Re: [Haskell-cafe] type constructor section for (- Bool), _not_ ((-) Bool)
On Tue, Sep 03, 2013 at 11:33:46AM +, AntC wrote: I'm probably being dumb, but Hoogle nor the wiki are helping me. I want an instance and type improvement constraint of the form instance (f ~ (- Bool)) = C Foo (f b) where ... The first arg to C is driving type improvement, for example: instance (f ~ []) = C Bar (f b) where ... (The real instances are more complex, and involve overlap, of course.) I'm trying to write a section to get the improved type (b - Bool), but (- Bool) or ((- Bool) b) is invalid syntax. There is no operator section syntax for types. Moreover, this is not just an issue of syntax: it is impossible to partially apply a type constructor to anything other than its first argument, because there is no type-level lambda. This is valid, but wrong: ((-) Bool) b -- gives (Bool - b). I could do: data FlipFun b -- abstract instance (f ~ FlipFun) = C Foo (f b) where ... And a type function inside the class to generate the type. But then I'd have to apply the type function for all instances, and in most places it'd be id. That's the only way to do it that I know of. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] One-element tuple
On Fri, Aug 16, 2013 at 01:35:22AM +, AntC wrote: There's an annoying inconsistency: (CustId 47, CustName Fred, Gender Male) -- threeple (CustId 47, CustName Fred)-- twople -- (CustId 47)-- oneple not! () -- nople (That is, it's annoying if you're trying to make typeclass instances for extensible/contractable tuples. Yes, I know I could use HLists.) I'm not happy with either approach I've tried: data Oneple a = Oneple a -- (or newtype) (Oneple $ CustId 47) -- too verbose type Oneple a = [a] [CustId 47] -- at least looks bracket-y What do you do? This is what the OneTuple package is for: http://hackage.haskell.org/package/OneTuple -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Call for Participation: Workshop on Functional Art, Music, Modeling and Design
== FARM 2013: Call for Participation ACM SIGPLAN Workshop on Functional Art, Music, Modeling and Design Boston, Massachusetts, USA 28th September, 2013 (directly after ICFP) http://www.cis.upenn.edu/~byorgey/farm13/ == The functional programming community is largely interested in writing beautiful programs. This workshop is intended to gather researchers and practitioners interested in writing beautiful programs that generate beautiful artifacts. Such artifacts may include visual art, music, 3D sculptures, animations, GUIs, video games, physical models, architectural models, choreographies for dance, poetry, and even physical objects such as VLSI layouts, GPU configurations, or mechanical engineering designs. The goal of FARM is to gather together researchers, practitioners, and educators in this interdisciplinary field, as well as anyone else with even a casual interest in the area. We wish to share ideas, look for common ground, and encourage more activity. We also hope to legitimize work in the field and facilitate potential collaboration among the participants. Registration Deadline for early registration: 22 August 2013 https://regmaster3.com/2013conf/ICFP13/register.php This is the registration site for ICFP 2013 and all the affiliated workshops including FARM 2013. Accepted papers and demonstrations -- - Samuel Aaron and Alan F. Blackwell. From Sonic Pi to Overtone: Creative Musical Experiences with Domain-Specific and Functional Languages - Henrik Bäärnhielm, Mikael Vejdemo-Johansson and Daniel Sundström. Using Haskell as DSL for controlling immersive media experiences (Demo) - Guillaume Baudart, Louis Mandel and Marc Pouzet. Programming Mixed Music in ReactiveML - Jean Bresson, Raphael Foulon and Marco Stroppa. Reduction as a Transition Controller for Sound Synthesis Events - Kelsey D'Souza. PySTEMM - A STEM Learning Tool for Exploring and Building Executable Concept Models (Demo) - Andy Gill and Brent A. Yorgey. Functional active animation (Demo) - Jason Hemann and Eric Holk. Visualizing the Turing Tarpit - Paul Hudak. Euterpea: From Signals to Symphonies (Demo) - David Janin, Florent Berthaut, Myriam Desainte-Catherine, Yann Orlarey and Sylvain Salvati. The T-Calculus : towards a structured programing of (musical) time and space - David Janin and Florent Berthaut. LiveTuiles for tiled composition of audio patterns (Demo) - Thomas Jordan. Spontaneous Musical Explorations of Visible Symmetric Structures (Demo) - Hendrik Vincent Koops, José Pedro Magalhães and W. Bas de Haas. A Functional Approach To Automatic Melody Harmonisation - José Pedro Magalhães, Bas De Haas, Gijs Bekenkamp, Dion ten Heggeler and Tijmen Ruizendaal. Chordify: Chord Transcription for the Masses (Demo) - Donya Quick and Paul Hudak. Grammar-Based Automated Music Composition in Haskell - Chung‐chieh Shan and Dylan Thurston. Braiding in circles (Demo) Workshop Organization - Workshop Chair: Paul Hudak Program Chair: Conal Elliott Publicity Chair: Brent Yorgey Program Committee - - Daniel Cukier (AgileAndArt) - Conal Elliott (Tabula) (chair) - Kathleen Fisher (Tufts University) - Richard Gabriel (IBM Research) - George Giorgidze (University of Tübingen) - Paul Hudak (Yale University) - José Pedro Magalhães (University of Oxford) - Alex McLean (University of Leeds) - John Peterson (Western State Colorado University) - Michael Sperber (Active Group) - Henning Thielemann (Martin-Luther-Universität Halle-Wittenberg) - Brent Yorgey (University of Pennsylvania) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Do combinatorial algorithms have a matroid strucutre XOR non-matroid structure?
On Thu, Jul 11, 2013 at 03:39:02PM -0700, KC wrote: I ask this on this mailing list because there are quite a few mathematically oriented people here. If you accept the Law of Excluded Middle, everything either has a matroid structure, or not. On the other hand, if you do not accept it, then there may be some combinatorial algorithms which have neither (because we have not found a matroid structure, or proved one does not exist). Either way, I do not understand the point of your question. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Music / MIDI help
Maybe Euterpea? http://haskell.cs.yale.edu/euterpea/download/ On Wed, Jul 10, 2013 at 08:20:08AM -0700, Mark Lentczner wrote: I'm a little lost in the bewildering array of music packages for Haskell, and need some help. I'm looking to recreate one of my algorithmic music compositions from the 1980s. I can easily code the logic in Haskell. I'm looking for a the right set of packages and SW so that I can: a) generate short sequences and play them immediately, preferrably in ghci, -- but 'runHaskell Foo.hs | barPlayer' would be acceptable 2) generate MIDI files I'm on OS X. So far what I've found is: Haskore, the midi package, and the jack package - and then I'd need some MIDI software synth for the Mac, and Jack based patcher Or perhaps I want SuperCollider, and the Haskell bindings - but that seems rather low level for my needs here (I don't really need to patch together my instruments, and I don't want to have re-write the whole timing framework from scratch.) So - What's a quick easy path here? - Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Open Source project suitable for 2-3 persons this fall?
On Thu, Jul 04, 2013 at 05:26:59PM +0200, Anders Bech Mellson wrote: Is there any project that needs working this fall which could be used as a university project? I am in the university (M.Sc. in software development), so I am mainly looking for project ideas (preferably concrete ones). We are 2-3 students that have ~10 hours pr week for 3 months to work on a project. Is there a listing somewhere with project ideas for contributing to the Haskell community? I am a bit late, but there are quite a few things that could be done for the diagrams project [1]. Some project ideas are at [2], and more can be found on the bug tracker [3]. [1] http://projects.haskell.org/diagrams/ [2] http://www.haskell.org/haskellwiki/Diagrams/Projects [3] https://github.com/diagrams/diagrams-lib/issues?state=open -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Call for Demo Proposals: Workshop on Functional Art, Music, Modeling and Design
Hi all, Below is the call for demonstration proposals for FARM 2013. Please forward to anyone who might be interested -- apologies if you receive multiple copies! Brent Yorgey publicity chair for FARM 2013 == FARM 2013: Call for Demo Proposals ACM SIGPLAN Workshop on Functional Art, Music, Modeling and Design Boston, Massachusetts, USA 28th September, 2013 (directly after ICFP) http://www.cis.upenn.edu/~byorgey/farm13/ == Do you enjoy writing beautiful code to produce beautiful artifacts? Have something cool to show off at the intersection of functional programming and visual art, music, sound, modeling, visualization, or design? FARM 2013 is seeking proposals for 10-20 minute demonstrations to be given during the workshop. For example, a demonstration could consist of a short tutorial, an exhibition of some work, or even a livecoding performance. Slots for demonstrations will be shorter than slots for accepted papers, and will not be published as part of the formal proceedings, but can be a great way to show off interesting work and get feedback from other workshop participants. A demonstration slot could be a particularly good way to get feedback on work-in-progress. Scope - The functional programming community is largely interested in writing beautiful programs. This workshop is intended to gather researchers and practitioners interested in writing beautiful programs that generate beautiful artifacts. Such artifacts may include visual art, music, 3D sculptures, animations, GUIs, video games, physical models, architectural models, choreographies for dance, poetry, and even physical objects such as VLSI layouts, GPU configurations, or mechanical engineering designs. The framework used need not be purely functional (“mostly functional” is fine); may be based on abstractions such as higher-order functions, monads, arrows, or streams; and may be manifested as a domain specific language or tool. Theoretical foundations, language design, implementation issues, and applications are all within the scope of the workshop. Important dates --- - Demonstration proposals due: Wednesday, 31 July 2013, 18:00 EDT (UTC-4) - Author notification: Monday, 5 August 2013 - Workshop: Saturday, 28 September 2013 (the day after ICFP) A demo proposal should consist of a 1 page abstract, in PDF format, explaining the proposed content of the demonstration and why it would be of interest to the attendees of FARM. Proposals will be judged on interest and relevance to the stated goals and themes of the workshop. Submissions can be made via EasyChair at https://www.easychair.org/conferences/?conf=farm2013. Organizers -- Workshop Chair: Paul Hudak Program Chair: Conal Elliott Publicity Chair: Brent Yorgey Program Committee - Daniel Cukier (University of São Paulo) Conal Elliott (Tabula) (chair) Kathleen Fisher (Tufts University) Richard Gabriel (IBM Research) George Giorgidze (University of Tübingen) Paul Hudak (Yale University) José Pedro Magalhães (University of Oxford) Alex McLean (University of Leeds) John Peterson (Western State Colorado University) Michael Sperber (Active Group) Henning Thielemann Brent Yorgey (University of Pennsylvania) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GADTs and pattern matching
On Wed, Jun 19, 2013 at 11:11:16AM +0100, Francesco Mazzoli wrote: At Wed, 19 Jun 2013 10:03:27 + (UTC), AntC wrote: Hi Francesco, I think you'll find that the 'annoyance' is nothing to do with GADTs. I suggest you take the type signature off of foo1, and see what type ghc infers for it. It isn't :: a - Foo a - Int. [...] Yep, that message explains what's going on well enough for me. Did you read the rest of the code? That ought to work, because GHC infers and uses the type equality (something like ‘v ~ Var v1’) and uses it to coerce the ‘x’. And, surprise surprise, if the argument order is switched, it works! data Foo v where Foo :: forall v. Foo (Maybe v) foo1 :: Foo a - a - Int foo1 Foo Nothing = undefined foo1 Foo (Just x) = undefined Yes, I was going to suggest switching the argument order before reading your message. This is an interesting way in which you can observe that Haskell does not really have multi-argument functions. All multi-argument functions are really one-argument functions which return functions. So a function of type foo1 :: a - (Foo a - Int) must take something of type a (for *any* choice of a, which the caller gets to choose) and return a function of type (Foo a - Int). *Which* function is returned (e.g. one that tries to pattern match on the Foo) makes no difference to whether foo1 typechecks. On the other hand, a function of type foo2 :: Foo a - (a - Int) receives something of type Foo a as an argument. It may pattern-match on the Foo a, thus bringing into scope the fact that (a ~ Maybe v). Now when constructing the output function of type (a - Int) it may make use of this fact. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: Nomyx 0.2 beta, the game where you can change the rules
This is great fun, more people should come and join us! =) http://www.nomyx.net:8000/Nomyx we are playing game demo3. -Brent On Fri, Jun 14, 2013 at 05:57:57PM +0200, Corentin Dupont wrote: Hello everybody! Here it comes, the second beta release [1] of Nomyx, the only game where You can change the rules!! This is an implementation of a Nomic [2] game in Haskell (I believe the first complete implementation of a Nomic game on a computer). In a Nomyxgame you can change the rules of the game itself while playing it. The players can submit new rules or modify existing ones, thus completely changing the behaviour of the game through time. The rules are managed and interpreted by the computer. They must be written in the Nomyx language, which is a subset of Haskell. At the beginning, the initial rules are describing: - how to add new rules and change existing ones. For example a unanimity vote is necessary to have a new rule accepted. - how to win the game. For example you win the game if you have 5 rules accepted. But of course even that can be changed! Here is a video introduction and first tutorial of the game: http://vimeo.com/58265498 The game is running here: www.nomyx.net:8000/Nomyx I have set up a forum where players can learn about Nomyx and discuss the rules they intend to propose: www.nomyx.net/forum The example file gives a lot of examples of rules that you can submit: www.nomyx.net:8000/src/Language/Nomyx/Examples.hs Changes from V0.1: - new login system: you can now login with your Google, Yahoo, Live Journal, Myspace, OpenId or Facebook accounts (thanks to happstack-authenticate)! - new DSL for voting (see below) - styling: rule code colorized, better settings and help - use cookies to store the user ID (as suggested on this mailing list) - new error system to handle exceptions in rules (with ErrorT) - use lenses I set up a little DSL to create elections (elect one of the players for a special role) or referendums (a yes/no question). You create in one line within Nomyx an vote with unanimity or majority, a quorum and different ballot systems. See here: http://www.nomyx.net/forum/viewtopic.php?f=3t=1518 Let's test it! If you are interested, please go to this forum thread and we'll set up a small team to start a match! http://www.nomyx.net/forum/viewtopic.php?f=4t=1517 The demo game is running here: www.nomyx.net:8000/Nomyx then select game demo2. As the first player of the game, I changed the initial unanimity vote to a simple majority, with a minimum of 2 players voting. Having your new rules accepted will be easy! Let's see who will win :) Cheers, Corentin [1] http://hackage.haskell.org/package/Nomyx [2] www.nomic.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GADTs and pattern matching
Good point. I stand corrected. -Brent On Wed, Jun 19, 2013 at 11:42:23AM -0300, Felipe Almeida Lessa wrote: Brent, maybe I'm misunderstanding what you're saying, but I don't think that the order of the arguments is playing any role here besides defining the order in which the pattern matches are desugared. To illustrate, -- This does work foo1' :: a - Foo a - Int foo1' m Foo = case m of Nothing - undefined Just _ - undefined Despite having the same type as foo1, foo1' does work because now I've pattern matched on the GADT first. As soon as I do that, its equality constraint of (a ~ Maybe v) enters into scope of the case branches. Cheers, On Wed, Jun 19, 2013 at 7:59 AM, Brent Yorgey byor...@seas.upenn.edu wrote: On Wed, Jun 19, 2013 at 11:11:16AM +0100, Francesco Mazzoli wrote: At Wed, 19 Jun 2013 10:03:27 + (UTC), AntC wrote: Hi Francesco, I think you'll find that the 'annoyance' is nothing to do with GADTs. I suggest you take the type signature off of foo1, and see what type ghc infers for it. It isn't :: a - Foo a - Int. [...] Yep, that message explains what's going on well enough for me. Did you read the rest of the code? That ought to work, because GHC infers and uses the type equality (something like ‘v ~ Var v1’) and uses it to coerce the ‘x’. And, surprise surprise, if the argument order is switched, it works! data Foo v where Foo :: forall v. Foo (Maybe v) foo1 :: Foo a - a - Int foo1 Foo Nothing = undefined foo1 Foo (Just x) = undefined Yes, I was going to suggest switching the argument order before reading your message. This is an interesting way in which you can observe that Haskell does not really have multi-argument functions. All multi-argument functions are really one-argument functions which return functions. So a function of type foo1 :: a - (Foo a - Int) must take something of type a (for *any* choice of a, which the caller gets to choose) and return a function of type (Foo a - Int). *Which* function is returned (e.g. one that tries to pattern match on the Foo) makes no difference to whether foo1 typechecks. On the other hand, a function of type foo2 :: Foo a - (a - Int) receives something of type Foo a as an argument. It may pattern-match on the Foo a, thus bringing into scope the fact that (a ~ Maybe v). Now when constructing the output function of type (a - Int) it may make use of this fact. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Second Call for Papers: Workshop on Functional Art, Music, Modeling, and Design (colocated with ICFP)
