Re: Type families in kind signatures with TypeInType

On Fri, Sep 23, 2016 at 3:00 PM, Simon Peyton Jones wrote: > Interesting. Is this case also an example, or is it a non-feature? > > > > class C t where > > type K t :: Type > > type T t :: K t -> Type > > > > m :: t -> T t a > > > > > > Ah, that’s quite

Re: Type families in kind signatures with TypeInType

On Fri, Sep 23, 2016 at 3:19 AM, Simon Peyton Jones wrote: > This is an example of https://ghc.haskell.org/trac/ghc/ticket/12088. > Interesting. Is this case also an example, or is it a non-feature? class C t where type K t :: Type type T t :: K t -> Type m

Re: default roles

On Thu, Oct 10, 2013 at 10:09 PM, Edward Kmett ekm...@gmail.com wrote: Wait, that sounds like it induces bad semantics. Can't we use that as yet another way to attack the sanctity of Set? class Ord a = Foo a where badInsert :: a - Set a - Set a instance Foo Int where badInsert =

Re: default roles

On Wed, Oct 9, 2013 at 3:21 PM, Richard Eisenberg e...@cis.upenn.edu wrote: Now I think we're on the same page, and I *am* a little worried about the sky falling because of this. (That's not a euphemism -- I'm only a little worried.) Well, maybe I should be more worried. The whole idea of

Re: default roles

On Thu, Oct 10, 2013 at 12:11 PM, Simon Peyton-Jones simo...@microsoft.comwrote: Does GND make sense in cases where the superclasses aren't also derived? If I had a type T whose Ord instance made use of the Eq instance for some reason, and then I made a newtype T' with a new Eq instance and a

Re: [Haskell-cafe] Lenses: Should I declare Getters?

On Tue, Sep 10, 2013 at 1:31 AM, Charlie Paul charli...@gmail.com wrote: I've been looking through Edward Kmett's lens library, and I'm a bit befuddled about Getters. In my own code, why would I want to have something be a Getter instead of a plain function? As far as I can see, a plain

Re: [Haskell-cafe] Applicative is like an Arrow

On Sat, Aug 17, 2013 at 8:23 AM, Mathijs Kwik math...@bluescreen303.nlwrote: damodar kulkarni kdamodar2...@gmail.com writes: Thanks for this nice analogy and explanation. This brings monad transformers to my mind. without monad transformers, the monads are bit crippled in their

Re: [Haskell-cafe] Can not use ST monad with polymorphic function

On Thu, Nov 29, 2012 at 7:50 AM, Dmitry Kulagin dmitry.kula...@gmail.comwrote: Thank you, MigMit! If I replace your type FoldSTVoid with: data FoldMVoid = FoldMVoid {runFold :: Monad m = (Int - m ()) - m ()} then everything works magically with any monad! That is exactly what I wanted,

Re: [Haskell-cafe] type variable in class instance

I'm not sure I understand On Tue, Sep 11, 2012 at 11:06 AM, Corentin Dupont corentin.dup...@gmail.com wrote: Yes. That's fantastic! This GADT is the missing piece of my puzzle. I transformed a bit your solution, polluting it with some classes instances and fleshing the functions: data

Re: [Haskell-cafe] Platform Versioning Policy: upper bounds are not our friends

As I see it, there are four possibilities for a given version of dependency: 1. The version DOES work. The author (or some delegate) has compiled the package against this version and the resulting code is considered good. 2. The version SHOULD work. No one has tested against this version, but the

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

On Sun, Jun 17, 2012 at 2:26 AM, Tillmann Rendel ren...@informatik.uni-marburg.de wrote: Hi, David Menendez wrote: As you noticed, you can get somewhat better performance by using the combinators that convert to S.Set internally, because they eliminate redundant computations later

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

On Sat, Jun 16, 2012 at 3:57 AM, Tillmann Rendel ren...@informatik.uni-marburg.de wrote: George Giorgidze wrote: I would like to announce the first release of the set-monad library. On Hackage: http://hackage.haskell.org/package/set-monad Very cool. Seems to work fine. But I am wondering

Re: Known problems with promoted tuples and lists in GHC 7.4.1?

Message- | From: glasgow-haskell-users-boun...@haskell.org [mailto:glasgow-haskell- | users-boun...@haskell.org] On Behalf Of David Menendez | Sent: 06 June 2012 23:50 | To: José Pedro Magalhães | Cc: glasgow-haskell-users@haskell.org Mailing List | Subject: Re: Known problems with promoted

Known problems with promoted tuples and lists in GHC 7.4.1?

