May 2009 - Haskell-Cafe

IO trouble
by Xiao-Yong Jin 14 May '09

14 May '09

Hi, I can't really describe it in the subject. So let me try to do it here. I have two functions > f :: a -> b > g :: (a -> b) -> c -> d and I use them as > gf :: c -> d > gf = g f Now I want to handle exceptions in f and redefine f as in f' > f' :: a -> IO (Either e b) So my question is how to define gf' now to use f' instead of f? > gf' :: c -> IO (Either e d) Thanks in advance. Xiao-Yong -- c/* __o/* <\ * (__ */\ <

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hsffig and duplicate typedef declarations
by Dean Herington 14 May '09

14 May '09

I have a large body of C/C++ code at work that I'd like to be able to access from Haskell via FFI. Because the interface to this code is broad, hsffig would seem to be ideal for the task. I've run across one serious hitch, though. The existing #include file graph is complicated and ends up declaring some typedefs multiple times (albeit in consistent ways). While gcc (for example) rejects such practice, the Windows C compiler we're using accepts it. Does anyone know how feasible it would be to get hsffig to accept such practice as well? I've started looking at the hsffig code (and discovered that the C grammar hsffig uses seems to get confused by duplicate typedefs), but thought I'd ask the list in parallel with my further study. Thanks. Dean

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question on the Prelude .. vis-a-vis
by Vasili I. Galchin 14 May '09

14 May '09

Hello, I am seriously punching my way to build Swish via .cabal ... My head is totally to the wall .... punch .. punch ..... Graham Lyle has written some seriously beautiful code .... I am trying to get to adhere to contemporary Haskell namespace convention ..... I still awaiting response from Graham vis-a-vis posting on Hackage ... I strongly think that in bioinformatics and also oil/gas industry(<< I am stuck here everyday ;^)) that Swish is a strong arena of discussion! In any case .. there are some issues: 1) I strongly suspect that in Swish 0.2.1 that some of Graham's libaries are already superseded by the Haskell prelude , e.g. HUnit, Parsec(!!!), his Sort directory/library .. Don ...please 2) Graham wrote a deterministic finite automaton ..... which is giving some grieve namespace-wise ..... please see following Swish/HaskellRDF/Dfa/Dfa.lhs:1:0: Failed to load interface for `Prelude': it is a member of package base, which is hidden vigalchin here is a fragement of Dfa.lhs: > {-# OPTIONS -fglasgow-exts #-} > {-# OPTIONS -fallow-undecidable-instances #-} > module Swish.HaskellRDF.Dfa.Dfa ( > Re(..), > matchRe, > matchRe2 > ) where > {- ???? > import Control.Monad.Identity > import Control.Monad.Reader > import Control.Monad.State > import Data.FiniteMap > import List > import Data.Array > -} import IOExts The type of a regular expression. > data Re t "Dfa.lhs" 609 lines, 18871 characters Very kind regards, Vasili

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ANN: Bookshelf
by Emil Axelsson 14 May '09

14 May '09

This is the first release of Bookshelf, a simple document organizer with some wiki functionality. Documents in a directory tree are displayed as a set of HTML pages. Documents in Markdown format are converted to HTML automatically using Pandoc. The manual http://www.cs.chalmers.se/~emax/bookshelf/Manual.shelf.html describes the full functionality. Bookshelf is available on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Bookshelf or through its Darcs repository: http://www.cs.chalmers.se/~emax/darcs/Bookshelf/ I'm not aware of any bugs. I hope it works on Windows, but I haven't tested. Cheers, / Emil

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forall vs "=>"
by Daryoush Mehrtash 13 May '09

13 May '09

What is the difference between forall as in: runST<http://www.haskell.org/ghc/docs/6.10-latest/html/libraries/base/Control-Mon…>:: ( forall s. ST<http://www.haskell.org/ghc/docs/6.10-latest/html/libraries/base/Control-Mon…>s a) -> a and the "=>" as in evalStateT<http://www.haskell.org/ghc/docs/6.6/html/libraries/mtl/Control-Monad-State.…>:: Monad<http://www.haskell.org/ghc/docs/6.6/html/libraries/base/Control-Monad.html#…>m => StateT<http://www.haskell.org/ghc/docs/6.6/html/libraries/mtl/Control-Monad-State.…>s m a -> s -> m a thanks daryoush

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ANN: priority-sync-0.1.0.1: Cooperative task prioritization.
by Christopher Lane Hinson 13 May '09

