Re: [Haskell-cafe] Re: Difference between div and /
Richard O'Keefe schrieb: On Jun 3, 2010, at 1:13 AM, Maciej Piechotka wrote: On Wed, 2010-06-02 at 14:01 +1200, Richard O'Keefe wrote: For what applications is it useful to use the same symbol for operations obeying (or in the case of floating point operations, *approximating* operations obeying) distinct laws? If the given operations do share something in common. For example * is usually commutative. However you do use it with quaternions (Hamilton product). You even write ij = k despite the fact that ji = -k. I think you just made my point: Commutativity is NOT one of the standard properties that * is EXPECTED to possess. However, it IS one of the properties that + is expected to possess, which is why Java's abuse of + for string concatenation is so bad. Java's (+) is not even associative: (text + 2) + 3 = text23 text + (2+3) = text5 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Sockets get bound to wrong port on Windows
Antoine Latter aslat...@gmail.com writes:
*Main PortNum
47138
The PortNum constructor should rarely be used directly
So, shouldn't the constructor be hidden, and exported from an .Internal
module?
- it contains the port number in network-order. You should try:
Or perhaps even better, the type could be:
data PortNum = PortNum { msb, lsb :: Word8 }
so that we avoid this kind of confusion?
-k
--
If I haven't seen further, it is by standing in the footprints of giants
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Re: [Haskell-cafe] The state of Hackage: what are we doing about it?
On Thursday 03 June 2010 06:27:43 am Don Stewart wrote: I've been posting CSV files of the download statistics here: http://www.galois.com/~dons/hackage/hackage-downloads.csv The next quarter's aggregated downloads are due soon. The Arch Haskell site uses these stats to compute some popularity metrics: http://www.galois.com/~dons/arch-haskell-status.html with that data, it should be rather easy to compute some kind weights for the packages and to prefer the popular packages during the search. In the long run it would be nice to get this statistics more frequently, e.g. monthly. We see, that within a quarter there are a lot of new packages. Uwe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Process priority
I've had a hunt around in System.Process, but I can't discover any way to adjust the priority of the process you just spawned. Am I missing something, or has this just not been implemented yet? (I must confess, I don't know whether Windows and Unix both have the same ideas about priority numbers...) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [web-devel] Re: [Haskell-cafe] Google Summer of Code: BlazeHTML RFC
On Thu, May 27, 2010 at 8:31 PM, Matt Parker moonmaster9...@gmail.com wrote: will it be possible to easily interleave IO values into the HTML? like instead of the [1,2,3] ul $ forM_ [1, 2, 3] (li . string . show) what if it was a function that returned IO [1,2,3] (maybe 1,2,3 came out of a database). will the forM_ handle that OK? Depends on how you write the code. More precisely, it depends on in which monad the forM_ takes place. Also, I would not recommend interleaving IO values into the HTML, because the HTML is pure -- you usually don't want to mix that with IO. I'd rather write something like: numbers - getFromDataBase return $ ul $ forM_ numbers (li . string . show) Or it could be possible to store your templates in a separate modules, and they would all have a pure type signature: templateX :: Arg1 - Arg2 - Html a I think this would be the preferred way, because it allows a separation between the pure View code and the IO-interleaved Controller code in a web application. Kind regards, Jasper Van der Jeugt On Thu, May 27, 2010 at 8:31 PM, Matt Parker moonmaster9...@gmail.com wrote: will it be possible to easily interleave IO values into the HTML? like instead of the [1,2,3] ul $ forM_ [1, 2, 3] (li . string . show) what if it was a function that returned IO [1,2,3] (maybe 1,2,3 came out of a database). will the forM_ handle that OK? On Thu, May 27, 2010 at 12:19 PM, Matt Parker moonmaster9...@gmail.com wrote: Blaze HTML looks wonderful to me (especially with the do notation), and better then Hamlet for one reason: writing idiomatic haskell for stuff like this: ul $ forM_ [1, 2, 3] (li . string . show) instead of the Hamlet style: %ul $forall children.person child %li $child$ which, i don't know, for some reason, made me feel like i was back in PHP land. -matt On Thu, May 27, 2010 at 7:08 AM, Alberto G. Corona agocor...@gmail.com wrote: As a user, I have too many HTML generators, a few of them with Ajax and none with server-side event handling (like ASPX or JSPX). Ajax is complicated but server side event handling is what I really miss because it is simple from the user point of view, my ervents could be handled in haskell code rather than in javaScript and I implicitly could use the advantages of dinamic HTML and Ajax without the need to know them at all. Imagine a dynamic Web application with 100% haskell code made with dynamic widgets created by third party developers. So, anyone want to create a HTML templating system with server side event handling? It is not terribly hard to do. (I refer to ASP.NET documentation or the JavaServer Faces framework). By the way, I vote for XML templating or else, combinator templating that produce XHML templating because it can be handled by a future graphical IDE. 2010/5/27 Jasper Van der Jeugt jasper...@gmail.com Hey Bas, How about also providing an enumerator back-end? http://hackage.haskell.org/packages/archive/iteratee/0.3.5/doc/html/Data-Iteratee-Base.html#t%3AEnumeratorGM Then your library can integrate more easily with the snap framework: http://snapframework.com Sure, I can do that. But I already tested integration with the snap framework, the best path here seems to call the `writeLBS` function from the snap framework on the `L.ByteString` that BlazeHtml produces (`writeLBS` internally uses an enumerator). Kind regards, Jasper Van der Jeugt On Thu, May 27, 2010 at 10:38 AM, Bas van Dijk v.dijk@gmail.com wrote: Q14: Do you see any problems with respect to integrating BlazeHtml in your favourite web-framework/server? How about also providing an enumerator back-end? http://hackage.haskell.org/packages/archive/iteratee/0.3.5/doc/html/Data-Iteratee-Base.html#t%3AEnumeratorGM Then your library can integrate more easily with the snap framework: http://snapframework.com Regards, Bas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ web-devel mailing list web-de...@haskell.org http://www.haskell.org/mailman/listinfo/web-devel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to build an Indicator Type for a type class?