Are there any known issues involving type-level pairs and lists? I've hit a few baffling type errors that went away when I refactored my code to use locally-defined pairs and lists instead of those provided by the prelude. More worryingly, I had one function that would stop passing the type

Re: [Haskell-cafe] Monads, do and strictness

On Sat, Jan 21, 2012 at 1:45 PM, David Barbour dmbarb...@gmail.com wrote: On Sat, Jan 21, 2012 at 10:08 AM, Roman Cheplyaka r...@ro-che.info wrote: * David Barbour dmbarb...@gmail.com [2012-01-21 10:01:00-0800] As noted, IO is not strict in the value x, only in the operation that generates

Re: Unit unboxed tuples

On Sat, Dec 24, 2011 at 7:15 AM, Duncan Coutts duncan.cou...@googlemail.com wrote: On 23 December 2011 20:09, Stefan Holdermans ste...@vectorfabrics.com wrote: Here are the kinds of the type constructors:                 (,,) :: * - * - * - *                 (,) :: * - * - *                

Re: [Haskell-cafe] Alternative versus Monoid

On Wed, Dec 21, 2011 at 12:20 PM, Conor McBride co...@strictlypositive.org wrote: On 21 Dec 2011, at 14:07, Erik Hesselink hessel...@gmail.com wrote: On Wed, Dec 21, 2011 at 14:10, Bas van Dijk v.dijk@gmail.com wrote:  The semantics of Maybe are clear: it's

Re: [Haskell-cafe] [Alternative] change some/many semantics

On Wed, Dec 21, 2011 at 12:37 PM, wren ng thornton w...@freegeek.org wrote: On 12/19/11 10:20 PM, David Menendez wrote: On Mon, Dec 19, 2011 at 6:37 PM, wren ng thorntonw...@freegeek.org  wrote: On 12/14/11 10:58 PM, Gregory Crosswhite wrote: Of course, this is not a simple change at all

Re: [Haskell-cafe] Alternative versus Monoid

On Wed, Dec 21, 2011 at 8:10 AM, Bas van Dijk v.dijk@gmail.com wrote: On 16 December 2011 16:26, Yves Parès limestr...@gmail.com wrote: 1) What about the First type? Do we {-# DEPRECATE #-} it? Personnaly, I'm in favor of following the same logic than Int: Int itself is not a monoid. You

Re: [Haskell-cafe] [Alternative] change some/many semantics

On Mon, Dec 19, 2011 at 6:37 PM, wren ng thornton w...@freegeek.org wrote: On 12/14/11 10:58 PM, Gregory Crosswhite wrote: Of course, this is not a simple change at all because it would have to be done in such a way as to respect the ordering of actions --- that is, we can't have each action

Re: [Haskell-cafe] ismzero operator possible without equal constraint

On Sat, Dec 3, 2011 at 3:55 PM, Antoine Latter aslat...@gmail.com wrote: On Sat, Dec 3, 2011 at 10:55 AM, edgar klerks edgar.kle...@gmail.com wrote: Hi list, I am using MonadSplit (from http://www.haskell.org/haskellwiki/New_monads/MonadSplit )  for a project and now I want to make a library

Re: [Haskell-cafe] Interpreter with Cont

On Mon, Nov 21, 2011 at 2:13 PM, Tim Baumgartner baumgartner@googlemail.com wrote: Free Monads. It's amazing to be confronted again with notions I learned more than ten years ago for groups. I have to admit that I'm probably not yet prepared for a deeper understanding of this, but hopefully

Re: [Haskell-cafe] Interpreter with Cont

On Sat, Nov 19, 2011 at 3:29 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Sat, Nov 19, 2011 at 6:08 PM, Tim Baumgartner baumgartner@googlemail.com wrote: I have not yet gained a good understanding of the continuation monad, but I wonder if it could be used here. What would a

Re: [Haskell-cafe] Data Flow Programming in FP

On Tue, Jun 21, 2011 at 12:14 PM, Edward Kmett ekm...@gmail.com wrote: The essence of data flow programming describes how you can use comonads to model the semantics of dataflow languages. One of the best stops from there is probably, Dave Menendez's response on the Haskell mailing list back

Re: [Haskell-cafe] Probably type checker error.

