[Haskell] Haskell Weekly News

*Top Picks:* - Oskar Wickström rewrites the Oden-to-Go transpiler from Racket to Haskell . Oden is an FP language comprising an ML type system and LISP syntax. Oskar explains that he made the migration because

[Haskell] Haskell Weekly News

mber of a whole family of programs, including those that are likely to succeed it"? He would have warmly congratulated you on your discovery.) -- Kim-Ee Yeoh ___ Haskell mailing list Haskell@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell

[Haskell] Haskell Weekly News

*Top Picks:* - Team GHC announces the first release candidate of version 8.0 . New features include: - Strict and StrictData extensions - TypeFamilyDependencies

[Haskell] Haskell Weekly News

Folks: Recall the quote from the May Day 2015 issue: The MLs and Haskell remind me of Brian Eno's line about how the first Velvet Underground album only sold 30,000 copies, but "everyone who bought one of those 30,000

[Haskell] On Hiatus Until January 2016: Haskell Weekly News

Regrettably, I must announce that Haskell Weekly News will go on hiatus until the new year. I recognize that the last issue was back in September. It's been said that "The more a man possesses over and above what he uses, the more careworn he becomes." In my case, mundane possessions have indeed

[Haskell] Haskell Weekly News

*Top picks:* - Neil Mitchell reports a stack overflow with 7.10.2 maximumBy that regresses from 7.8.3. His sixth sense points to the Foldable-Traversable coup (aka BBP: Burning

[Haskell] Haskell Weekly News

*Top picks:* - Gabriel Gonzalez evaluates Haskell https://github.com/Gabriel439/post-rfc/blob/master/sotu.md in the style of a State-of-the-Union address. He rates Haskell from Immature to Mature to Best-in-class under 28 headings, the first four being *Compilers,* *Server-side web

[Haskell] Fwd: Haskell Weekly News

*Editorial:*Over a month has elapsed since the last issue. Is the Weekly News turning into the Monthly News? No. I've been working on getting full-length articles into the News. Imagine articles that investigate, analyze, and give the low-down on hoary issues like cabal hell that cannot be

[Haskell] Haskell Weekly News

*Top Picks:* - Andrew Gibiansky http://www.reddit.com/r/haskell/comments/37uqqk/ihaskell_online_help_choose_demo_code_snippets/ announces the Mathematica-inspired REPL 2.0 IHaskell as a web-app you can play with right now http://try.jupyter.org/. Bouquets include: This is an

[Haskell] Haskell Weekly News

*Top Picks:* - Tony Day, Brisbane-based investment strategist and high-frequency-trading hacker, rides 100% idiomatic Haskell http://tonyday567.github.io/blog/mvc-todo/ into the Single Page (web)-App http://en.wikipedia.org/wiki/Single-page_application space. How? He spins the

[Haskell] Haskell Weekly News

*Top Picks:* - Is Servant http://haskell-servant.github.io/the most type-safe HTTP server library ever? Are the type signatures hard to read https://news.ycombinator.com/item?id=9519782#up_9520750? In addition to its utmost relevance as a web library, Servant is also an awesome case

[Haskell] Haskell Weekly News

*Top Picks:* - Haskell wins a bumper crop of 18 accepted Google Summer of Code proposals http://www.reddit.com/r/haskell/comments/342rvp/google_summer_of_code_18_projects_accepted/. Mentor offers total 44, another thumpin' sign of life. Kudos to Edward Kmett, Johan Tibell, Shachaf

Re: [Haskell] Haskell Weekly News

Another Lennart, last name Spitzner, creates another genie that turns type signatures into programs. Unlike Djinn, Exference http://haskell.1045720.n5.nabble.com/ANN-exference-a-different-djinn-td5807986.html makes no promises over termination. Your wish is my command even at the expense of

[Haskell] Haskell Weekly News

*Top picks:* - Bot attack on Trac https://mail.haskell.org/pipermail/ghc-devs/2015-March/008557.html pummels GHC HQ productivity! Do you know a thing or two about hardening web apps? Can you help? - A month ago

[Haskell] Haskell Weekly News

is what keeps HWN going, so let me thank you in return for sharing the love, for I remain Yours editorially, Kim-Ee Yeoh p.s. Stay tuned for an upcoming editorial on what the future holds for HWN. -- Kim-Ee ___ Haskell mailing list Haskell@haskell.org http

[Haskell] Haskell Weekly News

*Top picks:* Jasper Van der Jeugt http://jaspervdj.be/posts/2015-02-24-lru-cache.html shows how you can write an intuitive, obviously correct LRU cache perfectly polymorphic in both the key and value types of the cache lookup function. (Reddit discussion.)