On 06/02/2010 03:59 AM, Brent Yorgey wrote: Perhaps something here may be of use? http://okmij.org/ftp/Haskell/types.html#class-based-overloading Enlightening. Thanks a lot. For the curious, here is my solution: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=25907#a25907 I'm gonna read the HList paper now... Best regards, Steffen http://okmij.org/ftp/Haskell/types.html#class-based-dispatch -Brent On Mon, May 31, 2010 at 01:32:18PM +0200, Steffen Schuldenzucker wrote: Dear Cafe, let: data True data False class C a (arbitrary instances for C may follow) Now, how to obtain an Indicator Type for C, i.e. a type IndC that is defined via a type family / fundep / ... , so that IndC a = Trueforall a which are instances of C IndC a = False for all other a. I've collected some failed approaches here[1]. My key problem is that if I define (in the 3rd try): instance (C a) = IndC3 a True , it does *not* mean Define this instance for all a which are an instance of C, but Define the instance IndC3 a True for all types a, but it's not gonna work if a is not an instance of C. Does anyone have another idea? Background: After having implemented type-level lists[2] and a quicksort on them[3], I'd like to have type-level sets. In their most simple implementation, sets are just (unsorted) lists like this: data Nil data Cons a b class Elem x l (instances for Elem so that Elem x l iff x is an element of the list l) Now I want: type family Insert x s :: * Insert x s = s forall (x, s) with (Elem x s) Insert x s = Cons x sfor all other (x, s). Thanks a lot! Steffen [1] http://hpaste.org/fastcgi/hpaste.fcgi/view?id=25832#a25832 [2] Kiselyov, Peyton-Jones, Shan: Fun with type functions http://research.microsoft.com/en-us/um/people/simonpj/papers/assoc-types/fun-with-type-funs/typefun.pdf [3] I rewrote this algorithm using type families instead of fundeps: http://www.haskell.org/haskellwiki/Type_arithmetic#An_Advanced_Example_:_Type-Level_Quicksort ___ 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] Re: Problems with Haskell Platform
Ivan Lazar Miljenovic wrote: Pete Chown 1...@234.cx writes: Is there a way of making Cabal install dependencies using the system package manager, then? If you mean cabal-install, then no, there's no integration on either side. That's what I thought. As a result of this, you may find that you end up creating private builds of packages which are shipped by your distribution. You ask Cabal to install a package, which is not shipped by your distribution. Cabal will then build that package's dependencies, *even if* those dependencies should really be installed using your distribution's package manager. This is exactly the same with C programs. Yes and no. If I download the source of a C library and build my own shared libraries, my programs might not work on machines where the distribution's version of that library is in use. The particular problem in the Haskell world, though, is that Cabal will create this situation by default. (I believe current versions of ghc insist on linking entirely dynamically or entirely statically. This makes the situation worse, because the lack of a shared library for X prevents the use of shared libraries for anything else.) No, 6.12 defaults to statically but allows dynamic linking as well. That's not what I meant. What I meant is that you can't link against some Haskell libraries statically, and some dynamically. When linking C this isn't a problem. If you don't have a shared version of a particular library, gcc will pick the static version instead. You can even choose static or dynamic for each individual library: $ gcc foo.c -o foo -lz $ ldd foo linux-gate.so.1 = (0x00d0b000) libz.so.1 = /lib/libz.so.1 (0x00dd5000) libc.so.6 = /lib/tls/i686/cmov/libc.so.6 (0x00152000) /lib/ld-linux.so.2 (0x00a69000) $ gcc foo.c -o foo -Wl,-Bstatic -lz -Wl,-Bdynamic $ ldd foo linux-gate.so.1 = (0x00918000) libc.so.6 = /lib/tls/i686/cmov/libc.so.6 (0x00db) /lib/ld-linux.so.2 (0x002e5000) Really? For C, Gentoo ships very few which either default or have the option of static libraries, and I assume the same is true for binary distributions. Sorry I misunderstood what you were saying; you're right. I'm not familiar with Gentoo, but on Ubuntu virtually everything defaults to shared libraries. You can choose static if you really want it, though, as in the example above. Pete ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Difference between div and /
On Thu, 2010-06-03 at 12:44 +1200, Richard O'Keefe wrote: On Jun 3, 2010, at 1:13 AM, Maciej Piechotka wrote: On Wed, 2010-06-02 at 14:01 +1200, Richard O'Keefe wrote: For what applications is it useful to use the same symbol for operations obeying (or in the case of floating point operations, *approximating* operations obeying) distinct laws? If the given operations do share something in common. For example * is usually commutative. However you do use it with quaternions (Hamilton product). You even write ij = k despite the fact that ji = -k. I think you just made my point: Commutativity is NOT one of the standard properties that * is EXPECTED to possess. I don't think that many people expect * to be not commutative (I'm not speaking about people who deal with Mathematics - I mean 'average person' and 'average programmer'). If you look at the Int and Double instance of Random in the Random.hs that comes with Hugs, you'll see they use different code. It's not because of any problem with / per se but because they need genuinely different algorithms. Point taken. Regards signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Re: Difference between div and /
On Wed, 2010-06-02 at 16:11 +0200, Henning Thielemann wrote: Sorry, I missed this post. Maciej Piechotka schrieb: Well - i tried to write some package dealing with distributions etc. If you have something like that: instance ... = Distribution (Linear a) a where rand (Linear f s) g = let (gf, gt) = genRange g (v, g') = next g in (g', f + (fromIntegral v * s) / fromIntegral (gt - gf)) (I haven't check it but IMHO it is right implementation) Now I have following options: - Implement per Int/Int8/... - Implement IntegerLinear and FractionalLinear separatly That is, what you need is a general division with rounding. But you might more generally want a custom type class with a method that selects an element from a set for given parameters gf, gt, v. This way, you could also handle distributions on Enumeration types. You certainly you do not want, say a division operation on Monday, Tuesday, ..., Sunday, but having a probability distribution of weekdays is very reasonable. Btw. you may want to have a look at: http://hackage.haskell.org/package/probability Hmm. Thanks - however I fail to figure out how to do something like: generate a random number with normal distribution with average avg and standard deviation stdev. Regards signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] cabal update doesn't work on Windows XP
Hi, Has anyone managed to get cabal to run on Windows? I'm running Windows XP. There are lots of other things, including old version of Haskell tools, installed, but it's too costly to try installing cabal on a fresh machine image. Whenever I do cabal update, the response is Unsuccessful HTTP code 403. That looks like the hackage server isn't responding, but other software tools (browsers, etc) on the computer can download the hackage database; the only program that can't get it is cabal. This problem occurs with all cabal 1.6, 1.8, with downloaded executables, with versions I've compiled, with the version in the Haskell Platform. Needless to say, these problems don't occur on Linux. Best wishes, John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wire GUI
