[Haskell-cafe] Function decoration pattern on wiki

2013-01-20 Thread Derek Elkins
I created the following page on the wiki to capture one pattern that occurs often in Edward Kmett's lens library. http://www.haskell.org/haskellwiki/Function_decoration_pattern Feel free to rename it or add comments, examples, clarifications, additional notes or extensions to the technique.

Re: [Haskell-cafe] [Haskell] ANNOUNCE: set-monad

2012-06-21 Thread Derek Elkins
that even -standard- types fail to satisfy even the laws that you perhaps can interpret the Haskell Report as requiring. There have been violations of type safety due to assuming instances satisfied laws that they didn't. On 20 June 2012 04:03, Derek Elkins derek.a.elk...@gmail.com wrote

Re: [Haskell-cafe] [Haskell] ANNOUNCE: set-monad

2012-06-19 Thread Derek Elkins
Un-top-posted. See below. On 19 June 2012 02:21, Derek Elkins derek.a.elk...@gmail.com wrote: On Jun 18, 2012 4:54 PM, George Giorgidze giorgi...@gmail.com wrote: Hi Derek, On 16 June 2012 21:53, Derek Elkins derek.a.elk...@gmail.com wrote: The law that ends up failing is toList

Re: [Haskell] ANNOUNCE: set-monad

2012-06-16 Thread Derek Elkins
On Sat, Jun 16, 2012 at 3:47 AM, Dan Burton danburton.em...@gmail.com wrote: Convenience aside, doesn't the functor instance conceptually violate some sort of law? fmap (const 1) someSet The entire shape of the set changes. fmap (g . h) = fmap g . fmap h This law wouldn't hold given

Re: [Haskell-cafe] Reference for technique wanted

2010-10-31 Thread Derek Elkins
Well, you can get A Novel Representation of Lists and Its Application to the Function 'Reverse' by John Hughes online published in 1986 which is referenced by Wadler's 1987 The Concatenate Vanishes and references Richard Bird's 1984 paper Transformational programming and the paragraph problem

Re: [Haskell-cafe] Reference for technique wanted

2010-10-31 Thread Derek Elkins
On Sun, Oct 31, 2010 at 7:27 PM, Richard O'Keefe o...@cs.otago.ac.nz wrote: On 1/11/2010, at 12:05 PM, Gregory Collins wrote: They're called difference lists: As a matter of fact the original context was precisely difference lists in logic programming.

Re: [Haskell-cafe] Reference for technique wanted

2010-10-31 Thread Derek Elkins
On Sun, Oct 31, 2010 at 9:02 PM, wren ng thornton w...@freegeek.org wrote: On 10/31/10 7:10 PM, Derek Elkins wrote: Well, you can get A Novel Representation of Lists and Its Application to the Function 'Reverse' by John Hughes online published in 1986 which is referenced by Wadler's 1987

Re: [Haskell-cafe] Proving stuff about IORefs

2010-10-17 Thread Derek Elkins
On Sun, Oct 17, 2010 at 6:49 AM, Miguel Mitrofanov miguelim...@yandex.ru wrote: On 17 Oct 2010, at 05:21, Ben Franksen wrote: I want to prove that  f r == do    s1 - readIORef r    r' - newIORef s1    x - f r'    s3 - readIORef r'    writeIORef r s3    return x That is not true.

Re: [Haskell-cafe] Proving stuff about IORefs

2010-10-16 Thread Derek Elkins
On Sat, Oct 16, 2010 at 9:21 PM, Ben Franksen ben.frank...@online.de wrote: I have a formal proof where I am stuck at a certain point. Suppose we have a function  f :: IORef a - IO b I want to prove that  f r == do    s1 - readIORef r    r' - newIORef s1    x - f r'    s3 - readIORef

Re: [Haskell-cafe] Re: Eta-expansion destroys memoization?

2010-10-12 Thread Derek Elkins
On Tue, Oct 12, 2010 at 4:34 AM, Bertram Felgenhauer bertram.felgenha...@googlemail.com wrote: Simon Marlow wrote: Interesting.  You're absolutely right, GHC doesn't respect the report, on something as basic as sections!  The translation we use is   (e op)  ==  (op) e once upon a time,

Re: [Haskell-cafe] Eta-expansion destroys memoization?

2010-10-07 Thread Derek Elkins
On Thu, Oct 7, 2010 at 8:44 AM, Luke Palmer lrpal...@gmail.com wrote: On Thu, Oct 7, 2010 at 6:17 AM, Brent Yorgey byor...@seas.upenn.edu wrote: The source code seems to be easy to read, but I don't think I understand that. For me I think if I change the first line from fib = ((map fib' [0

[Haskell-cafe] Fwd: Bug in Parsec.Token

2010-08-02 Thread Derek Elkins
This is a forward of a message from March 4th. -- Forwarded message -- From: Derek Elkins derek.a.elk...@gmail.com Date: Thu, Mar 4, 2010 at 9:43 PM Subject: Re: Bug in Parsec.Token To: Don Stewart d...@galois.com Cc: Greg Fitzgerald gari...@gmail.com, Antoine Latter aslat

Re: [Haskell-cafe] Expression dye

2010-07-14 Thread Derek Elkins
http://hackage.haskell.org/package/simple-reflect This is what is used in lambdabot. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Using the ContT monads for early exits of IO ?