Re: [Haskell] Haskell Weekly News: Issue 316

On Thu, Feb 5, 2015 at 4:07 PM, Simon Peyton Jones simo...@microsoft.com wrote: We really need a successor! Please, please. I have offered to continue HWN. If picked, I intend to bring it back to the informed news source that it was circa early 2000s. I'm cognizant of the diversification of

Re: GHC 7.10 regression when using foldr

On Tue, Jan 20, 2015 at 6:45 PM, Edward Kmett ekm...@gmail.com wrote: I can at least say that the incident rate for cases seems to be very low, especially when it is contrasted against the pain users have had with using the existing Foldable/Traversable imports where virtually everything in

Re: [Haskell] ANNOUNCE: vty-5.1 and vty-examples-5.0

On Sat, Jun 7, 2014 at 11:26 PM, Corey O'Connor coreyocon...@gmail.com wrote: vty 5.1 is out: - http://hackage.haskell.org/package/vty All parts of vty have received care and a whole bunch of testing. The absence of haddock-generated html will impede adoption of the latest and greatest

Re: [Haskell-cafe] Alternative name for return

On Thu, Aug 8, 2013 at 7:40 AM, Timon Gehr timon.g...@gmx.ch wrote: You make the distinction between evaluate, Which essentially means applying reduction rules to an expression until the result is a value. and execute or run, etc. This is not functional. How would you know? I think

Re: [Haskell-cafe] Some philosophy (Was: Alternative name for return)

On Fri, Aug 9, 2013 at 10:44 PM, Jerzy Karczmarczuk jerzy.karczmarc...@unicaen.fr wrote: I decided to reread some philosophical texts, and I suggest one for your evening reading. Indiscrete Thoughts by Gian-Carlo Rota, published by Birkhäuser in 1997. Available on the Web. I'm rather fond

Re: [Haskell-cafe] Identity of indiscernibles

On Thu, Aug 8, 2013 at 11:05 PM, Tom Ellis tom-lists-haskell-cafe-2...@jaguarpaw.co.uk wrote: On Thu, Aug 08, 2013 at 03:38:41PM +0200, Jerzy Karczmarczuk wrote: One could simply implement IO as a free monad Interesting. I wonder how. See [1] for an explanation of free monads in general.

Re: [Haskell-cafe] Release Candidates for Haskell Platform 2013.2

On Mon, May 13, 2013 at 9:39 PM, Mark Lentczner mark.lentcz...@gmail.comwrote: *Some of the release candidates for Haskell Platform 2013.2 are up.* Kudos! Exactly 7 days from the scheduled date, as stated. Hope to give them a whirl once the other OSes are baked. -- Kim-Ee

Re: [Haskell-cafe] Markdown extension for Haddock as a GSoC project

On Mon, Apr 29, 2013 at 8:42 AM, Alexander Solla alex.so...@gmail.comwrote: I've been scoffed at during interviews for saying I solve problems on paper before I start typing! That has to suck. I hope you're properly avenged when you find work in a savvier, respectful competitor and KICK THEIR

Re: [Haskell-cafe] Why were datatype contexts removed instead of fixing them?

On Thu, Apr 25, 2013 at 6:36 PM, Joe Quinn headprogrammingc...@gmail.comwrote: data Foo a where Foo :: Eq a = a - Foo a is equivalent to data Foo a = Eq a = Foo a but is different from data Eq a = Foo a = Foo a (Yup, tripped up a few of us already!) -- Kim-Ee

Re: [Haskell-cafe] NaN as Integer value

On Sun, Apr 14, 2013 at 3:28 PM, wren ng thornton w...@freegeek.org wrote: Whereas the problematic values due to infinities are overspecified, so no matter which answer you pick it's guaranteed to be the wrong answer half the time. Part of this whole problem comes from the fact that floats

Re: [Haskell-cafe] Is there an escape from MonadState+MonadIO+MonadError monad stack?