GHC 6.12 introduces MonoLocalBinds, which disables polymorphic values in let statements. Your original code works for me if I use -XNoMonoLocalBinds -XNoMonomorphismRestriction. On Mon, Jun 20, 2011 at 9:02 AM, Serguey Zefirov sergu...@gmail.com wrote: The fact is that (Num a) context works and

Re: [Haskell-cafe] Type Constraints on Data Constructors

On Wed, Jun 8, 2011 at 3:15 PM, Malcolm Wallace malcolm.wall...@me.com wrote: data Bar f a = Foo f = Bar {bar :: f a} The class context on the data constructor buys you nothing extra in terms of expressivity in the language.  All it does is force you to repeat the context on every function

Re: [Haskell-cafe] ArrowLoop and streamprocessors

On Thu, Mar 31, 2011 at 11:01 AM, Matthew Steele mdste...@alum.mit.edu wrote: On Mar 30, 2011, at 5:29 PM, Mathijs Kwik wrote: So loop really doesn't seem to help here, but I couldn't find another way either to feed outputs back into the system. What I need is: Either A B ~ Either C B - A ~

Re: [Haskell-cafe] Defining subtraction for naturals

On Thu, Mar 17, 2011 at 2:35 PM, wren ng thornton w...@freegeek.org wrote: Another question on particulars. When dealing with natural numbers, we run into the problem of defining subtraction. There are a few reasonable definitions: (1) If the result would drop below zero then throw an

Re: [Haskell-cafe] Generalizing catMaybes

On Sat, Jan 8, 2011 at 12:05 PM, Conor McBride co...@strictlypositive.org wrote: On 8 Jan 2011, at 15:27, Henning Thielemann wrote: On Sat, 8 Jan 2011, Conor McBride wrote: On 8 Jan 2011, at 11:14, Henning Thielemann wrote: For me, the solutions of Dave Menendez make most sense:

Re: [Haskell-cafe] Generalizing catMaybes

On Sat, Jan 8, 2011 at 5:07 PM, Tony Morris tonymor...@gmail.com wrote: Thanks guys for all the solutions. A slight correction below. On 09/01/11 03:54, David Menendez wrote: Naturally, if you also have pure and fmap, you also have a monad. You have a pointed functor but not necessarily

Re: [Haskell-cafe] Set monad

On Sat, Jan 8, 2011 at 4:53 PM, Lennart Augustsson lenn...@augustsson.net wrote: It so happens that you can make a set data type that is a Monad, but it's not exactly the best possible sets. There's also the infinite search monad, which allows you to search infinite sets in finite time,

Re: [Haskell-cafe] Generalizing catMaybes

On Fri, Jan 7, 2011 at 9:56 PM, Tony Morris tonymor...@gmail.com wrote:  I am wondering if it possible to generalise catMaybes: (Something f, SomethingElse t) = t (f a) - t a I have being doing some gymnastics with Traversable and Foldable and a couple of other things from category-extras

Re: [Haskell-cafe] Intro to monad transformers

On Sun, Dec 26, 2010 at 2:00 PM, michael rice nowg...@yahoo.com wrote: instance Monad m = MonadPlus (MaybeT m) where mzero = MaybeT $ return Nothing mplus x y = MaybeT $ do maybe_value - runMaybeT x case maybe_value of

Re: [Haskell-cafe] type class design

On Tue, Dec 21, 2010 at 4:30 AM, Jean-Marie Gaillourdet j...@gaillourdet.net wrote: Hi, sorry for answering to such an old thread. David Menendez d...@zednenem.com writes: On Fri, Oct 29, 2010 at 8:33 AM, Tillmann Rendel ren...@informatik.uni-marburg.de wrote: Hi, Uwe Schmidt wrote

Re: [Haskell-cafe] Type Directed Name Resolution

On Thu, Nov 11, 2010 at 8:16 PM, John Lask jvl...@hotmail.com wrote: consider length ... I have records with the attribute length, length can be given as an Int, Double, Float or maybe as a constructed type Length, length's use as a record selector would also clash with List.length. All these

Re: Re: [Haskell-cafe] Type Directed Name Resolution

On Thu, Nov 11, 2010 at 10:00 PM, John Lask jvl...@hotmail.com wrote: On Thu, Nov 11, 2010 at 8:16 PM, John Laskjvl...@hotmail.com  wrote: consider length ... I have records with the attribute length, length can be given as an Int, Double, Float or maybe as a constructed type Length,

Re: [Haskell-cafe] type class design

On Fri, Oct 29, 2010 at 8:33 AM, Tillmann Rendel ren...@informatik.uni-marburg.de wrote: Hi, Uwe Schmidt wrote: In the standard Haskell classes we can find both cases, even within a single class. Eq with (==) as f and (/=) as g belongs to the 1. case Note that the case of (==) and (/=)

Re: Implicit 'forall' in data declarations

On Mon, Oct 25, 2010 at 3:16 AM, Simon Peyton-Jones simo...@microsoft.com wrote: | On a related note, these are also apparently allowed (in 6.10.4): |     f :: forall a. (Eq a = a - a) - a - a |    -- the Eq context prevents the function from ever being called. That's not true.  E.g.        