2010-06-10 Thread Derek Elkins
Or... one could just use the exceptions that are already built into the IO monad... 2010/6/10 Yitzchak Gale g...@sefer.org: Lennart Augustsson wrote: I would not use the continuation monad just for early exit.  Sounds like the error monad to me. I.e., the Either/ErrorT monad. But the

Re: [Haskell-cafe] Clean proof -- correction

2010-05-23 Thread Derek Elkins
On Sun, May 23, 2010 at 11:38 AM, Daniel Fischer daniel.is.fisc...@web.de wrote: On Sunday 23 May 2010 18:24:50, R J wrote: Correction:  the theorem is     h . either (f, g) = either (h . f, h . g) Still not entirely true, const True . either (undefined, undefined) $ undefined = True

Re: [Haskell-cafe] Mechanics of type-level proxies through branding?

2010-05-22 Thread Derek Elkins
On Sat, May 22, 2010 at 8:36 PM, Dave Neuer dave.ne...@pobox.com wrote: Hi. I'm a Haskell newbie, and I've been reading Oleg's work about lightweight dependent types in Haskell, and I've been trying to figure out if I understand how branding works (warning bells already, I know). At

Re: [Haskell-cafe] Speed of Error handling with Continuations vs. Eithers

2010-05-15 Thread Derek Elkins
On Sat, May 15, 2010 at 2:28 PM, Max Cantor mxcan...@gmail.com wrote: Where is my bind statement doing a case analysis? Isn't it just propagating, in a sense, the case analysis that came from values coming into the monad via return or via throwError? What you did was reimplement the Either

Re: [Haskell-cafe] Speed of Error handling with Continuations vs. Eithers

2010-05-15 Thread Derek Elkins
On Sat, May 15, 2010 at 9:20 PM, Antoine Latter aslat...@gmail.com wrote: On Fri, May 14, 2010 at 4:25 PM, Derek Elkins derek.a.elk...@gmail.com wrote: You did it wrong.  All you did was Church encode the Either type. Your bind is still doing a case-analysis.  All you have to do is use ContT

Re: [Haskell-cafe] Speed of Error handling with Continuations vs. Eithers

2010-05-14 Thread Derek Elkins
You did it wrong. All you did was Church encode the Either type. Your bind is still doing a case-analysis. All you have to do is use ContT r (Either e). The bind implementation for ContT is completely independent of the underlying monad. It doesn't even require the m in ContT r m to be a

Re: [Haskell-cafe] Speed of Error handling with Continuations vs. Eithers

2010-05-14 Thread Derek Elkins
On Fri, May 14, 2010 at 4:53 PM, Antoine Latter aslat...@gmail.com wrote: On Fri, May 14, 2010 at 4:25 PM, Derek Elkins derek.a.elk...@gmail.com wrote: You did it wrong.  All you did was Church encode the Either type. Your bind is still doing a case-analysis.  All you have to do is use ContT

Re: [Haskell-cafe] Why is TChan GHC specific?

2010-05-13 Thread Derek Elkins
On Thu, May 13, 2010 at 10:49 AM, Edward Amsden eca7...@cs.rit.edu wrote: On Wed, May 12, 2010 at 3:29 PM, Peter Robinson thaldy...@gmail.com wrote: As far as I know, TChan needs the 'retry' combinator which requires GHC's RTS. Same is true for TMVar, I think. (sorry for the doubling peter,

Re: [Haskell-cafe] Domains and Co-Domains

2010-03-29 Thread Derek Elkins
2010/3/29 Günther Schmidt gue.schm...@web.de: Hi, I can easily see how one identifies the domain and co-domain of a unary function. How would the domain of a function be expressed that takes more than one argument and arguments of different type? All functions in Haskell are unary.

[Haskell] ANNOUNCE: Parsec 3.1.0

2010-03-03 Thread Derek Elkins
Parsec is a monadic combinator library that is well-documented, simple to use, and produces good error messages. Parsec is not inherently lazy/incremental and is not well-suited to handling large quantities of simply formatted data. Parsec 3 adds to Parsec the ability to use Parsec as a monad

[Haskell-cafe] ANNOUNCE: Parsec 3.1.0

2010-03-03 Thread Derek Elkins
Parsec is a monadic combinator library that is well-documented, simple to use, and produces good error messages. Parsec is not inherently lazy/incremental and is not well-suited to handling large quantities of simply formatted data. Parsec 3 adds to Parsec the ability to use Parsec as a monad

Re: [Haskell-cafe] Re: Real-time garbage collection for Haskell

2010-02-28 Thread Derek Elkins
On Sun, Feb 28, 2010 at 10:03 AM, Heinrich Apfelmus apfel...@quantentunnel.de wrote: Luke Palmer wrote: I have seen some proposals around here for SoC projects and other things to try to improve the latency of GHC's garbage collector.  I'm currently developing a game in Haskell, and even 100ms

Re: [Haskell-cafe] Naive booleans and numbers - type-checking fails

2010-01-24 Thread Derek Elkins
On Sun, Jan 24, 2010 at 3:12 PM, Stephen Tetley stephen.tet...@gmail.com wrote: Doesn't the simply typed lambda calculus introduce if-then-else as a primitive precisely so that it can be typed? Its not an illuminating answer to your question and I'd welcome clarification for my own

Re: [Haskell-cafe] Re: could we get a Data instance for Data.Text.Text?