On Wed, Jun 2, 2010 at 5:29 PM, Andrew Coppin andrewcop...@btinternet.com wrote: Thanks to the people who replied about this. I would also like to thank my ISP for classifying the entire lot as spam and not showing it to me. *sigh* Blobs sounds interesting, but seems to require wxHaskell rather than Gtk2hs. I may be able to use some of the ideas from it though. I haven't had time to watch the YouTube video with sound yet. I note that Sifflet allows you to connect a function to its arguments and use gtk2hs. It then allows you to move the function and args around and even rearrange them automatically, so it seems relevant to your need. -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] cabal update doesn't work on Windows XP
Whenever I do cabal update, the response is Unsuccessful HTTP code 403. That looks like the hackage server isn't responding, but other software tools (browsers, etc) on the computer can download the hackage database; the only program that can't get it is cabal. Do you use an http proxy? If so, you'll need to set the HTTP_PROXY env var. Alistair Invesco Fund Managers Limited, Company No. 898166, FSA No. 119298 Invesco Asset Management Limited, Company No. 949417, FSA No. 122674 Invesco Global Investment Funds Limited, Company No. 1046873, FSA No. 141663 Invesco Perpetual Life Limited, Company No. 3507379, FSA No. 188249 Invesco UK Limited, Company No. 3004959 The first four listed companies are authorised and regulated by the Financial Services Authority. All companies are incorporated in England and registered at 30 Finsbury Square, London EC2A 1AG. UK Group VAT No. 245 055 771. * Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. * ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Re: Difference between div and /
On Thu, 3 Jun 2010, Maciej Piechotka wrote: Hmm. Thanks - however I fail to figure out how to do something like: generate a random number with normal distribution with average avg and standard deviation stdev. Unfortunately the package is restricted to discrete distributions so far. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: random-fu 0.1.0.0
Announcing the 0.1.0.0 release of the random-fu library for random number generation[1]. This release hopefully stabilizes the core interfaces (those exported from the base module Data.Random). Warning to anyone upgrading from earlier releases: 'Discrete' has been renamed 'Categorical', the entropy source classes have been redesigned, and many things are no longer exported from the root module Data.Random (In particular, DevRandom - this is not available on windows, so it will likely move to its own package eventually so that client code dependencies on it will be made explicit). Unfortunately, Hackage appears to have choked on some of the package's dependencies (specifically, 2 dependencies also depend on time, and were built using different versions) so its documentation (which I put quite a bit of work into) is not displayed on the Hackage site. In the past I have dealt with that by uploading new versions with hacks to make sure the thing builds, but I really would rather not continue to do so. Is there any procedure by which I can request a manual rebuild of the package so that its documentation will be generated and displayed? Incidentally, this is a recurring problem I have run into several times for several packages. Can we *please* come up with a way for sdist or similar to just include pre-built documentation? Or if I were to spend some time working on such a thing, would it be accepted (assuming it was done up to all applicable standards of quality)? For now, I have added some pre-built haddock docs to the repository so that they may be browsed online[2] (if code.haskell.org ever starts responding to my HTTP requests. It's just not my day today, I guess). [1] http://hackage.haskell.org/package/random-fu-0.1.0.0 [2] http://code.haskell.org/~mokus/random-fu/doc/haddock/index.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Re: Difference between div and /
On Thu, 3 Jun 2010, Maciej Piechotka wrote: Hmm. Thanks - however I fail to figure out how to do something like: generate a random number with normal distribution with average avg and standard deviation stdev. Unfortunately the package is restricted to discrete distributions so far. Shameless self-advertisement: The random-fu package (whimsically named, sorry) implements a modest variety of continuous distributions with what I believe to be a user-friendly and flexible interface. This thread inspired me to finish up and upload the 0.1 release (just announced on haskell-cafe as well). The public interface is slightly different from earlier releases and the haddock docs for the new one failed to build on hackage, but earlier versions have essentially the same end-user interface aside from some changes in the module export lists so if you'd like to get an idea of the basic spirit of the system you can browse the docs for the earlier releases. Alternatively, feel free to browse the source and steal some of the implementations (many of which were, in turn, translated from other sources such as wikipedia or the Numerical Recipes book). Unfortunately, the old documentation is much sparser and terser than the new documentation that failed to build, but if nothing else you can download and build the docs yourself for the new one. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Efficient string construction
(I've done a basic Google search on this with no results. Apologies if this has been asked before.) I am coding a web application in which the content is a Unicode string built up over multiple functions and maintained in a State structure. I gather that the String module is inefficient and that Data.Text would be a better choice. Is it more efficient to build up a list of Text objects over time and combine them together with a single Data.Text.concat for the final output or to run Data.Text.append for each new string so that I am maintaining a single Text object rather than a list? As Data.Text.append requires copying both strings each time, my gut feeling is that concat would be much more efficient, but Haskell has surprised me before, so I wanted to check. Kevin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient string construction
On Thursday 03 June 2010 16:03:11, Kevin Jardine wrote: (I've done a basic Google search on this with no results. Apologies if this has been asked before.) I am coding a web application in which the content is a Unicode string built up over multiple functions and maintained in a State structure. I gather that the String module is inefficient and that Data.Text would be a better choice. Is it more efficient to build up a list of Text objects over time and combine them together with a single Data.Text.concat for the final output or to run Data.Text.append for each new string so that I am maintaining a single Text object rather than a list? As Data.Text.append requires copying both strings each time, my gut feeling is that concat would be much more efficient, but Haskell has surprised me before, so I wanted to check. Kevin I'd say, use Data.Text.Lazy and its 'fromChunks' function if you produce the string chunkwise. That avoids copying. Perhaps Data.ByteString[.Lazy].UTF8 is an even better choice than Data.Text (depends on what you do). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Simplest reference for how to build GHC head + get it running w/ cabal/haskell-platform?
