April 2007 - Haskell-Cafe

Getting the number of seconds since epoch from System.Time.ClockTime
by Martin Percossi 01 May '07

01 May '07

Hello haskell-cafe, In System.Time, data ClockTime = TOD Integer Integer , where the first integer represents the number of seconds since epoch, and the other represents the number of picoseconds. Is there a way of retrieving the first part? (In Haskell 98, the ClockTime type is abstract). TIA Martin My music: http://www.youtube.com/profile?user=thetonegrove

3 2

FIT for Haskell
by Philipp Volgger 01 May '07

01 May '07

Who wrote FIT for Haskell on http://darcs.haskell.org/FIT/? Does anybody know if the version is stable?

2 1

Creating pseudo terminals
by Tom Hawkins 30 Apr '07

30 Apr '07

How can I create a pseudo terminal in Linux with Haskell? Nothing is jumping out at me in the standard library. I haven't done this before in any language, so any tips would be appreciated. From what I gather, a call to posix_openpt or openpty returns a master and a slave, or alternatively opening /dev/ptmx followed by calls to grantpt and unlockpt. I'm building a load balancing and sharing system similar to Platform's LSF. The pseudo terminal is for interactive jobs running on a remote machine. Thanks for any help! -Tom

3 3

Type-level programming problem
by Thomas Schilling 30 Apr '07

30 Apr '07

Hi, I have a type class similar to this one. data T class Foo ns a b c | ns -> a, ns -> b, ns -> c where mkFoo :: ns defaultA :: a defaultB :: c -> IO b defaultC :: [T] -> c f :: c -> b -> a -> (b, Int) The idea is, that I define classes of components where the data types of the methods are component-specific. I therefore use a namespace to define the component types (associated types would be nicer, but are not widely supported). Given a few sample instances, I can define a configuration: data X; data XA = XA; data XB = XB; data XC = XC instance Foo X XA XB XC where mkFoo = undefined defaultA = XA defaultB XC = return XB defaultC _ = XC f _ b _ = (b,0) mkX = mkFoo :: X data Y; data YA = YA; data YB = YB; data YC = YC instance Foo Y YA YB YC where mkFoo = undefined defaultA = YA defaultB YC = return YB defaultC _ = YC f _ b _ = (b,1) mkY = mkFoo :: Y config = mkX .*. mkY .*. HNil Using this configuration, I now want to define various functions that work on As, Bs or Cs, respectively. For example, I'd like to have a :: XA :*: XB :*: HNil a = hMap DefaultA config but I fail to figure out how to define DefaultA. I tried with this one: data DefaultA instance Foo ns a b c => Apply DefaultA ns a where apply _ _ = defaultA but I get: Could not deduce (Foo ns1 a b1 c1) from the context (Apply MakeAs ns a, Foo ns a b c) arising from use of `defaultA' at /Users/nominolo/Devel/Haskell/testcase1.hs:126:16-23 Possible fix: add (Foo ns1 a b1 c1) to the class or instance method `apply' In the expression: defaultA In the definition of `apply': apply _ _ = defaultA In the definition for method `apply' I guess I need some type class that also binds b and c. Or maybe I need to do some things completely different at all. Ideally, I'd hope to keep the work for adding new Foo instances as low as possible, though. I attached the relevant parts of the HList implementation and the code. Any suggestions? /Thomas

1 0

RE:Cross-over from Haskell.org [Haskell] Re: Newbie: what are the advantages of Haskell?
by Taillefer, Troy (EXP) 30 Apr '07

30 Apr '07

Udo, I am cross posted/migrated this to Haskell-cafe per Simons request sorry for the late response I don't check this email on weekends I really dislike Perl as a programming language but I have to strongly disagree about your statements about CPAN and the quality of its contents. I have worked professional in Perl (Feel free to feel sorry for me) for over a year and I have always been impressed with what I could find in CPAN. Perl obviously has a niche and is "well supported by its community". Perl is popular so it must have some merit. I don't subscribe to the flawed reasoning that Perl Hackers just don't know any better or that they are dumb, or intellectual inferior in some way. Programmers have very good and valid reason for choosing their tools and I will have words for those who irrational state otherwise especially in a belittling manner I am pro choice. I am going to borrow some Ebonics "Don't language Hate Appreciate" Troy -----Original Message----- From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Udo Stenzel Sent: Saturday, April 28, 2007 7:06 AM To: haskell(a)haskell.org Subject: Re: [Haskell] Re: Newbie: what are the advantages of Haskell? Michael T. Richter wrote: > I wish I knew the language better so I could start working on those > libraries. Which ones? "those libraries" cannot come into existence until someone says what's actually missing. (The bulk of CPAN is crap and is certainly not worth being reimplemented.) -Udo -- "Object-oriented programming is an exceptionally bad idea which could only have originated in California." -- E. W. Dijkstra

1 0

Indexing of content at haskell.org by search engines
by Henning Thielemann 30 Apr '07

30 Apr '07

I have noticed that only parts haskell.org are indexed by Google. E.g. mail archives of Haskell-Cafe and HaskellWiki are not indexed, but cvs.haskell.org, darcs.haskell.org and hackage.haskell.org are.