Please submit something to FARM --- the deadline is fast approaching! == FARM 2013: Call for Papers ACM SIGPLAN Workshop on Functional Art, Music, Modeling and Design Boston, Massachusetts, USA 28th September, 2013 (directly after ICFP) http://www.cis.upenn.edu/~byorgey/farm13/ == Scope - The functional programming community is largely interested in writing beautiful programs. This workshop is intended to gather researchers and practitioners interested in writing beautiful programs that generate beautiful artifacts. Such artifacts may include visual art, music, 3D sculptures, animations, GUIs, video games, physical models, architectural models, choreographies for dance, poetry, and even physical objects such as VLSI layouts, GPU configurations, or mechanical engineering designs. The framework used need not be purely functional (“mostly functional” is fine); may be based on abstractions such as higher-order functions, monads, arrows, or streams; and may be manifested as a domain specific language or tool. Theoretical foundations, language design, implementation issues, and applications are all within the scope of the workshop. Important dates --- - Submissions due: Friday, 14 June 2013, 23:59 UTC-11 (American Samoa time [1]) - Author notification: Thursday, 11 July 2013 - Final papers due: Thursday, 25 July 2013 - Workshop: Saturday, 28 September 2013 (the day after ICFP) [1] http://www.timeanddate.com/worldclock/fixedtime.html?msg=FARM+submissions+dueiso=20130614T2355p1=1033 Proceedings --- There will be a formal proceedings published by ACM Press. Accepted papers will be included in the ACM Digital Library; see http://authors.acm.org/main.cfm for information on the options available to authors. Authors are also encouraged to submit auxiliary material for publication along with their paper (source code, data, videos, images, etc.); authors retain all rights to the auxiliary material. Submission details -- We solicit submissions in two categories: - Full papers. A full paper is limited to 12 pages, and will be evaluated according to its relevance, correctness, significance, originality, and clarity. It should explain its contributions, identify what has been accomplished, explain why it is significant, and compare it with previous work. - Aesthetic applications. An aesthetic application paper is limited to 6 pages, and will be judged primarily on the effective and elegant use of FP to generate aesthetic artifacts (though the criteria for full papers are still relevant). Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines. The text should be in a 9-point font in two columns. Submissions can be made via EasyChair at https://www.easychair.org/conferences/?conf=farm2013 Organizers -- Workshop Chair: Paul Hudak Program Chair: Conal Elliott Publicity Chair: Brent Yorgey Program Committee - Daniel Cukier (University of São Paulo) Conal Elliott (Tabula) (chair) Kathleen Fisher (Tufts University) Richard Gabriel (IBM Research) George Giorgidze (University of Tübingen) Paul Hudak (Yale University) José Pedro Magalhães (University of Oxford) Alex McLean (University of Leeds) John Peterson (Western State Colorado University) Michael Sperber (Active Group) Henning Thielemann Brent Yorgey (University of Pennsylvania) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Yi Google summer of code project
Generally, for a successful proposal you need to already find someone who is willing to mentor the project. Honestly, I do not think working on Yi would make for a very strong proposal. It is definitely a cool piece of software, and definitely worth working on, but it does not have a very large userbase and so the benefit of this project to the Haskell community would be small. -Brent On Mon, Apr 22, 2013 at 02:12:02PM -0400, Gmail wrote: Hello again, I forgot to ask if I need to find myself a mentor or one will be assigned to me by haskell.org? Many thanks, Bastien On 4/21/13 5:57 PM, Bastien Jacot-Guillarmod wrote: Hello, I'm interested in doing some improvments on the Yi editor for my Google summer of code by implementing a completion pop up list for any buffer and a smart completion for haskell. But I don't really know if this kind of project could be acceptable, for the following reason: 1) Should a GSoC project be mostly a working experience or also a learning one? I am not the most seasoned haskell programmer, but I really which to dive into a real-life project in this language. 2) Is it too long, too small? I don't have too many years of programmation in haskell behind me even if I have done some functionnal programming in other languages (Scala most of the time), hence I don't want to take something that will be overwhelming. 3) is Yi associated with haskell.org or it is not possible to have a project on Yi while being mentored by haskell? Thanks for your insight! Regards, Bastien Jacot-Guillarmod, 3rd CS bachelor student at EPFL (Lausanne) -- View this message in context: http://haskell.1045720.n5.nabble.com/Yi-Google-summer-of-code-project-tp5729090.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell compilation errors break the complexity encapsulation on DSLs
On Tue, Apr 23, 2013 at 12:49:59PM +0200, Alberto G. Corona wrote: Hi I ever was worried about the barrier that the complexity of the Haskell errors impose to users of DSLs. Many DSLs look so simple that even someone without knowledge of Haskell can make use of them for some domains. However when the program is compiled then al the monsters of the deep appear in the surface: polymorphisms, undefined instances, type errors reported in a line produced by a type assumption in another, etc. This is a problem for an industrial use of Haskell in the large scale. For obvious reasons. Indeed. For example, in my experience this is a big problem for diagrams. The question: Is it possible to develop a GHC extension that attach (or prepend) such an explanation to the ghc error? Or any other alternative that carry out the same functionality. Surely it is possible. I have wanted this too. I guess the majority of the work would just be in coming up with a good, general design which is useful but not too difficult to implement. If anyone wanted to undertake such a project I would be happy to contribute some ideas. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unbound: rebind and unrebind
Hi Eric,
On Sun, Apr 14, 2013 at 10:57:43AM -0700, Eric Dobson wrote:
I am working at reimplementing the library Unbound to understand how
it works. One issue I have come up with is that an equation that I
thought held true doesn't. The equation is: Forall e::Rebind a b, e
`aeq` (uncurry rebind . unrebind $ e) = True. That is that spliting
the binding of a rebind and then adding it back should be the
identity. The issue is that Rebind does not freshen its pattern
variables on unrebind, because it assumes that a higher level unbind
already did that if required. But I believe this is not sufficient as
there is not necesarily a higher level Bind to be ubound as shown by
this program:
You're right that you *can* write a program involving a Rebind without
a higher level Bind. But you *should not*. This is explained in the
documentation [1] and in the paper [2]. Briefly, there are two classes of types,
term types and pattern types. You should only use term types to
represent data in your programs. Rebind constructs a pattern type,
and as such should only be used in the context of an enclosing Bind.
It would be much nicer if we were able to track this distinction
directly in Haskell's type system and somehow prevent users from using
pattern types directly, but we do not know of a way to do this.
-Brent
[1]
http://hackage.haskell.org/packages/archive/unbound/0.4.1.1/doc/html/Unbound-LocallyNameless.html#g:4
[2] Stephanie Weirich, Brent A. Yorgey, and Tim Sheard. Binders
Unbound. ICFP'11, September 2011, Tokyo,
Japan. http://www.cis.upenn.edu/~byorgey/papers/binders-unbound.pdf.
{-# LANGUAGE TemplateHaskell, UndecidableInstances,
FlexibleInstances, MultiParamTypeClasses #-}
module Main where
import Unbound.LocallyNameless
data Exp = Var (Name Exp) deriving Show
$(derive [''Exp])
instance Alpha Exp
instance Subst Exp Exp where
isvar (Var x) = Just (SubstName x)
x :: Name Exp
x = string2Name x
y :: Name Exp
y = string2Name y
rebindPass :: Alpha a = Rebind Exp a - Rebind Exp a
rebindPass = (uncurry rebind . unrebind)
main :: IO ()
main = do
let rebound = (rebind (Var y) (Embed (Var x)))
print $ rebound
let substed = subst x (Var y) rebound
print $ substed
print $ unrebind substed
print $ rebindPass substed
Which outputs:
Var y {Var x}
Var y {Var y}
(Var y,{Var y})
Var y {Var 0@0}
If the equation holds true then the second and fourth lines should be
identical but they are not. Can someone explain why this is the
correct behavior or if the implementation is incorrect?
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[Haskell-cafe] Call for Papers: Workshop on Functional Art, Music, Modeling, and Design (colocated with ICFP)
== FARM 2013: Call for Papers ACM SIGPLAN Workshop on Functional Art, Music, Modeling and Design Boston, Massachusetts, USA 28th September, 2013 (directly after ICFP) http://www.cis.upenn.edu/~byorgey/farm13/ == Scope - The functional programming community is largely interested in writing beautiful programs. This workshop is intended to gather researchers and practitioners interested in writing beautiful programs that generate beautiful artifacts. Such artifacts may include visual art, music, 3D sculptures, animations, GUIs, video games, physical models, architectural models, choreographies for dance, poetry, and even physical objects such as VLSI layouts, GPU configurations, or mechanical engineering designs. The framework used need not be purely functional (“mostly functional” is fine); may be based on abstractions such as higher-order functions, monads, arrows, or streams; and may be manifested as a domain specific language or tool. Theoretical foundations, language design, implementation issues, and applications are all within the scope of the workshop. Important dates --- - Submissions due: Friday, 14 June 2013, 23:59 UTC-11 (American Samoa time [1]) - Author notification: Thursday, 11 July 2013 - Final papers due: Thursday, 25 July 2013 - Workshop: Saturday, 28 September 2013 (the day after ICFP) [1] http://www.timeanddate.com/worldclock/fixedtime.html?msg=FARM+submissions+dueiso=20130614T2355p1=1033 Proceedings --- There will be a formal proceedings published by ACM Press. Accepted papers will be included in the ACM Digital Library; see http://authors.acm.org/main.cfm for information on the options available to authors. Authors are also encouraged to submit auxiliary material for publication along with their paper (source code, data, videos, images, etc.); authors retain all rights to the auxiliary material. Submission details -- We solicit submissions in two categories: - Full papers. A full paper is limited to 12 pages, and will be evaluated according to its relevance, correctness, significance, originality, and clarity. It should explain its contributions, identify what has been accomplished, explain why it is significant, and compare it with previous work. - Aesthetic applications. An aesthetic application paper is limited to 6 pages, and will be judged primarily on the effective and elegant use of FP to generate aesthetic artifacts (though the criteria for full papers are still relevant). Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines. The text should be in a 9-point font in two columns. Submissions can be made via EasyChair at https://www.easychair.org/conferences/?conf=farm2013 Organizers -- Workshop Chair: Paul Hudak Program Chair: Conal Elliott Publicity Chair: Brent Yorgey Program Committee - Daniel Cukier (AgileAndArt) Conal Elliott (Tabula) (chair) Kathleen Fisher (Tufts University) Richard Gabriel (IBM Research) George Giorgidze (University of Tübingen) Paul Hudak (Yale University) José Pedro Magalhães (University of Oxford) Alex McLean (ICSRiM) John Peterson (Western State Colorado University) Michael Sperber (Active Group) Henning Thielemann (Martin-Luther-Universität Halle-Wittenberg) Brent Yorgey (University of Pennsylvania) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANN: adobe-swatch-exchange-0.1.0.0
(Redirecting follow-up to haskell-cafe) Very cool! I have been hoping someone will find a way to integrate kuler.adobe.com with diagrams, and this will help a lot. =) https://github.com/diagrams/diagrams-lib/issues/77 -Brent On Wed, Apr 03, 2013 at 06:49:34PM -0500, Jeremy Shaw wrote: I am pleased to annouce the release of adobe-swatch-exchange 0.1.0.0. My primary motivation in writing this is to make it easier to download color swatches from http://kuler.adobe.com/ and test them on my site. Though, perhaps there is already a great way of doing this and I didn't look hard enough. But, the end result is we can now read and write .ASE files in Haskell and convert them to .css. So that probably opens up some new possibilities. I have provided both a library and an executable. I have also used this as a way to test the waters with github, https://github.com/stepcut/ase2css I heard putting things on github will get me all sorts of contributors. I suggest someone start with haddock comments. ;) Cheers! - jeremy ___ Haskell mailing list hask...@haskell.org http://www.haskell.org/mailman/listinfo/haskell ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal install pandoc
On Fri, Mar 29, 2013 at 08:05:47AM -0230, Roger Mason wrote: Thank you for your response. 'ghc-pkg check' shows some problems: http://pastebin.ca/2344794 On 03/28/2013 08:01 PM, Patrick Wheeler wrote: So I printed off the requirements for pandoc on a empty ghc-7.6.2 install you can find it at: http://hpaste.org/84794 I do not see any odd package versions listed in what you posted so far. No promise I will be able to help afterwards but it might help to see the full log, and then again with verbosity turned on. So seperate pastes for: * `cabal install pandoc --dry-run` * `cabal install pandoc --dry-run --verbose=2` * `cabal install pandoc --dry-run --verbose=3` You might also want to run a `ghc-pkg check` to check to see if your packages are consistent/unbroken. 'ghc-pkg check' shows some problems: http://pastebin.ca/2344794 It looks like your entire Haskell Platform installation is completely hosed. Sad to say, but I think your best bet is to simply reinstall the Haskell Platform. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enumerating functions at runtime
On Sat, Mar 23, 2013 at 08:26:52PM -0700, Luke Evans wrote: I'm curious about using Haskell for metaprogramming. It looks like I can dynamically compile, load and run some Haskell with the plugins package. Actually I've briefly tried this and it seems to work for some simple cases at least. Now I would like to be able to enumerate precompiled public functions in modules that I might use as building blocks in such dynamic compilation. So far I'm not seeing anything that does this directly. Can anyone provide some pointers? If it's just not possible to introspect on compiled modules, then I suppose I could use external metadata of my own, or even perhaps haddock info if it exists, to attempt to generate this info. Clearly though, that's nowhere near as good as extracting the info from something the compiler built directly. I have no idea how it works, but I'm pretty sure yi does this --- e.g. if you hit M-x (when in emacs emulation mode) and then tab-complete, you see a list of all the available functions. Maybe you want to take a look at the yi source code and see how they do it. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Excercise on tagless final interpreters
On Thu, Mar 21, 2013 at 11:32:21AM +0100, matteo vezzola wrote:
I'm playing with tagless final interpreters reading [1], using a very simple
language:
class Ints repr where
int :: Integer - repr Integer
(.+.) :: repr Integer - repr Integer - repr Integer
(.*.) :: repr Integer - repr Integer - repr Integer
(.-.) :: repr Integer - repr Integer
(.=.) :: repr Integer - repr Integer - repr Bool
newtype P repr t = P { unP :: Bool - repr t }
instance Ints repr = Ints (P repr) where
int n = P $ \ s - if s then int n else (.-.) (int n)
(.-.) n = P $ unP n . not
n .+. m = P $ \ s - unP n s .+. unP m s
n .*. m = P $ \ s - unP n s .*. unP m s
n .=. m = P $ \ s - unP n s .=. unP m s
Incidentally, these last two lines seem wrong. It is not the case
that -(n*m) = (-n)*(-m) or that n = m iff (-n) = (-m).