On Sun, Apr 7, 2013 at 5:03 AM, Ömer Sinan Ağacan omeraga...@gmail.com wrote: That's interesting, thanks! Do you have any recommendations about which file to start reading? AFAIK, GHC is _huge_. Without a discussion of your interests, it's hard to say. Certainly, I'd set up the reading

Re: [Haskell-cafe] code-as-config, run-time checks and error locations

On Sun, Apr 7, 2013 at 12:23 AM, Steffen Schuldenzucker sschuldenzuc...@uni-bonn.de wrote: For the moment I think it would be enough to auto-insert the location of calls to a certain set of functions. Have you tried assert [1]? [1]

Re: [Haskell-cafe] meaning of referential transparency

On Sun, Apr 7, 2013 at 12:43 AM, Henning Thielemann lemm...@henning-thielemann.de wrote: Can someone enlighten me about the origin of the term referential transparency? I can lookup the definition of referential transparency in the functional programming sense in the Haskell Wiki and I can

Re: [Haskell-cafe] meaning of referential transparency

/uday_reddy_sharpens_up_referential_transparency/ This was a fascinating exchange and I'm glad to be reminded to revisit it :). On Sat, Apr 6, 2013 at 11:13 AM, Kim-Ee Yeoh k...@atamo.com wrote: On Sun, Apr 7, 2013 at 12:43 AM, Henning Thielemann lemm...@henning-thielemann.de wrote: Can someone enlighten me about

Re: [Haskell-cafe] Is there an escape from MonadState+MonadIO+MonadError monad stack?

On Sun, Apr 7, 2013 at 4:22 AM, Ömer Sinan Ağacan omeraga...@gmail.com wrote: I'm a hobbyist Haskell programmer and my use of Haskell is mostly consists of writing interpreters, simple virtual machines, and type checkers. One thing I'm not happy about my Haskell programs is, almost all of my

Re: [Haskell-cafe] code-as-config, run-time checks and error locations

On Sun, Apr 7, 2013 at 4:37 AM, Steffen Schuldenzucker sschuldenzuc...@uni-bonn.de wrote: Reading through that now... [1] http://hackage.haskell.org/trac/ghc/wiki/ExplicitCallStack If you're reading that page, you probably also want to get up to speed on the latest. The thread titled RFC:

Re: [Haskell-cafe] Possible GSoC project

On Thu, Apr 4, 2013 at 10:03 PM, Ketil Malde ke...@malde.org wrote: Not very much, some knowledge of string edit distance and dynamic programming would be good, but if not, it's something I can straighten out with a student in an afternoon, I think. Just a suggestion: People love quizzes

Re: [Haskell-cafe] GSoC Project Proposal: Markdown support for Haddock

On Fri, Apr 5, 2013 at 3:04 AM, Simon Heath icefo...@gmail.com wrote: I humbly suggest reStructuredText rather than Markdown, which is what is used by the Python community for documentation. Since it's specifically made for documentation it may be nicer. But, I don't want to spark a format

Re: [Haskell-cafe] GSoC Project Proposal: Markdown support for Haddock

On Fri, Apr 5, 2013 at 10:44 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: I don't think so; this was one of the big issues recently when people were trying to get Gruber to actually _do_ something with Markdown as there were all these corner cases. In that case, surely this is an

Re: [Haskell-cafe] Haskell is a declarative language? Let's see how easy it is to declare types of things.

(Folks, let's rescue this increasingly tendentious thread.) Some points to ponder: (1) Any can be often be clarified to mean all, depending on how polymorphic functions are exegeted. In a homotopy-flavored explanation of natural transformation, its components (read parametric instances) exist

Re: [Haskell-cafe] Haskell is a declarative language? Let's see how easy it is to declare types of things.

Hi Tillmann, On Wed, Apr 3, 2013 at 11:59 PM, Tillmann Rendel ren...@informatik.uni-marburg.de wrote: From the type-theoretic point of view, I guess this is related to your view of what a polymorphic function is. Do you have a reference to the previous conversation? but we moved further and

Re: [Haskell-cafe] Parsec community and up-to-date documentation

On Mon, Mar 25, 2013 at 5:19 AM, Konstantine Rybnikov k...@k-bx.com wrote: as a beginner had a lot of headache starting from outdated documentation in various places, lack of more tutorials, confusion between Text.Parsec and Text.ParseCombinator modules and so on. You're indeed right. While

Re: [Haskell-cafe] Need some advice around lazy IO

On Tue, Mar 19, 2013 at 2:01 PM, Konstantin Litvinenko to.darkan...@gmail.com wrote: Yes. You (and Dan) are totally right. 'Let' just bind expression, not evaluating it. Dan's evaluate trick force rnf to run before hClose. As I said - it's tricky part especially for newbie like me :) To place

Re: [Haskell-cafe] Open-source projects for beginning Haskell students?

