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 ra

Re: [Haskell-cafe] Alternative name for return

On Thu, Aug 8, 2013 at 7:40 AM, Timon Gehr 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 thin

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

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

On Mon, May 13, 2013 at 9:39 PM, Mark Lentczner wrote: > *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 wrote: > 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 ASSES! -- Kim-Ee

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

On Thu, Apr 25, 2013 at 6:36 PM, Joe Quinn wrote: > 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 ___ H

Re: [Haskell-cafe] NaN as Integer value

On Sun, Apr 14, 2013 at 3:28 PM, wren ng thornton 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 *do* decide to

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 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 environment, namely an edit

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

On Sun, Apr 7, 2013 at 4:37 AM, Steffen Schuldenzucker 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: rewrite-with-location proposal

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 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 > programs have

Re: [Haskell-cafe] meaning of "referential transparency"

reddit.com/r/haskell/comments/xgq27/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 wrote: >> >> On Sun, Apr 7, 2013 at 12:43 AM, Henning Thielemann >> wr

Re: [Haskell-cafe] meaning of "referential transparency"

On Sun, Apr 7, 2013 at 12:43 AM, Henning Thielemann 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 lookup the > meaning of "re

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

On Sun, Apr 7, 2013 at 12:23 AM, Steffen Schuldenzucker 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] http://hackage.haskell.org/packages/archive/base/4.6.0.1/doc/html/Control-Exception.htm

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") exi

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

On Fri, Apr 5, 2013 at 10:44 AM, Ivan Lazar Miljenovic 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 opportunity to convene

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

On Fri, Apr 5, 2013 at 3:04 AM, Simon Heath 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 argument. Could

Re: [Haskell-cafe] Possible GSoC project

On Thu, Apr 4, 2013 at 10:03 PM, Ketil Malde 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 and brain tease

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 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 further towards the System-F-i

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

On Mon, Mar 25, 2013 at 5:19 AM, Konstantine Rybnikov 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 I solved m

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

On Tue, Mar 19, 2013 at 2:01 PM, Konstantin Litvinenko 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 this in perspective,

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 diff

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

On Mon, Feb 25, 2013 at 9:42 PM, Simon Peyton-Jones wrote: > 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 manually binding

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 recurs

Re: [Haskell-cafe] Parser left recursion

On Sun, Feb 24, 2013 at 8:03 PM, Roman Cheplyaka 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 and why. > Whi

Re: [Haskell-cafe] Parser left recursion

On Sun, Feb 24, 2013 at 7:47 PM, Roman Cheplyaka 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. I don't s

Re: [Haskell-cafe] Parser left recursion

On Sun, Feb 24, 2013 at 7:09 PM, Roman Cheplyaka 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 codata. -- Kim

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

On Thu, Jan 24, 2013 at 6:23 AM, wren ng thornton 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 smug: "A bi

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

On Wed, Jan 23, 2013 at 5:28 PM, Felipe Almeida Lessa < felipe.le...@gmail.com> wrote: > don't worry about asking the mailing list beforehand (unless you want to, > of course). > > Seconded! Just a cursory sweep of this thread reveals so much learning and discovery taking place that would be utte

Re: [Haskell-cafe] Type hierarchy

On Wed, Jan 16, 2013 at 11:22 PM, Thiago Negri 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 them, roll a G

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 cons

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

On Fri, Jan 4, 2013 at 7:27 PM, David Thomas wrote: > 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 optimized away in s

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 h

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

On Thu, Dec 27, 2012 at 11:48 PM, Rustom Mody wrote: > On Thu, Dec 27, 2012 at 8:26 PM, Kim-Ee Yeoh 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 that... Look! >

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 wrote: > Prelude> :t [[1,2],3] > > you have a list wi

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: [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 wrote: > If you require the cir

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 w

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? Rea

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 wrote: > SPJ's IFPL is an excellent starting point to learn the innards of Haskell. > It allows a well-acculturated individual to grab the

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 (readi

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

only" > and I am not focused on it. > > --Joerg > > > 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

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] > http://martinfowler.com/bliki/**DomainSpecificLanguage.html