-Brent
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Re: [Haskell-cafe] A question about data declaration
On Thu, Mar 21, 2013 at 06:18:46PM +0530, C K Kashyap wrote: Hi, I have a situation where I need to define a data type T such that data T = C1 Int | C2 Char | C3 T However, I want to enforce a constraint that C3 only allows (C2 Char) and not (C1 Int). That is If C3 should only be able to hold a C2 Char, then why have it hold a T at all? i.e. why not data T = C1 Int | C2 Char | C3 Char but I suppose your real problem is probably more complicated, in which case I would recommend using a GADT as others have suggested. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Open-source projects for beginning Haskell students?
On Mon, Mar 11, 2013 at 11:50:38AM -0700, Ben wrote: On Mar 11, 2013, at 11:26 AM, Jason Dagit wrote: Myself and several of my friends would find it useful to have a plotting library that we can use from ghci to quickly/easily visualize data. Especially if that data is part of a simulation we are toying with. Therefore, this proposal is for: A gnuplot-, matlab- or plotinum-like plotting API (that uses diagrams as the backend?). The things to emphasize: * Easy to install: No gtk2hs requirement. Preferably just pure haskell code and similar for any dependencies. Must be cross platform. * Frontend: graphs should be easy to construct; customizability is not as important * Backend: options for generating static images are nice, but for the use case we have in mind also being able to render in a window from ghci is very valuable. (this could imply something as purely rendering to JuicyPixels and I could write the rendering code) * What I would hope from you is a willingness to exchange email and/or chat with the student(s) over the course of the project, to give them a bit of guidance/mentoring. I am certainly willing to help on that front, but of course I probably don't know much about your particular project. I am willing/able to take on the mentoring aspect :) i second this, but with a different emphasis. i would like a ggplot2-type DSL for generating graphs, for data analysis and exploration. i agree with : * it would be great to have no gtk2hs / cairo requirement. (i guess this means text rendering in the diagrams-svg backend needs to be solved.) i guess in the near-term, this is less important to me -- having a proper plotting DSL at all is an important start. * frontend : graphs should be easy to construct, but having some flexibility is important. the application here is being able to explore statistical data, with slicing, grouping, highlighting, faceting, etc. * backend : static images are enough for me, interactive is a plus. most importantly : it should be fast enough to work pleasantly with large datasets. ggplot2 is pretty awesome but kills my machine, routinely. Not to throw cold water on these ideas (which sound fantastic!), but the scope of this sounds more like a GSoC project than something a beginner could accomplish in 10-15 hours in the space of a few weeks. I'm looking not for project ideas but for small, concrete contributions they could make to existing open source projects. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Trouble installing and using Chart/cairo on windows 7
On Sun, Mar 03, 2013 at 05:38:02PM -0800, bri...@aracnet.com wrote: On Sun, 3 Mar 2013 19:58:37 -0500 Brent Yorgey byor...@seas.upenn.edu wrote: Good access to fonts and font metrics is the kicker. Otherwise I'd say to switch to using diagrams as a backend, hence getting a whole bunch of actual backends for free. I would love to see development of some good Haskell font packages -- maybe it would even make a good GSoC project? Unfortunately I don't know enough about it to even know what would be involved, or how much work it would be. I assume that to use diagram the font package would have to be a vector font system, or could bit-mapped fonts be used ? A vector font system would be ideal, as then you could go crazy turning glyphs into paths and doing whatever the heck you want with them using the diagrams framework. However, bit-mapped fonts could be used too (as long as there is a backend to support them), it would just be less useful. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Trouble installing and using Chart/cairo on windows 7
On Mon, Mar 04, 2013 at 02:30:55PM -0800, bri...@aracnet.com wrote: On Mon, 4 Mar 2013 17:27:29 -0500 Brent Yorgey byor...@seas.upenn.edu wrote: On Sun, Mar 03, 2013 at 05:38:02PM -0800, bri...@aracnet.com wrote: On Sun, 3 Mar 2013 19:58:37 -0500 Brent Yorgey byor...@seas.upenn.edu wrote: Good access to fonts and font metrics is the kicker. Otherwise I'd say to switch to using diagrams as a backend, hence getting a whole bunch of actual backends for free. I would love to see development of some good Haskell font packages -- maybe it would even make a good GSoC project? Unfortunately I don't know enough about it to even know what would be involved, or how much work it would be. I assume that to use diagram the font package would have to be a vector font system, or could bit-mapped fonts be used ? A vector font system would be ideal, as then you could go crazy turning glyphs into paths and doing whatever the heck you want with them using the diagrams framework. However, bit-mapped fonts could be used too (as long as there is a backend to support them), it would just be less useful. yes - seems to me that vector fonts are definitely the way to go. it seems like this problem has to already have a solution. maybe all that's needed is a font importer which understands some, already established, vector font representation. Well, there is the SVGFonts package: http://hackage.haskell.org/package/SVGFonts I don't have a good sense of how widely supported this representation is, or how easy it is to convert between it and other font representations. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Trouble installing and using Chart/cairo on windows 7
On Sun, Mar 03, 2013 at 09:22:15PM +0100, Arnaud Bailly wrote: Hello, I am trying to install timeplot and splot on a windows 7 host, using Haskell platform 2012.2.0.0, and I have troubles installing HSChart. First difficulties were installing cairo, which requires Gtk+ libraries and headers. I installed those using a Gtk+-bundle, first in c:\Program Files\. I had to move to d:\soft (eg. a directory without spaces) to be able to install cairo. Then I tried to install Chart and at first failed with a cryptic 'Exit Failure 1' error from cabal. I succeeded when I redirected cabal output to a file, eg: cabal install out 21 whereas a plain 'cabal install' failed. Then I managed to install splot and timeplot. I then tried to use Chart to draw a simple chart, following http://hackage.haskell.org/packages/archive/Chart/0.16/doc/html/Graphics-Rendering-Chart-Simple.htmland it hang forever with a CPU at 100%. No idea if it's related, but hanging forever with the CPU at 100% reminds me of this: http://code.google.com/p/diagrams/issues/detail?id=71 Unfortunately, GTK + cairo are notoriously difficult to install on OSX and Windows. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Trouble installing and using Chart/cairo on windows 7
On Mon, Mar 04, 2013 at 11:26:23AM +1100, Tim Docker wrote: On 04/03/13 07:22, Arnaud Bailly wrote: Then I managed to install splot and timeplot. I then tried to use Chart to draw a simple chart, following http://hackage.haskell.org/packages/archive/Chart/0.16/doc/html/Graphics-Rendering-Chart-Simple.html and it hang forever with a CPU at 100%. As the author of the Chart library, I'm sorry to say I don't know. Chart is developed under linux, and I do occasional testing under osx, but I don't use windows at all. Chart is a pure haskell library sitting over cairo, so it is most likely a cairo problem rather than a chart one, but I realise this doesn't help you. Do the examples that come with the haskell binding to cairo work for you? Windows and gtk continues to be problematic for many users. I'd love to see an alternative backend for the chart library, but I would need a graphics API that installs easily under windows, osx and linux, and provides good access to fonts and font metrics. Any suggestions? Good access to fonts and font metrics is the kicker. Otherwise I'd say to switch to using diagrams as a backend, hence getting a whole bunch of actual backends for free. I would love to see development of some good Haskell font packages -- maybe it would even make a good GSoC project? Unfortunately I don't know enough about it to even know what would be involved, or how much work it would be. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Split and substitution using regex-pcre
On Fri, Mar 01, 2013 at 08:30:20AM +1300, Alistair Bayley wrote: You cannot bend the split package to your needs? http://hackage.haskell.org/packages/archive/split/0.2.1.2/doc/html/Data-List-Split.html Some combination of splitWhen and a pcre-based predicate? This won't work; splitWhen operates only on single list elements, not on substrings. -Brent On 24 February 2013 22:44, Simon Marechal si...@banquise.net wrote: I could not find the perl-equivalents of these functions on Hackage, so I quickly wrote mine. Code is there: https://github.com/bartavelle/pcre-utils It should behave like perl (not really tested actually), and do strange things like : splitCompile a b Right [b] splitCompile a baaa Right [b] This will go on Hackage as I need it for the language-puppet package, but I am interested in comments, especially concerning the namespaces: * is the name of this package OK ? * is the name of the package OK ? * should I work with the regex-pcre maintainer to try to merge it ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal install ghc-mod installs 3 years old version
On Sun, Feb 24, 2013 at 02:33:55PM +, Niklas Hambüchen wrote: You are right, my ghc-7.4.2 was broken in ghc-pkg list; I fixed the problem by killing my .cabal folder (as so often). Surely you mean by killing your .ghc folder? I do not see what effect killing your .cabal folder could possibly have on broken packages. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type checking the content of a string
On Fri, Feb 22, 2013 at 06:44:06PM +0100, Corentin Dupont wrote: Hi all, I have a program able to read another program as a string, and interpret it (using Hint). I'd like to make unit tests, so I have a file Test.hs containing a serie of test programs as strings. However, how could I be sure that these test program are syntactically valid, at compile time? If you just want to check whether a program is syntactically valid, you can use the haskell-src-exts package to parse it. If you also want to do some type checking you can try the haskell-type-exts package. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hackage suggestion: Gather the list of the licenses of all dependencies of a package
On Sat, Dec 15, 2012 at 08:13:44AM +0100, Petr P wrote: This is strange, I thought that cpphs should be specified in build-tools:, not in build-depends:. http://www.haskell.org/cabal/users-guide/developing-packages.html#build-information Best regards, Petr Presumably the reason to list it in build-depends instead of build-tools is that in the latter case cabal will not automatically install it as a dependency. But you are right that this is a strange situation, since if it is being used only as a preprocessor, semantically it ought to be listed in build-tools. -Brent 2012/12/13 Michael Snoyman mich...@snoyman.com On Thu, Dec 13, 2012 at 9:51 PM, Daniel Trstenjak daniel.trsten...@gmail.com wrote: On Thu, Dec 13, 2012 at 08:40:09PM +0200, Michael Snoyman wrote: If you have a commercial use for cpphs, and feel the terms of the (L)GPL are too onerous, you have the option of distributing unmodified binaries (only, not sources) under the terms of a different licence (see LICENCE-commercial). I think that depedencies to binaries, like cpphs, should be treated differently than depedencies to libraries, because using a (L)GPL-ed binary mostly hasn't any implications for a commercial user and also for the output of a (L)GPL-ed binary usually the (L)GPL doesn't apply. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe In the case of cpphs, there's no way to determine that we're using it as a library or an executable, since it's just listed in the build-depends. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: diagrams-0.6