What's the easiest reference for how to build GHC head and get it up and running with cabal/haskell-platform? I simply installed 6.12 + haskell-platform then built ghc-6.13.xx and rebuilt only the packages I needed with cabal install --reinstall. Perhaps this is not the recommended way. Indeed, something must be wrong because I can't build certain packages. (I have problems with base dependencies.) For example: $ cabal install QuickCheck Resolving dependencies... cabal: cannot configure QuickCheck-1.2.0.0. It requires base ==3.* For the dependency on base ==3.* there are these packages: base-3.0.3.1 and base-3.0.3.2. However none of them are available. base-3.0.3.1 was excluded because of the top level dependency base -any base-3.0.3.2 was excluded because of the top level dependency base -any Thanks! -Ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Proposal: Sum type branches as extended types (as Type!Constructor)
Extending sum types with data constructors would spare runtime errors or
exception control,
when applying functions to inappropriate branches, as in the example ...
data List a = Nil | Cons a (List a) -- List!Nil and List!Cons
-- as extended types
* Actual system, with runtime errors (as in GHC Data.List head) or
exception throwing
hd :: List a - a
hd (Cons x _) - x
hd Nil - error error: hd: empty list -- error or exception throwing
* Proposed system extending types with constructors as Type!Constructor:
User must do pattern matching before applying the constructor-specific
type function.
In ''var @ (Constructor _ _)'' the compiler should append the constructor
to the type as a pair (Type, Constructor) as an extended type for ''var''
No need for runtime errors or exception control
hd :: List!Cons a - a
hd (Cons x _) = x
using it:
headOf :: List a - Maybe a
headOf list = case list of
li @ (Cons _ _) - Just hd li -- extTypeOf li == ( 'List', 'Cons')
-- should pass typechecker for List!Cons
li @ Nil - Just hd li -- compiler error !!
-- extTypeOf ('List','Nil') don't match
_ - Just hd list -- compiler error !!
-- extTypeOf ('List',Nothing) don't match
Maybe we could take out importance on the number of _ wildcards (constructor
arity) with a syntax like.
li @ (Cons ...)
li @ (Nil ...)
Cheers!
Gabriel Riba Faura.
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Re: [Haskell-cafe] Efficient string construction
--- On Thu, 6/3/10, Daniel Fischer daniel.is.fisc...@web.de wrote: Perhaps Data.ByteString[.Lazy].UTF8 is an even better choice than Data.Text (depends on what you do). I thought that I had the differences between the three libraries figured out but I guess not now from what you say. I had thought that String was a simple but memory inefficient model, that Text was for, well text, and that bytestrings were for binary data (eg. images, audio files and applications that required a true view on each text byte). So why is there a UTF8 implementation for bytestrings? Does that not duplicate what Text is trying to do? If so, why the duplication? When is each library more appropriate? Kevin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: Sum type branches as extended types (as Type!Constructor)
On 3 Jun 2010, at 16:14, Gabriel Riba wrote:
Extending sum types with data constructors would spare runtime errors or
exception control,
when applying functions to inappropriate branches, as in the example ...
data List a = Nil | Cons a (List a) -- List!Nil and List!Cons
-- as extended types
* Actual system, with runtime errors (as in GHC Data.List head) or
exception throwing
hd :: List a - a
hd (Cons x _) - x
hd Nil - error error: hd: empty list -- error or exception throwing
* Proposed system extending types with constructors as Type!Constructor:
User must do pattern matching before applying the constructor-specific
type function.
In ''var @ (Constructor _ _)'' the compiler should append the constructor
to the type as a pair (Type, Constructor) as an extended type for ''var''
No need for runtime errors or exception control
hd :: List!Cons a - a
hd (Cons x _) = x
using it:
headOf :: List a - Maybe a
headOf list = case list of
li @ (Cons _ _) - Just hd li -- extTypeOf li == ( 'List', 'Cons')
-- should pass typechecker for List!Cons
li @ Nil - Just hd li -- compiler error !!
-- extTypeOf ('List','Nil') don't match
_ - Just hd list -- compiler error !!
-- extTypeOf ('List',Nothing) don't match
Maybe we could take out importance on the number of _ wildcards (constructor
arity) with a syntax like.
li @ (Cons ...)
li @ (Nil ...)
This looks fairly similar to total functional programming, though putting the
onus on the caller to make sure it meets preconditions, rather than the callee
to make sure it's the right type.
In total functional programming we would say
head :: List a - Maybe a
head (Cons x _) = Just x
head Nil = Nothing
We'd then allow the caller to deal with the maybe any way it likes (commonly
with fmap, or with the maybe function).