2010-01-23 Thread Derek Elkins
On Sat, Jan 23, 2010 at 4:57 PM, Jeremy Shaw jer...@n-heptane.com wrote:  On Sat, Jan 23, 2010 at 7:57 AM, Neil Mitchell ndmitch...@gmail.com wrote: No, that's definitely not correct, or even remotely scalable as we increase the number of abstract types in disparate packages. Yes..

Re: [Haskell-cafe] Re: Why no merge and listDiff?

2010-01-22 Thread Derek Elkins
On Wed, Jan 20, 2010 at 9:42 AM, Will Ness will_...@yahoo.com wrote: Derek Elkins derek.a.elkins at gmail.com writes: On Sun, Jan 17, 2010 at 2:22 PM, Will Ness will_n48 at yahoo.com wrote: Hello cafe, I wonder, if we have List.insert and List.union, why no List.merge (:: Ord

Re: [Haskell-cafe] Why no merge and listDiff?

2010-01-17 Thread Derek Elkins
On Sun, Jan 17, 2010 at 2:22 PM, Will Ness will_...@yahoo.com wrote: Hello cafe, I wonder, if we have List.insert and List.union, why no List.merge (:: Ord a = [a] - [a] - [a]) and no List.minus ? These seem to be pretty general operations. Presumably by List.minus you mean the (\\)

Re: [Haskell-cafe] lawless instances of Functor

2010-01-04 Thread Derek Elkins
On Tue, Jan 5, 2010 at 7:49 AM, Steffen Schuldenzucker sschuldenzuc...@uni-bonn.de wrote: Hi Paul, Paul Brauner wrote: Hi, I'm trying to get a deep feeling of Functors (and then pointed Functors, Applicative Functors, etc.). To this end, I try to find lawless instances of Functor that

Re: [Haskell-cafe] lawless instances of Functor

2010-01-04 Thread Derek Elkins
On Tue, Jan 5, 2010 at 7:14 AM, Paul Brauner paul.brau...@loria.fr wrote: Hi, I'm trying to get a deep feeling of Functors (and then pointed Functors, Applicative Functors, etc.). To this end, I try to find lawless instances of Functor that satisfy one law but not the other. I've found one

Re: [Haskell-cafe] Re: Re: Data.Ring -- Pre-announce

2010-01-04 Thread Derek Elkins
On Tue, Jan 5, 2010 at 5:13 AM, Maciej Piechotka uzytkown...@gmail.com wrote: On Mon, 2010-01-04 at 07:17 -0700, Luke Palmer wrote: On Mon, Jan 4, 2010 at 6:51 AM, Maciej Piechotka uzytkown...@gmail.com wrote: About comonad - not exactly as every comonad is copointed and the only possible

Re: [Haskell-cafe] lawless instances of Functor

2010-01-04 Thread Derek Elkins
On Tue, Jan 5, 2010 at 8:15 AM, Dan Piponi dpip...@gmail.com wrote: On Mon, Jan 4, 2010 at 3:01 PM, Derek Elkins derek.a.elk...@gmail.com wrote: Ignoring bottoms the free theorem for fmap can be written: If h . p = q . g then fmap h . fmap p = fmap q . fmap g When I play with http

Re: [Haskell-cafe] lawless instances of Functor

2010-01-04 Thread Derek Elkins
On Tue, Jan 5, 2010 at 8:22 AM, Brent Yorgey byor...@seas.upenn.edu wrote: On Mon, Jan 04, 2010 at 11:49:33PM +0100, Steffen Schuldenzucker wrote: data Foo a = Foo a instance Functor Foo where     fmap f (Foo x) = Foo . f . f $ x Then: fmap id (Foo x) == Foo . id . id $ x == Foo x fmap

Re: [Haskell-cafe] Re: How Can Haskell Be Saved?

2009-12-13 Thread Derek Elkins
What does Haskell need to be saved from? (Its growing popularity and mushrooming library?) Arguably John Earle's emails suggest that the answer to this is Yes. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org

Re: [Haskell-cafe] From function over expression (+, *) derive function over expression (+)

2009-12-04 Thread Derek Elkins
On Fri, Dec 4, 2009 at 11:26 AM, Radek Micek radek.mi...@gmail.com wrote: Hello. I have two types for expression: data Expr = Add Expr Expr | Mul Expr Expr | Const Int data AExpr = AAdd AExpr AExpr | AConst Int The first one supports addition and multiplication and the second only

Re: [Haskell-cafe] Re: Optimizing Parsec 3 -- was: Wiki software?

2009-12-04 Thread Derek Elkins
On Fri, Dec 4, 2009 at 11:01 PM, Evan Laforge qdun...@gmail.com wrote: On Fri, Dec 4, 2009 at 1:09 PM, John MacFarlane j...@berkeley.edu wrote: On Mon, Nov 23, 2009 at 12:29 PM, Antoine Latter aslat...@gmail.com wrote: I finally had some time to test it.  After running it multiple times (of

Re: [Haskell-cafe] Great Programs to Read?