Re: Implicit 'forall' in data declarations

On Fri, Oct 22, 2010 at 4:20 AM, Simon Peyton-Jones simo...@microsoft.com wrote: Does anyone listening to this thread have an opinion?  Just to summarise, Sebastian's proposal is that Haskell's implicit quantification (adding foralls) would occur *only* right at the top of a  type

Re: [Haskell-cafe] Restricted type classes

On Thu, Sep 9, 2010 at 11:33 PM, wren ng thornton w...@freegeek.org wrote: On 9/9/10 1:04 AM, David Menendez wrote: Fascinating. I figured there might be a counter-example involving seq, but this is pretty subtle. In particular, would it be fair to say that in Haskell-without-seq, E (f

Re: [Haskell-cafe] Restricted type classes

On Wed, Sep 8, 2010 at 11:17 PM, wren ng thornton w...@freegeek.org wrote: On 9/7/10 4:21 AM, Daniel Fischer wrote: On Tuesday 07 September 2010 05:22:55, David Menendez wrote: In fact, I think *every* appropriately-typed function satisfies that law. Does anyone know of a counter-example

Re: [Haskell-cafe] Restricted type classes

On Mon, Sep 6, 2010 at 7:51 AM, John Lato jwl...@gmail.com wrote: On Sun, Sep 5, 2010 at 7:18 PM, David Menendez d...@zednenem.com wrote: On Sun, Sep 5, 2010 at 8:40 AM, John Lato jwl...@gmail.com wrote: On Sat, Sep 4, 2010 at 12:34 PM, David Menendez d...@zednenem.com wrote: On Fri

Re: [Haskell-cafe] Operator precedence

On Mon, Sep 6, 2010 at 1:37 PM, michael rice nowg...@yahoo.com wrote: A concrete library? I'm playing around with Data.Bits. It has .. and .|. which I assume are functions (rather than operators) because I don't see and infix statement for them. Correct? .|. and .. are operators because

Re: [Haskell-cafe] Operator precedence

On Mon, Sep 6, 2010 at 2:21 PM, Daniel Díaz danield...@asofilak.es wrote: El Lun, 6 de Septiembre de 2010, 7:50 pm, David Menendez escribió: Operators default to infixl 9 unless specified otherwise, so no infix declaration is needed. Why there is a default infix? Why it is 9? That's what

Re: [Haskell-cafe] Restricted type classes

On Mon, Sep 6, 2010 at 10:22 PM, wren ng thornton w...@freegeek.org wrote: On 9/6/10 1:33 PM, David Menendez wrote: For that matter, can you even describe what pure is intended to do without reference to*  or join? As already stated: fmap f . pure = pure . f That's pretty general. For lists

Re: [Haskell-cafe] Restricted type classes

On Sun, Sep 5, 2010 at 8:40 AM, John Lato jwl...@gmail.com wrote: On Sat, Sep 4, 2010 at 12:34 PM, David Menendez d...@zednenem.com wrote: On Fri, Sep 3, 2010 at 8:23 AM, John Lato jwl...@gmail.com wrote: +1 for using the proper constraints, and especially for bringing over Pointed

Re: [Haskell-cafe] Restricted type classes

On Sun, Sep 5, 2010 at 8:47 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: I _can_ think of a data type that could conceivably be an instance of Pointed but not Applicative: a BloomFilter (though there's not really any point in having a BloomFilter with only one value that I can

Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0

On Sat, Sep 4, 2010 at 11:07 AM, John Millikin jmilli...@gmail.com wrote: On Fri, Sep 3, 2010 at 23:02, David Menendez d...@zednenem.com wrote: Yes, using foreign namespaces is one of the things recommended against when serving XHTML as text/html. This says nothing about documents following

Re: [Haskell-cafe] Restricted type classes

On Fri, Sep 3, 2010 at 8:23 AM, John Lato jwl...@gmail.com wrote: Do you have a kind * implementation of Foldable?  I'd be interested in seeing it, because I was unable to create a usable implementation (based upon the RMonad scheme) on my last attempt. I always figured it would look something

Re: [Haskell-cafe] On to applicative

On Sat, Sep 4, 2010 at 2:06 PM, michael rice nowg...@yahoo.com wrote: The two myAction functions below seem to be equivalent and, for this small case, show an interesting economy of code, but being far from a Haskell expert, I have to ask, is the first function as small (code wise) as it

Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0

On Fri, Sep 3, 2010 at 12:40 AM, John Millikin jmilli...@gmail.com wrote: Haddock is generating files with an .html extension, which causes webservers to serve it using text/html, the incorrect MIME-type. Secton 5.1 of the XHTML recommendation states: XHTML Documents which follow the