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Re: [Haskell-cafe] Parselib sample
Hey Doaitse, Could you please post the full code available? On Thu, Jun 3, 2010 at 1:01 AM, S. Doaitse Swierstra doai...@swierstra.netwrote: If you want to use the easier long-standing libraries from Utrecht, we can provide you with a parser for full Haskell, which you can find in the Utrecht Haskell Compiler (UHC) distribution. In 2002 Alexey Rodriguez produced a C fron-end, using the UUlibs combinators. I am attaching the file with the parser so you can take a look. If you want to have access to the full compiler, which was not maintained, I can make the full code available on a website. I think it is also instructive to start with looking at simpler parsers, e.g. for the bibtex format, which is available from: https://subversion.cs.uu.nl/repos/project.STEC.uulib/uulib/trunk/examples/ Doaitse On 1 jun 2010, at 13:06, C K Kashyap wrote: Hi, Is there a not-so-trivial parser implementation with Parselib? Parser for a C like language would be good. I searched and found Haskell++ - http://www.cs.chalmers.se/~rjmh/Software/h++.htmlhttp://www.cs.chalmers.se/%7Erjmh/Software/h++.html However, I'd prefer to look at a parser for a C like language. -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient string construction
On Thursday 03 June 2010 17:26:36, Kevin Jardine wrote: --- On Thu, 6/3/10, Daniel Fischer daniel.is.fisc...@web.de wrote: Perhaps Data.ByteString[.Lazy].UTF8 is an even better choice than Data.Text (depends on what you do). I thought that I had the differences between the three libraries figured out but I guess not now from what you say. I had thought that String was a simple but memory inefficient model, that Text was for, well text, and that bytestrings were for binary data (eg. images, audio files and applications that required a true view on each text byte). Well, not necessarily. String can be quite memory efficient. As a stupid example, length (replicate 1000 'a') will need less memory than the equivalents using ByteString or Text. Less stupidly, if the String is lazily produced and consumed from head to last, String is memory efficient. And it's not necessarily much slower than ByteString or Text. In fact, String is sometimes faster than Text (cf. e.g. http://www.haskell.org/pipermail/haskell-cafe/2010-May/078220.html and following). When you have to deal with text that is ASCII or latin1 (or some other encoding with a byte - char correspondence), plain ByteStrings are usually by far the fastest method. But that's of course a severe restriction. So why is there a UTF8 implementation for bytestrings? Does that not duplicate what Text is trying to do? If so, why the duplication? I think Data.ByteString.UTF8 predates Data.Text. When is each library more appropriate? Generally, ByteString for binary data or text, when you know it's safe and you need the speed. For text, either String or Data.Text may be the better choice. IIRC, Data.Text uses utf-16 (or some other 16-bit encoding), so if you receive utf-8 encoded text, Data.ByteString.UTF8 can be the better choice. I haven't much experience with either Data.Text or Data.ByteString.UTF8, so I can't say much about their relative merits. Kevin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] design question/font metrics
Maybe you could check out the FTGL package for inspiration on using the freetype as a conventional C library. I was going to try to write a Hackage package but realised I know nothing about typography and had to start reading the intro. on Freetype's homepage (which is pretty good, actually). Maybe I'll try it on the weekend. I needed something to measure the size in pixels of some text for a given font and point size, so I used libgd and manually analysed the pixels. It wasn't fast but it worked perfectly. So, Gery, if you don't really need speed all that much, that's a quick route to success. Otherwise maybe we could work on something with the Freetype library. On 1 June 2010 18:22, Stephen Tetley stephen.tet...@gmail.com wrote: Hi Brandon Even that's not simple - freetype is essentially a framework for writing font processors rather than a conventional C library[*]. Saner perhaps is to write a C program using freetype to do the exact job you have in mind, then bind to your C program. Best wishes Stephen [*} Probably why several people Including me have attempted a binding, but no-one has delivered one. On 1 June 2010 17:18, Brandon S. Allbery KF8NH allb...@ece.cmu.edu wrote: The saner way to do this is to write a binding to freetype2. ___ 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] Efficient string construction
You might also look at Data.Rope from the rope library, which provides an O(1) append for strict bytestring chunks, and the ability to decode UTF-8 chars from the result. http://hackage.haskell.org/packages/archive/rope/0.6.1/doc/html/Data-Rope.html I'd also be happy to work with you if the current API falls short of your needs. -Edward Kmett On Thu, Jun 3, 2010 at 10:03 AM, Kevin Jardine kevinjard...@yahoo.comwrote: (I've done a basic Google search on this with no results. Apologies if this has been asked before.) I am coding a web application in which the content is a Unicode string built up over multiple functions and maintained in a State structure. I gather that the String module is inefficient and that Data.Text would be a better choice. Is it more efficient to build up a list of Text objects over time and combine them together with a single Data.Text.concat for the final output or to run Data.Text.append for each new string so that I am maintaining a single Text object rather than a list? As Data.Text.append requires copying both strings each time, my gut feeling is that concat would be much more efficient, but Haskell has surprised me before, so I wanted to check. Kevin ___ 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] Proposal: Sum type branches as extended types (as Type!Constructor)
On 3 June 2010 16:14, Gabriel Riba griba2...@gmail.com wrote:
Maybe we could take out importance on the number of _ wildcards
(constructor
arity) with a syntax like.
li @ (Cons ...)
li @ (Nil ...)
can't you already use {} to get rid of the underscores?
li@(Cons {})
li@(Nil {})
--
Ozgur Akgun
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Re: [Haskell-cafe] The state of Hackage: what are we doing about it?
si: On Thursday 03 June 2010 06:27:43 am Don Stewart wrote: I've been posting CSV files of the download statistics here: http://www.galois.com/~dons/hackage/hackage-downloads.csv The next quarter's aggregated downloads are due soon. The Arch Haskell site uses these stats to compute some popularity metrics: http://www.galois.com/~dons/arch-haskell-status.html with that data, it should be rather easy to compute some kind weights for the packages and to prefer the popular packages during the search. In the long run it would be nice to get this statistics more frequently, e.g. monthly. We see, that within a quarter there are a lot of new packages. I have scripts, and access to the apache logs -- so its just a matter of free time to work on this. That's the goal though. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Sockets get bound to wrong port on Windows
Am 03.06.2010 07:34 schrieb Bardur Arantsson: On 2010-06-03 05:10, Matthias Reisner wrote: Hi, there's something wrong with port numbers in the Network.Socket module of package network. Printing values gives: *Main PortNum 47138 *Main PortNum 47138 Try (fromIntegral ) :: PortNumber (Yes, it's weird.) Cheers, Bardur ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Hi Bardur, indeed, this is weird. Thanks for the hint! Regards, Matthias ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Sockets get bound to wrong port on Windows
Am 03.06.2010 08:05 schrieb Ketil Malde:
Antoine Latter aslat...@gmail.com writes:
*Main PortNum
47138
The PortNum constructor should rarely be used directly
So, shouldn't the constructor be hidden, and exported from an .Internal
module?
- it contains the port number in network-order. You should try:
Or perhaps even better, the type could be:
data PortNum = PortNum { msb, lsb :: Word8 }
so that we avoid this kind of confusion?
-k
Hi,
since this is really not obvious, I'd second to hide the constructor or
at least a note should be added to the docs how to use PortNumber correctly.
