- Haskell-Cafe - Haskell.org

Division: Is there a way to simultaneously find the quotient and remainder?
by caseyh＠istar.ca 14 May '11

14 May '11

:)

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Sending messages up-and-down the iteratee-enumerator chain [Was: iterIO-0.1]
by oleg＠okmij.org 14 May '11

14 May '11

David Mazie'res wrote: > What you really want is the ability to send both upstream and > downstream control messages. Right now, I'd say iterIO has better > support for upstream control messages, while iteratee has better > support for downstream messages, since iteratee can just embed an > Exception in a Stream. (I'm assuming you could have something like a > 'Flush' exception to cause output to be flushed by an Iteratee that > was for some reason buffering some.) > Can you explain how iteratee could keep track of the stream position? > I'm not saying it's impossible, just that it's a challenging puzzle to > make the types come out and I'd love to see the solution. The code described in this message does exactly that. We illustrate enumerator's telling something to iteratees in the middle of the stream (to Flush their buffers) as well as iteratee's asking an enumerator of something (the stream position). The chunk of a stream and EOF are themselves `control' messages that an enumerator may send; the request for a new chunk, just like the request for a stream position, is just one of the requests an iteratee may ask. The set of messages an enumerator may send and the set of requests an iteratee may ask are both treated as open unions. We illustrate the explicit coding of open unions, to let the type checker ensure that what an iteratee may ask an enumerator can answer, and what an enumerator may tell an iteratee can understand. In process calculus lingo, we implement external (to iteratee) choice, internal choice, and a form of session types. For clarity, we implement a greatly simplified version of iteratees. We assume a single-character chunk, which an iteratee always consumes. Chunking of a stream and look-ahead are orthogonal concerns and have been discussed already. The stream represents the external, producer choice: > data Stream ie = > Chunk Char -- the current character > | SExc ie -- A message from the enumerator The chunk is an ever-present option; other choices include EOF and Flush: > data EOF = EOF > data Flush = Flush The iteratee represents the internal, consumer choice: > data Iter ee ie a = > Done a > | Cont (Stream ie -> Iter ee ie a) > | IExc (ee (Iter ee ie) a) -- other requests Cont is a typical request from an iteratee. It is so typical that we wire it in (we could've treated it as other requests, like Tell). The iteratee is parametrised by what messages it understands and what requests it may ask. Iteratees compose as a monad: > instance Bindable ee => Monad (Iter ee ie) where > return = Done > Done a >>= f = f a > Cont k >>= f = Cont (\x -> k x >>= f) > IExc ee >>= f = IExc (comp ee f) All requests must be bindable, so they can percolate > class Bindable ee where > comp :: Monad m => ee m a -> (a -> m b) -> ee m b An exception is a sort of request (especially if the exception is resumable) > data Err m a = Err (() -> m a) > instance Bindable Err where > comp (Err k) f = Err (\x -> k x >>= f) Another sort of request is to tell the position > data Tell m a = Tell (Int -> m a) > instance Bindable Tell where > comp (Tell k) f = Tell (\x -> k x >>= f) We use Either (or higher-kinded E2) to build unions: > class Sum e c where > inj :: e -> c > prj :: c -> Maybe e > class Sum2 (e :: (* -> *) -> * -> *) (c :: (* -> *) -> * -> *) where > inj2 :: e m a -> c m a > prj2 :: c m a -> Maybe (e m a) Iteratees are explicit in what they receive on the stream, the external choices they may handle. But they leave the requests polymorphic to ease composing with other iteratees which may asks more requests. Here is the simplest iteratee, which doesn't do anything but asks for trouble > ierr :: Sum2 Err c => Iter c ie a > ierr = IExc . inj2 $ Err (\_ -> ierr) A typical iteratee, like the head below, asks for little and accepts little: > iehead :: Sum2 Err c => Iter c EOF Char > iehead = Cont step > where > step (Chunk a) = Done a > step (SExc EOF) = ierr We can ask for the current position: > itell :: Sum2 Tell c => Iter c ie Int > itell = IExc . inj2 $ Tell Done Enumerators, in contrast, are explicit in what requests they may satisfy, but implicit in what they may send on the stream. A typical, small enumerator requires that an iteratee understand at least EOF, and answers no requests beyond errors. > en_str :: Sum EOF ie => String -> Iter Err ie x -> Iter Err ie x > en_str _ i@Done{} = i > en_str _ (IExc x) | Just (Err _) <- prj2 x = ierr > en_str "" (Cont k) = k eof > en_str (h:t) (Cont k) = en_str t $ k (Chunk h) A typical enumeratee, like the following keeper of positions, is explicit in requests it accepts: only Tell and Err. The Tell requests are satisfied and not propagated. The stream messages are relayed from the outer to the inner stream: > en_pos :: Int -> Iter (E2 Err Tell) ie x -> Iter Err ie x > en_pos _ (Done x) = return x > en_pos n (Cont k) = Cont (\s -> en_pos (n+1) (k s)) > en_pos _ (IExc x) | Just (Err _) <- prj2 x = ierr > en_pos n (IExc x) | Just (Tell k) <- prj2 x = en_pos n (k n) Here are some of the examples: > t1 = irun $ en_str "x" iehead > -- Type error! en_str doesn't know how to handle Tell > -- tb2 = irun $ en_str "x" itell We interpose en_pos enumeratee to deal with positional requests, so we can run the whole example: > t5 = irun $ en_str "xab" $ en_pos 0 $ iter > where > iter = do > x <- iehead > y <- ietell > return (x,y) The complete code is available at http://okmij.org/ftp/Haskell/Iteratee/UpDown.hs