1 0

Re: [Haskell] Re: Newbie: what are the advantages of Haskell?
by Rafael 30 Apr '07

30 Apr '07

I'll study these ways to debugging Haskell, and in accordance with my final work plan I'll decide the better way to follow.. For the moment i'm studing Haskell things, but in the next times I'll might decide it. A lot of thanks Neil and Simon. On 4/30/07, Simon Marlow <simonmarhaskell(a)gmail.com> wrote: > Rafael wrote: > >> Hi > >> > >> HTTP. We also need better availability of libraries, and a more > >> standard and reliable way to install them and specify their > >> dependencies. We could also do with a good debugger. These are being > >> addressed by the Google Summer of Code project. > > > > Hi Neil, a good debugger ? What is in Google Summer of Code about it ? > > > > I just found it: > > http://hackage.haskell.org/trac/summer-of-code/ticket/6 > > that havent student related. > > > > I was studing about debuging techs for haskell to build a nice > > debugging enviorment in HIDE or some other IDE. It's my bacharelor > > final work. > > We're building some debugging features into GHCi. This started with Pepe > Iborra's Summer of Code project last year, and more recently Bernie Pope > reworked the breakpoint support during his internship here at MSR Cambridge. We > are actively working on polishing what we have for inclusion in the next major > GHC release. > > The GHCi debugger is based on imperative debugging techniques: breakpoints, > single stepping, etc. It's a live debugger rather than post-mortem. We > focussed on accessibilty, rather than functionality: so the debugger is always > on, and it works with everything that you can compile in GHCi. It lacks some of > the advanced debugging features you'll find in Hat, for example, but we hope it > makes up for that by being more broadly accessible. > > More information on the debugger is here: > > http://hackage.haskell.org/trac/ghc/wiki/NewGhciDebugger > > although note that development is ongoing and more features have been added > since the wiki was last updated. > > All the debugging functionality is exposed by the GHC API, so it's certainly > possible to build debugging support into an IDE based on GHC. > > Cheers, > Simon >

1 0

ANN: The Monad.Reader - Issue7
by Wouter Swierstra 30 Apr '07

30 Apr '07

I am pleased to announce that the latest issue of The Monad.Reader is now available: http://www.haskell.org/haskellwiki/The_Monad.Reader Issue 7 consists of the following four articles: * Matthew Naylor A Recipe for controlling Lego using Lava * Yaron Minsky Caml Trading: Experiences in Functional Programming on Wall Street * Duncan Coutts Book Review: “Programming in Haskell” by Graham Hutton * Dimitry Golubovsky, Neil Mitchell, Matthew Naylor Yhc.Core – from Haskell to Core The Monad.Reader is a quarterly magazine about functional programming. It is less-formal than journal, but somehow more enduring than a wiki page or blog post. If you'd like to submit something to the next issue of The Monad.Reader, please get in touch. I haven't fixed the deadline for the next issue just yet; I hope to send out an official call for copy in the coming weeks. Wouter This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

1 0

COM and Haskell
by Justin Bailey 30 Apr '07

30 Apr '07

All, I'm interested in automating Excel using Haskell. I'm writing a little program for my wife and it'd be nice to fill out an Excel spreadsheet for her (with formatting so I don't think CSV will cut it). A bit of Googling didn't turn up anything interesting. Has any work been done on using Excel (or more generally, COM) from Haskell? Thanks for any pointers! Justin p.s. I'm aware of the article "Spreadsheet for Functional Programmers" article and Neil Mitchell's post about HsExcel - but those go the wrong way :(

14 18

PartitionBy (was: Behavior groupBy)
by Hans van Thiel 29 Apr '07

29 Apr '07

Hello All, As usual, my first attempt could be better.. -- partitions a list according to an equivalence relation import Data.List (partition) partitionBy :: (a -> a -> Bool) -> [a] -> [[a]] partitionBy eq [] = [] partitionBy eq ls = x:(partitionBy eq y) where (x,y) = partition ((head ls) `eq`) ls example> partitionBy (\x y -> (last x) == (last y)) ["abc","bd","bdc","abd"] result> [["abc","bdc"],["bd","abd"]] Of course, any crits would be appreciated, but maybe this will save somebody some time.. Thanks, Hans van Thiel

1 0