2009-11-30 Thread Derek Elkins
On Mon, Nov 30, 2009 at 6:22 AM, Michael Lesniak mlesn...@uni-kassel.de wrote: Hello, In terms of  to become a great programmer, you need to read great programs[1] what are great programs written in Haskell (for your personal definition of great), which source code is freely available on

Re: [Haskell-cafe] Re: implementing recursive let

2009-11-26 Thread Derek Elkins
On Wed, Nov 25, 2009 at 3:48 PM, Ben Franksen ben.frank...@online.de wrote: Derek Elkins wrote: The following code works fine for me, so it seems you are missing some details that may help. [...snip code...] Thank you! Indeed I did simplify the code when writing the message -- because I

Re: [Haskell-cafe] I miss OO

2009-11-25 Thread Derek Elkins
On Wed, Nov 25, 2009 at 2:51 PM, Michael Mossey m...@alumni.caltech.edu wrote: I'm fairly new to Haskell, and starting to write some big projects. Previously I used OO exclusively, mostly Python. I really miss the namespace capabilities... a class can have a lot of generic method names which

Re: [Haskell-cafe] implementing recursive let

2009-11-24 Thread Derek Elkins
The following code works fine for me, so it seems you are missing some details that may help. {-# LANGUAGE RecursiveDo, GeneralizedNewtypeDeriving, TypeSynonymInstances, MultiParamTypeClasses #-} import Control.Monad import Control.Monad.State import Control.Monad.Error import

Re: [Haskell-cafe] Experiments with defunctionalization, church-encoding and CPS

2009-11-01 Thread Derek Elkins
On Tue, Oct 13, 2009 at 4:44 AM, Eugene Kirpichov ekirpic...@gmail.com wrote: I took a toy problem - find the first node satisfying a predicate in a binary tree, started with a naive Maybe-based implementation - and experimented with 3 ways of changing the program:  - Church-encode the Maybe  

Re: [Haskell-cafe] why cannot i get the value of a IORef variable ?

2009-10-22 Thread Derek Elkins
On Thu, Oct 22, 2009 at 1:32 PM, David Menendez d...@zednenem.com wrote: On Thu, Oct 22, 2009 at 2:23 AM, Gregory Crosswhite gcr...@phys.washington.edu wrote: For clarity, one trick that uses unsafePerformIO which you may have seen posted on this list earlier today is the following way of

Re: [Haskell-cafe] Monadic correctness

2009-10-17 Thread Derek Elkins
On Sat, Oct 17, 2009 at 3:24 PM, Andrew Coppin andrewcop...@btinternet.com wrote: Edward Z. Yang wrote: Excerpts from Andrew Coppin's message of Sat Oct 17 15:21:28 -0400 2009: Suppose we have   newtype Foo x   instance Monad Foo   runFoo :: Foo x - IO x What sort of things can I do to

Re: [Haskell-cafe] x - String

2009-10-16 Thread Derek Elkins
See vacuum: http://hackage.haskell.org/package/vacuum ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] is proof by testing possible?

2009-10-12 Thread Derek Elkins
On Mon, Oct 12, 2009 at 8:15 PM, Joe Fredette jfred...@gmail.com wrote: Sadly not enough, I understand the basics, but the whole proof = this diagram commutes thing still seems like voodoo to me. There is a section coming up in my Topology ISP that will be on CT. So I hope that I will be able

Re: [Haskell-cafe] Documentation (was: ANN: text 0.5, a major revision of the Unicode text library)

2009-10-11 Thread Derek Elkins
On Sun, Oct 11, 2009 at 8:55 AM, Iain Barnett iainsp...@gmail.com wrote: On 11 Oct 2009, at 13:58, John Lato wrote: For anyone writing introductions to generic programming, take this as a plea from Haskellers everywhere.  If one of the RWH authors can't understand how to make use of these

Re: [Haskell-cafe] Introspection on types.

2009-10-01 Thread Derek Elkins
On Thu, Oct 1, 2009 at 6:22 PM, Gregory Propf gregorypr...@yahoo.com wrote: Is there a way to tell, let's say, how many constructors there are for a type?  Or do I need one of the haskell extensions I've read about? Use Data.Data and derive Data for the types you are interested in or instance

Re: [Haskell-cafe] Why the stack overflow?

2009-09-19 Thread Derek Elkins
On Sat, Sep 19, 2009 at 6:54 AM, Daniel Fischer daniel.is.fisc...@web.de wrote: Am Samstag 19 September 2009 12:37:41 schrieb staafmeister: Hi haskell-cafe, Why does rlist 10 [] gives stack overflow in ghci? rlist 0 l = return l rlist n l = do {x - randomRIO (1,maxBound::Int); let nl =

Re: [Haskell-cafe] Do I have this right? Remembering Memoization!

2009-09-15 Thread Derek Elkins
But pedantically even the function: quux :: Int - Int quux x = trace Quux (bar 12) optmain :: IO () optmain = quux 10 `seq` quux 11 `seq` return () might print only once if GHC at the optimization level selected recognizes that quux doesn't depend on its argument and rewrote your code

Re: [Haskell-cafe] What does it mean that objects are fixpoints? (OO'Haskell)

2009-09-15 Thread Derek Elkins
On Tue, Sep 15, 2009 at 10:14 AM, Manuel Simoni msim...@gmail.com wrote: Hello! I'm trying to wrap my head around OO'Haskell's notion of objects as fixpoints. Is OO'Haskell's use of mfix simply a use of something like a monadic Y-combinator to give the object access to its own identity?