Question is: does the task even have to involve the the production of Haskell code? Is it possible that both the student and the community-at-large would benefit further from expository-style artifacts? Some possible activities: (1) producing documentation for popular packages that cater to

Re: [Haskell-cafe] RFC: rewrite-with-location proposal

On Mon, Feb 25, 2013 at 9:42 PM, Simon Peyton-Jones simo...@microsoft.comwrote: One idea I had, which that page does not yet describe, is to have an implicit parameter, something like ?loc::Location** +1 Implicit params has a bad rap in some circles because of counterintuitive behavior when

Re: [Haskell-cafe] Parser left recursion

On Sun, Feb 24, 2013 at 7:09 PM, Roman Cheplyaka r...@ro-che.info wrote: Thus, your recursion is well-founded — you enter the recursion with the input strictly smaller than you had in the beginning. Perhaps you meant /productive/ corecursion? Because the definition A ::= B A you gave is

Re: [Haskell-cafe] Parser left recursion

On Sun, Feb 24, 2013 at 7:47 PM, Roman Cheplyaka r...@ro-che.info wrote: Or perhaps you meant that the production itself, when interpreted as a definition, is corecursive? I was merely thrown off by your mention of well-founded and the assertion that you're left with a strictly smaller input.

Re: [Haskell-cafe] Parser left recursion

On Sun, Feb 24, 2013 at 8:03 PM, Roman Cheplyaka r...@ro-che.info wrote: It may become more obvious if you try to write two recursive descent parsers (as recursive functions) which parse a left-recursive and a non-left-recursive grammars, and see in which case the recursion is well-founded

Re: [Haskell-cafe] Parser left recursion

On Sun, Feb 24, 2013 at 10:04 PM, Tillmann Rendel ren...@informatik.uni-marburg.de wrote: The recursion is well-founded if (drop n1 text) is smaller then text. So we have two cases, as Roman wrote: If the language defined by B contains the empty string, then n1 can be 0, so the recursion is

Re: [Haskell-cafe] ANN: monad-bool 0.1

On Thu, Jan 24, 2013 at 6:23 AM, wren ng thornton w...@freegeek.org wrote: NotOnHackage: a package repository just like Hackage, except the packages are just documentation on why there is no such package. Love the idea! It'll make us even more unique among other PLs and even more ways to be

Re: [Haskell-cafe] Type hierarchy

On Wed, Jan 16, 2013 at 11:22 PM, Thiago Negri evoh...@gmail.com wrote: The C spec allows the use of GLboolean values where GLenums are expected. Some fixes off the top of my head (caveats apply): * define a lift :: GLboolean - GLenum * use a typeclass GLenumlike * if there aren't too many of

Re: [Haskell-cafe] A Meetup Group for MN Haskellers

Hey Danny, Good job taking the lead! Wish you all success because I think meetups have so many underrated benefits. (Where I am in a city 10 million, i.e. Jakarta, Indonesia, you'd think it would be a piece of cake, but so far no dice. Me and another guy are working on this ) Have you

Re: [Haskell-cafe] Object Oriented programming for Functional Programmers

On Fri, Jan 4, 2013 at 7:27 PM, David Thomas davidleotho...@gmail.comwrote: Well, hidden - it *is* right there in the type signature still, it just doesn't *look* like an argument. If you squint hard enough, (=) looks like (-). Or maybe the other way round. Whatever. :) It also might be

Re: [Haskell-cafe] Object Oriented programming for Functional Programmers

There's OOHaskell, which you can google for. The name's such a nice example of an aptronym: it's the Overlooked Object-oriented Haskell. -- Kim-Ee On Mon, Dec 31, 2012 at 2:58 AM, Daniel Díaz Casanueva dhelta.d...@gmail.com wrote: Hello, Haskell Cafe folks. My programming life (which has

