October 2008 - Haskell-Cafe

The Haskell type inference feature I'd really like to see
by Dan Piponi 24 Oct '08

24 Oct '08

I'd like to be able to write something like > map zipWith ([1,2,3] >>= printMyInferredType) and have the compiler treat 'printMyInferredType' as undefined, but also produce the side effect of printing out its inferred type. What's the easiest way to simulate this with what we have now? -- Dan

2 1

Re: [Haskell-cafe] Crash!
by Andrew Coppin 24 Oct '08

24 Oct '08

Thomas DuBuisson wrote: > So if you have such a specific portion of the code you think is to > blame, perhaps you could simple comment that out (return () instead of > write the file) and see if it crashes? I understand people avoidance > of brute force guess problem-compile-test cycles, but it seems you > have good evidence supporting this guess. Yeah, I can try different optimisation levels and so forth. I'm actually wondering if my code is writing off the end of an array and this "just happens" to hit some data structure used by GTK+? (In which case, minute changes in linkage, etc., would disturb the bug.) Does anybody know of any tools for definitely pinning down stuff like this? Surely C programmers have their code crash several hundred times a day due to bugs like this... > Also, be sure the thunks are evaluated - if the writing of the file > is what is forcing the evaluation (and thus triggering the condition) > then you need to separate these two cases. That's the fun part about Haskell, eh? ;-) However, in this instance, there's that much explicit mutation in the I/O monad on unboxed (and therefore strict) arrays that I'm pretty sure that isn't the problem. By the time the save-PNG function is called, the data already exists in the address space managed by GTK+. It has to, or GTK+ wouldn't be able to save it. Unless my *pure* code is somehow generating an access violation - which would surely indicate an actual compiler *bug*... (This seems laughably unlikely.)

2 2

universal algebra "support" in Haskell?
by Galchin, Vasili 24 Oct '08

24 Oct '08

Hello, I see that there is a "Monoid" class from Data.Monoid. What other algebras like Group, Ring, etc. have support in Haskell? Thanks, Vasili

5 9

RE: [Haskell] Current XML libraries status
by Mitchell, Neil 24 Oct '08

24 Oct '08

Redirected to haskell-cafe, since that's where all discussions should go (haskell = announcments only) > > Does some one have made performance tests on the different XML > > libraries for Haskell? I have a 20MB xml file that I want > to read. I > > remember from my earlier experiments (years ago) that all libraries > > were too slow and were consuming too much memory. > > For my XML needs, I ended up just using the TagSoup library > to extract the parts I wanted. At least this allows lazy > processing of large files (a typical file is in the 1 to 4 GB range). > > Performance is acceptable, and Neil is rumored to have a plan > to improve it further. I have a plan, I have the pseudo-code, and I have the notes. I currently don't have the time - but hopefully I'll find the time at some point. Thanks Nmeil ============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ==============================================================================

1 0

darcs hacking sprint TOMORROW!
by Eric Kow 24 Oct '08

24 Oct '08

Hi all, Just pointing out that the darcs hacking sprint is taking place tomorrow (Saturday and Sunday 25-26 October)! Our Brighton and Portland venues are still open, so if you are thinking of dropping by, let us know :-) http://wiki.darcs.net/index.html/Sprints Cheers, -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

1 0

distributed systems reading group
by Jason Dusek 24 Oct '08

24 Oct '08

I'm looking for good reading group for distributed systems. I've worked through a number of papers on my own and would like to work out some ideas with other folks who have an interest. I've read a little bit of Lynch, a bit more of Lamport and some of Chandra's work, as well as numerous slides, &c. * The impossibility results are sobering, but always leave a way out -- they make some assumption that one can dispense with in practice (for example, that processes start with different values). * The possibility results generally make untenable assumptions -- for example, that there is no link failure. I appreciate that this is not a matter of direct interest to the list, but I expect to find interested people here. -- _jsn

1 0

Sorry, but I'm in the mood (again)
by Achim Schneider 24 Oct '08

24 Oct '08

http://www.haskell.org/haskellwiki/?title=Special:Categories What are the mathematical properties of those Categories? Do they share common axioms? -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

2 2

Re: universal algebra "support" in Haskell?
by Galchin, Vasili 24 Oct '08

24 Oct '08

Hi Russell and others, Please "cc" me on all responses to my post 'universal algebra "support" in Haskell'. I am interested in algebras and non-algebras like pre-order, post-order, etc. support in Haskell! Thanks, Vasili

1 0

A heretic question
by Achim Schneider 24 Oct '08

24 Oct '08

What kind of things, barring coding on Haskell-less platforms and library interfaces would you choose to do in C++? I'm asking 'cos I'm learning C++ and can't get the proper motivation to do any program I can think of in it: If I need abstraction, I'm thinking Haskell or Scheme, and if I'm thinking performance, C itself more than suffices. Plus template programming makes me shudder because of its atrocities against clear and straightforward FP, but that's a different matter. Coming to think of it, a compiler from a clean syntax to C++ templates sounds like a fun project... which I'd do in Haskell. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

17 30

Linking and unsafePerformIO
by Mauricio 23 Oct '08

23 Oct '08

Hi, If I have a Haskell wrapper (with unsafe...) over a function that's never going to return different values and is always side-effect free, but can change depending on compile time options of its library; my program is running, and then the version of my library is updated by my distribution smart instalation system, which does update versions of libraries in use; is it possible that I get a wrong behavior of my program? I do not understand enough about package management to understand how running programs or libraries are updated, and less about how linking works between Haskelll and libraries on other languages, so I don't know if my program is guaranteed to stay with a single version of a library for each run. (Sure this is a weird situation, but I do like to think about worst cases.) Thanks, Mauríco

13 20