- Haskell-Cafe - Haskell.org

the trivial monad- thoughts and a question
by Brian Hurt 13 Jan '08

13 Jan '08

So, I've been playing around with what I call the trivial monad: module TrivialMonad where data TrivialMonad a = M a recover :: TrivialMonad a -> a recover (M x) = x instance Monad TrivialMonad where (M x) >>= f = f x (M x) >> f = f return x = M x fail s = undefined This is actually a surprisingly usefull little sucker- it allows you to "demonadify" code. Which is usefull when you have some places where you want to use the code within a monad, and some places where you don't. You write the base bit of code monadically, and then demonadify it as needed. The first question I have is it is possible to implement this guy without wrapping the value in a constructor? What I'd like to do is replace the: data TrivialMonad a = M a with something like: type TrivialMonad a = a and then be able to junk the recover function. The second question I have is: is there any hope of getting something like this into the standard library? Thanks, Brian

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ANN: Haskell Cryptographic Library 4.1.0
by Dominic Steinitz 12 Jan '08

12 Jan '08

I'd like to announce the release of a new version of the library following various contributions (contributors are bcc'd). Additions include: BubbleBabble, TEA, HMAC and more large word support. It no longer includes Base64. This is provided by http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dataenc-0.10.1. Many thanks to all contributors. Dominic. PS I always mention this but the library really needs to be reviewed holistically and possibly restructured given the advent of bytestrings. If anyone would like to volunteer to do this or take over as library maintainer, please let me know.

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Gtk2HS and GHC 6.8.2
by Peter Verswyvelen 12 Jan '08

12 Jan '08

It seems GHC 6.8.2 fixes a couple of bugs in GHC 6.8.1. Gtk2HS does not yet detect my GHC 6.8.2 installation, but I guess it is 100% compatible. Is it possible to get the Gtk2HS installer detect GHC 6.8.2? I'm on Windows. Thanks, Peter

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Linq (FP in C#)
by Hugh Perkins 12 Jan '08

12 Jan '08

Linq went live in C# in November, as part of .Net 3.5. It adds lots of FP-things to C#. It's really fun to be able to use Haskell-ish things in C#. Manipulating lists and collections just got *much* easier. Things it does: - map, fold, filter are all there (they're called "select", "agregate", "where") - limited support for laziness (since .Net 2.0; you can write a lazy "zip" function; I couldnt figure out how to write a lazy "unzip" function) - you can extend the methods available on all lists and collections - lambda expressions - type inferrence (technically, this is part of .Net 3.x, rather than specific to Linq). Things it doesnt do: - recursion doesnt seem particularly optimized (quick 2 minute test, I could be wrong) - no way to enforce purity It's an interesting vindication of the ideas in Haskell that C#, a big mainstream language, has integrated ideas from it, and that they're in production today.

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Typo in ByteString documentation
by Johan Tibell 12 Jan '08

12 Jan '08

In Data.ByteString.Unsafe in the documentation of unsafePackAddress the documentation reads: "Use unsafePackAddress if you know the length of the string statically." I assume that unsafePackAddressLen is the being function referred to here. If I was sitting in front of my laptop I would send you a patch. :) -- Johan

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where is the FFI glue code for STM?
by Galchin Vasili 12 Jan '08

12 Jan '08

Hello, I see where the top level code (written in Haskell)for STM. I have found STM.c;however, I can't seem to find the FFI glue code.? Thanks, Vasili

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Not to load Prelude
by Maurício 11 Jan '08

11 Jan '08

Hi, Is it possible not to load Prelude module when compiling a Haskell module? Or instruct ghc to “unload” it? Thanks, Maurício

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Next PDXFunc Meeting (Portland/Oregon FP Group): Monday, January 14, 7pm, CubeSpace
by Don Stewart 11 Jan '08

11 Jan '08

Join us at the next meeting of pdxfunc, the Portland Functional Programming Study Group, on Monday, 14th January, at CubeSpace. ------------------------------------------------------------------------ We'll have presentations, demos and discussions. We welcome programmers interested in all functional languages and our meetings have content for coders of all skill levels. If interested, please also subscribe to our mailing list at http://groups.google.com/group/pdxfunc PRESENTATIONS (1) Justin Bailey: Exploring Haskell's space and time profiling tools A presentation on the space and time profiling tools available for GHC Haskell, featuring slides and interactive demos. Heap profiling tools and methods will be discussed, along with a demonstration of how to use them to detect a space leak. Time profiling tactics will be covered using "cost-centre" annotations to help select candidates for optimization. Recommendations will be given on how to read the "Core" language with an eye for optimization. Justin Bailey (jgbailey(a)gmail.com) has been programming professionally for 12 years, and is currently a Computer Science master's student at Portland State University. Until 2006, he coded exclusively with object-oriented languages like Java and C#, but then discovered Haskell and hasn't looked back. He's released a Haskell library for building command-line applications called HCL, made contributions to several other Haskell libraries, and continues to hack Haskell every day he can. (2) Iavor Diatchki: Writing parsing combinators with Haskell A presentation on parsing combinators, given as a hands-on demonstration for developing a small library to parse JSON data using Haskell. The entire process will be shown from scratch, starting with defining the concept of JSON values, using pretty-printer combinators to turn values into strings, and finally using parser combinators to turn strings into values. Iavor S. Diatchki is an engineer at Galois Inc., where he uses functional programming for the development of high assurance software. Iavor obtained his PhD degree in 2007. His research focused on various aspect of using functional languages for the development of low-level systems software such as OS kernels.

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Field updates in a state monad
by Michael Roth 11 Jan '08

11 Jan '08

Hello list, still playing with monads and states, I have the following question: Given: import Control.Monad.State.Lazy data MyData = MyData { content :: String } foobar :: State MyData String foobar = do gets content Ok, that looks nice and tidy. But: foobar2 :: State MyData () foobar2 = do modify $ \x -> x { content = "hello haskell"} ...looks not so nice. Exists there a way to write this cleaner without writing countless "set_xyz" helper functions? Michael

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Re: [Haskell-cafe] Re: Why purely in haskell?
by Miguel Mitrofanov 11 Jan '08

11 Jan '08

> However, the fact that (0 / 0) == (0 / 0) yields False is quite shocking. Just for the record: the following is from Firebug (JavaScript debugger for Firefox) session: >>> a = 0/0 NaN >>> a == a false >>> a === a false

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