I am pleased to announce the release of version 0.6 of diagrams [1], a full-featured framework and embedded domain-specific language for declarative drawing. Check out the gallery [2] for examples of what it can do! [3,4] [1] http://projects.haskell.org/diagrams [2] http://projects.haskell.org/diagrams/gallery.html [3] http://mathlesstraveled.com/2012/11/05/more-factorization-diagrams/ [4] http://projects.haskell.org/diagrams/gallery/PythagoreanTree.html Highlights of this release include: - Diagrams now comes with a native-Haskell SVG backend [5] by default. If you were holding off on trying diagrams because you couldn't install cairo, you no longer have an excuse! - Proper support for subdiagrams: previous versions of diagrams-core had a mechanism for associating names with a pair of a location and an envelope. Now, names are associated with actual subdiagrams (including their location and envelope, along with all the other information stored by a diagram). This enables cool techniques like constructing a diagram in order to position its subelements and then taking it apart again, or constructing animations via keyframing. - Traces: in addition to an envelope, each diagram now stores a trace, which is like an embedded raytracer: given any ray (represented by a base point and a vector), the trace computes the closest point of intersection with the diagram along the ray. This is useful for determining points on the boundary of a diagram, e.g. when drawing arrows between diagrams. - The core data structure underlying diagrams has been completely refactored and split out into its own separate package, dual-tree [6]. - Support for GHC 7.6. - Many more new features, bug fixes, and improvements! See the release notes [7] for complete details, and the diagrams wiki [8] for help migrating from 0.5 to 0.6. [5] http://hackage.haskell.org/package/diagrams%2Dsvg [6] http://hackage.haskell.org/package/dual%2Dtree [7] http://projects.haskell.org/diagrams/releases.html Try it out -- For the truly impatient: cabal install diagrams Diagrams is supported under GHC 7.0 through 7.6, with the exception that the cairo and gtk backends do not build under GHC 7.0 (but the SVG backend does), and the gtk backend does not build under GHC 7.6. To get started with diagrams, read the quick tutorial [9], which will introduce you to the fundamentals of the framework. For those who are less impatient and want to really dig in and use the power features, read the user manual [10]. [8] http://www.haskell.org/haskellwiki/Diagrams/Migrate0.6 [9] http://projects.haskell.org/diagrams/tutorial/DiagramsTutorial.html [10] http://projects.haskell.org/manual/diagrams-manual.html Get involved Subscribe to the project mailing list [11], and/or come hang out in the #diagrams IRC channel on freenode.org for help and discussion. Make some diagrams. Fix some bugs [12]. Submit your cool examples for inclusion in the gallery [13] or your cool code for inclusion in the diagrams-contrib [14] package! [11] http://groups.google.com/group/diagrams-discuss [12] http://github.com/diagrams/ [13] http://projects.haskell.org/diagrams/gallery.html [14] http://hackage.haskell.org/package/diagrams%2Dcontrib Happy diagramming! Brought to you by the diagrams team: - Michael Sloan - Ryan Yates - Brent Yorgey with contributions from: - Sam Griffin - Niklas Haas - Peter Hall - Claude Heiland-Allen - Deepak Jois - John Lato - Felipe Lessa - Chris Mears - Ian Ross - Vilhelm Sjöberg - Jim Snavely - Luite Stegeman - Kanchalai Suveepattananont - Michael Thompson - Scott Walck ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Maintainer of fixpoint
On Wed, Dec 05, 2012 at 08:22:32PM +0100, Petr P wrote: Dear Haskellers, I've made some minor improvements of fixpoint package http://hackage.haskell.org/package/fixpoint. I tried to contact the original maintainer twice, but without success. The package hasn't been updated for 4 years. How should I proceed? Should I start a new fork of the package? Or is there a way how to take over an orphaned package? Thanks for help, Petr Pudlak I should also point out that I think the (much more recent) recursion-schemes package implements everything in 'fixpoint' and a lot more besides. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Design of a DSL in Haskell
(Sorry, forgot to reply to the list initially; see conversation below.) On Mon, Dec 03, 2012 at 03:49:00PM +0100, Joerg Fritsch wrote: Brent, I believe that inside the do-block (that basically calls my interpreter) I cannot call any other Haskell function that are not recognized by my parser and interpreter. This seems to just require some sort of escape mechanism for embedding arbitrary Haskell code into your language. For example a primitive embed :: a - CWMWL a (assuming CWMWL is the name of your monad). Whether this makes sense, how to implement embed, etc. depends entirely on your language and interpreter. However, as you imply below, this may or may not be possible depending on the type a. In that case I suggest making embed a type class method. Something like class Embeddable a where embed :: a - CWMWL a I still get the feeling, though, that I have not really understood your question. I am also trying to learn how I could preserve state from one line of code of my DSL to the next. I understand that inside the interpreter one would use a combination of the state monad and the reader monad, but could not find any non trivial example. Yes, you can use the state monad to preserve state from one line to the next. I am not sure what you mean by using a combination of state and reader monads. There is nothing magical about the combination. You would use state + reader simply if you had some mutable state as well as some read-only configuration to thread through your interpreter. xmonad is certainly a nontrivial example but perhaps it is a bit *too* nontrivial. If I think of any other good examples I'll let you know. -Brent On Dec 3, 2012, at 1:23 PM, Brent Yorgey wrote: On Sun, Dec 02, 2012 at 03:01:46PM +0100, Joerg Fritsch wrote: This is probably a very basic question. I am working on a DSL that eventuyally would allow me to say: import language.cwmwl main = runCWMWL $ do eval (isFib::, 1000, ?BOOL) I have just started to work on the interpreter-function runCWMWL and I wonder whether it is possible to escape to real Haskell somehow (and how?) either inside ot outside the do-block. I don't think I understand the question. The above already *is* real Haskell. What is there to escape? I thought of providing a defautl-wrapper for some required prelude functions (such as print) inside my interpreter but I wonder if there are more elegant ways to co-loacate a DSL and Haskell without falling back to being a normal library only. I don't understand this sentence either. Can you explain what you are trying to do in more detail? -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Kleisli composition is not in the Monad signature?
On Fri, Nov 30, 2012 at 02:33:54AM +0100, Ben Franksen wrote: Brent Yorgey wrote: On Thu, Nov 29, 2012 at 03:52:58AM +0100, Ben Franksen wrote: Tony Morris wrote: As a side note, I think a direct superclass of Functor for Monad is not a good idea, just sayin' class Functor f where fmap :: (a - b) - f a - f b class Functor f = Apply f where (*) :: f (a - b) - f a - f b class Apply f = Bind f where (=) :: (a - f b) - f a - f b class Apply f = Applicative f where unit :: a - f a class (Applicative f, Bind f) = Monad f where Same goes for Comonad (e.g. [] has (=) but not counit) ... and again for Monoid, Category, I could go on... Hi Tony even though I dismissed your mentioning this on the Haskell' list, I do have to admit that the proposal has a certain elegance. However, before I buy into this scheme, I'd like to see some striking examples for types with natural (or at least useful) Apply and Bind instances that cannot be made Applicative resp. Monad. Try writing an Applicative instances for (Data.Map.Map k). It can't be done, but the Apply instance is (I would argue) both natural and useful. I see. So there is one example. Are there more? I'd like to get a feeling for the abstraction and this is hard if there is only a single example. Any data type which admits structures of arbitrary but *only finite* size has a natural zippy Apply instance but no Applicative (since pure would have to be an infinite structure). The Map instance I mentioned above falls in this category. Though I guess I'm having trouble coming up with other examples, but I'm sure some exist. Maybe Edward knows of other examples. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambda case
Oh, PLEASE people. Let's not have another round of bikeshedding about
this AFTER the feature is already implemented!
-Brent
On Fri, Nov 30, 2012 at 01:25:27PM +0100, Herbert Valerio Riedel wrote:
Jon Fairbairn jon.fairba...@cl.cam.ac.uk writes:
[...]
“\case” complicates lambda, using “of” simply breaks “case … of …”
into two easily understood parts.
Just some observation (I'm rather late to the lambda-case discussion, so
this might have been already pointed out previously):
if the reserved keyword 'of' was to take the place of '\case', shouldn't
then
'case' exp
w/o the 'of' { alts }-part become a separately valid expression (with
'case' essentially meaning 'flip ($)') to really break it up into two
independent parts? Then 'case exp of { alts }' wouldn't be a special
form anymore, but would just result from combining 'case' and 'of';
'case' wouldn't even need to be a reserved keyword (and thus the grammar
could be simplified), if it wasn't for the current grammar which
requires to isolate a \case-expression by using () or $, consider e.g.:
{-# LANGUAGE LambdaCase #-}
import System.Environment
case' :: b - (b - c) - c
case' = flip ($)
main = do
s - getArgs
case' s $ \case -- image '\case' was actually '\of' or 'of'
[x] - putStrLn (Hello ++ x)
_ - putStrLn wrong number of arguments given
just my 2¢
cheers,
hvr
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Re: [Haskell-cafe] Why Kleisli composition is not in the Monad signature?
On Thu, Nov 29, 2012 at 03:52:58AM +0100, Ben Franksen wrote: Tony Morris wrote: As a side note, I think a direct superclass of Functor for Monad is not a good idea, just sayin' class Functor f where fmap :: (a - b) - f a - f b class Functor f = Apply f where (*) :: f (a - b) - f a - f b class Apply f = Bind f where (=) :: (a - f b) - f a - f b class Apply f = Applicative f where unit :: a - f a class (Applicative f, Bind f) = Monad f where Same goes for Comonad (e.g. [] has (=) but not counit) ... and again for Monoid, Category, I could go on... Hi Tony even though I dismissed your mentioning this on the Haskell' list, I do have to admit that the proposal has a certain elegance. However, before I buy into this scheme, I'd like to see some striking examples for types with natural (or at least useful) Apply and Bind instances that cannot be made Applicative resp. Monad. Try writing an Applicative instances for (Data.Map.Map k). It can't be done, but the Apply instance is (I would argue) both natural and useful. Also, it is not clear to me what laws should hold for them. http://hackage.haskell.org/package/semigroupoids defines all of these and specifies laws, presumably derived in a principled way. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] delete http://www.haskell.org/haskellwiki/Haskell_IDE
On Wed, Nov 28, 2012 at 07:08:16PM +0200, Roman Beslik wrote: Hi. There is more verbose page http://www.haskell.org/haskellwiki/IDEs . I registered on http://www.haskell.org/haskellwiki/ , but have not found the Delete Page command, wiki software help pages, or feedback channel, so I'm writing here. Deleting pages is rather drastic and not enabled for normal users. It is probably not a good idea anyway -- what if there are other pages that link to it? Just delete all the content and replace it with a redirect to the IDEs page. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal configure cabal build cabal install
On Sun, Nov 25, 2012 at 06:09:26PM -0500, Albert Y. C. Lai wrote: If you begin with cabal configure, the correct idiom is: cabal configure [flags] cabal build [cabal haddock, if you want] cabal copy cabal register Even this does not do the same thing as 'cabal install', because it does not download and install any dependencies (whereas 'cabal install' does). -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Taking over ghc-core
On Fri, Nov 16, 2012 at 03:25:35PM -0500, Jay Sulzberger wrote: On Fri, 16 Nov 2012, Carter Schonwald carter.schonw...@gmail.com wrote: how would ghc-core enable targetting core for Agda? On Wed, Nov 14, 2012 at 6:32 PM, Andreas Abel andreas.a...@ifi.lmu.dewrote: Excellent! With ghc-core being maintained again, we can start thinking about compiling Agda to core instead of hs. Andreas I would like to be able to take the textual version of Core output by GHC and use that text as input to the next stage of compilation. oo--JS. Note that the ghc-core package only does pretty-printing of GHC core. Whether GHC can parse a textual representation of GHC core (like Jay and, presumably, Andreas want) is unrelated to the ghc-core package. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] local type denotation
Turn on the ScopedTypeVariables extension (e.g. by putting {-#
LANGUAGE ScopedTypeVariables #-} at the top of your file), and add an
explicit 'forall a.' to the type signature of f.
-Brent
On Wed, Nov 14, 2012 at 04:03:57PM +0400, Serge D. Mechveliani wrote:
Please,
how to correctly set an explicit type for a local value in the body of
a polymorphic function?
Example (tested under ghc-7.6.1):
data D a = D1 a | D2 a (a - a)
f :: Eq a = D a - a
f (D1 x) = x
f (D2 x g) = let -- y :: Eq a = a
y = g x
in if x == y then x else g y
main = putStr $ shows (f (D2 (1 :: Int) succ)) \n
This is compiled byghc --make Main
Now I need, for a certain reason, to explicitly set the type for y in
`let', with the meaning:
this very `a' which is in the signature for f
(and I think that this type Haskell assignes to y in y = g x).
I need to declare this type in a separate line: y :: what ever it is.
Both `y :: a' and `y :: Eq a = a' are not compiled.
