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Question concerning Haskell Foundation
by Vasili I. Galchin 09 May '09

09 May '09

Hello, With Haskell Foundation, 1) Can we still publish packages on Hackage? 2) Is Hackage going away? Regards, Vasili

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Writing a compiler in Hakell
by Rouan van Dalen 09 May '09

09 May '09

Hi everyone. I am designing my own programming language. I would like to know what is the best way to go about writing my compiler in haskell. What are the tools available in haskell that can help with compiler construction? I know about Happy. Is that a good tool to use? The compiler is intended for serious use and I would like it to be very efficient, maybe competing with compilers written in C. It should also be very easy to extend as the languoge grows. Are there any good books that you can recommend on compiler construction in general and specific to haskell? On another note, how is the operator + implemented in haskell? is there a primitve (say #+) that is wrapped by the haskell operator +? Maybe something like: (+) :: a -> a -> a v1 + v2 = #+ v1 v2 Thanks in advance Rouan.

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Can HLint help spot space leaks? (was: Re: [Haskell-cafe] Generating Haskell with associated types (and kind annotations))
by Jason Dagit 09 May '09

09 May '09

On Fri, May 8, 2009 at 8:49 AM, Neil Mitchell <ndmitchell(a)gmail.com> wrote: > > I've used the project extensively in HLint > (http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlint) and > it works fantastically. Hi Neil, A bit off-topic, but your post reminded me: Does HLint currently help the user find space leaks? For example, does it recommend strict folds instead of lazy folds? I looked at the FAQ but this was not listed. I don't really know how feasible this is. Thanks, Jason

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Generating Haskell with associated types (and kind annotations)
by Daniel Peebles 09 May '09

09 May '09

Hi all, I was wondering whether anyone had any suggestions on a good way to generate repetitive code with associated types and kind annotations. I'd like to use TH but as far as I understand, it doesn't support this yet (I think associated types are in HEAD but not kinds), so for now I've been using ruby with string interpolation, which feels rather ugly. It means that I have to edit the ruby script and regenerate the file in question each time I make a change, which doesn't fit in very nicely with cabal (or my patience) and so on. Ideally, I'd have something that I can write mostly like real Haskell (with "holes" to substitute values into), that can be integrated nicely into the cabal build system without using custom external preprocessors or anything like that. Any ideas? Thanks, Dan

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ANNOUNCE: hpc-strobe-0.1: Hpc-generated strobes for a running Haskell program
by Thorkil Naur 08 May '09

08 May '09

I am pleased to announce the initial release of hpc-strobe: Hpc-generated strobes for a running Haskell program. hpc-strobe is a rudimentary library that demonstrates the possibility of using Hpc (Haskell Program Coverage) to inspect the state of a running Haskell program. hpc-strobe-0.1 has been uploaded to hackage: http://hackage.haskell.org/packages/archive/hpc-strobe/0.1/hpc-strobe-0.1.t… In ordinary use of Hpc, a single so-called tix file is produced at the end of a run. The tix file records how many times each expression has been used during the run. This can be used to mark up the source code, identifying expressions that have not been used. hpc-strobe uses the basic machinery provided by Hpc to produce multiple tix files, also called strobes, representing the coverage at different times while the program is running. By subtracting such two tix files, again using Hpc machinery, a tix file representing the expressions used between the times of recording the subtracted tix files is produced. This may be used, for example, to get a better idea of what a long-running program is doing. It could also be used as a profiling tool, getting information about how many times individual expressions are used. A program is included whose strobe differences produce a crude rendering of an analog clock when they are used to mark up the source code using Hpc. Please see the attached example (gunzip the file, point you browser to it, scroll down to view the canvas function). Use of the library involves a simple change of the main function and also requires the program to be enabled for hpc. At the time of writing, this means using a fairly recent version of GHC and compiling the Haskell code with the -fhpc option. For additional details, see the README included in the package. Best regards Thorkil