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

rdware > 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

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

On Tue, Dec 4, 2012 at 4:53 PM, Joerg Fritsch 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 get a deep DSL

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 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 -- old-school op

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

On Sat, Dec 1, 2012 at 1:16 AM, Mark Thom 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 evaluation is all laid out ther

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 wrote: > Problem is following short program: > list = [1,2,3,4

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 wrote: > > [cabal haddock, if you want] > > cabal copy > > cabal register > > Even this does no

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? -- Ki

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 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 *f.x* , ie he sho

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

On Tue, Oct 16, 2012 at 9:37 PM, AUGER Cédric 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 (and requires some

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 techni

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 no

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

s the identity. > > The general idea of course is Goedel's recursor R. > >R b a 0 = a >R b a (Succ n) = b n (R b a n) > > which easily generalizes to lists. The enclosed code shows the list > encoding that has constant-time cons, head, tail and trivially > express

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 pattern-match

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 procee

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, g

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 ma

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 Mo

Re: [Haskell-cafe] pointfree-trouble

al question was how to make 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 =

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 con

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 considerat

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

ctor#Applicative_transfomers > > - jeremy > > 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

[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 app

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 > *** Ex

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 :: Boo

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 -

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 p

[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 va

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' app

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

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

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 -> Swis

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] 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 L

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 classic

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

Re: [Haskell-cafe] forall & ST monad

Jonathan Cast-2 wrote: > > Taking the `let open' syntax from `First-class > Modules for Haskell' [1], we can say > > let open runST' = runST in > let > ref = runST' $ newSTRef 0 > !() = runST' $ writeSTRef ref 1 > !() = runST' $ writeSTRef ref 2 > in runST' $ readSTRef ref >

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 t

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 tha

Re: [Haskell-cafe] forall & ST monad

chrieb Wolfgang Jeltsch: >> Am Montag, 16. Februar 2009 19:04 schrieb Kim-Ee Yeoh: >> > Despite its rank-2 type, runST really doesn't have anything to do with >> > existential quantification. >> >> First, I thought so too but I changed my mind. To my knowled

Re: [Haskell-cafe] forall & ST monad

Peter Verswyvelen-2 wrote: > > I'm having trouble understanding the explanation of the meaning of the > signature of runST at > http://en.wikibooks.org/wiki/Haskell/Existentially_quantified_types > > I could try to read the article a couple of times again, but are there any > other good reading

Re: Re: [Haskell-cafe] Looking for pointfree version

> import Control.Applicative > > data Pair a = a :*: a > > instance Functor Pair where > f `fmap` (x :*: y) = f x :*: f y > > instance Applicative Pair where > (f :*: g) <*> (x :*: y) = f x :*: f y The last f needs to be a g. > pure x = x :*: x > > pointfree :: (a -> b -> c

Re: [Haskell-cafe] forall & ST monad

Peter Verswyvelen-2 wrote: > > I could try to read the article a couple of times again, but are there any > other good readings about these existentially quantified types and how the > ST monad works? > The primary source is if I'm not mistaken, the following "State in Haskell" paper: http:/

Re: [Haskell-cafe] Looking for pointfree version

On the same note, does anyone have ideas for the following snippet? Tried the pointfree package but the output was useless. pointwise op (x0,y0) (x1,y1) = (x0 `op` x1, y0 `op` y1) Edsko de Vries wrote: > > Perfect! Beautiful. I was hoping there'd be a simple solution like that. > > Thanks! >

Re: Re: [Haskell-cafe] Problems with strictness analysis?

Luke Palmer-2 wrote: > > I would like to know or to develop a way to allow abstract > analysis of time and space complexity. > In the same way that type inference and strictness analysis can be seen as instances of abstract interpretation, so can complexity inference. I agree that the interpl

Re: [Haskell-cafe] Problems with strictness analysis?