Please, copy the answer to mech...@botik.ru
Thanks,
--
Sergei
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Re: [Haskell-cafe] Teaching Haskell @ MOOCs like Coursera or Udacity
On Thu, Oct 18, 2012 at 11:49:08PM +0530, niket wrote: I am a novice in Haskell but I would love to see the gurus out here teaching Haskell on MOOCs like Coursera or Udacity. Dr Martin Odersky is doing it for Scala here: https://www.coursera.org/course/progfun I would love to see Haskell growing on such new platforms! Just as a counterpoint, putting together a MOOC is a *ton* of work, with (in my opinion) not much benefit for a topic like Haskell where it is already possible to access lots of quality instructional materials online. I would rather see Haskell gurus put their time and effort into producing more awesome code (or into curating existing instructional materials). Just my 2c. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Explicitly passing an argument to an arrow
On Wed, Oct 03, 2012 at 10:41:25AM +0200, Alfredo Di Napoli wrote: Hello everyone, sorry for the dumb question but I'm wrapping my head around arrow just from this morning. Consider this toy function to swap argument of a tuple: swapA' :: (Arrow a) = a ((b,c), (b,c)) (c,b) swapA' = swapFirst swapSecond where swapFirst = first $ arr snd swapSecond = second $ arr fst It works but requires to pass a tuple of tuple, namely ((b,c), (b,c)). How can I explicitly pass my tuple of tuple to swapFirst so I can simply invoke swapA' (1,2) and get the correct result? Like this? swapA' = dup swapFirst swapSecond where dup = id id ... I'm afraid I'm not confident I really understand your question, however, so if that doesn't answer it, try asking again! -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: New wiki page and mailing list for combinatorics and Haskell
Quite a while ago there was a mailing list thread where the idea was brought up of creating a mailing list for those interested in combinatorics in the setting of Haskell. Well, I've finally gotten around to it. If you're interested in (probably extremely low-traffic) discussion and announcements relating to doing combinatorics in Haskell (computing combinatorial/ number-theoretic functions; exhaustive or random generation of combinatorial objects; type algebra; etc.), please join! http://projects.haskell.org/cgi-bin/mailman/listinfo/combinatorics There is also a wiki page for collecting information here: http://www.haskell.org/haskellwiki/Combinatorics -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] guards in applicative style
Lorenzo is correct, but actually for the wrong reason. =) The *type* of guard is a historical accident, and the fact that it requires MonadPlus doesn't really tell us anything. Let's take a look at its implementation: guard :: (MonadPlus m) = Bool - m () guard True = return () guard False = mzero 'return' is not specific to Monad; we could just as well use 'pure'. 'mzero' is a method of 'MonadPlus' but there is no reason we can't use 'empty' from the 'Alternative' class. So we could define guardA :: Alternative f = Bool - f () guardA True = pure () guardA False = empty (As another example, consider the function 'sequence :: Monad m = [m a] - m [a]'. Actually this function does not need Monad at all, it only needs Applicative.) However, guardA is not as useful as guard, and it is not possible to do the equivalent of the example shown using a list comprehension with a guard. The reason is that whereas monadic computations can make use of intermediate computed values to decide what to do next, Applicative computations cannot. So there is no way to generate values for x and y and then pass them to 'guardA' to do the filtering. guardA can only be used to conditionally abort an Applicative computation using information *external* to the Applicative computation; it cannot express a condition on the intermediate values computed by the Applicative computation itself. -Brent On Wed, Sep 12, 2012 at 03:52:03PM +0100, Lorenzo Bolla wrote: I'm no expert at all, but I would say no. guard type is: guard :: MonadPlus m = Bool - m () and MonadPlus is a monad plus (ehm...) mzero and mplus (http://en.wikibooks.org/wiki/Haskell/MonadPlus). On the other hand Applicative is less than a monad (http://www.haskell.org/haskellwiki/Applicative_functor), therefore guard as is cannot be defined. But, in your specific example, with lists, you can always use filter: filter (uncurry somePredicate) ((,) $ list1 * list2 (somePredicate ???)) hth, L. On Wed, Sep 12, 2012 at 3:40 PM, felipe zapata tifonza...@gmail.com wrote: Hi Haskellers, Suppose I have two list and I want to calculate the cartesian product between the two of them, constrained to a predicate. In List comprehension notation is just result = [ (x, y) | x - list1, y -list2, somePredicate x y ] or in monadic notation result = do x - list1 y - list2 guard (somePredicate x y) return $ (x,y) Then I was wondering if we can do something similar using an applicative style result = (,) $ list1 * list2 (somePredicate ???) The question is then, there is a way for defining a guard in applicative Style? Thanks in advance, Felipe Zapata. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] package categories
On Sat, Sep 08, 2012 at 11:04:34AM +0400, Sergey Mironov wrote: Hello list. Do we have a guideline for selecting correct category for a package being developed? I'd like to choose between Web.MyLib and Network.MyLib. Or probably just MyLib if I feel ambitious? Sergey. MyLib is discouraged. I'm sure either Web.MyLib or Network.MyLib would be fine. I don't know of any guidelines. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: grid-1.1
On Thu, Sep 06, 2012 at 09:42:19AM +, Amy de Buitléir wrote: I'm happy to announce a new package called grid: http://hackage.haskell.org/package/grid https://github.com/mhwombat/grid/wiki (wiki) Looks neat! By the way, the URLs within the Haddock documentation are formatted improperly (because Haddock interprets the forward slashes as italic markers). You should place the URLs within angle brackets like http://github.com/foo/bar and Haddock will turn them into real clickable links. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal install fails due to recent HUnit
On Mon, Aug 27, 2012 at 10:52:59AM -0700, Bryan O'Sullivan wrote: On Mon, Aug 27, 2012 at 9:57 AM, Erik Hesselink hessel...@gmail.com wrote: I'm seeing this again, on abstract-deque-0.1.6. Ross, can you fix it again? Hang on a second. The reason you're seeing build breakage is that the .cabal files of the broken packages were edited in-place without communicating with any of the package authors. I understand that the collective intentions around this were good, but by fixing things without telling anyone, package maintainers have no way to know that anything has happened. Now we are seeing the problem begin to recur as people issue new releases that don't incorporate those changes. For the record, abstract-deque was neither one of the packages fixed previously, nor does its .cabal file even contain a test section at all, much less one with a conditional. So if cabal-install-0.10 is failing to read it, it is because of some different problem. But I agree with Bryan in principle that we need a more principled approach. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] explicit annotations on kind polymorphism for data types
Correct. I just meant that you can use a lowercase x or a lowercase chi (χ). Any lowercase characters (as defined by Unicode) can be used as identifiers. -Brent On Thu, Aug 23, 2012 at 11:09:41AM -0400, dude wrote: Not in 7.4.2, correct? -- dude On 08/22/2012 09:58 AM, Brent Yorgey wrote: I believe in the paper it is actually a lowercase Greek chi (χ), which should work too. ;) -Brent On Wed, Aug 22, 2012 at 08:15:48AM +0200, José Pedro Magalhães wrote: Nope, but it should work on 7.6 (also on the release candidate). The 'X' should be lowercase, though, like type variables. Cheers, Pedro On Wed, Aug 22, 2012 at 12:01 AM, dude d...@methodeutic.com wrote: Hello All: I'm working through Giving Haskell a Promotion. Section 2.4 presents an explicitly annotated data type declaration similar to the following: data EqRefl (a::X)(b::X) where Refl :: forall X. forall (a::X). EqRefl a a Has this been implemented in GHC 7.4.2? 7.8.3 in the GHC User Guide leads me to believe it has not. -- dude __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- -- dude ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] model theory for type classes
On Thu, Aug 23, 2012 at 01:25:39PM +0100, Patrick Browne wrote: If there is no model expansion could it be because of the constructor discipline, which only allows variables, and constructors in the LHS argument patterns. Indeed, a variable name as a pattern on the LHS of a function definition has nothing to do with any names which might be in scope. It is simply a pattern which matches anything. I am not sure what (if anything) this says about model expansions. constant::Int constant = (1::Int) fun1::Int - Int fun1 (constant::Int) = 8 fun1 returns 8 for all inputs. The fact that fun1's definition uses the name 'constant' which happens to have the same name as something in scope is irrelevant. For example, this is precisely the same as the above: constant :: Int constant = 1 fun1 :: Int - Int fun1 foo = 8 -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] explicit annotations on kind polymorphism for data types
I believe in the paper it is actually a lowercase Greek chi (χ), which should work too. ;) -Brent On Wed, Aug 22, 2012 at 08:15:48AM +0200, José Pedro Magalhães wrote: Nope, but it should work on 7.6 (also on the release candidate). The 'X' should be lowercase, though, like type variables. Cheers, Pedro On Wed, Aug 22, 2012 at 12:01 AM, dude d...@methodeutic.com wrote: Hello All: I'm working through Giving Haskell a Promotion. Section 2.4 presents an explicitly annotated data type declaration similar to the following: data EqRefl (a::X)(b::X) where Refl :: forall X. forall (a::X). EqRefl a a Has this been implemented in GHC 7.4.2? 7.8.3 in the GHC User Guide leads me to believe it has not. -- dude __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Platform Versioning Policy: upper bounds are not our friends
On Thu, Aug 16, 2012 at 06:07:06PM -0400, Joey Adams wrote: On Wed, Aug 15, 2012 at 3:38 PM, Bryan O'Sullivan b...@serpentine.com wrote: I propose that the sense of the recommendation around upper bounds in the PVP be reversed: upper bounds should be specified only when there is a known problem with a new version of a depended-upon package. I, too, agree. Here is my assortment of thoughts on the matter. Here's some bad news: with cabal 1.14 (released with Haskell Platform 2012.2), cabal init defaults to bounds like these: build-depends: base ==4.5.*, bytestring ==0.9.*, http-types ==0.6.* I'm not sure why you think this is bad news. I designed this to conform exactly to the current PVP. If the PVP is changed then I will update cabal init to match. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Platform Versioning Policy: upper bounds are not our friends
On Thu, Aug 16, 2012 at 05:30:07PM +0300, Yitzchak Gale wrote: For actively maintained packages, I think the problem is that package maintainers don't find out promptly that an upper bound needs to be bumped. One way to solve that would be a simple bot that notifies the package maintainer as soon as an upper bound becomes out-of-date. This already exists: http://packdeps.haskellers.com/ -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] hGetContents Illegal byte sequence / ghc-pkg
On Sat, Aug 11, 2012 at 12:13:45PM +0100, Benjamin Edwards wrote: Hello café, I have a program that is crashing, and I have no idea why: module Main where import System.Process (readProcessWithExitCode) main :: IO () main = do _ - readProcessWithExitCode ghc-pkg [describe, hoopl] putStrLn Should never get here this is using the process package from hackage. The program crashes with minimal-test: fd:5: hGetContents: invalid argument (invalid byte sequence) minimal-test: thread blocked indefinitely in an MVar operation inspecting the source of readProcessWithExitCode yields an obvious explanation to the MVar problem, but I don't understand why hGetContents is so offended. The 'invalid argument' error from hGetContents indicates that a wrong encoding is being assumed. I don't know enough about how putStr/hGetContents decide on an encoding, but in any case it works for me (that is, it prints Should never get here). The likely sticking point is that one of the authors of hoopl, João Dias, has a name which contains U+00E3: LATIN SMALL LETTER A WITH TILDE. Try doing ghc-pkg describe hoopl hoopl.txt file hoopl.txt to get an indication of what encoding is being used, or manually take a look at the bytes being generated using ghc-pkg describe hoopl | hexdump -C I don't know what the solution is but at least this should give some additional information. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ALife category
On Thu, Aug 02, 2012 at 01:50:50PM +, Amy de Buitléir wrote: I'm developing a framework for artificial life experiments that I would like to make available on Hackage eventually. I've read all the guidance and proposals I could find for where to place packages in the hierarchy: http://www.haskell.org/haskellwiki/Hierarchical_module_names http://www.cs.york.ac.uk/fp/libraries/layout.html http://www.cs.york.ac.uk/fp/libraries/layoutSM.html I've also examined the current hierarchy of modules: http://hackage.haskell.org/packages/archive/pkg-list.html The current hierarchy has a top-level AI category, so it would seem logical to me to add a top-level ALife category and put my package under that. But perhaps it would be best not to start a new top-level category? I could put my package under AI, because my framework does support the use of AI, and wouldn't look too out of place with the other packages there. (Moving the discussion to haskell-cafe; haskell@haskell is generally for announcements and such.) It seems to me that you might be confusing two separate things. Cabal packages may list one or more categories, which are used to group packages on the main list of packages: http://hackage.haskell.org/package/ . In general, I would say that you should avoid creating a new top-level category. Hierarchical module names are something different. The 'Category' specified in the .cabal file does NOT have to be the same as the first component of your module names (though for many packages it is). For example, it would be perfectly fine to specify 'AI' as the category, and then have module names like ALife.Foo and so on. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how to select random elements of a Data.Set?
On Fri, Jul 20, 2012 at 01:24:57PM +, jwaldmann wrote: Dear all, how would I quickly select an element of a Set (as in Data.Set) uniformly at random? Via the API, this can only be done in linear time? (via toList) If I could access the tree structure, then of course it could be logarithmic. If you had access to the Set constructors, this would be very easy, as each node caches a size. Unfortunately there does not appear to be any way to do this in sub-linear time via the exposed API, because there is no way to directly access the subtrees. I wonder about the wisdom of exporting a function like -- | Partition a set into two approximately equal-sized subsets. -- If @divide s == (s1,s2)@, then -- * @s1 `intersect` s2 == empty@ -- * @s1 `union` s2 == s@ -- * The sizes of @s1@ and @s2@ differ by at most a constant factor -- (currently, 3). divide :: Set a - (Set a, Set a) which would give you enough to implement what you want, without breaking the Set abstraction. (However, even though technically it doesn't break any abstraction, it still smells somewhat implementation-dependent...) -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to add constraint to .cabal?
On Thu, Jul 19, 2012 at 09:37:52AM +0800, Magicloud Magiclouds wrote: Hi, Say I have a package that only appends --constraint=template-haskell==2.7.0.0 --constraint=warp-tls==1.2.1 could I install it. Now I want to release the package, then how could I have these constraint into the .cabal so the user would not get troubled? Using the build-depends field. See http://www.haskell.org/cabal/users-guide/developing-packages.html#build-information -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Adding to the haskell wiki
On Mon, Jul 16, 2012 at 02:00:46PM +0200, Nathan Hüsken wrote: Hey, I have been a passive member of the haskell community for quite some time now. I have benefit from the community a lot through the mailing list, the haskell webpage and other channels. Thanks for all that! Now I am trying to give a little bit back, and I started a blog about writing javascript games in haskell using UHC and haste. I am not an expert in haskell nor javascript, but I am collecting information from various sources and put it together in the blog so that others with a similar goal my have a smoother start. Writing a blog is one thing, but of course I also want people who are interested in the topic to find it. Never being an active member of the community, I wonder if I should do. I guess I should add it to the haskellwiki. But I am unsure where. It certainly falls in the games category, but the page only lists game projects. The blog can be found here: http://jshaskell.blogspot.de/ If you want people to find your blog, a better idea is to have it added to the Planet Haskell blog aggregator. [1] Then write blog posts which are interesting enough that people will post them to the Haskell reddit. I doubt putting a link to your blog on the Haskell wiki will make much difference, though you are certainly welcome to of course. [1] http://planet.haskell.org/ -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Best way to build a GHC backend?