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Manatee-0.2.2 release!
by Lazycat Manatee 14 May '11

14 May '11

Hi all, Manatee-0.2.2 release! New features in Manatee-0.2.2: * Build new package "manatee-all", now you just need command "cabal install manatee-all" to upgrade new version. * Make keymap window and completion window will show correctly in Gnome3. * Fixed webkit-0.12.2 depend problem, because webkit-0.12.2 need some APIs just exist in gtk2hs darcs, so manatee-0.2.2 use webkit-0.12.1 * Fixed curl compile problem, at least curl-1.3.7, curl-1.3.6 have compile problem with GHC-0.7.3 Please let me know if you have problem about Manatee. :) Cheers, -- Andy

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Fwd: Work on Collections Processing Arrows?
by David Barbour 13 May '11

13 May '11

[Apparently I forgot to hit reply-all.] Thanks for your response, Adam. On Tue, May 10, 2011 at 1:25 PM, Adam Megacz <megacz(a)cs.berkeley.edu> wrote: > > class (GArrowMap a (**) u c) => GArrowJoin a (**) u c where > > join :: a d (c r) -> a (c d) (c r) > > I like these; I think you're on the right track. The last one reminds > me of concatMap. > That might be a better name for it. I was thinking in terms of a relational join. > > Perhaps what you want is > > gac_drop :: a (c u) u > > ... which is a bit like ga_cancell and ga_cancelr, but for a whole > collection rather than one input at a time. > That sounds reasonable, but also looks like users would need mapA to ever leverage it. I was imagining that some models might provide mapA_ without mapA, i.e. only allowing further composition through side-effects similar to a 'for' loop in a C-family language. This is not very composition friendly, of course, but it might be easier to implement and sufficient for the job. -- | process each element in a collection, then cancel it. class (GArrow a (**) u) => GArrowMap_ a (**) u c where ga_map_ :: a d u -> a (c d) u -- | process each element in a collection; the result is subject to -- further composition. class (GArrowMap_ a (**) u c) => GArrowMap a (**) u c where ga_map :: a d r -> a (c d) (c r) > By the way, I've started [2] using type families for the "aggregate" > GArrow classes like GArrowSTLC. This greatly reduces the syntactic > noise in the types -- you only have one type parameter instead of four. > The price is that a single type can't be an instance of these classes in > more than one way (see Section 3.6.1 of [3] for why this is important). > Sounds good. I look forward to seeing where that goes. I use type and data families quite heavily in my own models - they're much friendlier for inference. > > In my own case, 'c' might be representing an asynchronous or > > distributed, reactive collection, so the ability to restrict > > expressiveness is important for performance. > > Certainly. The multiplicative disjunction [4] of linear logic is the > "binary" version of this: (A \bindnasrepma B) is sort of like an A and a > B in geographically distant locations; if you have a (Int \bindnasrepma > Int) you have two Int's, but in order to (for example) add them together > you must use some sort of communication primitive to get them both to > the same place. > I must admit to some confusion that you likened asynchronous/distributed products used in 'synch' to 'additive conjunction' in the earlier message (help for asynchronous arrows) and the same concept to multiplicative disjunction here. Elements in such a product may exist at different times (i.e. production latencies from some initial event) as well as different locations. > It sounds like you want a sort of "collection version" of multiplicative > disjunction. I bet Data Paralell Haskell's parallel array type-former > (([::]) :: * -> *) would be an instance of this class. > Data Parallel Haskell is all about performance, doesn't really admit to parallel semantics or asynchronous side-effects as a result of mapping arrows across the collection. To the extent it qualifies, I suspect so would a normal list. Dave