Re: [Haskell-cafe] Building a monoid, continuation-passing style

2009-09-15 Thread Derek Elkins
On Mon, Sep 14, 2009 at 10:25 AM, Martijn van Steenbergen mart...@van.steenbergen.nl wrote: Hello cafe, Inspired by Sean Leather's xformat package [1] I built a datatype with which you can build a monoid with holes, yielding a function type to fill in these holes, continuation-passing style.

Re: [Haskell-cafe] Record update fusion (or how should I call it?)

2009-09-06 Thread Derek Elkins
The first thing I would do i is verify that the compiler is not already doing this. On Sun, Sep 6, 2009 at 7:50 AM, Peter Verswyvelenbugf...@gmail.com wrote: I've seen a couple of package being announced that provide first class labels, and other packages already existed for this (Grapefruit

Re: [Haskell-cafe] How to calculate de number of digits of an integer? (was: Is logBase right?)

2009-08-22 Thread Derek Elkins
2009/8/22 Eugene Kirpichov ekirpic...@gmail.com: Use 'round' instead of 'truncate'. Prelude let numDigits = (+1) . round . logBase 10 . fromIntegral Prelude map (numDigits . (10^)) [0..9] [1,2,3,4,5,6,7,8,9,10] round won't work because 999 is close to 1000. You simply need to use logBase

Re: [Haskell-cafe] How to calculate de number of digits of an integer? (was: Is logBase right?)

2009-08-22 Thread Derek Elkins
On Sat, Aug 22, 2009 at 12:31 PM, Derek Elkinsderek.a.elk...@gmail.com wrote: 2009/8/22 Eugene Kirpichov ekirpic...@gmail.com: Use 'round' instead of 'truncate'. Prelude let numDigits = (+1) . round . logBase 10 . fromIntegral Prelude map (numDigits . (10^)) [0..9] [1,2,3,4,5,6,7,8,9,10]

Re: Re[2]: [Haskell-cafe] Re: Where do I put the seq?

2009-08-21 Thread Derek Elkins
On Fri, Aug 21, 2009 at 5:04 AM, Lennart Augustssonlenn...@augustsson.net wrote: On Fri, Aug 21, 2009 at 10:52 AM, Bayley, Alistair alistair.bay...@invesco.com wrote: From: haskell-cafe-boun...@haskell.org [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Bulat Ziganshin To: Peter

Re: DDC compiler and effects; better than Haskell? (was Re: [Haskell-cafe] unsafeDestructiveAssign?)

2009-08-12 Thread Derek Elkins
On Tue, Aug 11, 2009 at 3:51 PM, Robin Greengree...@greenrd.org wrote: On Wed, 12 Aug 2009 11:37:02 +0200 Peter Verswyvelen bugf...@gmail.com wrote: Yes, sorry. But I think I already found the answer to my own question. DDC functions that are lazy don't allow side effects:

Re: [Haskell-cafe] unsafeDestructiveAssign?

2009-08-12 Thread Derek Elkins
On Wed, Aug 12, 2009 at 4:41 AM, John Latojwl...@gmail.com wrote: Hi Job, I don't think this hypothetical function could exist; you may as well call it  notEverSafeOhTheHumanity and be done with it. Since Haskell provides no guarantees about when (if ever) any given function/data will be

Re: [Haskell-cafe] A voyage of undiscovery

2009-07-16 Thread Derek Elkins
On Thu, Jul 16, 2009 at 2:52 PM, Andrew Coppinandrewcop...@btinternet.com wrote: Ross Mellgren wrote: It's not where -- let also works Prelude let { foo x = x } in (foo 1, foo True) (1,True) Awesome. So by attempting to implement Haskell's type system, I have discovered that I actually

Re: [Haskell-cafe] Colour tutorial (Was: AC-Vector, AC-Colour and AC-EasyRaster-GTK)

2009-07-11 Thread Derek Elkins
On Fri, Jul 10, 2009 at 12:42 AM, rocon...@theorem.ca wrote: On Thu, 9 Jul 2009, rocon...@theorem.ca wrote: You can use by lib without worrying about the CIE.  You can use my library without ever importing or using the word CIE.  However, the CIE stuff is there for those who need it.

Re: [Haskell-cafe] Colour tutorial (Was: AC-Vector, AC-Colour and AC-EasyRaster-GTK)

2009-07-11 Thread Derek Elkins
On Sat, Jul 11, 2009 at 12:54 PM, Derek Elkinsderek.a.elk...@gmail.com wrote: On Fri, Jul 10, 2009 at 12:42 AM, rocon...@theorem.ca wrote: On Thu, 9 Jul 2009, rocon...@theorem.ca wrote: You can use by lib without worrying about the CIE.  You can use my library without ever importing or using

Re: [Haskell-cafe] Leaner Haskell.org frontpage

2009-07-09 Thread Derek Elkins
On Thu, Jul 9, 2009 at 12:31 PM, Jason Dagitda...@codersbase.com wrote: On Thu, Jul 9, 2009 at 10:00 AM, Thomas ten Cate ttenc...@gmail.com wrote: By the way, the most valuable pixels, right at the top of the page, are wasted on wiki stuff. Compare http://www.haskell.org/ with, for

