September 2008 - Haskell-Cafe

Unicode and Haskell
by Mattias Bengtsson 09 Sep '08

09 Sep '08

Today i wrote some sample code after a Logic lecture at my university. The idea is to represent the AST of propositional logic as an ADT with some convenience functions (like read-/show instances) and then later perhaps try to make some automatic transformations on the AST. After construction of the Show instances i found the output a bit boring and thought that some Unicode math symbols would spice things up. What happens can be seen in the attached picture (only 3k, that's ok right?). My terminal supports UTF-8 (when i do cat Logic.hs i can see the unicode symbols properly). What might be the problem? regards Mattias

2 3

haskell core definition
by Vlad Skvortsov 09 Sep '08

09 Sep '08

Hi, I'm trying to profile my haskell code (see thread "profiling in haskell") and to get more insight I made GHC produce the haskell Core code. However, I'm not quite sure how to interpret it, is there a definition (quick search didn't reveal one)? Also, how do I demangle the names? It seems that, for example, 'base:GHC.Base.ZC' is a (:) function on strings, but where how am I supposed to figure that out? Thanks! -- Vlad Skvortsov, vss(a)73rus.com, http://vss.73rus.com

5 4

Hackage -> MacPorts?
by John MacFarlane 09 Sep '08

09 Sep '08

It would be great if there were an automated or semi-automated way of generating a MacPorts Portfile from a HackageDB package, along the lines of dons' cabal2arch. Has anyone been working on such a thing? And, are any haskell-cafe readers MacPorts committers? John

8 14

packages and QuickCheck
by Conal Elliott 09 Sep '08

09 Sep '08

How do folks like to package up QuickCheck tests for their libraries? In the main library? As a separate repo & package? Same repo & separate package? Keeping tests with the tested code allows testing of non-exported functionality, but can add quite a lot of clutter. My current leaning is to split a package "foo" into packages "foo" and "foo-test", but first I'd like to hear about others' experiences, insights, and preferences. Thanks, - Conal

2 2

haskell job offer.
by Lionel Barret De Nazaris 09 Sep '08

09 Sep '08

We (Gamr7, see at the bottom) are looking from a senior dev/Technical director. We don't really care about the title but we want someone good (who doesn't ?). We need someone able to model *and* code well (No architect who never codes). The ability to communicate well with a team is also a big plus. You don't need to speak French (we are in France) but a reasonably good English is mandatory. If You : • like coding 4+ hours straight. • like to solve a coding problem elegantly (and are bothered if can't) • like and read *real* CS books (SICP, EGB, TAOCP, etc...) • code in Haskell, python and c++. • are a gamer (this one is optional) • are interested in computer graphics (optional too) You fit the bill. We would like to talk to you. Contact us (contact at gamr7 dot com). What we offer: • interesting problems and creative freedom • quality of life (no overtime, sunny countryside, French food and low rent) • a pay in Euros • comfortable workplace, etc... • coding in Haskell, python. The boss *really * codes . He likes Haskell, Python, Reddit, and wants the team to be there for the long run (i.e happy). He also modestly wrote and posted this jobs offer. About : Gamr7 is a startup focused on procedural city generation for the game and simulation market. We are located in France, near Lyon. -- Best Regards, lionel Barret de Nazaris, Gamr7 Founder & CTO ========================= Gamr7 : Cities for Games http://www.gamr7.com

2 3

Re: [Haskell-cafe] Can you do everything without shared-memory concurrency?
by Richard A. O'Keefe 09 Sep '08