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Work on Collections Processing Arrows?
by David Barbour 13 May '11

13 May '11

Has anyone developed a typeclass model for (Control.Monad.mapM) and related functions for arrows? I've a preliminary model, using Adam Megacz's Generalized Arrows, of the form: class (GArrowDrop a (**) u) => GArrowMap_ a (**) u c where mapA_ :: a d u -> a (c d) u class (GArrow a (**) u c) => GArrowMap a (**) u c where mapA :: a d r -> a (c d) (c r) class (GArrowMap a (**) u c) => GArrowJoin a (**) u c where join :: a d (c r) -> a (c d) (c r) class (GArrow a (**) u) => GArrowUnion a (**) u c where union :: a ((c r) ** (c r)) (c r) class (GArrowMap a (**) u c, GArrow a (++) v) => GArrowPartition a (**) u (++) v c where partition :: a d (q ++ r) -> a (c d) ((c q) ** (c r)) Motivations: regular arrows (including GArrows) expose simple products for behavior, but those have a static 'width' and don't seem suitable for processing large values. ArrowApply would give me a dynamic amount of processing, but seems excessively expressive. In my own case, 'c' might be representing an asynchronous or distributed, reactive collection, so the ability to restrict expressiveness is important for performance. I'm wondering if you know of any other work along the same lines. Thank you, Dave

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Re: [Haskell-cafe] cabal-latest
by Jason Dagit 13 May '11

13 May '11

On Thu, May 12, 2011 at 7:24 AM, Guy <guytsalmaves-h(a)yahoo.com> wrote: > http://www.haskell.org/cabal/release/cabal-latest/ points to version > 1.8.0.4. Is this correct? > Replying to this on Haskell-Cafe and cabal-dev lists. The latest version is 1.10.x and ships with the HP. I bet that link is just needs to be updated. Jason

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old versions of cabal install
by Evan Laforge 13 May '11

13 May '11

If you search for "cabal install", the first link is http://hackage.haskell.org/trac/hackage/wiki/CabalInstall, which in turn leads to http://haskell.org/cabal/download.html. It looks very official and canonical and all that, but that page has an old version of cabal install that will no longer compile with ghc7 because it requires old libraries. Of course it won't tell you that right off, first it will install a whole bunch of old stuff, charge you a fiver, and then emit some "constraint can't be satisfied" msgs which if you have some experience with haskell and cabal already should eventually tip you off that something's wrong. Is there someone out there who has permissions to either take that page down, or replace it with a link to the new version at http://hackage.haskell.org/package/cabal-install? I updated http://hackage.haskell.org/trac/hackage/wiki/CabalInstall to point to the platform and to the hackage page, but the cabal page at http://haskell.org/haskellwiki/Cabal-Install still links to http://haskell.org/cabal/download.html. Should I just replace the haskellwiki page with a link to the hackagewiki one? I would try to port over any up to date info of course.