Re: [Haskell-cafe] On to applicative

On Thu, Sep 2, 2010 at 10:45 AM, michael rice nowg...@yahoo.com wrote: Can you think of a situation for \x - f x or \x y z - x + ord y - head z that would require x (y z) to have their type(s) declared (ala Pascal), or is it always inferred by what appears to the right of -? I think

Re: [Haskell-cafe] On to applicative

On Thu, Sep 2, 2010 at 9:16 PM, michael rice nowg...@yahoo.com wrote: This may be a dumb question, but here goes. Types Maybe, Either, List, are types and also instances of Functor (and Monad). Assuming (-) is also a type, where can I find its type definition? (-) is a built-in type. You

Re: [Haskell-cafe] Arrow transformers: how to make them wright?

On Tue, Aug 31, 2010 at 2:07 PM, Permjacov Evgeniy permea...@gmail.com wrote:  A Control.Arrow in base package introduces an arrow type, and ghc have good support for arrow notation. Many things, avaible in monads, are avaible in arrows as well. There is an arrows package, that introduces some

Re: [Haskell-cafe] Re: String vs ByteString

On Fri, Aug 13, 2010 at 10:43 AM, Johan Tibell johan.tib...@gmail.com wrote: Here's a rule of thumb: If you have binary data, use Data.ByteString. If you have text, use Data.Text. Those libraries have benchmarks and have been well tuned by experienced Haskelleres and should be the fastest and

Re: [Haskell-cafe] Yet another monad transformer or silly usage of Either?

2010/7/25 Eugeny N Dzhurinsky b...@redwerk.com: Hello, everybody! I am trying to develop some sort of library, which supposed to sign into a WEB service, then perform some requests with it. Initially I designed methods in the following way data DServError = InvalidCredentials |

Re: [Haskell-cafe] Design for 2010.2.x series Haskell Platform site

On Sat, Jul 17, 2010 at 2:10 PM, Don Stewart d...@galois.com wrote: andrewcoppin: Don Stewart wrote: allbery: like to repeat one request: Please, please, please make it easier to - Download older versions of HP. - Find out which HP release contains what. - Figure out what the difference

Re: [Haskell-cafe] Actually loading a Cabal package in GHCi

On Sun, Jul 11, 2010 at 3:25 PM, d...@patriot.net wrote: Prelude Haskore :l Haskore no location info: module `Haskore' is a package module Failed, modules loaded: none. You need to use :m here. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/

Re: [Haskell-cafe] checking types with type families

On Sat, Jul 3, 2010 at 3:32 AM, Kevin Quick qu...@sparq.org wrote: On Wed, 23 Jun 2010 00:14:03 -0700, Simon Peyton-Jones simo...@microsoft.com wrote: I'm interested in situations where you think fundeps work and type families don't.  Reason: no one knows how to make fundeps work cleanly with

Re: [Haskell-cafe] Template Haskell sees into abstract data types

On Sat, Jul 3, 2010 at 7:20 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Serguey Zefirov sergu...@gmail.com writes: I cannot directly create my own class instances for them because of that. But I found that I can write Template Haskell code that could do that - those data types

Re: [Haskell-cafe] Associated types

On Thu, Jul 1, 2010 at 2:09 PM, Andrew Coppin andrewcop...@btinternet.com wrote: Consider the following:  class Path p where ...  class Path p = CompletePath p where ...  class Path p = IncompletePath p where   type CompletedPath p :: * Obviously, the idea is that CompletedPath Foo

Re: [Haskell-cafe] Associated types

On Thu, Jul 1, 2010 at 2:35 PM, Christopher Lane Hinson l...@downstairspeople.org wrote: On Thu, 1 Jul 2010, Christopher Lane Hinson wrote: Something like this should work: class (Path p, CompletePath (CompletedPath p)) = IncompletePath p where   type CompletedPath p :: * AIUI, this

Re: [Haskell-cafe] Re: The mother of all functors/monads/categories

On Sun, Jun 27, 2010 at 1:26 PM, Sebastian Fischer s...@informatik.uni-kiel.de wrote: Hi Max, very interesting observations! By the way, you can use this stuff to solve the restricted monad problem (e.g. make Set an instance of Monad). This is not that useful until we find out what the

Re: [Haskell-cafe] Fwd: signficant improvements to the containers package

On Fri, Jun 25, 2010 at 12:58 AM, Ivan Miljenovic ivan.miljeno...@gmail.com wrote: On 25 June 2010 14:41, David Menendez d...@zednenem.com wrote: On Thu, Jun 24, 2010 at 3:08 AM, Ivan Miljenovic ivan.miljeno...@gmail.com wrote: As an aside, Alex Mason and I are discussing the possibility