Re: [Haskell-cafe] Leaner Haskell.org frontpage

2009-07-09 Thread Derek Elkins
On Thu, Jul 9, 2009 at 5:17 PM, Jason Dagitda...@codersbase.com wrote: On Thu, Jul 9, 2009 at 3:11 PM, Derek Elkins derek.a.elk...@gmail.com wrote: On Thu, Jul 9, 2009 at 12:31 PM, Jason Dagitda...@codersbase.com wrote: On Thu, Jul 9, 2009 at 10:00 AM, Thomas ten Cate ttenc

Re: [Haskell-cafe] Cabal fun [Half-integer]

2009-06-28 Thread Derek Elkins
On Sun, Jun 28, 2009 at 4:11 PM, Antoine Latteraslat...@gmail.com wrote: On Sun, Jun 28, 2009 at 3:42 PM, Andrew Coppinandrewcop...@btinternet.com wrote: Andrew Coppin wrote: Alrighty then, so how I just do Setup configure, and now Setup sdist, and then I can upload the result to Ha-- oh,

Re: [Haskell-cafe] Pike's Newsqueak talk

2009-06-05 Thread Derek Elkins
On Fri, Jun 5, 2009 at 8:14 PM, Tim Newsham news...@lava.net wrote: I just watched http://video.google.com/videoplay?docid=810232012617965344 It's a great talk that is suprisingly relevant to Haskell programming (although at first blush it looks a bit unrelated). (It refs a lot of older work

Re: [Haskell-cafe] Parsec float

2009-05-30 Thread Derek Elkins
On Sat, May 30, 2009 at 1:12 PM, Jason Dusek jason.du...@gmail.com wrote: 2009/05/30 Bartosz Wójcik bar...@sudety.it: ...reading RWH I could not memorize what those liftM funtions meant.  The basic one, `liftM`, means `fmap`, though specialized for  functors that are monads.    Prelude

Re: [Haskell-cafe] [] == []

2009-05-30 Thread Derek Elkins
On Fri, May 29, 2009 at 5:36 AM, Max Rabkin max.rab...@gmail.com wrote: On Fri, May 29, 2009 at 12:29 PM, Paul Keir pk...@dcs.gla.ac.uk wrote: f''' = ([]::[()]) == ([]::[()]) (Very pretty.) So why doesn't ghc have 'default' instances? It does. I believe Num defaults to Integer and then to

Re: [Haskell-cafe] Parsec float

2009-05-29 Thread Derek Elkins
On Fri, May 29, 2009 at 4:02 AM, Tillmann Vogt tillmann.v...@rwth-aachen.de wrote: Bartosz Wójcik wrote: Hi Everybody (especially Parsec Creator), is there any reason why float parses only positive numbers? I find following defition: float           = lexeme floating   ? float floating  

Re: [Haskell-cafe] Kind of confusing

2009-05-12 Thread Derek Elkins
On Tue, 2009-05-12 at 14:09 +0100, Philippa Cowderoy wrote: On Mon, 2009-05-11 at 20:43 -0400, Anton van Straaten wrote: Serious question: what is the significance of the question mark and double question marks in those signatures, or better yet, where can I read about it? I've

Re: [Haskell-cafe] ANNOUNCE: Utrecht Haskell Compiler (UHC) -- first release

2009-04-19 Thread Derek Elkins
On Sun, 2009-04-19 at 20:46 -0400, Dan Doel wrote: On Sunday 19 April 2009 7:11:51 pm wren ng thornton wrote: Yes, however, because consumers (e.g. @f@) demand that their arguments remain polymorphic, anything which reduces the polymorphism of @a@ in @x@ will make it ineligible for being

Re: [Haskell-cafe] Wishful thinking: a text editor that expands function applications into function definitions

2009-04-02 Thread Derek Elkins
On Thu, 2009-04-02 at 18:01 -0600, Duane Johnson wrote: So I was thinking about a killer feature for a text editor. Wouldn't it be neat if you could expand function calls into their definitions, in-place? For example, suppose we have minus defined like so, somewhere in another file:

Re: [Haskell-cafe] do you have to use fix with forkio?

2009-03-07 Thread Derek Elkins
On Sat, 2009-03-07 at 23:12 +0100, Martijn van Steenbergen wrote: Derek Elkins wrote: Both are poorish style. reader - forkIO $ forever $ do (nr', line) - readChan; when (nr /= nr') $ putStrLn hdl line This is fine assuming you always want to re-enter the loop. If you want to loop

Re: [Haskell-cafe] Naturality condition for inits

2009-03-07 Thread Derek Elkins
On Sat, 2009-03-07 at 22:18 +, R J wrote: Here's another Bird problem that's stymied me: The function inits computes the list of initial segments of a list; its type is inits :: [a] - [[a]]. What is the appropriate naturality condition for inits? A natural transformation is between two

Re: [Haskell-cafe] do you have to use fix with forkio?

