- Haskell-Cafe - Haskell.org

help me ! who has vty ?
by clisper 19 Sep '07

19 Sep '07

who has vty for haskell? I can't find the right one so who can mail one to me ? thanks 2007-09-19 clisper

2 1

Re: [Haskell] Functor ((,) a)
by Matthew Brecknell 19 Sep '07

19 Sep '07

Janis Voigtlaender: > What do I have to import to get the Functor ((,) a) instance? (redirected to haskell-cafe) Control.Monad.Instances, believe it or not.

1 0

Re: [Haskell] Swapping parameters and type classes
by Simon Marlow 19 Sep '07

19 Sep '07

Ian Lynagh wrote: > On Tue, Sep 18, 2007 at 03:48:06PM +0100, Andrzej Jaworski wrote: >> Responding to Simon Peyton-Jones' reminder that this is a low-bandwidth list I >> was obscure and commited a blunder. >> >> This one and many other threads here are started undoubtedly by experts [sorry >> guys:-)] and coffee brake should work for them, but on numerous occasions >> threads here spawn beginner type questions. So, my thinking was that it is >> perhaps against the tide trying to stop them. >> Why not to make the list Haskell a first contact general practitioner? Then >> creating e.g. "Announcements & Challenge" or "Announcements & ask guru" list >> could take the best from "Haskell" but also would make it less front line and >> thus more elitist, which should imply the manner by itself. > > I proposed renaming > haskell@ -> haskell-announce@ > haskell-cafe@ -> haskell@ > in http://www.haskell.org/pipermail/haskell-cafe/2007-July/028719.html I suggested the same thing at the time we created haskell-cafe, but the concensus was in favour of haskell-cafe. At the time I didn't think it would work - for a long time, the number of subscribers to both lists was almost the same - but now I have to admit I think haskell-cafe is a big win for the community. The -cafe extension gives people the confidence to post any old chatter without fear of being off-topic, and I'm sure this has helped the community to grow. Those of us who grew up with Usenet (RIP) are more at home with the foo/foo-announce split, and it's certainly quite conventional for mailing-list naming too, but on the whole I don't think doing things differently has really done us any harm and it may well have been a stroke of genius :-) Cheers, Simon

3 2

Re: [Haskell-cafe] Missing Symbol
by PR Stanley 19 Sep '07

19 Sep '07

> > Hi > > What symbol would you replace the "?" with: > > the identity function > > id x = x? > >I don't think I'd have anything where the ? symbol is. > >id x = x works just fine. Ah, that's interesting because there's a "." to the right of x in my scanned doc. Still, if no symbol is necessary, so much the better! Cheers, Paul

1 0

Missing Symbol
by PR Stanley 19 Sep '07

19 Sep '07

Hi What symbol would you replace the "?" with: the identity function id x = x? My scanned copy of the Hutton book contains some rather interesting characters. In fact, the OCR program has placed a "." in place of most symbols - e.g. ->, <- ^, <=, \=, etc. Fortunately, I'm able to guess the correct operator in the majority of the cases. Cheers, Paul

1 0

ANN: hstats-0.1
by Marshall Beddoe 19 Sep '07

19 Sep '07

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hstats-0.1 I've just released hstats, a statistical computing module for the Haskell language. Current functionality includes: mean, median, mode, range, standard/average deviation, variance, iqr, kurtosis, skew, covariance, and correlation. I have plans on adding more rank correlation functions, histograms & chi square tests. darcs repo: http://www.sftank.net/code/hstats

1 0

Building "production stable" software in Haskell
by Peter Verswyvelen 18 Sep '07

18 Sep '07

The way I see it as a newcomer, Haskell shifts the typical imperical programming bugs like null pointers and buffer overruns towards "space/time leaks", causing programs that either take exponentially long to complete, stack overflow, or fill up the swap file on disc because they consume gigabytes of memory. Other bugs I found are incomplete pattern matches at runtime, but I already got an email of how to fix this using an external tool, although it would be nice if this is part of the compiler/linker itself. How well and how can a Haskell program be tested to make sure it does not cause these space/time bugs? What tools are typically used? Thanks, Peter

22 49

yi-gtk
by clisper 18 Sep '07

18 Sep '07

who knows how to compile yi-gtk? i tried,but it told me mine miss gtk. 2007-09-18 clisper

2 1

Type-Marking finite/infinte lists?
by Joachim Breitner 18 Sep '07

18 Sep '07

Hi, today while mowing the lawn, I thought how to statically prevent some problems with infinte lists. I was wondering if it is possible to somehow mark a list as one of finite/infinite/unknown and to mark list-processing functions as whether they can handle infinte lists. For example, it is known that a list produced by repeat or cycle is always infinte, that foldl can’t handle infinte lists (while foldr might). length should never be called on an infinte list, and map’s output is infinite iff the input list is. So the compiler might use this information to emit errors like “line 42: program will not terminate: length applied to infinite list” or warnings “line 23: termination not guaranteed: foldl applied to possible infinte list”. I guess you can’t know it for all lists (halting problem...), but for those where it is possible, it would be nice to tell. Or am I missing something? Can this be implemented using some guru type system hacking? Greetings, Joachim -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: joachimbreitner(a)amessage.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

7 9

Re: [Haskell] Blocked STM & GC question
by Jules Bean 18 Sep '07

18 Sep '07

Simon Marlow wrote: > Ashley Yakeley wrote: >> If I have a thread that's blocked on an STM retry or TChan read, and >> none of its TVars are referenced elsewhere, will it get stopped and >> garbage-collected? >> >> I have in mind a pump thread that eternally reads off a TChan and >> pushes the result to some function. If the TChan is forgotten >> elsewhere, will the permanently blocked thread still sit around using >> up some small amount of memory, or will it be reaped by the garbage >> collector? > > In this case, your thread should receive the BlockedIndefinitely exception: > > http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Exceptio… > > > If the system is idle for a certain amount of time (default 0.3s, change > it with the +RTS -I option) a full GC is triggered, which will detect > any threads that are blocked on unreachable objects, and arrange to send > them the BlockedIndefinitely exception. Including MVars? Your quoted text suggests 'Yes' but the docs you link to suggest 'No'. Jules

2 1