Regards,
Matthias
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Re: [Haskell-cafe] Process priority
* Andrew Coppin andrewcop...@btinternet.com [2010-06-03 08:27:21+0100] I've had a hunt around in System.Process, but I can't discover any way to adjust the priority of the process you just spawned. Am I missing something, or has this just not been implemented yet? (I must confess, I don't know whether Windows and Unix both have the same ideas about priority numbers...) For POSIX systems you have 'nice' and 'setProcessPriority' in System.Posix.Process. -- Roman I. Cheplyaka :: http://ro-che.info/ Don't let school get in the way of your education. - Mark Twain ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: Sum type branches as extended types (as Type!Constructor)
On 06/03/2010 10:14 AM, Gabriel Riba wrote: No need for runtime errors or exception control hd :: List!Cons a - a hd (Cons x _) = x This is already doable using GADTs: data Z data S n data List a n where Nil :: List a Z Cons :: a - List a n - List a (S n) hd :: List a (S n) - a hd (Cons x _) = x tl :: List a (S n) - List a n tl (Cons _ xs) = xs - Jake ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal -j
What, if anything, stands in the way of parallelizing Cabal installs, make -j style? Louis Wasserman wasserman.lo...@gmail.com http://profiles.google.com/wasserman.louis ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Weird socket problem on Mac OS X
Hello,
I have the following code which works ok on Linux and Windows XP, but
fails on Mac OS X with error message:
Connect: does not exist (connection refused)
The server:
doStartstate = do pr - liftIO $ runProcess ...
liftIO $ threadDelay 50
st - get
put st { slimHandle = Just pr }
The client:
fetchAnswers st msgs = liftIO $! do let port = PortNumber $
fromInteger $ port $ config st
cnx - connectTo localhost port
Help most welcome, thanks
Arnaud
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Re: [Haskell-cafe] ANN: random-fu 0.1.0.0
On Jun 3, 2010, at 6:34 AM, mo...@deepbondi.net wrote: Announcing the 0.1.0.0 release of the random-fu library for random number generation[1]. This release hopefully stabilizes the core interfaces (those exported from the base module Data.Random). Great work, I'm upgrading now. The only feature suggestion I can suggest is the addition of a convolution operator to combine distributions (reified as RVar's in this implementation, though of course the difference between a random variable over a distribution and the distribution is rather thin) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal -j
wasserman.louis: What, if anything, stands in the way of parallelizing Cabal installs, make -j style? Parallelizing ghc --make http://vimeo.com/6572966 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal -j
On 4 June 2010 00:05, Don Stewart d...@galois.com wrote: wasserman.louis: What, if anything, stands in the way of parallelizing Cabal installs, make -j style? Parallelizing ghc --make http://vimeo.com/6572966 Unless Louis meant what's stopping cabal-install from installing dependancies in parallel instead of serial? In which case; nothing? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient string construction
On Thu, Jun 3, 2010 at 9:16 AM, Daniel Fischer daniel.is.fisc...@web.dewrote: String can be quite memory efficient. As a stupid example, length (replicate 1000 'a') will need less memory than the equivalents using ByteString or Text. Actually, this will be fused with Data.Text, and should execute more quickly and in less space than String. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal -j
chrisdone: On 4 June 2010 00:05, Don Stewart d...@galois.com wrote: wasserman.louis: What, if anything, stands in the way of parallelizing Cabal installs, make -j style? Parallelizing ghc --make http://vimeo.com/6572966 Unless Louis meant what's stopping cabal-install from installing dependancies in parallel instead of serial? In which case; nothing? Oh, sorry, dependencies (package level parallelism) vs modules (ghc --make level parallelism) -- don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal -j
Heh, I'm interested in both, but I'm feeling like I needed a new project, and I thought this might make a good one =) Louis Wasserman wasserman.lo...@gmail.com http://profiles.google.com/wasserman.louis On Thu, Jun 3, 2010 at 5:42 PM, Don Stewart d...@galois.com wrote: chrisdone: On 4 June 2010 00:05, Don Stewart d...@galois.com wrote: wasserman.louis: What, if anything, stands in the way of parallelizing Cabal installs, make -j style? Parallelizing ghc --make http://vimeo.com/6572966 Unless Louis meant what's stopping cabal-install from installing dependancies in parallel instead of serial? In which case; nothing? Oh, sorry, dependencies (package level parallelism) vs modules (ghc --make level parallelism) -- don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.ByteString.Lazy.hPut and timeouts?
On Wed, Jun 2, 2010 at 7:55 PM, Jeremy Shaw jer...@n-heptane.com wrote: I know that some OSes provide a per socket timeout that I can set in my application code (instead of a system-wide timeout that can only be set by root). But that does not seem like a very portable solution. SO_SENDTIMEO is your portable friend (can't remember whether it's exposed by the network package, though). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: Sum type branches as extended types (as Type!Constructor)
Jake McArthur wrote: On 06/03/2010 10:14 AM, Gabriel Riba wrote: No need for runtime errors or exception control hd :: List!Cons a - a hd (Cons x _) = x This is already doable using GADTs: data Z data S n data List a n where Nil :: List a Z Cons :: a - List a n - List a (S n) hd :: List a (S n) - a hd (Cons x _) = x tl :: List a (S n) - List a n tl (Cons _ xs) = xs Sure, it is the whipping boy of dependent types afterall. However, * Haskell's standard lists (and Maybe, Either,...) aren't GADTs, * last I heard GADTs are still a ways off from being accepted into haskell', * and, given that this is the whipping boy of dependent types, you may be surprised to learn that pushing the proofs of correctness through for the standard library of list functions is much harder than it may at first appear. Which is why, apparently, there is no standard library for length-indexed lists in Coq.