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Re: [Haskell-cafe] where does ghc specify ar options
by Duncan Coutts 10 Mar '09

10 Mar '09

On Mon, 2009-03-09 at 21:08 -0400, Alexy Khrabrov wrote: > Duncan -- > > On Mar 9, 2009, at 8:14 PM, Duncan Coutts wrote: > > BTW, how did you get the package installed in that location? Did it > > involve copying into a temp dir and copying again? I believe that on > > OSX, copying a .a file breaks the ar index. This is because for > > reasons > > best known to themselves Apple decided that the index is only valid if > > its timestamp is the same as the last modification time of the file. > > Oh -- and that's because instead of the supplied bootstrap.sh I used > one off some website, and it used /tmp which somehow put stuff in > there and registered it there. I then unregistered it and removed it > and redid the cabal-install, and it worked with my patched ar. Ahhh. So is there anything in Cabal or the bootstrap.sh that needs to be fixed for this problem? Duncan

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where does ghc specify ar options
by Alexy Khrabrov 10 Mar '09

10 Mar '09

When bootstrapping cabal-install 0.6.2 on Mac OSX Leopard (Intel), I get a problem when linking: Linking dist/build/cabal/cabal ... ld: in /private/var/folders/mw/mwJSf7ErEa4w8nWyKyyqD++++TY/-Tmp-/zlib-0.5.0.0/dist/build/libHSzlib-0.5.0.0.a, archive has no table of contents This had happened with other ar'chives on my Mac before where it hadn't for some others. In all cases the fix was to make sure ranlib is run on the archive in question, or s is passed to ar during the creation. I have the latest XCode 312m gcc build 5490, and ghc 6.10.1 from MacPorts. In order to ensure ar cr becomes ar crs, I need to find out where in the ghc build process is it known how to create .a files? Where can an "ar cr" be changed to "ar crs" on a system-wide ghc build basis? Cheers, Alexy

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Re: ANN: Future 1.1.0 concurrency library
by Neal Alexander 10 Mar '09

10 Mar '09

ChrisK wrote: > Hello, > > As a side effect of the discussion of the new C++ future/promise > features at http://lambda-the-ultimate.org/node/3221 I have implemented > a Haskell package called "future" at > > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/future > > This ought to do what C++ standard futures/promises do, plus a bit > more. The main operation is > > > forkPromise :: IO a -> IO (Promise a) > > This sets the "IO a" operation running in a fresh thread. The eventual > result can be accessed in many ways (non-blocking, blocking, blocking > with timeout). > > > let one :: Int; one = 1 > > p <- forkPromise (return (one+one)) > > x <- get > > y <- wait > > x is an Int with value 2. > y is an (Either SomeException Int) with value (Right 2). > > The useful thing about futures, as opposed to various IVar packages, is > handling the case where the forked operation ends with an exception. > The exception becomes the return value of the promise. The "get" > operation rethrows it, the "wait" operation returns it as (Left ...). > > There is also an "abort" command to kill a promise. The dead promise > may then have an exceptions as its value. > > The "plus a bit more" than C++ is the nonblocking "addTodo" feature. > This takes a continuation function from the "Either SomeException a" to > an IO operation. These continuation functions get queued and they are > run immediately after the the forked operation completes. Once > completed any new "addTodo" continuations run immediately. > > These continuations allow you to race a list of action and take the > first one done, or to collect the answers as they complete into a Chan. > Both of those options are demonstrated in Future.hs as racePromises and > forkPromises. > > It should be safe to use "unsafePerformIO . get" or "unsafePeformIO . > wait" to get lazy access to the result, which is itself immutable once set. > > Cheers, > Chris I used something similar to this for a monadic opengl "RPC" mechanism. The need was for transparently creating OGL objects from any context. Returning thunks that block on the result when finally evaluated works out real nice in practice. Its easy to manage, and performs better than dealing with several OS threads and GL contexts.

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I want to write a compiler
by Loup Vaillant 10 Mar '09