2009-03-05 Thread Derek Elkins
On Thu, 2009-03-05 at 16:12 -0800, Jonathan Cast wrote: On Thu, 2009-03-05 at 15:36 -0800, Daryoush Mehrtash wrote: In this chat server implementation http://www.haskell.org/haskellwiki/Implement_a_chat_server forkIO is used with fix as in: reader - forkIO $ fix $ \loop - do

Re: [Haskell-cafe] Theory about uncurried functions

2009-03-03 Thread Derek Elkins
On Tue, 2009-03-03 at 10:43 +0100, Peter Verswyvelen wrote: Lambda calculus is a nice theory in which every function always has one input and one output. Functions with multiple arguments can be simulated because functions are first class and hence a function can return a function. Multiple

Re: [Haskell-cafe] Uses of `fix' combinator

2009-02-19 Thread Derek Elkins
On Thu, 2009-02-19 at 17:00 +0300, Khudyakov Alexey wrote: Hello, While browsing documentation I've found following function -- | @'fix' f@ is the least fixed point of the function @f@, -- i.e. the least defined @x@ such that @f x = x...@. fix :: (a - a) - a fix f = let x = f x in x

Re: [Haskell-cafe] forall ST monad

2009-02-19 Thread Derek Elkins
On Thu, 2009-02-19 at 05:53 -0800, Kim-Ee Yeoh wrote: There's a lot to chew on (thank you!), but I'll just take something I can handle for now. Dan Doel wrote: An existential: exists a:T. P(a) is a pair of some a with type T and a proof that a satisfies P (which has

Re: [Haskell-cafe] Intergalactic Telefunctors

2009-02-15 Thread Derek Elkins
On Sun, 2009-02-15 at 18:53 +0100, Tillmann Rendel wrote: Gregg Reynolds wrote: BTW, I'm not talking about Haskell's Functor class, I guess I should have made that clear. I'm talking about category theory, as the semantic framework for thinking about Haskell. In that case, I even less

Re: [Haskell-cafe] Re: Can this be done?

2009-02-12 Thread Derek Elkins
On Thu, 2009-02-12 at 19:55 -0500, Chung-chieh Shan wrote: wren ng thornton w...@freegeek.org wrote in article 4993bbee.9070...@freegeek.org in gmane.comp.lang.haskell.cafe: It's ugly, but one option is to just reify your continuations as an ADT, where there are constructors for each

Re: [Haskell-cafe] Haskell Fest

2009-02-09 Thread Derek Elkins
On Mon, 2009-02-09 at 16:54 -0800, Lyle Kopnicky wrote: Looks like a lot of fun! http://www.haskellchamber.com/page6.html I could readily go there. Maybe I could pick up a beauty at the pageant. ___ Haskell-Cafe mailing list

Re: [Haskell-cafe] Bind as a sequencing operator (Was: evaluation semantics of bind)

2009-02-07 Thread Derek Elkins
On Thu, 2009-02-05 at 11:47 -0700, m...@justinbogner.com wrote: Jake McArthur j...@pikewerks.com writes: m...@justinbogner.com wrote: | Oops, sent this off list the first time, here it is again. | | Jake McArthur j...@pikewerks.com writes: | m...@justinbogner.com wrote: | | Bind is a

Re: [Haskell-cafe] morphisms in IO

2009-02-07 Thread Derek Elkins
On Thu, 2009-02-05 at 20:52 -0600, Gregg Reynolds wrote: I'm working on a radically different way of looking at IO. Before I post it and make a fool of myself, I'd appreciate a reality check on the following points: a) Can IO be thought of as a category? I think the answer is yes. No.

Re: [Haskell-cafe] Re: ANN: #haskell-in-depth IRC channel

2009-02-03 Thread Derek Elkins
On Wed, 2009-02-04 at 14:32 +0900, Benjamin L.Russell wrote: On Wed, 04 Feb 2009 00:15:48 +, Philippa Cowderoy fli...@flippac.org wrote: [...] If you need to know how to use monads so you can do IO, #haskell-in-depth isn't the place. On the other hand, if you want to discuss how

Re: [Haskell-cafe] type and data constructors in CT

2009-01-31 Thread Derek Elkins
On Sat, 2009-01-31 at 11:00 -0600, Gregg Reynolds wrote: Hi, I think I've finally figured out what a monad is, but there's one thing I haven't seen addressed in category theory stuff I've found online. That is the relation between type constructors and data constructors. The typical

Re: [Haskell-cafe] Monoids and newtypes

2009-01-27 Thread Derek Elkins
On Tue, 2009-01-27 at 08:51 -0800, Anish Muttreja wrote: On Thu, 22 Jan 2009 09:46:19 -0800, Derek Elkins derek.a.elk...@gmail.com wrote: The old wiki had an excellent page that has not been replicated either verbatim or in spirit in the new wiki. http://web.archive.org/web

Re: [Haskell-cafe] ANN: filestore 0.1

2009-01-25 Thread Derek Elkins
On Sun, 2009-01-25 at 09:32 +, Magnus Therning wrote: Bulat Ziganshin wrote: Hello Gwern, Sunday, January 25, 2009, 2:56:07 AM, you wrote: my usual complaint: it will be great to see all announces duplicated in main haskell list I always only announce things on haskell-cafe.