On Sun, Jul 08, 2012 at 09:21:08AM -0600, Jonathan Geddes wrote: I agree that the Raison d'être for a .NET or JVM backend is interop. Perhaps that's not worth the effort of an entirely new backend. JavaScript is a different beast, however. I said before: From my point of view, languages that cannot run on one of the 3 aforementioned platforms will become irrelevant. (with the exception of C, of course). I'll take that one step further and say that for web applications it is becoming increasingly difficult to justify using a language that WILL NOT run both client and server. JavaScript (with NodeJS), Clojure (with ClojureScript), and Dart are just a few examples. I really believe that with a solid JavaScript backend, Haskell would be an ideal web application language. Am I alone in that belief? What can I do to get the ball rolling on that? I should point out that the ball already IS rolling -- ranging from EDSLs that compile to JavaScript [1,2] to macro systems [3] to more serious full-featured efforts [4,5]. There's even a wiki page listing all these and more [6]. The yesod developers share your view that Haskell would benefit from some sort of JavaScript backend; see [7] as well as the ensuing discussion on Reddit [8]. See also Elm [9], which compiles to HTML+CSS+JavaScript and has some Haskell integration [10]. Rather than trying to start yet another effort, what about contributing to one of these ongoing ones? -Brent [1] http://www.ittc.ku.edu/csdlblog/?p=88 [2] http://www.ittc.ku.edu/csdl/fpg/node/125 [3] http://www.haskell.org/haskellwiki/JMacro [4] http://uu-computerscience.github.com/uhc-js/ [5] https://github.com/ghcjs/ghcjs [6] http://www.haskell.org/haskellwiki/The_JavaScript_Problem [7] http://www.yesodweb.com/blog/2012/04/client-side [8] http://www.reddit.com/r/haskell/comments/sm72n/client_side_yesod_an_frpinspired_approach/ [9] http://elm-lang.org/ [10] http://www.reddit.com/r/haskell/comments/uugne/announcing_elm_02_haskell_integration_yesod/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] combining predicates, noob question
On Sat, Jul 07, 2012 at 09:42:01PM -0300, Sebastián Krynski wrote: Ok , thanks for the answers, I understand now what liftM2 does. In this case would it be silly to use combinerPred (and maybe a newType Predicate a = a - Bool) for the sake of readability or shoud I stick with a - Bool and liftM2? No, not silly. Use whatever you find most readable. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] combining predicates, noob question
On Fri, Jul 06, 2012 at 03:17:54PM -0300, Felipe Almeida Lessa wrote: On Fri, Jul 6, 2012 at 2:11 PM, Sebastián Krynski skryn...@gmail.com wrote: As I was using predicates (a - bool) , it appeared the need for combining them with a boolean operator (bool - bool - bool) in order to get a new predicate combining the previous two. So I wrote my function combinerPred (see code below). While I think this is JUST ok, i'm feeling a monad in the air. So.. where is the monad? combinerPred :: (a - Bool) - (a - Bool) - (Bool - Bool - Bool) - (a - Bool) combinerPred pred1 pred2 op = \x - op (pred1 x) (pred2 x) That's the `(-) a` monad: import Control.Applicative combinerPred :: (a - Bool) - (a - Bool) - (Bool - Bool - Bool) - (a - Bool) combinerPred pred1 pred2 op = op $ pred1 * pred2 By the way, I find it more natural to make 'op' the first argument, because it is more useful to partially apply combinerPred to an operation that it is to some predicates. Also, in that case combinerPred is simply liftA2: import Control.Applicative combinerPred :: (Bool - Bool - Bool) - (a - Bool) - (a - Bool) - (a - Bool) combinerPred = liftA2 -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] class instances for kinds with finite ty constrs, does this make sense?
On Thu, Jun 07, 2012 at 07:32:45PM +0100, ex falso wrote: we always have to put the class restriction (TupleLength l) there, even though all possible type constructors of [*] have a TupleLength instance defined! Yes, and this is a feature, for at least two reasons. First: to the extent that Haskell's type system corresponds to a logic, it corresponds to a constructive one. Types/propositions are inhabited/proved by explicit terms/evidence. But this request (and [1]) essentially boil down to a desire for double negation elimination: if there *can't* *not* be a certain instance, then the compiler should infer that there *is* one. This seems weird to me (though perhaps I've just drunk too much of the constructivism kool-aid). Second, on a more practical level, the ability to omit class constraints like this would make reasoning about types much more non-local and difficult, since a type like foo :: Bar a - Baz may or may not implicitly expand to something like foo :: SomeClass a = Bar a - Baz (which could have important implications for things like inlining, sharing, etc. -- cf the monomorphism restriction), but figuring out whether it does or not requires knowing (a) the definition of Bar and all the instances that are in scope, and (b) whether or not SomeClass's methods ever get called from foo (or anything it calls, recursively). I'd much rather explicitly write the SomeClass constraint if I want it, and be guaranteed that it won't be added if I don't. In summary, these constraints may be superfluous in a strictly logical sense, but (a) not in the kind of logic that Haskell uses, and (b) the pain and suffering caused by removing them would far outweigh the tiny bit of typing that would be saved. -Brent [1] http://haskell.1045720.n5.nabble.com/Data-Kinds-and-superfluous-in-my-opinion-constraints-contexts-td5689436.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Restricted Monad question
On Mon, Jun 04, 2012 at 11:35:20AM +0200, Ismael Figueroa Palet wrote: Hi, I was wondering about defining a restricted monad, and found out this blog post: http://blog.omega-prime.co.uk/?p=127 In GHC 7.4.1 still the recommended way is using the rmonad package, right? You can do it however you want, I don't think there's really a recommended way. But using the rmonad package is certainly more convenient. I guess the tricks with ConstraintKinds explained in the blog are used for internal implementation of RMonad? No, the rmonad package has been around since long before the ConstraintKinds extension was even conceived. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Installation of the New Haskell Platform
On Mon, Jun 04, 2012 at 11:04:36AM -0400, Victor Miller wrote: Before I install it (on on Mac OS X Lion) is there anything, manually, that I need to do in order to keep all of the cabal packages that I've installed, or are the reinstalled automatically? Neither. If you install a new version of GHC, you must reinstall any cabal packages you want, because they must be recompiled with the new GHC. Note that cabal-install does have a special command cabal install world which (IIUC) is supposed to help automate this process, although I can't vouch for it since I have never tried it. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Formalisation for types of monads
On Wed, May 23, 2012 at 09:24:06AM +0200, Ertugrul Söylemez wrote: Yves Parès yves.pa...@gmail.com wrote: Note about []: Don't even mention foldl. The folding combinator for lists is foldr, period. Yes, I do agree. I came to this when I realized foldr gave the church encoding of a list. Not only that. The foldr combinator has an identity fold and implements actual structural recursion. That's pretty much what a Church encoding is. Though I agree it's probably best not to mention the phrase Church encoding to beginning students. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cool tools
On Thu, May 17, 2012 at 03:05:22PM +0100, Chris Dornan wrote: I have been playing around with the latest cabal-install (0.14.0) and it is working really nicely. Having unpacked a cabal bundle you can now type 'cabal install' inside the root and it will work everything out as if you had asked to install directly from the repo -- very nice. I should point out that cabal-install has actually had this feature for a long time. Which of course in no way detracts from your point (quite the opposite, in fact). -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Learn you
I am curious how the title was translated. Of course, the English title Learn You a Haskell for Great Good uses intentionally ungrammatical/unidiomatic English for humorous effect. Is the Japanese title also ungrammatical/unidiomatic Japanese? Or do Japanese speakers not find that humorous? -Brent On Wed, May 02, 2012 at 03:59:18PM +0900, Kazu Yamamoto wrote: Hello cafe, Translating Learn You a Haskell for Great Good into Japanese was finished and will be published on 22 May. I guess it's worth watching its cover page: http://www.amazon.co.jp/%E3%81%99%E3%81%94%E3%81%84Haskell%E3%81%9F%E3%81%AE%E3%81%97%E3%81%8F%E5%AD%A6%E3%81%BC%E3%81%86-Miran-Lipova%C4%8Da/dp/4274068854 There are two translators: Tanaka is the author of peggy and Muranushi is the author of Monadius. Regards, --Kazu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Multi-site haddock documentation with proper links?
It is possible. I have done it for http://projects.haskell.org/diagrams/doc/index.html But it is not fun, and it took me several days of work (spread over two weeks) to figure out the proper magic incantations to get everything to work properly. I really ought to write up a blog post with instructions; I'll try to do that soon. -Brent On Tue, Apr 24, 2012 at 08:34:53PM -0400, Ryan Newton wrote: Hello cafe, For various reasons, some packages don't build documentation on hackage: http://hackage.haskell.org/package/accelerate Therefore I want to locally install documentation for a set of packages like this and host them on a separate website. I want all of these ~ten packages' haddock documentation to be properly interlinked with eachother, but also to link to Hackage for types and classes defined in other modules. Is this possible? Hackage haddocks are all interlinked, but that is simply because hackage is one giant local install, right? If it's not possible (and it seems not) do any haddock devs have pointers on how to implement this? Thanks, -Ryan P.S. Someone recommended to me the following simple hack -- just use sed to rewrite the links after haddock generates the html. I think I'll do that for the time being unless someone has a better suggestion. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] is the evaluation order deterministic when using applicative with IO
On Fri, Mar 16, 2012 at 12:30:13PM +0100, Twan van Laarhoven wrote: If you want to avoid the side effects of boolTest2 when boolTest1 returns true, you will need to implement a monadic or, something like orM ma mb = do a - ma if a then return True else mb Note also that it is *not possible* to have this short-circuiting behavior using only Applicative. The structure of an Applicative computation is always fixed up front, and cannot depend on intermediate values. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Open-source projects for beginning Haskell students?
Hi everyone, I am currently teaching a half-credit introductory Haskell class for undergraduates. This is the second time I've taught it. The last time, for their final project I gave them the option of contributing to an open-source project; a couple groups took me up on it and I think it ended up being a modest success. So I'd like to do it again this time around, and am looking for particular projects I can suggest to them. Do you have an open-source project with a few well-specified tasks that a relative beginner (see below) could reasonably make a contribution towards in the space of about four weeks? I'm aware that most tasks don't fit that profile, but even complex projects usually have a few simple-ish tasks that haven't yet been done just because no one has gotten around to it yet. If you have any such projects, I'd love to hear about it! Here are a few more details: * The students will be working on the projects from approximately the end of this month through the end of April. * By relative beginner I mean someone familiar with the material listed here: http://www.cis.upenn.edu/~cis194/lectures.html and just trying to come to terms with Applicative and Monad. They definitely do not know much if anything about optimization/profiling, GADTs, the mtl, or Haskell-programming-in-the-large. (Although part of the point of the project is to teach them a bit about programming-in-the-(medium/large)). * What I would hope from you is a willingness to exchange email and/or chat with the student(s) over the course of the project, to give them a bit of guidance/mentoring. I am certainly willing to help on that front, but of course I probably don't know much about your particular project. thanks! -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: diagrams 0.5
I am pleased to announce the release of version 0.5 of diagrams [1], a full-featured framework and embedded domain-specific language for declarative drawing. Check out the gallery [2] for examples of what it can do! [1] http://projects.haskell.org/diagrams [2] http://projects.haskell.org/diagrams/gallery.html Highlights of this release include: - A new diagrams-contrib [3] package of user-contributed modules, which so far contains code for tree drawing, Apollonian gaskets, planar tilings, wrapped layout, and turtle graphics. - Experimental support for animation, built on top of the new active [4] library. - Numerous small additions and improvements, including more general rounded rectangle shapes and better text support. - Much better performance in some common situations, such as laying out a very long list of diagrams using 'cat' and related combinators. - Added support for GHC 7.4. See the release notes [5] for complete details, and the diagrams wiki [6] for help migrating code from 0.4 to 0.5 (changes should be minimal). [3] http://hackage.haskell.org/package/diagrams%2Dcontrib [4] http://hackage.haskell.org/package/active [5] http://projects.haskell.org/diagrams/releases.html [6] http://www.haskell.org/haskellwiki/Diagrams/Migrate0.5 Try it out -- For the truly impatient: cabal install gtk2hs-buildtools cabal install diagrams Diagrams is supported under GHC 6.12, 7.0, 7.2, and 7.4. However, getting cairo to build can be tricky on some platforms; see the diagrams wiki [8] for more information and workarounds regarding specific platforms. (A new native SVG backend is in the works, targeted for the 0.6 release.) To get started with diagrams, read the quick tutorial [9], which will introduce you to the fundamentals of the framework. For those who are even less impatient but want to really dig in and use the power features, read the user manual [10]. [7] http://projects.haskell.org/gtk2hs/development/#development [8] http://www.haskell.org/haskellwiki/Diagrams [9] http://projects.haskell.org/diagrams/tutorial/DiagramsTutorial.html [10] http://projects.haskell.org/diagrams/manual/diagrams-manual.html Get involved Subscribe to the project mailing list [11], and/or come hang out in the #diagrams IRC channel on freenode.org for help and discussion. Make some diagrams. Fix some bugs [12]. Submit your cool examples for inclusion in the gallery or your cool code for inclusion in the diagrams-contrib package! [11] http://groups.google.com/group/diagrams-discuss [12] http://code.google.com/p/diagrams/issues/list Happy diagramming! Brought to you by the diagrams team: - Peter Hall - Ian Ross - Michael Sloan - Ryan Yates - Brent Yorgey with contributions from: - Sam Griffin - Claude Heiland-Allen - John Lato - Vilhelm Sjoberg - Luite Stegeman - Kanchalai Suveepattananont - Scott Walck ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The (!) operation
On Thu, Mar 08, 2012 at 07:53:48PM +0100, Christopher Done wrote: On 8 March 2012 18:32, Anthony Cowley acow...@seas.upenn.edu wrote: Perhaps Data.Key meets your needs? http://hackage.haskell.org/packages/archive/keys/2.1.2/doc/html/Data-Key.html Ah, perhaps indeed. Thanks! On 8 March 2012 19:12, Francesco Mazzoli f...@mazzo.li wrote: The type signature that you wrote is very generic and doesn't help in introducing effects while retrieving the indexed value, which I imagine is what you wanted to do. Because Maybe is already a monad and it's nice to fail in the monad of choice, e.g. if I'm in the list monad I get empty list instead, or if I'm in the Result monad from JSON it'll fail in there. ‘Course fail is suboptimal and MonadError might be better. Monads have nothing to do with failure. Instead of Monad you would want to use something like MonadZero or MonadError. However, these are also suboptimal because in monads which carry extra information about the failure (i.e. anything other than [] or Maybe), the lookup function now has to make up an error message, when it almost certainly it doesn't know enough to give a good one. This is why the use of Maybe is encouraged: Maybe is the *initial* instance of MonadZero, so you can map from it to failure in whatever monad you happen to be using. Instead of being an annoyance this is encouraged style, because in doing the conversion *you* get to pick a meaningful error message. For example fromMaybe (throwError WidgetNotFound) (lookup foo blah) or fromMaybe (Left Missing wurble specification: flozz) (lookup foo blah) -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FreeSect -- generalised sections syntax extension
On Sat, Mar 03, 2012 at 10:37:10PM -0500, Ras Far wrote: letters correspond to grammar, words, or meaning. So we've got love, too (Aramaic word “Abba” = love of God or so...) Not quite, it's a familiar/intimate form of father, cf English papa, dada or daddy. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Does somebody know about these functions?