09 Sep '08

On 9 Sep 2008, at 8:15 am, Kyle Consalus wrote: > Anyway, for the time being I believe there are operations that can be > done with shared memory > that can't be done with message passing if we make "good performance" > a requirement. One of our people here has been working on Distributed Shared Memory for some years. It's a programming model where you write AS IF you had shared memory, but you really don't. He actually uses plain C with a library, but I've got a student project to wrap some syntax around that. typedef struct Foo { ... variables ... } Foo; typedef struct Bar { ... variables ... } Bar; shared Foo foo; shared Bar bar; shared (const *f = &foo) { ... here we have read access to f->variables ... } shared (*b = &bar) { ... here we have read-write access to b->variables ... } Underneath, it's message passing. When you get a view on a shared region, a copy is fetched from the cheapest source that has a current copy. When you release a write view, you become the holder of the only current copy. Compressed differences are sent around the local net. Zhiyi Huang's library is called VODCA. There's a plug-compatible version developed by his colleagues in China called Maotai, so the _same_ code can be run on a multicore system or on a network of workstations. The trick is to choose the chunk size of your problem so that computation and communication costs are in the right balance. This certainly seems to be adequate for numerical software, raytracing, game playing, ... One issue is that real shared memory comes at a price that most people don't know they are paying. We wouldn't need MOESI protocols or the related bus traffic if there were known to be no sharing, and one of the things that gets in the way of massive multicore is keeping caches coherent. No shared memory => no coherence problem => no extra bus traffic => faster. -- If stupidity were a crime, who'd 'scape hanging?

1 0

Re: [Haskell-cafe] Can you do everything without shared-memory concurrency?
by Richard A. O'Keefe 09 Sep '08

09 Sep '08

I think the demonstration is in Hoare's book on co-operating sequential processes, but if you have pure processes and message passing, you can simulate conventional variables. Here's an Erlang version: variable_loop(State) -> receive {ask,Sender} -> Sender!{self(),State}, variable_loop(State) ; {tell,New_State} -> variable_loop(New_State) end. new_variable(Initial_State) -> spawn(fun () -> variable_loop(Initial_State) end). fetch(Variable) -> Variable!{ask,self()}, receive {Variable,State} -> State end. store(Variable, New_State) -> Variable!{tell,New_State}. new_array(Size, Initial_State) -> list_to_tuple([new_variable(Initial_State) || Dummy <- lists:seq(1, Size)]). fetch(Array, Index) -> fetch(element(Index, Array)). store(Array, Index, New_State) -> store(element(Index, Array), New_State). The simulation of (shared) mutable variables and arrays in pure CSP is very similar. This pretty much _has_ to be possible in any language that has concurrent processes that can communicate in some fashion. There are also quite elementary ways to simulate locking. So we can solve any concurrent problem that, say, C++ with Intel's TBB library, or Java with java.util.concurrent, or any other such language can solve. We can even get ourselves just as far into extremely serious trouble as we can using those languages, it's just that we don't _have_ to. -- If stupidity were a crime, who'd 'scape hanging?

1 0

Re: building unix package on windows
by David Hotham 08 Sep '08

08 Sep '08

But the unix package isn't actually required to build HAppS on Windows. If you remove the dependency from the .cabal file (and also remove the -DUNIX build option) then you'll be fine.

1 0

monadic map on a Data.IntMap
by minh thu 08 Sep '08

08 Sep '08

Hi, Is there something like a fmapM_ ? In particular, I'd like to mapM_ a Data.IntMap instead of a List Thank you, Thu

4 4

Re: [Haskell-cafe] HXT from schema to data model
by Uwe Schmidt 08 Sep '08

08 Sep '08

Hello Pierre-Edouard, > Is there a way to generate a data model and a set of picklers from an XML (or > RelaxNG) Schema using the HXT tool box? the generation of a DTD out of the picklers is in an experimental stage. The generation of a RelaxNG Schema is technically possible, but it's an open project. It's on our TODO list for HXT. Validation with RelaxNG within HXT is complete. What is missinig is a complete datatype library for XML Schema Datatypes. The still missing part of the W3C XML Schema datatype library are the datatypes for date and time, all others are implemented. Cheers, Uwe -- Uwe Schmidt FH Wedel http://www.fh-wedel.de/~si/

1 0