Re: [Haskell-cafe] Fwd: signficant improvements to the containers package

On Thu, Jun 24, 2010 at 3:08 AM, Ivan Miljenovic ivan.miljeno...@gmail.com wrote: As an aside, Alex Mason and I are discussing the possibility of taking advantage of AusHack *shameless plug* to write some kind of classes for the different types of containers with a hierarchy.  I know about

Re: [Haskell-cafe] MonadCatchIO-transformers and ContT

On Mon, Jun 21, 2010 at 7:04 AM, Neil Brown nc...@kent.ac.uk wrote: Here's my speculation, based on glancing at the libraries involved: I believe the reason for this may be the MonadCatchIO instance for ContT: === instance MonadCatchIO m = MonadCatchIO (ContT r m) where   m `catch` f =

Re: [Haskell-cafe] Re: Different choice operations in a continuation monad

On Fri, Jun 18, 2010 at 12:44 PM, Heinrich Apfelmus apfel...@quantentunnel.de wrote: Sebastian Fischer wrote: Edward Kmett wrote: Sebastian Fischer wrote: Heinrich Apfelmus wrote: newtype CMaybe a = CMaybe (forall r. (a - Maybe r) - Maybe r) Yes, with this type `orElse` has the same type as

Re: Proposal to solve Haskell's MPTC dilemma

On Thu, May 27, 2010 at 10:39 AM, Carlos Camarao carlos.cama...@gmail.com wrote: Isaac Dupree: Your proposal appears to allow /incoherent/ instance selection. This means that an expression can be well-typed in one module, and well-typed in another module, but have different semantics in the

[Haskell-cafe] Re: Proposal to solve Haskell's MPTC dilemma

On Thu, May 27, 2010 at 10:39 AM, Carlos Camarao carlos.cama...@gmail.com wrote: Isaac Dupree: Your proposal appears to allow /incoherent/ instance selection. This means that an expression can be well-typed in one module, and well-typed in another module, but have different semantics in the

Re: [Haskell-cafe] Proposal to solve Haskell's MPTC dilemma

On Fri, May 21, 2010 at 3:56 AM, Max Bolingbroke batterseapo...@hotmail.com wrote: On 21 May 2010 01:58, Carlos Camarao carlos.cama...@gmail.com wrote: But this type-correct program would become not typeable if instances such as the ones referred to before (by Daniel Fischer) I was thinking

Re: [Haskell-cafe] FW: Why does this Ord-class instance crash?

2010/5/21 R J rj248...@hotmail.com: Why does the following, trivial  code snippet below hang GHCi when I type Scalene Failure, and what's the fix? An instance of Ord must declare compare or (=). You only defined (), so () is using the default definition. Here are the defaults: compare x y

Re: [Haskell-cafe] Type of (= f) where f :: a - m b

On Mon, May 10, 2010 at 5:51 AM, Milind Patil milind_pa...@hotmail.com wrote: For a function f ::  a - m b f = undefined I am having trouble understanding how the type of (= f) is (= f) :: m a - m b where, by definition, type of (=) is (=) :: (Monad m) = m a - (a - m b) - m b I

Re: [Haskell-cafe] IO (Either a Error) question

On Sat, May 8, 2010 at 1:16 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: David Menendez d...@zednenem.com writes: On Sat, May 8, 2010 at 12:15 AM, Ivan Lazar Miljenovic Well, any time you have a do-block like this you're using failable patterns: maybeAdd       :: Maybe Int

Re: [Haskell-cafe] IO (Either a Error) question

On Fri, May 7, 2010 at 10:26 PM, John Meacham j...@repetae.net wrote: On Fri, May 07, 2010 at 08:27:04PM -0400, Dan Doel wrote: Personally, I don't really understand why unfailable patterns were canned (they don't seem that complicated to me), so I'd vote to bring them back, and get rid of

Re: [Haskell-cafe] IO (Either a Error) question

On Sat, May 8, 2010 at 12:15 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: David Menendez d...@zednenem.com writes: I wonder how often people rely on the use of fail in pattern matching. Could we get by without fail or unfailable patterns? ensureCons :: MonadPlus m = [a] - m

Re: Haskell 2010 libraries

On Fri, Apr 30, 2010 at 8:19 AM, Malcolm Wallace malcolm.wall...@cs.york.ac.uk wrote: Because I suggest that portablebase re-export the haskell2010 API in its entirety, it would be impossible to use both packages explicitly at the same time from a single module - users would need to choose one