Re: [Haskell-cafe] Non polymorphic numerals option -- avoiding type classes

Hi David, it looks like Rustom's aware that haskell's not lisp. What he really wants methinks is a way to suppress type classes altogether! That or a NoOverloadedNumerals extension. -- Kim-Ee On Thu, Dec 27, 2012 at 4:03 PM, David Virebayre dav.vire+hask...@gmail.com wrote: Prelude :t

Re: [Haskell-cafe] Non polymorphic numerals option -- avoiding type classes

On Thu, Dec 27, 2012 at 11:48 PM, Rustom Mody rustompm...@gmail.com wrote: On Thu, Dec 27, 2012 at 8:26 PM, Kim-Ee Yeoh k...@atamo.com wrote: What he really wants methinks is a way to suppress type classes altogether! That or a NoOverloadedNumerals extension. I'm not really sure about

Re: [Haskell-cafe] MPTC or functional dependencies?

Petr, Your subject header is misleading: FDs don't make sense without MPTCs. As you acknowledge at the end, what you're ultimately asking is: to FD or not to FD. Note also, the contemporary debate has shifted to TFs (type families) vs FDs. -- Kim-Ee On Fri, Dec 21, 2012 at 7:38 PM, Petr P

Re: [Haskell-cafe] arr considered harmful

Hey Conal, I have something (another circuits formulation) that's almost an arrow but doesn't support arr. Have you seen Adam Megacz's generalized arrows? http://www.cs.berkeley.edu/~megacz/garrows/ -- Kim-Ee On Fri, Dec 21, 2012 at 7:55 AM, Conal Elliott co...@conal.net wrote: If you

Re: [Haskell-cafe] Substituting values

This is reminiscent of the Either (exception) monad where Left values, the exceptions, pass through unaltered, and Right values are transformable, i.e. acted on by functions. But I have no idea what you're trying to achieve in the bigger picture. Help us help you by fleshing out your use case.

Re: How to use C-land variable from Cmm-land?

When 32 bits are assigned to any of the standard registers, the upper 32 bits are implicitly set to zero. Intel is weird. Didn't AMD invent the 64-bit extensions? -- Kim-Ee On Sun, Dec 9, 2012 at 3:07 PM, Axel Simon axel.si...@in.tum.de wrote: On 09.12.2012, at 00:12, Yuras Shumovich

Re: [Haskell-cafe] Exploring Programming Language Theory

SPJ's IFPL is an excellent starting point to learn the innards of Haskell. It allows a well-acculturated individual to grab the base of the trunk and start climbing the branches, which means reading the research papers (SPJ's website, mainly though not exclusively), all the way to the leaves

Re: [Haskell-cafe] Exploring Programming Language Theory

I should add that IFPL has important chapters written by authors other than Simon. -- Kim-Ee On Sun, Dec 9, 2012 at 5:58 AM, Kim-Ee Yeoh k...@atamo.com wrote: SPJ's IFPL is an excellent starting point to learn the innards of Haskell. It allows a well-acculturated individual to grab the base

Re: [Haskell-cafe] mtl: Why there is Monoid w constraint in the definition of class MonadWriter?

The only thing we can tell from the Monad laws is that that function f should be associative. That f is associative is a very small step away from f forming a monoid. What about listen :: m a - m (w, a)? What laws should it hold that are compatible with those of the monad and those of tell?

Re: [Haskell-cafe] Design of a DSL in Haskell

On Dec 5, 2012, at 2:59 AM, Kim-Ee Yeoh wrote: On Wed, Dec 5, 2012 at 8:32 AM, Tillmann Rendel ren...@informatik.uni-marburg.de wrote: I mean internal == embedded, independently of deep vs. shallow, following Martin Fowler [1]. [1] http://martinfowler.com/bliki

Re: [Haskell-cafe] Design of a DSL in Haskell

On Tue, Dec 4, 2012 at 4:53 PM, Joerg Fritsch frit...@joerg.cc wrote: is a shallow embedded DSL == an internal DSL and a deeply embedded DSL == an external DSL or the other way around? Roughly speaking, yes. But a deep DSL doesn't mean you've got to have a parser tokenizer IO input. You can

Re: [Haskell-cafe] Design of a DSL in Haskell

Simulation and Synthesis, The Internals and Externals of Kansas Lava for a fuller definition. http://www.ittc.ku.edu/csdl/fpg/sites/default/files/Gill-10-TypesKansasLava.pdf Other communities may have their own definitions. On 4 December 2012 10:01, Kim-Ee Yeoh k...@atamo.com wrote: On Tue

Re: [Haskell-cafe] Design of a DSL in Haskell

On Wed, Dec 5, 2012 at 8:32 AM, Tillmann Rendel ren...@informatik.uni-marburg.de wrote: I mean internal == embedded, independently of deep vs. shallow, following Martin Fowler [1]. [1]

Re: [Haskell-cafe] Is anyone working on a sparse matrix library in Haskell?