10 Mar '09

This is a homework question. I am mainly looking for guidance or pointers. Source code, even. (Not GHC's, though, it is too complicated for me right now. The AST of STG is fine, but the rest kinda scares me.) Ideally, I would very much like to compile to C. The requirements are easily stated. My language must -> be lazy by default, -> support algebraic data types and case expressions (unless I can get away with encoding them as functions), -> have some kind of FFI with C (I suppose it imply some support for unboxed values). There is also the first class functions thing, but lambda lifting is okay. I don't care about any kind of execution efficiency. I just want my compiler to be As Simple As Possible. Eventually, I intend to bootstrap. Then, I will start dreaming about doing better than the Mighty Simons. (I can dream, right?) I figured I would start by the back-end. I began to write 15 pathetic lines of code to start an STG machine. Needles to say, I am stuck. I don't know where to start. I am already familiar with some papers. In particular, [1] (on template instantiation), [2] and [3]. I once wrote a simple graph reducer using template instantiation (about 20 lines at most). I have chosen the STG machine because I thought i would be easier to get an FFI and case exprs out of it. Maybe I am wrong, and template instantiation is really easier. There is also the BRISK machine, and GRIN. But the paper I read were less readable to me than the three mentioned. So, If any of you can give me some pointer or guidance or advice about where to start, I would be very grateful. Loup [1] http://www.cs.otago.ac.nz/cosc459/books/pjlester.pdf [2] http://research.microsoft.com/~simonpj/Papers/spineless-tagless-gmachine.ps… [3] http://research.microsoft.com/~simonpj/Papers/eval-apply/index.htm

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Minimum Int?
by Colin Paul Adams 09 Mar '09

09 Mar '09

Is there a function that yields the minimum value of Int on an implementation? -- Colin Adams Preston Lancashire

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Partial pattern matching
by Peter Verswyvelen 09 Mar '09

09 Mar '09

In Haskell, a data constructor can be used partially applied: data Pair a b = P a b f = P 1 however, I cannot do "partial pattern matching", e.g firstCoord (P x) = x does not work. I guess a very important reason must exist why this is the case?

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Parsing floating point numbers
by Bjorn Buckwalter 09 Mar '09

09 Mar '09

Hi all, What is your preferred method of parsing floating point numbers (from String to Float/Double)? Parsec it seems only does positive floats out of the box and PolyParse requires the float to be on scientific form (exponential). While I've worked around these shortcomings in the past I feel that I am reinventing the wheel as surely I am not the only to run into these limitations. How do you parse your floats? Can you recommend a parsing library that handles them solidly? (For my current needs the formats accepted by "read" are sufficient, but I want reasonable error handling (Maybe or Either) instead of an exception on bad inputs.) Thanks, Bjorn Buckwalter

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Purely Functional Data Structures
by Gü?nther Schmidt 09 Mar '09

09 Mar '09

Hi, is the above mentioned book still *the* authority on the subject? I bought the book, read about 10 pages and then put it back on the shelf. Um. In my app I have to deal with 4 csv files, each between 5 - 10 mb, and some static data. I had put all that data into an Sqlite3 database and used SQL on it. But, as the requirements keep changing the SQL becomes a bit messy. I guess we've all had that experience. So I'm wondering if I will find clues in this book how to do my querying and handling of moderately large data in a more haskellish way and be able to drop the SQL. Your suggestions appreciated. Günther

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How to make a dock window for xmonad using gtk2hs?
by Magicloud Magiclouds 09 Mar '09

09 Mar '09

Hi, I am using gtk2hs to make some sidebar thing for xmonad. Well, after I tried a few ways, I still cannot make it dock like xmobar. It just covered other windows at the edge of the screen. Could someone give me a sample or something I could learn from? Thanks. -- 竹密岂妨流水过山高哪阻野云飞

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STG's? [was: I want to write a compiler]
by Rick R 09 Mar '09

09 Mar '09

Where can I find more information on STGs? Google search doesn't bring up anything too enlightening. My curiosity was piqued by http://www.cs.chalmers.se/~gedell/ssc/index.html. Of course it doesn't indicate how these should be built or the format. On Sun, Mar 8, 2009 at 6:41 PM, Loup Vaillant <loup.vaillant(a)gmail.com>wrote: > Thanks to the courage you all gave me, I found the strength to go on. > > Template instantiation seems to be the easiest path, so I decided to > follow it. I think I solved the problem about primitives and FFI I > though it had. Namely, how the hell do I compile primitive calls with > an arbitrary number of arguments. > > Starting from the Tutorial of Peyton Jones and Lester, I added a new > node type to help guide the order of evaluation. Basically, this "Seq" > node takes the address of two other nodes. It pushes them both on the > stack, like an application node would. (That is because I don't want a > dump, but I could as well create a new stack and and push the previous > one on the dump.) > > Note the nodes which are evaluated this way must not have a functional > head normal form (primitive or supercombinator). That would leak past > the beginning of the stack. > > When the node is finally evaluated (e.g. points to a HNF, like a boxed > integer), the topmost and second topmost pointers on the stack are > swapped. (or the topmost pointer of the stack and the topmost pointer > of the topmost stack on the dump are swapped). > > With a suitable compilation scheme, that should guarantee that > primitives have their arguments already evaluated. (And avoid infinite > loops). > > Now, I just have to implement it. :-) > > Cheers, > Loup. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- We can't solve problems by using the same kind of thinking we used when we created them. - A. Einstein

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