13 May '09

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/priority-sync $ cabal install priority-sync git clone http://www.downstairspeople.org/git/priority-sync.git Feedback will be greatly appreciated. This package is a spin-off from my work on roguestar, where I need to do significant background processing while retaining enough resources to perform smooth animation. The following is the front-page documentation for the package. In a simple use case, we want to run some expensive tasks in prioritized order, so that only one task is running on each CPU (or hardware thread) at any time. For this simple case, four operations are needed: simpleTaskPool, schedule, claim, and startQueue. let expensiveTask = threadDelay 1000000 pool <- simpleTaskPool forkIO $ claim Acquire (schedule pool 1) $ putStrLn "Task 1 started . . ." >> expensiveTask >> putStrLn "Task 1 completed." forkIO $ claim Acquire (schedule pool 3) $ putStrLn "Task 3 started . . ." >> expensiveTask >> putStrLn "Task 3 completed." forkIO $ claim Acquire (schedule pool 2) $ putStrLn "Task 2 started . . ." >> expensiveTask >> putStrLn "Task 2 completed." threadDelay 100000 -- contrive to wait for all tasks to become enqueued putStrLn "Starting pool: " startQueue pool threadDelay 4000000 -- contrive to wait for all tasks to become dequeued A TaskPool combines Rooms and Queues in an efficient easy-to-use-interface. Rooms provide fully reentrant synchronization to any number of threads based on arbitrary resource constraints. For example, the Room from a simpleTaskPool is constrained by GHC.numCapabilities. Queues provide task prioritization. A Queue systematically examines (to a configurable depth) all waiting threads with their priorities and resource constraints and wakes the most eagerly prioritized thread whose constraints can be satisfied. TaskPools are not thread pools. The concept is similar to IO Completion Ports. There are no worker threads. If a number of threads are waiting, the thread that is most likely to be processed next is woken and temporarily serves as a working thread. Rooms, Queues, and TaskPools are backed by carefully written STM (software transactional memory) transactions. A salient feature is that, because any thread can participate, a TaskPool supports both bound threads and threads created with forkOnIO. Friendly, --Lane

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List of exports of a module - are there alternatives?
by Maurício 13 May '09

13 May '09

Hi, When we want to list which declarations are exported by a module we do: module Mod ( list of exports ) where ... Are there propositions to alternatives to that (I could not find one)? Like, say, add a "do export" or "do not export" tag to declarations we want to (not) export? (I think something like that could be nice when we have modules with 200 declarations and just a few are (not) going to be exported.) Thanks, Maurício

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Fundep Curiosity
by Christopher Lane Hinson 13 May '09

13 May '09

I've noticed that a large majority of fundeps I see in other people's libraries are written: class C a b | b -> a Where the dependent parameter appears first in the MPTC. Is there a reason for this? AFAIK, there isn't any semantic significance to the order of parameters in an MPTC. Why do many haskellers find this configuration more intuitive? Friendly, --Lane

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Data.Map.Map Pattern Matching
by Nico Rolle 13 May '09

13 May '09

Hi I tried this but it diddn't work in ghci: import qualified Data.Map as Map test :: Map.Map [Int] [[Int]] -> Bool test (fromList[((i:is), (j:js))]) = [i] == j i get the : "Parse error in pattern Failed." error. regards

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Re: [Haskell-cafe] caml build
by Vasili I. Galchin 13 May '09

13 May '09

oops ... yes. On Wed, May 13, 2009 at 11:29 AM, Nicolas Pouillard < nicolas.pouillard(a)gmail.com> wrote: > Excerpts from Vasili I. Galchin's message of Wed May 13 18:21:55 +0200 > 2009: > > Hello, > > > > I did a "cabal build -?" and discovered -v/--version. > > So **caml** build was a typo right ? > > > > > Vasili > > > > On Wed, May 13, 2009 at 2:42 AM, Nicolas Pouillard < > > nicolas.pouillard(a)gmail.com> wrote: > > > > > Excerpts from Vasili I. Galchin's message of Tue May 12 23:23:51 +0200 > > > 2009: > > > > Hi Nicolas, > > > > > > > > I am starting a "caml build". I want line by line which module > is > > > > being built so when I get an error I have a context to reason about > to > > > fix > > > > the problem. Got it? > > > > > > Maybe you mean "cabal build" ? > > > > > > > On Tue, May 12, 2009 at 7:23 AM, Nicolas Pouillard < > > > > nicolas.pouillard(a)gmail.com> wrote: > > > > > > > > > Excerpts from Vasili I. Galchin's message of Tue May 12 00:27:26 > +0200 > > > > > 2009: > > > > > > Hello, > > > > > > > > > > > > I have forgotten whether I sent this posting out. Sorry if > I > > > did (I > > > > > > didn't see on Haskell cafe archive). > > > > > > > > > > > > I am building Swish and getting an error. I want to follow > the > > > > > > progress of "swish build" ... I don't see an additional parameter > > > like > > > > > > verbose mode that will tell which swish component is being built. > ??? > > > > > > > > > > I don't get the relation with the subject of your post, can you > > > elaborate? > > > > > > > > > > Best regards, > > > > > > > > > > -- > > > > > Nicolas Pouillard > > > > > > > > > > > -- > > > Nicolas Pouillard > > > > > -- > Nicolas Pouillard >

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