David Menendez-2 wrote: > >> On Mon, 3 Nov 2008, Luke Palmer wrote: >> >> I was actually being an annoying purist. "f is strict" means "f _|_ = >> _|_", so strictness is a semantic idea, not an operational one. > > I think Luke was commenting on the terminology, not the optimization. > We have

Re: [Haskell-cafe] Object-oriented programming, Haskell and existentials

re: the importance of existential-cleansing On the one hand, it's easy to concur that existentials are simpler than the alternatives, the tortuous elimination of CC Shan's "translucent" existential being a case in point. And it's also easy to dismiss such caprice as a penchant for Houdinian e

Re: [Haskell-cafe] Lazy vs correct IO [Was: A round of golf]

oleg-30 wrote: > > I have not expected to see this Lazy IO code. After all, what could be > more against > the spirit of Haskell than a `pure' function with observable side effects. > What could even be more against the spirit of Haskell than the original theme of this thread, i.e. code that

Re: [Haskell-cafe] More on performance

Jon Harrop wrote: > > On Wednesday 04 June 2008 11:05:52 Luke Palmer wrote: >> Given unbounded time and space, you will still arrive at the same result >> regardless of the complexity. > > Given that the set of computers with unbounded time and space is empty, is > it > not fruitless to discu

Re: Re: [Haskell-cafe] Aren't type system extensions fun? [Further analysis]

s types emp^H^H^H ... uh, as He pleases. Anyway, the original point of it was semantic. Let's first explore the meaning of "the most general type." Type functions give one answer, intersection types another. -- Kim-Ee (yeoh at cs dot wisc dot edu) -- View this message in contex

Re: Re: [Haskell-cafe] Aren't type system extensions fun? [Further analysis]

Roberto Zunino-2 wrote: > > Alas, for code like yours: >foo = \f -> (f 'J', f True) > > there are infinite valid types too: >(forall a. a -> Int) -> (Int, Int) >(forall a. a -> Char)-> (Char, Char) >(forall a. a -> (a,a)) -> ((Char,Char),(Bool,Bool)) >... > > and it is much

Re: Re: [Haskell-cafe] Aren't type system extensions fun? [Further analysis]

Andrew Coppin wrote: > > So, after an entire day of boggling my mind over this, I have brought it > down to one simple example: > > (id 'J', id True) -- Works perfectly. > \f -> (f 'J', f True) -- Fails miserably. > > Both expressions are obviously perfectly type-safe, and yet the typ

Re: [Haskell-cafe] Short circuiting and the Maybe monad

Dan Piponi-2 wrote: > > In fact, you can use the Reader monad as a fixed size container monad. > Interesting that you say that. Reader seems to me more as an anti-container monad. -- View this message in context: http://www.nabble.com/Short-circuiting-and-the-Maybe-monad-tp17200772p17288351

Re: [Haskell-cafe] Couple of formal questions

I'm not sure there's a proof as such, more like a definitional absence of distinction between initiality and finality. In other words, the CPO framework is orthogonal to such extremality considerations. Perhaps someone here knows about work enriching CPOs in that direction. -- Kim-Ee Michael

Re: [Haskell-cafe] Wrong Answer Computing Graph Dominators

Dan Weston wrote: > > f . and == and . map f >where f = (not x ||) > > If and is defined with foldr, then the above can be proven for all > well-typed f, and for f = (not x ||) in particular, even if ys is null. > The law is painlessly extended to cover the null case automatically (and >

Re: [Haskell-cafe] Wrong Answer Computing Graph Dominators

Dan Weston wrote: > > Here, "any path" means all paths, a logical conjunction: > > and [True, True] = True > and [True ] = True > and [ ] = True > Hate to nitpick, but what appears to be some kind of a limit in the opposite direction is a curious way of arguing that: and [] =

Re: [Haskell-cafe] Functional programmer's intuition for adjunctions?

ajb-2 wrote: > > In Haskell, natural transformations are > functions that respect the structure of functors. Since you can't > avoid respecting the structure of functors (the language won't let you > do otherwise), you get natural transformations for free. (Free as > in theorems, not free as i

Re: [Haskell-cafe] Graphical graph reduction

dainichi wrote: > > Now to the point: Wouldn't it be great if I had a visual tool that > visually > showed me the graph while the above evaluation unfolded? I could use it to > show some of my co-workers to whom laziness is a mystery, what it's all > about. > Check out http://thyer.name/lambda

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