On Sun, Dec 2, 2012 at 10:52 AM, wren ng thornton w...@freegeek.org wrote: My goal for all this is in setting up the type system, not performance. I figure there are other folks who know and care a lot more about the numerical tricks of giving the actual implementations. You've got my support

Re: [Haskell] Status of Haskell'?

On Sat, Dec 1, 2012 at 3:36 AM, Gábor Lehel illiss...@gmail.com wrote: But in Haskell right now, for practical purposes, we don't have competing implementations. We have GHC. Isn't putting pressure on the community for a new standard a way to, umm, implement wished-for features in GHC

Re: [Haskell-cafe] How to incrementally update list

On Sat, Dec 1, 2012 at 1:16 AM, Mark Thom markjordant...@gmail.com wrote: Is there a paper or other single resource that will help me thoroughly understand non-strictness in Haskell? If performance is utterly vital the best resource is Core, as in, the ability to read it. The order of

Re: [Haskell-cafe] Why Kleisli composition is not in the Monad signature?

Ben, Now, on to Bind: the standard finite structure example for Bind is most probably the substitution thingy ... Danger of conflating a bunch of things here: (1) the substitution monadic effect is always also applicative and always also unital/pointed because monads are always applicative and

Re: [Haskell-cafe] How to incrementally update list

I want to incrementally update list lot of times, but don't know how to do this. Are you using the right data structure for the job? Maybe you want an array instead? -- Kim-Ee On Wed, Nov 28, 2012 at 6:43 PM, Branimir Maksimovic bm...@hotmail.comwrote: Problem is following short program:

Re: [Haskell-cafe] cabal configure cabal build cabal install

Nice tip, Albert! Good to know! One question I have is, is (runghc Setup.lhs) equivalent to (cabal) in runghc Setup.lhs $ [configure, build, install] ? On Mon, Nov 26, 2012 at 8:08 AM, Brent Yorgey byor...@seas.upenn.eduwrote: [cabal haddock, if you want] cabal copy cabal register Even

Re: [Haskell-cafe] Compilers: Why do we need a core language?

Is it impossible (very hard) to directly translate high-level language into machine code? There's a context to your question I don't understand, so let me ask: Wouldn't it be easier to break a big step into smaller baby steps? And if it's indeed easier why wouldn't you choose that route? --

Re: [Haskell-cafe] [Off-topic] How unimportant it is whether submarines can swim (EWD1056)

On Sun, Oct 28, 2012 at 11:29 AM, Rustom Mody rustompm...@gmail.com wrote: In particular, there is one small notational point that he insisted on towards the end of his career (and life) viz. where traditional mathematicians write *f(x) *and functional programmers write *f x*, he would write

Re: [Haskell-cafe] Why Kleisli composition is not in the Monad signature?

On Tue, Oct 16, 2012 at 9:37 PM, AUGER Cédric sedri...@gmail.com wrote: As I said, from the mathematical point of view, join (often noted μ in category theory) is the (natural) transformation which with return (η that I may have erroneously written ε in some previous mail) defines a monad

Re: [Haskell-cafe] Which advanced Haskell topics interest you

Something to consider is that it's not so much whether the material is basic, advanced, or intermediate; it's that the way it's being presented is boring and ineffective. Take the Head First Java book, which was deliberately engineered to overcome precisely this hitherto neglected aspect of

Re: [Haskell-cafe] Church vs Boehm-Berarducci encoding of Lists

Both are excellent points, thank you. Your mention of general recursion prompts the following: in 1995, ten years after publication of Boehm-Berarducci, Launchbury and Sheard investigated transformation of programs written in general recursive form into build-foldr form, with an eye towards the

Re: [Haskell-cafe] Church vs Boehm-Berarducci encoding of Lists

to lists. The enclosed code shows the list encoding that has constant-time cons, head, tail and trivially expressible fold and zip. Kim-Ee Yeoh wrote: So properly speaking, tail and pred for Church-encoded lists and nats are trial-and-error affairs. But the point is they need not be if we

Re: [Haskell-cafe] Church vs Boehm-Berarducci encoding of Lists

Oleg, Let me try to understand what you're saying here: (1) Church encoding was discovered and investigated in an untyped setting. I understand your tightness criterion to mean surjectivity, the absence of which means having to deal with junk. (2) Church didn't give an encoding for

Re: [Haskell-cafe] Where are the haskell elders?