Re: [Haskell-cafe] Re: Laws and partial values

2009-01-25 Thread Derek Elkins
On Sun, 2009-01-25 at 07:11 -0800, Jonathan Cast wrote: On Sun, 2009-01-25 at 10:46 +0100, Thomas Davie wrote: On 25 Jan 2009, at 10:08, Daniel Fischer wrote: Am Sonntag, 25. Januar 2009 00:55 schrieb Conal Elliott: It's obvious because () is a defined value, while bottom is not -

Re: [Haskell-cafe] ANN: filestore 0.1

2009-01-25 Thread Derek Elkins
On Sun, 2009-01-25 at 23:09 +0100, Magnus Therning wrote: On Sun, Jan 25, 2009 at 10:47 AM, Derek Elkins derek.a.elk...@gmail.com wrote: On Sun, 2009-01-25 at 09:32 +, Magnus Therning wrote: Bulat Ziganshin wrote: Hello Gwern, Sunday, January 25, 2009, 2:56:07 AM, you wrote

Re: [Haskell-cafe] Factory methods in Haskell

2009-01-24 Thread Derek Elkins
On Sat, 2009-01-24 at 15:43 -0600, Jeremy Shaw wrote: Hello, I was reading about the Factory Method Pattern on wikipedia, and noticed that the very first example was written in Haskell. Sweet! http://en.wikipedia.org/wiki/Factory_method_pattern#Haskell Unfortunately, it looks to me like

Re: [Haskell-cafe] mapM_ - Monoid.Monad.map

2009-01-23 Thread Derek Elkins
On Fri, 2009-01-23 at 13:39 -0800, George Pollard wrote: On Fri, 2009-01-23 at 21:30 +, Joachim Breitner wrote: Hi, Am Freitag, den 23.01.2009, 21:50 +0100 schrieb Henning Thielemann: However our recent Monoid discussion made me think about mapM_, sequence_, and friends. I

Re: [Haskell-cafe] Monoids and newtypes

2009-01-22 Thread Derek Elkins
On Thu, 2009-01-22 at 16:11 +0100, Ketil Malde wrote: One wart that was briefly mentioned during the Great Monoid Naming Thread of 2009 is the need to wrap types in newtypes to provide multiple instances of the same class with different semantics -- the archetypical example being Integer as a

Re: Re[2]: [Haskell-cafe] Comments from OCaml Hacker Brian Hurt

2009-01-22 Thread Derek Elkins
On Thu, 2009-01-22 at 11:32 -0600, Jeremy Shaw wrote: Hello, Just some minor suggestions and comments: The description might read better as two sentences: A class for monoids with various general-purpose instances. Monoids are types with an associative binary operation that has an

Re: [Haskell-cafe] Factoring into type classes

2009-01-19 Thread Derek Elkins
On Mon, 2009-01-19 at 21:18 +0100, Alberto G. Corona wrote: This is one of the shortcomings of haskell not to mention other programming languages. Mathemathicist would find it very annoying. Instead of instance Monoid Integer where mappend = (+) mempty = 0 instance Monoid

Re: [Haskell-cafe] Factoring into type classes

2009-01-19 Thread Derek Elkins
On Mon, 2009-01-19 at 12:10 -0800, Iavor Diatchki wrote: Hi, On Mon, Jan 19, 2009 at 11:06 AM, Jonathan Cast jonathancc...@fastmail.fm wrote: On Mon, 2009-01-19 at 10:59 -0800, Iavor Diatchki wrote: Hello, The multitude of newtypes in the Monoid module are a good indication that the

Re: [Haskell-cafe] Re: Haskell and C++ program

2009-01-19 Thread Derek Elkins
On Mon, 2009-01-19 at 22:12 -0500, S. Doaitse Swierstra wrote: On 17 jan 2009, at 22:22, Derek Elkins wrote: On Thu, 2009-01-15 at 13:40 +0100, Apfelmus, Heinrich wrote: Eugene Kirpichov wrote: Well, your program is not equivalent to the C++ version, since it doesn't bail on incorrect

Re: Improved documentation for Bool (Was: [Haskell-cafe] Comments from OCaml Hacker Brian Hurt)

2009-01-18 Thread Derek Elkins
On Sun, 2009-01-18 at 18:17 +0100, Benja Fallenstein wrote: On Sun, Jan 18, 2009 at 5:48 PM, rocon...@theorem.ca wrote: I noticed the Bool datatype isn't well documented. Since Bool is not a common English word, I figured it could use some haddock to help clarify it for newcomers. --

Re: [Haskell-cafe] Re: Haskell and C++ program

2009-01-17 Thread Derek Elkins
On Thu, 2009-01-15 at 13:40 +0100, Apfelmus, Heinrich wrote: Eugene Kirpichov wrote: Well, your program is not equivalent to the C++ version, since it doesn't bail on incorrect input. Oops. That's because my assertion show . read = id is wrong. We only have read . show = id

Re: [Haskell-cafe] Comments from OCaml Hacker Brian Hurt

2009-01-16 Thread Derek Elkins
On Fri, 2009-01-16 at 15:21 -0800, Jonathan Cast wrote: On Fri, 2009-01-16 at 18:14 -0500, Anton van Straaten wrote: Niklas Broberg wrote: I still think existential quantification is a step too far though. :-P Seriously, existential quantification is a REALLY simple concept, that

Re: [Haskell-cafe] Comments from OCaml Hacker Brian Hurt

2009-01-15 Thread Derek Elkins
Actually programming requires -far more- precision than mathematics ever has. The standards of formal and precise that mathematicians use are a joke to computer scientists and programmers. Communication is also more important or at least more center stage in mathematics than programming.

Re: [Haskell-cafe] Comments from OCaml Hacker Brian Hurt

2009-01-15 Thread Derek Elkins
On Thu, 2009-01-15 at 14:11 -0600, John Goerzen wrote: On Thu, Jan 15, 2009 at 07:46:02PM +, Andrew Coppin wrote: John Goerzen wrote: If we *must* insist on using the most obscure possible name for everything, can we at least write some documentation that doesn't require a PhD

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