On Tue, Feb 28, 2012 at 06:06:25PM +0100, Johan Holmquist wrote: inter :: (a - a - b) - [a] - [b] inter f [] = [] inter f l = map (uncurry f) $ zip l (tail l) I've never seen this function defined anywhere, but it looks nice. withPair :: (a' - b' - c) - (a - a') - (b - b') - (a,b) - c withPair f fa fb (a,b) = fa a `f` fb b Note that withPair f g h === uncurry f . (g *** h) although using withPair is probably nicer (it certainly involves fewer parentheses). -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using multiplate to get free variables from a syntax tree
On Thu, Feb 23, 2012 at 01:18:22PM -0800, Matt Brown wrote: Hi all, I'm reading the haskellwiki article on multiplate. Is it possible to modify the getVariablesPlate example to return the free variables? One idea I had is to store an environment in a reader monad, and use local to update the environment at a let expression. Couldn't figure it out, though. Any ideas? Hi Matt, I am not very familiar with Multiplate, but from what I can see it doesn't seem like this will work. The code for traversing Let looks like Let $ decl child d * expr child e The call to 'decl child d' can certainly have some sort of side-effects which can influence the processing of e -- but intuitively it seems to me there is no way to *localize* the effects only to e; it will also affect everything processed afterwards. If you really do want to compute free variables (not just test the limits of Multiplate), you may be interested in taking a look at Unbound: http://hackage.haskell.org/package/unbound -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how to print out intermediate results in a recursive function?
On Sat, Feb 04, 2012 at 12:23:07PM -0600, Qi Qi wrote: Hello, I have a question;how can I print out the intermediate number lists in a mergesort recursive function like the following one. merge [] ys = ys merge xs [] = xs merge (x:xs) (y:ys) = if x = y then x : merge xs (y:ys) else y : merge (x:xs) ys mergesort [] = [] mergesort [x] = [x] mergesort xs = let (as, bs) = splitAt (length xs `quot` 2) xs in merge (mergesort as) (mergesort bs) main = do print $ mergesort [5,4,3,2,1] In the main function, it only prints out the final number list. But I'd like to print out the number lists in every recursive level. How can I do that? Thanks. For visualizing intermediate steps for the purpose of debugging, there is also the very nice hood package: http://hackage.haskell.org/package/hood -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how to print out intermediate results in a recursive function?
On Sun, Feb 05, 2012 at 01:17:31AM -0600, Qi Qi wrote: Brilliant! That's what I was looking for. Thanks for all the replies. Sometimes, I suspect that Haskell not only makes easier of the hard things for imperative programming languages but also makes harder of some easy things. This is true. But usually these are things that you don't *want* to be easy, like shooting yourself in the kidney. (But these features are often described in ways that make them sound great, like flexible usage of bullet-placement tools.) Inserting arbitrary print statements into the middle of some code is difficult for a reason. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: combinatorics
On Fri, Feb 03, 2012 at 01:06:16AM -0500, wren ng thornton wrote: On 2/2/12 6:46 PM, Carter Schonwald wrote: On Thu, Feb 2, 2012 at 4:06 PM, Ivan Lazar Miljenovic wrote: On 3 February 2012 07:11, Brent Yorgey wrote: On Wed, Feb 01, 2012 at 01:53:03AM -0500, wren ng thornton wrote: [2] HaskellForMaths, gamma, statistics, erf, math-functions, combinat,... To this list I'd like to add 'species' and also the specialized 'multiset-comb' packages. The former doesn't build under recent GHCs but I plan to fix that (and continue extending the library) soon. Would people be interested in creating a mailing list for those interested in combinatorics+Haskell? I would. ditto I don't know how involved I'd be, but I'd join. It's just a side interest for me (more a curiosity than a hobby at this point), though I would definitely like to see things better organized and integrated since it seems like there are a bunch of folks with passing interest in the area, and it's someplace that Haskell could really shine. OK, I've emailed mail...@haskell.org requesting the creation of a combinator...@haskell.org mailing list (if anyone knows of a better way to go about this let me know). -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: combinatorics
On Wed, Feb 01, 2012 at 01:53:03AM -0500, wren ng thornton wrote: [2] HaskellForMaths, gamma, statistics, erf, math-functions, combinat,... To this list I'd like to add 'species' and also the specialized 'multiset-comb' packages. The former doesn't build under recent GHCs but I plan to fix that (and continue extending the library) soon. Would people be interested in creating a mailing list for those interested in combinatorics+Haskell? -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Natural Transformations and fmap
On Mon, Jan 23, 2012 at 09:06:52PM -0800, Ryan Ingram wrote: On Mon, Jan 23, 2012 at 8:05 PM, Daniel Fischer daniel.is.fisc...@googlemail.com wrote: On Tuesday 24 January 2012, 04:39:03, Ryan Ingram wrote: At the end of that paste, I prove the three Haskell monad laws from the functor laws and monoid-ish versions of the monad laws, but my proofs all rely on a property of natural transformations that I'm not sure how to prove; given type m :- n = (forall x. m x - n x) class Functor f where fmap :: forall a b. (a - b) - f a - f b -- Functor identity law: fmap id = id -- Functor composition law fmap (f . g) = fmap f . fmap g Given Functors m and n, natural transformation f :: m :- n, and g :: a - b, how can I prove (f . fmap_m g) = (fmap_n g . f)? Unless I'm utterly confused, that's (part of) the definition of a natural transformation (for non-category-theorists). Alright, let's pretend I know nothing about natural transformations and just have the type declaration type m :- n = (forall x. m x - n x) And I have f :: M :- N g :: A - B instance Functor M -- with proofs of functor laws instance Functor N -- with proofs of functor laws How can I prove fmap g. f :: M A - N B = f . fmap g :: M A - N B I assume I need to make some sort of appeal to the parametricity of M :- N. This is in fact precisely the free theorem you get from the parametricity of f. Parametricity means that f must act uniformly for all x -- which is an intuitive way of saying that f really is a natural transformation. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple type-class experiment turns out not so simple...
On Fri, Jan 06, 2012 at 10:51:58AM +, Steve Horne wrote: If I specify both extensions (-XMultiParamTypeClasses and -XFlexibleInstances) it seems to work, but needing two language extensions is a pretty strong hint that I'm doing it the wrong way. Not necessarily. These two extensions in particular (and especially the second) are quite uncontroversial. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Solved but strange error in type inference
The other much simpler solution no one has mentioned yet is to just
pull 'subsome' out as its own top-level declaration. Having such a
big function nested locally within a 'let' is ugly anyway, and it
makes it harder to test and debug than necessary.
-Brent
On Tue, Jan 03, 2012 at 05:44:01PM +0100, Yves Parès wrote:
Remove subsome type signature. You are redeclaring type variables which
obviously cannot match those of legSome.
This cannot work without scoped type variables (and ad-hoc foralls to bring
them to scope, of course).
2012/1/3 Yucheng Zhang yczhan...@gmail.com
As I investigated the code more carefully, I found that the type
unification
failure may not be related to the suspected class constraint on data
constructor.
I have made minor changes to the original code to remove the Ord
constraint,
including introducing a FakedMap with no requirement on Ord. The type
unification
failure continues:
Couldn't match type `nt1' with `nt'
`nt1' is a rigid type variable bound by
the type signature for
subsome :: [RRule nt1 t1 s1] - Either String ([t1], s1)
at xx.hs:34:19
`nt' is a rigid type variable bound by
the type signature for
legSome :: LegGram nt t s - nt - Either String ([t], s)
at xx.hs:29:1
Expected type: [Symbols nt1 t1]
Actual type: [Symbols nt t]
In the first argument of `makeWord', namely `r'
In the expression: makeWord r
The complete changed code follows:
data Symbols nt t = NT nt -- ^ non terminal
| T t -- ^ terminal
deriving (Eq, Ord)
type Sem s = [s]-s
data Rule nt t s = Rule { refined :: nt
, expression :: [Symbols nt t]
, emit :: Sem s
}
type RRule nt t s = ([Symbols nt t], Sem s)
data FakedMap a b = FakedMap
delete :: k - FakedMap k a - FakedMap k a
delete a b = b
lookup :: k - FakedMap k a - Maybe a
lookup a b = Nothing
data LegGram nt t s = LegGram (FakedMap nt [RRule nt t s])
legSome :: LegGram nt t s - nt - Either String ([t], s)
legSome (LegGram g) ntV =
case Main.lookup ntV g of
Nothing - Left No word accepted!
Just l - let sg = legSome (LegGram (Main.delete ntV g))
subsome :: [RRule nt t s] - Either String ([t], s)
subsome [] = Left No word accepted!
subsome ((r,sem):l) =
let makeWord [] = Right ([],[])
makeWord ((NT nnt):ll) =
do (m, ss) - sg nnt
(mm, sss) - makeWord ll
return (m++mm, ss:sss)
makeWord ((T tt):ll) =
do (mm, sss) - makeWord ll
return (tt:mm, sss)
in
case makeWord r of
Right (ll, mm) - Right (ll, sem mm)
Left err - subsome l
in subsome l
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Re: [Haskell-cafe] Reifying case expressions [was: Re: On stream processing, and a new release of timeplot coming]
On Mon, Dec 26, 2011 at 12:32:13PM +0400, Eugene Kirpichov wrote: 2011/12/26 Gábor Lehel illiss...@gmail.com On Sun, Dec 25, 2011 at 9:19 PM, Eugene Kirpichov ekirpic...@gmail.com wrote: Hello Heinrich, Thanks, that's sure some food for thought! A few notes: * This is indeed analogous to Iteratees. I tried doing the same with Iteratees but failed, so I decided to put together something simple of my own. * The Applicative structure over this stuff is very nice. I was thinking, what structure to put on - and Applicative seems the perfect fit. It's also possible to implement Arrows - but I once tried and failed; however, I was trying that for a more complex stream transformer datatype (a hybrid of Iteratee and Enumerator). * StreamSummary is trivially a bifunctor. I actually wanted to make it an instance of Bifunctor, but it was in the category-extras package and I hesitated to reference this giant just for this purpose :) Probably bifunctors should be in prelude. Edward Kmett has been splitting that up into a variety of smaller packages, for instance: http://hackage.haskell.org/package/bifunctors Actually it's not a bifunctor - it's a functor in one argument and contrafunctor in the other. Is there a name for such a structure? Bifunctor is usually used for such things as well. Data.Bifunctor only covers bifunctors which are covariant in both arguments. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Images in Haddock documentation: best practices?
Hi all, Although it doesn't seem to be documented in the user manual (!), Haddock supports inline images, using a url syntax. I'd like to include some images in the documentation for a package I'm writing, but not sure of the best way. I can, of course, just make the images available under my UPenn personal web space, and link to them from the documentation. But this seems fragile and ad-hoc. Ideally, I'd like to bundle the images along with the cabal package, and reference them locally from within the documentation. But I haven't figured out a way to do this. Any ideas? Has anyone ever included images in Haddock docs before? Is it possible to bundle them with the package and refer to them locally? Or does anyone have any other suggestions? Are there specific ways Haddock and/or cabal could be improved to make this easier? -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Alternative] some/many narrative
On Thu, Dec 15, 2011 at 07:29:20PM +1300, Chris Wong wrote: Okay, so how about the following as a user narrative for some and many? ... I was in the middle of writing my own version of Applicative when I stumbled on this intense debate. Here's what I wrote for the documentation: class (Applicative f, Monoid f) = Alternative f where Note that 'Monoid f' does not make sense, since the kinds do not match. Perhaps what you mean is (forall a. Monoid (f a)) but that is (currently) impossible to express. One could, of course, make a new typeclass class Monoid1 f where mempty1 :: f a mappend1 :: f a - f a - f a -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alternative versus Monoid
On Thu, Dec 15, 2011 at 06:49:13PM +1000, Gregory Crosswhite wrote:
So at the end of the day... what is the point of even making Maybe and []
instances of Alternative?
The Alternative and Monoid instances for [] are equivalent. However,
the Alternative and Monoid instances for Maybe are not. To wit:
(Just (Sum 4)) | (Just (Sum 3))
Just (Sum {getSum = 4})
(Just (Sum 4)) `mappend` (Just (Sum 3))
Just (Sum {getSum = 7})
-Brent
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Re: [Haskell-cafe] [Alternative] some/many narrative
On Thu, Dec 15, 2011 at 09:34:14AM -0800, Bryan O'Sullivan wrote: On Wed, Dec 14, 2011 at 10:29 PM, Chris Wong chrisyco+haskell-c...@gmail.com wrote: -- [Warning]: This is only defined for actions that eventually fail -- after being performed repeatedly, such as parsing. For pure values such -- as 'Maybe', this will cause an infinite loop. If an action of type Maybe a is written to always and unconditionally return Just some-value-or-other, *that's* when some or many will The way you phrased this sounds odd to me. Every action/value of type Maybe a will *either* always and unconditionally be Nothing, OR always and unconditionally be Just some-value-or-other. By referential transparency, those are the only options. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alternative versus Monoid
On Thu, Dec 15, 2011 at 09:05:13PM +, Conor McBride wrote:
On 15 Dec 2011, at 15:19, Brent Yorgey wrote:
On Thu, Dec 15, 2011 at 06:49:13PM +1000, Gregory Crosswhite wrote:
So at the end of the day... what is the point of even making
Maybe and [] instances of Alternative?
The Alternative and Monoid instances for [] are equivalent. However,
the Alternative and Monoid instances for Maybe are not. To wit:
(Just (Sum 4)) | (Just (Sum 3))
Just (Sum {getSum = 4})
(Just (Sum 4)) `mappend` (Just (Sum 3))
Just (Sum {getSum = 7})
The current monoid instance for Maybe is, in my view, unfortunate.
Types are about semantic purpose, not just data representation.
Many purposes can be represented in the same way. We should identify
the purpose of a type (or type constructor), then define instances
consistent with that purpose. And better, we acquire by instance
inference compound instances consistent with that purpose! (A similar
view is often articulated well by Conal Elliott. But perhaps it's
just a Con thing.)
The purpose of Maybe, it seems to me, is to model failure and
prioritized choice, after the manner of exceptions. It's clear
what the failure-and-prioritized-choice monoid is.
It so happens that the same data representation can be used to make
a semigroup into a monoid by attaching an identity element. That's
a different semantic purpose, which deserves a different type.
I agree. Moreover, the current Monoid instance for (Maybe a) does not
even achieve this, since it requires a *Monoid* instance on a, rather
than a semigroup.