Re: [Haskell-cafe] Rank-2 polymorphism and overloading

On Mon, Apr 26, 2010 at 2:55 PM, Thomas van Noort tho...@cs.ru.nl wrote: On 26-4-2010 20:12, Daniel Fischer wrote: Am Montag 26 April 2010 19:52:23 schrieb Thomas van Noort: ... Yes, y's type is more general than the type required by f, hence y is an acceptable argument for f - even z ::

Re: [Haskell-cafe] Proper Handling of Exceptional IEEE Floating Point Numbers

On Sat, Apr 24, 2010 at 5:56 AM, Barak A. Pearlmutter ba...@cs.nuim.ie wrote: Even deriving(Ord) only produces compare and relies on standard definitions for other methods. I don't think that's actually a problem.  Surely the IEEE Floating Point types would give their own definitions of not

Re: [Haskell-cafe] The instability of Haskell libraries

On Fri, Apr 23, 2010 at 10:11 PM, John Goerzen jgoer...@complete.org wrote: Don Stewart wrote: Oh, the Platform has very strict standards about APIs, When a package may be added:    http://trac.haskell.org/haskell-platform/wiki/AddingPackages That looks like a very solid document.  Does it

[Haskell-cafe] Re: Move MonadIO to base

On Sun, Apr 18, 2010 at 5:02 PM, wren ng thornton w...@community.haskell.org wrote: Heinrich Apfelmus wrote: Anders Kaseorg wrote: This concept can also be generalized to monad transformers: class MonadTrans t = MonadTransMorph t where    morph :: Monad m = (forall b. (t m a - m b) - m b)

Re: [Haskell-cafe] Integers v ints

On Thu, Apr 1, 2010 at 5:27 AM, Jens Blanck jens.bla...@gmail.com wrote: I was wondering if someone could give me some references to when and why the choice was made to default integral numerical literals to Integer rather than to Int in Haskell. Also, if you are aware of similar discussions in

Re: [Haskell-cafe] GHC vs GCC

On Sat, Mar 27, 2010 at 12:56 AM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: Using bang patterns didn't help almost anything here. Using rem instead of mod made the time go from 45s to 40s. Now, using -fvia-C really helped (when I used rem but not using mod). It went down to 10s.

Re: [Haskell-cafe] GHC vs GCC

On Sat, Mar 27, 2010 at 1:45 PM, Tillmann Rendel ren...@mathematik.uni-marburg.de wrote: Jan-Willem Maessen wrote: It's worth pointing out that there's a bit of bang-pattern mysticism going on in this conversation (which has not been uncommon of late!).  A non-buggy strictness analyzer should

Re: [Haskell-cafe] ANN: data-category, restricted categories

On Fri, Mar 26, 2010 at 11:07 AM, Edward Kmett ekm...@gmail.com wrote: On Fri, Mar 26, 2010 at 11:04 AM, Edward Kmett ekm...@gmail.com wrote: -- as long as you're ignoring 'seq' terminateSeq :: a - Unit terminateSeq a = a `seq` unit Er ignore that language about seq. a `seq` unit is

Re: [Haskell-cafe] Why is it so different between 6.12.1 and 6.10.4_1 ?

On Fri, Mar 26, 2010 at 8:20 PM, zaxis z_a...@163.com wrote: In 6.12.1 under archlinux let f x y z = x + y + z :t f f :: (Num a) = a - a - a - a :t (=) . f (=) . f :: (Num a) = a - ((a - a) - a - b) - a - b ((=) . f) 1 (\f x - f x) 2 5 In 6.10.4_1 under freebsd let f x y z = x + y + z

Re: [Haskell-cafe] Why is it so different between 6.12.1 and 6.10.4_1 ?

On Fri, Mar 26, 2010 at 8:59 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: zaxis z_a...@163.com writes: In 6.10.4_1 under freebsd let f x y z = x + y + z *Money :t f f :: (Num a) = a - a - a - a :t (=) . f (=) . f  :: (Monad ((-) a), Num a) = a - ((a - a) - a - b) - a - b

Re: [Haskell-cafe] Why is it so different between 6.12.1 and 6.10.4_1 ?

On Fri, Mar 26, 2010 at 9:13 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: David Menendez d...@zednenem.com writes: On Fri, Mar 26, 2010 at 8:59 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Some definitions and exports got changed, so in 6.12 the (- a) Monad

Re: [Haskell-cafe] Re: Occurs check error, help!