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ANN: AERN-Real-Double-2011.1
by Michal Konečný 13 May '11

13 May '11

Dear all, I am pleased to announce the first release of (a large part of) a newly designed AERN. AERN (approximating exact real numbers) is a set of Haskell libraries providing arbitrary precision interval arithmetic, polynomial arithmetic and distributed lazy exact real computation. Anyone is welcome to join in the development of AERN via http://code.google.com/p/aern/ . This release contains the following features: * Type classes for rounded arithmetic and rounded interval arithmetic with explicit control of rounding direction and the possibility to increase the rounding precision arbitrarily for types that support it. For example, type classes for types with rounded addition, multiplication, exponentiation etc. * Over 150 QuickCheck properties for these type classes, such as associativity of multiplication modulo rounding. * Interval arithmetic using Double endpoints, rounded outwards or inwards. Outwards rounding allows to safely approximate exact real arithmetic while a combination of both outwards and inwards rounding allows one to safely approximate exact interval arithmetic. Inverted intervals with Kaucher arithmetic are also supported. * For most of the type classes there are also in-place versions that act in the ST monad on mutable variables containing numbers or intervals. This facilitates some explicit memory allocation optimisation, especially for data on the C heap. The best starting point for experimenting with these features are the demo programs included in the bundle and the documentation for the AERN-Real-Double package: http://www-users.aston.ac.uk/~konecnym/aern/AERN-Real-Double (The HackageDB page does not have Haddock documentation because AERN fails to build with ghc 7.0.* due to a compiler bug.) The following features are planned for future releases: * Interval arithmetic with MPFR arbitrary precision endpoints. * Polynomial interval arithmetic with an optimised C core * Distributed exact real and geometric computation with lazy query-driven communication. For those familiar with the old AERN design, the main changes in the new design are: * use of many smaller type classes instead of few large ones * use of associated types instead of multi-parameter type classes * a much more systematic approach to representing the numerical order on real numbers and the information refinement (ie the inverse set inclusion) order on intervals * ability to specify different effort indicator types for each type of operation and each numerical type instead of Int. (For example, Double has () as its effort indicator for almost all operations while MPFR will have Precision as the effort indicator type.) * a more systematic approach to specifying QuickCheck properties and applying them to form test suites * a unified implementation of interval elementary operations (only sqrt and exp at the moment) that is efficient when applied to Double intervals as well as polynomial intervals * new support for in-place rounded numerical operations The current development team will be grateful for any feedback and suggestions. Best regards, Michal -- |o| Michal Konecny <mikkonecny(a)gmail.com> |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aston

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how to force hackage to use ghc 6.12.3
by Michal Konečný 13 May '11

13 May '11

Hi, I have been releasing packages on hackage that do not build with ghc 7.0.* due to a bug that will be fixed in ghc 7.2.1. (One of the packages is http://hackage.haskell.org/package/AERN-Basics) I was hoping hackage will try also ghc 6.12.3 but it does not. Is there some way I can change the cabal file to help hackage to compile it with 6.12.3 and generate haddock? The package requires base >= 4 so I cannot try base < 4. Michal -- |-| Dr. Michal Konecny, Computer Science, Aston University |-| Room MB212D | Tel +44 121 204 3462 | Fax +44 121 204 3681 |-| http://www.aston.ac.uk/~konecnym |-| OpenPGP key http://www.aston.ac.uk/~konecnym/ki.aston -- |o| Michal Konecny <mikkonecny(a)gmail.com> |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aston

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ANN: Newt - command-line template instantiation tool & library
by Rogan Creswick 13 May '11

13 May '11

I'm happy to announce Newt: a trivial tool for creating boilerplate. I frequently need to create projects with slight customizations -- I have a particular layout for cabal projects, and make files for LaTeX papers, etc... However, there are often fields that need to be updated in many places. (At times, even file or directory names need changed.) Newt makes this trivial. My objective was to provide a tool that allows you to very quickly take a project, mark the portions that must change with angle brackets, and use that as a source for myriad derivations of that project, or share the project for others to create their own instances. Newt scans the input (either a file, directory or stdin) for tags marked with "<<<tagName>>>" [1], then replaces those entries with values specified on the command line, producing either a new file, modifying the input template in place (--inplace), writing to stdout, or writing to a directory. A newt template for a cabal project is available on github: - http://github.com/creswick/Newt/tree/master/tests/testFiles/dirTemplates/ca… Newt is available on hackage[2], and the source is hosted on github[3]. The readme provides more details and examples: - http://github.com/creswick/Newt/blob/master/README.md --Rogan [1] The tag syntax can be changed with command-line flags, or by creating an instance of the Tag typeclass. See --help. [2] http://hackage.haskell.org/package/newt [3] http://github.com/creswick/Newt/

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