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Re: [Haskell-cafe] Re: Is Haskell a Good Choice for Web Applications? (ANN: Vocabulink)
by Kalman Noel 08 May '09

08 May '09

Daniel Carrera schrieb: > I think it largely depends on the learner. Some people find vocabulary > easier, or more interesting, others not. I have a hard time learning a > lot of isolated facts (e.g. vocabulary), but I find it easier and more > enjoyable to learn a rule that I can apply many times. But I know people > who are the exact opposite. I wouldn't want to make an absolute rule. Or like a local physics prof likes to put it: “I guess you all have an idea of Ohm's law? Or wait, right, for the medics being with us, here are the three Ohm's laws: U = RI, R = U/I, and I= U/R.” Kalman

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Poking fun at haskell and other programming languages
by Andrew Wagner 08 May '09

08 May '09

http://james-iry.blogspot.com/2009/05/brief-incomplete-and-mostly-wrong.html

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monad . comonad = id
by Jan Christiansen 08 May '09

08 May '09

Hi, I have a question regarding the connection between monads and comonads. I always thought of the comonad operations as being the inverse operations of the corresponding monad functions. As I do not know the underlying theory I thought I simply ask the masters. Is there a formal verification for this intuition? That is, are there always corresponding instances for monad and comonad such that the following laws are satisfied? extract . return == id join . duplicate == id If this is the case I would like to know what the corresponding monad for the following comond could be. This comonad treats lists as pointed sets where the first element is focused. instance Comonad [] where extract = head duplicate xs = init (zipWith (++) (tails xs) (inits xs)) Obviously we can define return x = [x]. But I do not know how to define join. Cheers, Jan

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Curry and Reader monad
by Daryoush Mehrtash 08 May '09

08 May '09

In the Is currying monadic?<http://greenokapi.net/blog/2009/05/07/is-currying-monadic/>post the author says: This is again a nested expression. So I wondered if you could again > "flatten" it with a monadic do block: > > let add3 = do > a <- get first parameter > b <- get second parameter > c <- get third parameter > > > return a+b+c > > OK, so I "know" that functions in Haskell (which uses currying for > functions as a general rule) are the "Reader monad". But I don't understand > it well enough to know if that means you can use Reader to implement the > above... > > (I don't understand Reader at all in fact. I must bang my head against it > again, but I find it very confusing - how the monad is represented, what the > functions are, and how they get magically applied.) > Any idea what he is talking about? Thanks Daryoush

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How difficult would creating a collaborative multi-user online virtual world application be in Haskell?
by Benjamin L.Russell 07 May '09

07 May '09

One question that has been coming up at the back of my mind for the past several weeks has been how difficult would it be to create a collaborative multi-user online virtual world application in Haskell. More specifically, last August, I came across a very interesting application called Croquet (see http://www.opencroquet.org/index.php/Main_Page) which happens to be based on Squeak (see http://www.squeak.org/) a dialect of Smalltalk. Croquet, in turn, provides the basis for Cobalt (see http://www.duke.edu/~julian/Cobalt/Home.html) a "virtual workspace browser and construction toolkit for accessing, creating, and publishing hyperlinked multi-user virtual environments" (according to the home page for that project). What struck me as especially interesting was how Croquet allows multiple users to collaborate together in a multi-user online virtual world in software development and other collaborative projects. As one application, the video clip on the upper-right-hand corner of the above-mentioned Croquet home page illustrates how a user can, by writing code from inside the application, create on-the-fly additional virtual environments, which can then be entered by either the programmer or other programmers. Other applications (shown in other video clips on the "Screenshots/Videos" page (see http://www.opencroquet.org/index.php/Screenshots/Videos) show alternative applications that include text-based annotations, a 3D spreadsheet, and writing a conventional blog from within a virtual world. Unfortunately, Smalltalk is an object-oriented language. If possible, I would like to see something similar in a functional programming language such as Haskell. Does anybody know whether duplicating this project in Haskell would be feasible? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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