Something I've noticed is the phenomenon of Help Vampires [1] on this list. Amy Hoy: As soon as an open source project, language, or what- have-you achieves a certain notoriety—its half-life, if you will— they swarm in, seemingly draining the very life out of the community itself. She

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

I'd write it as foo f = join .$ sequence . (f $) where (.$) :: (.$) :: Functor f = (a - b) - ((x - f a) - (x - f b)) x .$ y = (x $) . y is part of my line-noise toolbox. This join .* sequence family of functions is quite common. Should really have a name for them. Tony Morris-4 wrote:

Re: [Haskell-cafe] Finally tagless and abstract relational Algebra

Günther Schmidt wrote: Initially I had simply imported the CSV files into empty tables in a database and done the calculations directly in SQL, never ever again! [snip] But my 1st goal here is to express the algorithm. Sounds like you want a better DSL than SQL. You're in massive

Re: [Haskell-cafe] Finally tagless and abstract relational Algebra

The code we want to write is that which matches the way we think [snip] My way is to think hard about what the best way to think about things is. I'm in two minds. On the one hand, we're in violent agreement: The code we /want/ to write is that which matches the way we /want/ to think,

Re: [Haskell-cafe] pointfree-trouble

Here's another way of writing it: data Matrix a = Matr {unMatr :: [[a]]} | Scalar a deriving (Show, Eq) -- RealFrac constraint removed reMatr :: RealFrac a = ([[a]] - [[a]]) - (Matrix a - Matrix a) reMatr f = Matr . f . unMatr -- this idiom occurs a lot, esp. with newtypes Affixing

Re: [Haskell-cafe] pointfree-trouble

the reMatr function pointfree, as reMatr = Matr . (flip (.) unMatr) is not working. any ideas/explanation why it doesnt work? Kim-Ee Yeoh wrote: Here's another way of writing it: data Matrix a = Matr {unMatr :: [[a]]} | Scalar a deriving (Show, Eq) -- RealFrac constraint removed

Re: [Haskell-cafe] Is there a null statement that does nothing?

Hi Brent, Re: 'if expressions, not statements' is an elegant clarification, one definitely for the haskellwiki, if not there already. Just for completeness' sake, bottom is a value for any expression. Wouldn't making the else clause optional by defaulting to undefined worthy of consideration

[Haskell-cafe] ** for nested applicative functors?

Does anyone know if it's possible to write the following: ** :: (Applicative m, Applicative n) = m (n (a-b)) - m (n a) - m (n b) Clearly, if m and n were monads, it would be trivial. Rereading the original paper, I didn't see much discussion about such nested app. functors. Any help

Re: [Haskell-cafe] ** for nested applicative functors?

On Oct 12, 2009, at 11:22 AM, Kim-Ee Yeoh wrote: ** :: (Applicative m, Applicative n) = m (n (a-b)) - m (n a) - m (n b) -- View this message in context: http://www.nabble.com/%3C**%3E-for-nested-applicative-functors--tp25858792p25859274.html Sent from the Haskell - Haskell-Cafe mailing

Re: [Haskell-cafe] Essentials about type classes?

Hi Fredrik, Temaran wrote: data Dar = Dar String String deriving (Show, Eq) class Bar a where foo :: a - Int instance Bar Dar where foo(Dar n c) = length c but it keeps generating the same error; ERROR ./Bar.hs:16 - Inferred type is not general enough *** Expression:

Re: [Haskell-cafe] n00b question: defining datatype

Consider data Task = Task { title :: String, completed :: Bool, subtasks :: Maybe [Task] } Iain Barnett wrote: Hi, I'm trying to get my head around datatypes, and wondering how I might define a simple Task datatype in Haskell. data Task = Task { title :: String, completed :: Bool }

