In function `r2JT_info': (.text+0xb1): undefined reference to `gtkzm0zi9zi12zi1_GraphicsziUIziGtkziTypes_zdf662_closure' World.o: In function `r2JT_info': (.text+0xb8): undefined reference to `gtkzm0zi9zi12zi1_GraphicsziUIziGtkziTypes_zdf550_closure' ... collect2: ld returned 1 exit status The first command worked well with the ghc 6.6.1 came with ubuntu. I tried to uninstall my old gtk package, but this doesn't help. Any ideas? -- Yin Wang

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A question about functional dependencies
by alpheccar 23 Dec '07

23 Dec '07

I have defined a function on types thanks to functional dependencies. I use it like that: myFunction :: (TypeFunction MyComplexType f) => f -> f f is unique for MyComplexType. Is there a way to name f ? I would like to write: myFunction :: SimplifiedType -> SimplifiedType where TypeFunction MyComplexType SimplifiedType is an instance of the class TypeFunction. Of course, I don't want to write explicitly SimplifiedType otherwise I could just do type SimplifiedType = ... The idea is that I build a MyComplexType using type synonyms and type constructors. But, the result has a shape which is too complex. I simplify it into a canonical form that I can use in some algorithms at the type level. I suspect I will have to use the type constraint and that there is no way to name the result of a computation at the type level ? Thanks, Christophe.

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Fwd: stg_uncheckedShiftRL64 unresolved when compiling with GHC 6 8 2
by golubovsky＠gmail.com 23 Dec '07

23 Dec '07

Hi, I posted this to the HAppS discussion group, but maybe somebody is able to answer in the Cafe, at least where this unresolved symbol belongs to. It looks like the same problem was discussed earlier related to GHC 6.7, but I got this problem right now, compiling HPaste with HAppS (using SearchPath). The linker message is: =================================== During interactive linking, GHCi couldn't find the following symbol: stg_uncheckedShiftRL64 This may be due to you not asking GHCi to load extra object files, archives or DLLs needed by your current session. Restart GHCi, specifying the missing library using the -L/path/to/object/dir and - lmissinglibname flags, or simply by naming the relevant files on the GHCi command line. Alternatively, this link failure might indicate a bug in GHCi. If you suspect the latter, please send a bug report to: glasgow-haskell-b...@haskell.org =================================== Output from ghc-pkg -l: =================================== /home2/dima/install//lib/ghc-6.8.2/package.conf: Cabal-1.2.3.0, array-0.1.0.0, base-3.0.1.0, binary-0.4.1, bytestring-0.9.0.1, containers-0.1.0.1, directory-1.0.0.0, filepath-1.1.0.0, (ghc-6.8.2), haskell-src-1.0.1.1, haskell98-1.0.1.0, hpc-0.5.0.0, hscolour-1.6, html-1.0.1.1, mtl-1.1.0.0, network-2.1.0.0, old-locale-1.0.0.0, old- time-1.0.0.0, packedstring-0.1.0.0, parsec-2.1.0.0, pretty-1.0.0.0, process-1.0.0.0, random-1.0.0.0, readline-1.0.1.0, regex-base-0.72.0.1, regex-compat-0.71.0.1, regex-posix-0.72.0.2, rts-1.0, stm-2.1.1.0, template-haskell-2.2.0.0, unix-2.3.0.0, xhtml-3000.0.2.1, zlib-0.4.0.1 =================================== To save time I compiled only GHC without extralibs, and later installed packages that were msissng during compilation from extralibs or hackage. Are there any modules shown whose versions raise any suspicions? Thanks.

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