On Sun, Mar 21, 2010 at 11:31 PM, adamtheturtle kill2thr...@hotmail.com wrote: So I have the code shuffle :: Int - [a] - [a] shuffle i [] = [] shuffle i cards = (cards!!i) : shuffle (fst pair) (delete (cards!!i) cards)    where pair = randomR (0, 51) (mkStdGen 42) and it doesn't work, am I

Re: [Haskell-cafe] Re: Generating repeatable arbitrary values with QuickCheck 2

On Fri, Feb 5, 2010 at 3:39 PM, Ryan Ingram ryani.s...@gmail.com wrote: On Fri, Feb 5, 2010 at 5:19 AM, Martijn van Steenbergen mart...@van.steenbergen.nl wrote: Ryan Ingram wrote: Unfortunately, this makes things like  infinite_xs - sequence (repeat arbitrary) no longer work, since the

Re: [Haskell-cafe] Re: Generating repeatable arbitrary values with QuickCheck 2

On Tue, Feb 2, 2010 at 1:48 PM, Ryan Ingram ryani.s...@gmail.com wrote: Gen slightly breaks the monad laws: arbitrary = return is not the same as return () = const arbitrary because each bind splits the generator, so you end up with a different seed passed to arbitrary in these two cases.

Re: [Haskell-cafe] very strange utf8 problem

2010/2/1 Günther Schmidt gue.schm...@web.de: Hi all, I know this sounds daft but I do have good reason to ask. Is it possible that GHC's core itself has a problem with a particular Umlaut only? HDBC-ODBC won't read in data from an SQLite database as soon as it comes accross a *lowercase*

Re: [Haskell-cafe] Capped lists and |append|

On Fri, Jan 8, 2010 at 6:38 PM, John Millikin jmilli...@gmail.com wrote: Earlier today I uploaded the capped-list package; I didn't think there would be any interest, since it's a relatively trivial data structure, but already there's been three emails and an IRC convo about it. In short,

Re: [Haskell-cafe] (liftM join .) . mapM

On Tue, Dec 29, 2009 at 12:24 PM, Stephen Tetley stephen.tet...@gmail.com wrote: oo is one of of a family of functions I use often to avoid sectioning/composing mania. It's known to Raymond Smullyan fans as 'blackbird', though I call it oo as a pun on Standard MLs o (which is Haskells (.) of

Re: [Haskell-cafe] Parse do block problem

On Mon, Dec 21, 2009 at 11:14 PM, joeltt j...@harpsoft.com wrote: I'm trying to write my first Haskell program. The below is the first real logic block I've tried to write, unfortunately I get a The last statement in a 'do' construct must be an expression error when loading the method.

Re: [Haskell-cafe] Rebox Package or To Hackage or not to Hackage

On Tue, Dec 8, 2009 at 4:25 PM, Vitaliy Akimov vitaliy.aki...@gmail.com wrote: Hi John, I don't know if this is useful for you, but these are instances of Cofunctor's comap. For example if we use TypeCompose package we have: rebox f = unFlip . cofmap f . Flip Alternately, rebox = flip (.)

Re: [Haskell-cafe] What is the rank of a polymorphic type?

On Sun, Dec 6, 2009 at 8:39 AM, Dan Doel dan.d...@gmail.com wrote: Apologies for the double-reply... Your mail prompted me to finally get around to adding a mono/polytype system to an interpreter I've been working on for pure type systems, to see what a GHC-alike type system would look like.

Re: [Haskell-cafe] Are there standard idioms for lazy, pure error handling?

On Fri, Dec 4, 2009 at 1:14 PM, Jason McCarty jmcca...@sent.com wrote: wren ng thornton wrote:     concat1 :: T a b - (b - T a b) - T a b This could just as easily be  concat :: T a b - (b - T a c) - T a c right? It's a little weird to call this concatenation, but I bet it could come in

Re: [Haskell-cafe] Optimization with Strings ?

On Thu, Dec 3, 2009 at 12:32 PM, Alec Berryman a...@thened.net wrote: Emmanuel CHANTREAU on 2009-12-03 13:03:02 +0100: In my futur program, it use a lot of binary trees with strings (words) as leaf. There is just arround 1000 words and they will appear a lot of times. The program will

Re: [Haskell-cafe] Implicit newtype unwrapping

On Thu, Dec 3, 2009 at 6:28 AM, Joachim Breitner m...@joachim-breitner.de wrote: Hi, Am Donnerstag, den 03.12.2009, 11:13 + schrieb Matthew Pocock: Perhaps what you are looking for is a more powerful defining semantics? newtype MyFoo = Foo defining (Foo(..)) -- all class instances that

Re: [Haskell-cafe] Implicit newtype unwrapping

On Wed, Dec 2, 2009 at 7:16 PM, Martijn van Steenbergen mart...@van.steenbergen.nl wrote: So here's a totally wild idea Sjoerd and I came up with. What if newtypes were unwrapped implicitly? As several have suggested, this creates ambiguity. But it might be handy to have a way to declare a

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