[1] But more to the point, this proposal is different. Gabriel is advocating for a form of refinement types (aka weak-sigma types), not for type families. This is something I've advocated for in the past (under the name of difference types)[2] and am still an avid supporter of-- i.e., I'm willing to contribute to the research and implementation for it, given a collaborator familiar with the GHC code base and given sufficient community interest. The reason why length-indexed lists (and other type families) are surprisingly difficult to work with is because of the need to manipulate the indices in every library function. With refinement types predicated on the head constructor of a value, however, there is no need to maintain this information throughout all functions. You can always get the proof you need exactly when you need it by performing case analysis. The benefit of adding this to the type system is that (a) callees can guarantee that the necessary checks have already been done, thereby improving both correctness and efficiency, and (b) it opens the door for the possibility of moving the witnessing case analysis further away from the use site of the proof. While #b in full generality will ultimately lead to things like type families, there are still a number of important differences. Perhaps foremost is that you needn't define the proof index at the same point where you define the datatype. This is particularly important for adding post-hoc annotations to standard types like lists, Maybe, Either, etc. And a corollary to this is that you needn't settle on a single index for an entire programming community, nor do you impose the cost of multiple indices on users who don't care about them. In short, there's no reason why the equality proofs generated by case analysis should be limited to type equivalences of GADT indices. Value equivalences for ADTs are important too. [1] Though I'm working on one: http://community.haskell.org/~wren/coq/vecs/docs/toc.html [2] http://winterkoninkje.livejournal.com/56979.html -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal -j
Excerpts from Christopher Done's message of Fri Jun 04 00:39:23 +0200 2010: On 4 June 2010 00:05, Don Stewart d...@galois.com wrote: wasserman.louis: What, if anything, stands in the way of parallelizing Cabal installs, make -j style? Parallelizing ghc --make http://vimeo.com/6572966 Unless Louis meant what's stopping cabal-install from installing dependancies in parallel instead of serial? In which case; nothing? I think cabal-install compiles Setup without starting ghc or such (I may be wrong). This would be fixable. If you want to volunteer try hack-nix. It's based on the Nix distribution system which provides this feature natively. You can even ask others computers to help building dependencies quite easily. Downside: At the moment it will pull all depndencies (including kernel headers and glibc..) if you install it on a common linux system. Marc Weber ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: random-fu 0.1.0.0
The only feature suggestion I can suggest is the addition of a convolution operator to combine distributions (reified as RVar's in this implementation, though of course the difference between a random variable over a distribution and the distribution is rather thin) I don't think I understand. My familiarity with probability theory is fairly light. Are you referring to the fact that the PDF of the sum of random variables is the convolution of their PDFs? If so, the sum of random variables can already be computed as liftA2 (+) :: Num a = RVar a - RVar a - RVar a since RVar is an applicative functor (or using liftM2 since it's also a monad). Or perhaps you mean an operator that would take, say, 2 values of the 'Uniform' data type and return an instance of the 'Triangular' type corresponding to the convolution of the distributions? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Language Shootout reverse-complement benchmark
Inspired by this post I looked at the language shootout. There is one thing which strikes me: On http://shootout.alioth.debian.org/u64/performance.php?test=spectralnorm#about It sais for the spectralnorm benchmark that both Haskel GHC #4 and HaskellGHC produce bad output. For GHC I connt see what's wrong because 1.274224153 seems to be the correct result. But there really seems to be something wrong with GHC#4. -- Martin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Weird socket problem on Mac OS X
Hi Arnaud,
One thing you might want to try is to stop using the PortNumber data
constructor, and instead rely on 'fromInteger' to do the right thing.
The data constructor assumes that it's argument is in network byte order,
which won't always be the case.
It's not obvious that the constructor should be avoided - this is the second
time today I've seen this!
Take care,
Antoine
On Jun 3, 2010 5:13 PM, Arnaud Bailly arnaud.oq...@gmail.com wrote:
Hello,
I have the following code which works ok on Linux and Windows XP, but
fails on Mac OS X with error message:
Connect: does not exist (connection refused)
The server:
doStartstate = do pr - liftIO $ runProcess ...
liftIO $ threadDelay 50
st - get
put st { slimHandle = Just pr }
The client:
fetchAnswers st msgs = liftIO $! do let port = PortNumber $
fromInteger $ port $ config st
cnx - connectTo localhost port
Help most welcome, thanks
Arnaud
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Re: [Haskell-cafe] ANN: random-fu 0.1.0.0
On Jun 3, 2010, at 4:19 PM, mo...@deepbondi.net wrote: I don't think I understand. My familiarity with probability theory is fairly light. Are you referring to the fact that the PDF of the sum of random variables is the convolution of their PDFs? If so, the sum of random variables can already be computed as liftA2 (+) :: Num a = RVar a - RVar a - RVar a since RVar is an applicative functor (or using liftM2 since it's also a monad). Or perhaps you mean an operator that would take, say, 2 values of the 'Uniform' data type and return an instance of the 'Triangular' type corresponding to the convolution of the distributions? I think I had something like the former in mind. I didn't realize liftA2/M2 would do it.When I did this last, I just wrote a monadic action to sample values from different RVars. I should learn the higher order monad functions. On the other hand, it might be kind of nice if RVar's knew which PDF they are over. It's hard for me to see how that would be done with Haskell. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Problems with Haskell Platform
On 31 May 2010 20:14, Pete Chown 1...@234.cx wrote: I was just thinking, interactions between Cabal and the distribution package manager could get worse, as shared Haskell libraries become more common. Suppose a distribution ships a package 'foo', but not a package 'bar' which depends on it. The 'foo' package includes shared libraries. The user now installs 'bar' using Cabal. This causes Cabal to install 'foo' (because it is a dependency) and it won't use the distribution's package manager. This is a good valid point and one I have been worrying about myself sometimes. I often find myself hitting Ctrl-C at cabal install HACKAGE to run yum install ghc-DEPENDENCY-devel and before returning to run cabal install again. It would be nice to automate this in some way - cabal-install plugins, anyone?? Jens ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simplest reference for how to build GHC head + get it running w/ cabal/haskell-platform?