Note that the 'semigroups' package defines an 'Option' type which does
lift Semigroup instances to Monoid instances. I, for one, would be
quite in favor of changing the current Monoid (Maybe a) instance to
correspond to the failure-and-prioritized-choice semantics (i.e. the
semantics currently given to the 'First' wrapper).
-Brent
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Re: [Haskell-cafe] ANNOUNCE: hxournal-0.5.0.0 - A pen notetaking program written in haskell
On Wed, Dec 14, 2011 at 04:53:38PM +0100, Ivan Perez wrote: I think not. The version in hackage is still hxournal-0.5.0.0. Unless, of course, you can update a package that's already been submitted without increasing the version number. Is that possible? (I actually don't know) Thankfully, it is not. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Chuan-Kai Lin's Unimo framework
On Mon, Dec 12, 2011 at 03:17:38PM +0100, Jean-Luc Delatre wrote: Does anybody has an hands on experience of using Chuan-Kai Lin's Unimo framework? No, but if you want to define monads operationally I would instead recommend using the 'operational' package: http://hackage.haskell.org/package/operational It does actually have examples. Anyway, it seems like Unimo is not even on Hackage. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANNOUNCEMENT] xmobar 0.14
On Sun, Dec 11, 2011 at 05:09:44PM +0400, Sergey Mironov wrote: Hi. I am Awesome WM user thinking about swithcing to the xmonad. Could I take an opportunity and ask about mouse support in xmonad/xmobar ? Actually, I assume that xmobar does nothing with mouse, but what is a common way of showing something like main menu to the user? Is there an option of switching windows with mouse by pressing on some window's icon, just like common DE does? Yes, see http://xmonad.org/xmonad-docs/xmonad-contrib/XMonad-Hooks-EwmhDesktops.html xmonad itself does not provide something which the user can click on to switch windows, but if you use some other window-switcher program (e.g. one that comes with your favorite DE) the above module can be used to make xmonad to respond to it. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] More liberal than liberal type synonyms
On Wed, Dec 07, 2011 at 04:47:47PM +0100, Gábor Lehel wrote: On Wed, Dec 7, 2011 at 1:07 PM, Dmitry Kulagin dmitry.kula...@gmail.com wrote: For short, type synonyms work for mere aliases, but not for full-fledged type-level non-inductive functions. And sometimes we intuitively want to use them as such. Thank you, Yves! It is now more clear for me. Still, it seems that ability to use partially applied type synonyms would be very natural (and useful) extension to the language. It would allow to avoid boilerplate code associated with creating really new types instead of just using synonims for existing ones. The problem as I understand it is that partially-applied type synonyms are in effect type level lambdas, and type checking in the presence of type level lambdas requires higher-order unification, which is undecidable in general. Restricted cases might be possible, I'm not an expert in the field. GHC hackers could probably elaborate. [1] http://stackoverflow.com/questions/8248217/are-there-type-level-combinators-will-they-exist-in-some-future [2] http://en.wikipedia.org/wiki/Unification_(computer_science)#Higher-order_unification It's actually type *inference* that requires higher-order unification in the presence of type-level lambdas, not type checking. This might not be a huge deal: we just have to clearly state that enabling -XPartialTypeFunApps means that you may have to provide some explicit type annotations in places where type inference cannot figure things out. We already have extensions like this (e.g. RankNTypes). The bigger problem for the moment is that for various technical reasons, enabling partial applications of type functions can lead to unsoundness (i.e. typechecked programs which nonetheless crash at runtime) in the way that type equality is handled. For more details see http://stackoverflow.com/questions/7866375/why-does-ghc-think-that-this-type-variable-is-not-injective/7950614#7950614 I agree that the ability to use partially applied type synonyms/functions would be natural and useful. I hope we will eventually see a version of GHC which supports it but there are some nontrivial technical issues to be worked out first. -Brent On Wed, Dec 7, 2011 at 3:51 PM, Yves Parès limestr...@gmail.com wrote: Ah, maybe Dan could tell us if it works only with GHC 7. Dmitry, I had your problem many times. The last time was when I saw you could define the ContT monad in terms of Cont (the opposite is done in the mtl). It leads to a simpler code, but you are stucked when trying to define ContT as an instance of MonadTrans: data Cont r a = ... -- [instances of Monad Cont, blah blah blah] type ContT r m a = Cont r (m a) instance MonadTrans (ContT r) where -- This doesn't compile, even if it is logical lift = ... For short, type synonyms work for mere aliases, but not for full-fledged type-level non-inductive functions. And sometimes we intuitively want to use them as such. 2011/12/7 Dmitry Kulagin dmitry.kula...@gmail.com Dmitry, does your code work with LiberalTypeSynonyms extention activated? No, the same error: Type synonym `StateA' should have 1 argument, but has been given 0 But I have GHC 6.12.3 Dmitry 2011/12/7 Yves Parès limestr...@gmail.com: This is impossible: in the definition of 'StateT s m a', m must be a monad and then have the * - * kind. So you cannot pass (StateA a), because it has simply the * kind. Dmitry, does your code work with LiberalTypeSynonyms extention activated? 2011/12/7 Øystein Kolsrud kols...@gmail.com You should be able to write something like this: type StateB a b = StateT SomeOtherState (StateA a) b Best regards, Øystein Kolsrud On Wed, Dec 7, 2011 at 11:48 AM, Dmitry Kulagin dmitry.kula...@gmail.com wrote: Hi Dan, I am still pretty new in Haskell, but this problem annoys me already. If I define certain monad as a type synonym: type StateA a = StateT SomeState SomeMonad a Then I can't declare new monad based on the synonym: type StateB a = StateT SomeOtherState StateA a The only way I know to overcome is to declare StateA without `a': type StateA = StateT SomeState SomeMonad But it is not always possible with existing code base. I am sorry, if this is offtopic, but it seemed to me that the problem is realted to partially applied type synomyms you described. Thanks! Dmitry On Tue, Dec 6, 2011 at 10:59 PM, Dan Doel dan.d...@gmail.com wrote: Greetings, In the process of working on a Haskell-alike language recently, Ed Kmett and I realized that we had (without really thinking about it) implemented type synonyms that are a bit more liberal than GHC's. With LiberalTypeSynonyms enabled, GHC allows: type Foo a b = b - a type Bar f = f String Int
Re: [Haskell-cafe] (no subject)
On Mon, Nov 28, 2011 at 04:20:54PM -0600, Antoine Latter wrote: On Mon, Nov 28, 2011 at 4:12 PM, Willem Obbens dub...@hotmail.com wrote: Hello, I get this error when I try to derive an instance of the Show typeclass: Abc.hs:21:60: Couldn't match expected type `Vector' with actual type `[Point]' In the first argument of `show'', namely `xs' In the second argument of `(++)', namely `show' xs' In the second argument of `(++)', namely `, ++ show' xs' Failed, modules loaded: none. Here's the faulty code: newtype Point = Point Int instance Show Point where show (Point a) = [chr $ a + 48] data Vector = Vector [Point] instance Show Vector where show (Vector ys) = let show' (Vector [z]) = show z show' (Vector (x:xs)) = show x ++ , ++ show' xs show' (Vector []) = [] in ( ++ show' ys ++ ) You've made show' :: Vector - String, but I'm guessing you actually want to make it show' :: [Point] - String; i.e. get rid of the Vector constructors in the show' patterns. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A Mascot
On Thu, Nov 17, 2011 at 10:28:47AM +0100, Alexander Bernauer wrote: On Tue, Nov 15, 2011 at 08:18:04PM -0800, John Meacham wrote: People tend to concentrate on the lambda which cooresponds to the functional aspect of haskell when designing logos. Not nearly enough attention is paid to the other striking feature, the laziness. If we want to emphasize the lazyness, why not a sloth instead of a lamb? http://en.wikipedia.org/wiki/Sloth - is this cute or what ;-) Sloths are not lazy, they are just slow. I doubt that's the impression we want to give of Haskell. =) -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] capri cabal-dev virtualenv cab
On Tue, Nov 08, 2011 at 10:04:20AM -0800, Rogan Creswick wrote: On Mon, Nov 7, 2011 at 11:40 PM, Rustom Mody rustompm...@gmail.com wrote: Does anyone give me a little comparison of these? virtualenv: I'm not familiar with virtualenv, but from skimming the site, it looks like it does something very similar to cabal-dev, but focused on python. I'm not sure if it can be used with other languages / arbitrary tools or not. I'm guessing the OP was actually referring to 'virthualenv', which was recently released and works with Haskell (but is similar to virtualenv for python). It seems that virthualenv lets you set up independent environments including sandboxed builds and custom versions of GHC, etc., and switch between them. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is it possible to get the information of instances of a type?
On Wed, Oct 26, 2011 at 09:15:41AM -0700, Nathan Howell wrote: On Wed, Oct 26, 2011 at 6:53 AM, Magicloud Magiclouds magicloud.magiclo...@gmail.com wrote: But in Haskell, could I write a code to list the classes that a type instanced? TemplateHaskell as well. It's possible with TemplateHaskell. Look at classInstances and the ClassI data constructor. http://haskell.org/ghc/docs/7.0.4/html/libraries/template-haskell-2.5.0.0/Language-Haskell-TH.html#v:classInstances No, this lists all the instances of a class. OP asked for the classes of which a given type is an instace. Presumably it is possible, since Haddock does it! In the documentation generated for a type it lists classes of which the type is an instance. So you might want to look at how Haddock does it. I suspect the only way is through the GHC API. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is it possible to get the information of instances of a type?
On Wed, Oct 26, 2011 at 09:10:23PM +0400, MigMit wrote: Can't be done. Even if this particular module doesn't contain instance Class Type, it's quite possible that the said instance would be defined in another module, about which this one knows nothing about. That doesn't mean it can't be done, only that you would have to be explicit about which modules to look in. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: Monad.Reader Issue 19
I am pleased to announce that Issue 19 of The Monad.Reader, a special issue on parallelism and concurrency, is now available: http://themonadreader.files.wordpress.com/2011/10/issue19.pdf Issue 19 consists of the following three articles: * Mighttpd – a High Performance Web Server in Haskell by Kazu Yamamoto * High Performance Haskell with MPI by Bernie Pope and Dmitry Astapov * Coroutine Pipelines by Mario Blažević Feel free to browse the source files. You can check out the entire repository using darcs: darcs get http://code.haskell.org/~byorgey/TMR/Issue19 If you’d like to write something for Issue 20, please get in touch. The deadline will likely be in December; more details will be forthcoming. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: diagrams 0.4
On Mon, Oct 24, 2011 at 11:55:53AM -0700, David Barbour wrote: Thanks. Diagrams package seems it could be promising for a declarative UI model - i.e. integration with functional reactive programming and similar models - so long as I'm willing to sacrifice `native` look and feel, which doesn't seem like a big problem. Yes, I imagine it could. Not one of the use cases I personally had in mind -- but I've been hoping that people will find it useful for things I had not thought of. A couple more questions: 1) Am I right in assuming that Diagrams does very little `occlusion` of its own - i.e. when rendering a soda-straw view of a complex diagram, or masking large areas with a rectangle or sphere? There won't be any competition or redundancy with an external index and backend (e.g. Cairo-GL layer) occlusion? Right, diagrams currently doesn't do any sort of culling, occlusion, etc., that's all up to the backend. 2) Is there support for Cairo-like linear and radial gradients? Not yet, but it's on the todo list. Also, it seems that for Cairo rendering, we cannot currently supply our own Cairo context. renderDia Cairo (CairoOptions foo.png (PNG (100,100))) myDiagram This section of your manual is incomplete, I admit, but from browsing the code it seems you provide a simplified interface that fully encapsulates the Cairo rendering. Is there any way to render a diagram within the Cairo stack? or leverage Cairo's own experimental backends (like OpenGL)? You're right, currently there's no way do these sorts of things. However, there's no fundamental limitation here and adding this sort of functionality should not be hard, and I'd be quite open to extending the cairo backend in this direction. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: diagrams 0.4
On Mon, Oct 24, 2011 at 01:58:33PM -0700, Jason Dagit wrote: On Sun, Oct 23, 2011 at 11:47 AM, Brent Yorgey byor...@seas.upenn.edu wrote: I am pleased to announce the release of version 0.4 of diagrams, a full-featured framework and embedded domain-specific language for declarative drawing. What do you use for text support? I know at one point you were interested in my freetype2 binding (which is still very raw and immature), but you must be using gtk for font loading and rendering? At the moment, text is completely delegated to backends. diagrams itself doesn't do any font loading or rendering at all. However, the obvious downside to this is that the framework itself has no idea how big a given piece of text is and can't position it relative to other things. On the todo list is to use your freetype2 binding (or something like it) to actually do more work within the framework itself, so it can position text correctly, convert text outlines into paths, and so on. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: diagrams 0.4
On Mon, Oct 24, 2011 at 08:21:30AM +0530, Rustom Mody wrote: Thanks. This is attractive. I remember (vaguely) a 'live page' ie where one could enter (into the browser) changes to the diagrams code and see the results immediately. Is that page there? (Or am I mixing up with something else?) You might also have been thinking of Luite Stegeman's Wolfgang Lambda project, which supports diagrams in this way (as well as many other things!). There was an early preview version of it up for a little while which a bunch of people saw, but it's not ready for release yet. How does diagrams compare with graphviz? If this is an inappropriate (type-wrong?) question thats ok :-) Its just that when I last looked at graphviz I found the documentation somewhat impenetrable -- like much else in Hackage -- lots of types, no examples. graphviz is a special-purpose tool for doing graph layout and visualization. diagrams is a general-purpose framework for drawing anything at all. As for documentation, you do realize that the graphviz package on Hackage is a set of bindings? So there's a lot of helpful documentation at http://www.graphviz.org/ . One of my goals with diagrams is to have excellent documentation, so if you find anything that is unclear or poorly documented, please file a bug report (http://code.google.com/p/diagrams/issues/list)! -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: diagrams 0.4
On Mon, Oct 24, 2011 at 03:46:26PM +1100, Ivan Lazar Miljenovic wrote: Hmmm... might be interesting to try and use dot/neato/etc. to do the layout of a graph, and then use diagrams for the actual visualisation... I agree! This has been on my list of things-to-do-with-diagrams-eventually for quite a while. It shouldn't even be very hard since your graphviz bindings can so nicely round-trip a graph description through dot/neato/etc. (right?) graphviz is great at graph layout but not so hot at graph *drawing*. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