Re: [Haskell-cafe] Flipping *-*-* kinds, or monadic finally-tagless madness

Kim-Ee Yeoh wrote: As for fixing the original bug, I've found that the real magic lies in the incantation (Y . unY) inserted at the appropriate places. Aka unsafeCoerce, changing the phantom type |a|. The type of (Y . unY) is (Y . unY) :: forall a b c. Y c a - Y c b so modulo (Y c

Re: [Haskell-cafe] Flipping *-*-* kinds, or monadic finally-tagless madness

Hi Edward, Your runPretty version fits the bill nicely, thank you. I might still retain the state monad version because it allows generalizations beyond pretty-printing. As for fixing the original bug, I've found that the real magic lies in the incantation (Y . unY) inserted at the appropriate

[Haskell-cafe] Flipping *-*-* kinds, or monadic finally-tagless madness

I'm trying to write HOAS Show instances for the finally-tagless type-classes using actual State monads. The original code: http://okmij.org/ftp/Computation/FLOLAC/EvalTaglessF.hs Two type variables are needed: one to vary over the Symantics class (but only as a phantom type) and another to

Re: [Haskell-cafe] shadowing keywords like otherwise

Hi Vasili, This isn't really a shadowing/redefinition issue. Here's a perfectly legitimate snippet that compiles fine: f 0 = 0 f otherwise = 1+otherwise Redefinition is when you have: g = let otherwise = not in x -- Kim-Ee VasiliIGalchin wrote: swishParse :: String - String -

Re: [Haskell-cafe] shadowing keywords like otherwise

I meant, of course, g = let otherwise = not in otherwise Sorry for the noise. -- Kim-Ee Kim-Ee Yeoh wrote: Hi Vasili, This isn't really a shadowing/redefinition issue. Here's a perfectly legitimate snippet that compiles fine: f 0 = 0 f otherwise = 1+otherwise Redefinition

Re: [Haskell-cafe] shadowing keywords like otherwise

Whoops, you're right. Interestingly, the shadowing warnings vary between the 2 examples I gave, i.e. shadowing within 'function definition' vs 'binding group'. Felipe Lessa wrote: On Sun, Jun 28, 2009 at 12:49:12AM -0700, Kim-Ee Yeoh wrote: This isn't really a shadowing/redefinition

Re: [Haskell-cafe] What is an expected type ...

Could you suggest a better word pair to describe the dichotomy then? How about 'calculated' vs 'user-imposed' (or even, 'explicitly- signatured')? Dan Piponi-2 wrote: I really dislike this error message, and I think the terms are ambiguous. I think the words 'expected' and 'inferred' apply

Re: [Haskell-cafe] Functor and Haskell

Daryoush Mehrtash-2 wrote: I am not sure I follow how the endofunctor gave me the 2nd functor. As I read the transformation there are two catagories C and D and two functors F and G between the same two catagories. My problem is that I only have one functor between the Hask and List

Re: [Haskell-cafe] Functor and Haskell

Daryoush Mehrtash-2 wrote: singleton :: a - [a] singleton x = [x] Here F is the identity functor, and G is the list functor. And yes, C=D= category of (a subset of) Haskell types. Are you saying the function that goes from list functor to singleton funtor is a natural

Re: [Haskell-cafe] forall ST monad

Heinrich Apfelmus wrote: Now, (forall a. T[a]) - S is clearly true while exists a. (T[a] - S) should be nonsense: having one example of a marble that is either red or blue does in no way imply that all of them are, at least constructively. (It is true classically, but I

Re: [Haskell-cafe] forall ST monad

Wolfgang Jeltsch-2 wrote: Am Montag, 16. Februar 2009 19:22 schrieb Wolfgang Jeltsch: First, I thought so too but I changed my mind. To my knowledge a type (forall a. T[a]) - T' is equivalent to the type exists a. (T[a] - T'). It’s the same as in predicate logic – Curry-Howard in action.

Re: [Haskell-cafe] forall ST monad

Jonathan Cast-2 wrote: Summary: Existential types are not enough for ST. You need the rank 2 type, to guarantee that *each* application of runST may (potentially) work with a different class of references. (A different state thread). Interesting. What's going on in the example that

Re: [Haskell-cafe] forall ST monad

There's a lot to chew on (thank you!), but I'll just take something I can handle for now. Dan Doel wrote: An existential: exists a:T. P(a) is a pair of some a with type T and a proof that a satisfies P (which has type P(a)). In Haskell, T is some kind, and P(a) is some type

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