On 4 June 2010 00:57, Ryan Newton new...@mit.edu wrote: What's the easiest reference for how to build GHC head and get it up and running with cabal/haskell-platform? I simply installed 6.12 + haskell-platform then built ghc-6.13.xx and rebuilt only the packages I needed with cabal install --reinstall. Perhaps this is not the recommended way. You have to rebuild _everything_ with the new version of GHC. Indeed, something must be wrong because I can't build certain packages. (I have problems with base dependencies.) For example: $ cabal install QuickCheck Resolving dependencies... cabal: cannot configure QuickCheck-1.2.0.0. It requires base ==3.* For the dependency on base ==3.* there are these packages: base-3.0.3.1 and base-3.0.3.2. However none of them are available. base-3.0.3.1 was excluded because of the top level dependency base -any base-3.0.3.2 was excluded because of the top level dependency base -any Looks like GHC-6.13 has dropped base-3 compatability; as such, QuickCheck-1.x will not build as there is no variant that works with base-4. Is there any particular reason why you're not using QuickCheck-2.y ? -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: Sum type branches as extended types (as Type!Constructor)
On 4 June 2010 03:18, Ozgur Akgun ozgurak...@gmail.com wrote:
On 3 June 2010 16:14, Gabriel Riba griba2...@gmail.com wrote:
Maybe we could take out importance on the number of _ wildcards
(constructor
arity) with a syntax like.
li @ (Cons ...)
li @ (Nil ...)
can't you already use {} to get rid of the underscores?
li@(Cons {})
li@(Nil {})
Even better: you shouldn't need the parentheses:
l...@cons{}
l...@nil{}
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Re: Problems with Haskell Platform
On 4 June 2010 10:27, Jens Petersen peter...@haskell.org wrote: On 31 May 2010 20:14, Pete Chown 1...@234.cx wrote: I was just thinking, interactions between Cabal and the distribution package manager could get worse, as shared Haskell libraries become more common. Suppose a distribution ships a package 'foo', but not a package 'bar' which depends on it. The 'foo' package includes shared libraries. The user now installs 'bar' using Cabal. This causes Cabal to install 'foo' (because it is a dependency) and it won't use the distribution's package manager. This is a good valid point and one I have been worrying about myself sometimes. I often find myself hitting Ctrl-C at cabal install HACKAGE to run yum install ghc-DEPENDENCY-devel and before returning to run cabal install again. It would be nice to automate this in some way - cabal-install plugins, anyone?? How difficult is it just to create an RPM for yourself and then put it up in some repository for other people to use? I never use cabal-install to install packages at home (with the exception of testing versions of libraries I'm writing as I'm writing them); instead I create a new ebuild for whatever I want and then put that in the Haskell overlay for Gentoo. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: random-fu 0.1.0.0
On the other hand, it might be kind of nice if RVar's knew which PDF they are over. It's hard for me to see how that would be done with Haskell. If anyone knows a way this could be done while still allowing general functions to be mapped over RVars, I'd love to hear about it. My suspicion though is that it is not possible. It would be a very similar problem to computing the inverse of a function since the PDF is a measure of the size of the preimage of an event in the probability space (if I'm putting all those words together correctly ;)). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: Sum type branches as extended types (as Type!Constructor)
On Thu, Jun 3, 2010 at 8:14 AM, Gabriel Riba griba2...@gmail.com wrote:
Extending sum types with data constructors would spare runtime errors or
exception control,
when applying functions to inappropriate branches, as in the example ...
data List a = Nil | Cons a (List a) -- List!Nil and List!Cons
-- as extended types
* Actual system, with runtime errors (as in GHC Data.List head) or
exception throwing
hd :: List a - a
hd (Cons x _) - x
hd Nil - error error: hd: empty list -- error or exception throwing
* Proposed system extending types with constructors as Type!Constructor:
User must do pattern matching before applying the constructor-specific
type function.
In ''var @ (Constructor _ _)'' the compiler should append the constructor
to the type as a pair (Type, Constructor) as an extended type for ''var''
No need for runtime errors or exception control
hd :: List!Cons a - a
hd (Cons x _) = x
How will this proposal scale with data types that have multiple alternatives
that make sense? No natural examples come to mind so how about a contrived
example:
data List2 a = Nil | Cons a (List2 a) | Cons2 a a (List2 a)
Now I want to define hd for both Cons and Cons2, but not Nil. Do I use an
either type like this?
hd :: Either (List2!Cons a) (List2!Cons2 a) - a
It seems like some other syntax would be desirable here, maybe:
hd :: List2!{Cons, Cons2} a - a
How should it work for functions where no type signature is supplied?
Should it infer the type we would now and only enable the subset of
constructors when the type is explicit as above?
Jason
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Re: [Haskell-cafe] ANN: random-fu 0.1.0.0
Richard O'Keefe wrote: There's something in that package that I don't understand, and I feel really stupid about this. data RVarT m a type RVar = RVarT Identity class Distribution d t where rvar :: d t - RVar t rvarT :: d t - RVarT n t Where does n come from? Presumably from universal quantification in rvarT? That is, the implementation of rvarT should be polymorphic in n, in which case the particular n doesn't matter (as well it shouldn't, since if it did that'd interfere with the composability of the transformer). Though, since RVar is a synonym for RVarT, I can't imagine why rvar is a method instead of a shorthand defined outside of the class. (If RVar were primitive then I could imagine performance reasons, but since it isn't...) -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: random-fu 0.1.0.0
There's something in that package that I don't understand, and I feel really stupid about this. data RVarT m a type RVar = RVarT Identity class Distribution d t where rvar :: d t - RVar t rvarT :: d t - RVarT n t Where does n come from? There's no reason to feel stupid when faced with something unfamiliar. Even if you are familiar with monad transformers, this may not be a place you expect to find them, and 'n' in this case would usually be an 'm' in other places (it is the underlying monad being extended). Since I'm not sure at which level your unfamiliarity lies, I'll just give a from-scratch crash course. Feel free to ignore as much as is necessary, and please don't take this long-winded reply as any sort of condescension :). I'll refrain from introducing monads and monad transformers, as the internet is already full enough of those sorts of introductions. RVarT is a monad transformer that adds a source of random data to a preexisting monad, the latter being the role the 'n' serves in rvarT's type. RVar is just the pure version where the underlying monad (Identity) is sort of a type-level no-op. With that background in mind, the 2 methods of Distribution, rvar and rvarT, are exactly equivalent, just specialized so that the compiler can avoid unnecessary conversions in some cases. The types are even isomorphic, I believe, due to parametricity. Both methods take the distribution in question (the d t) and make an RVarT n t that has that distribution (RVar is RVarT Identity, so n == Identity). The reason the type variable is 'n' instead of 'm' as is more traditional is related to the types of the function runRVarT and similar functions for sampling the RVars: runRVarT :: (Lift n m, RandomSource m s) = RVarT n a - s - m a This involves 2 monads, and 'n' was used for the second of them. For consistency, 'n' is often used as the name of the corresponding variable in type signatures using RVarT. In runRVarT's type, 'n' is the monad underlying the random variable and 'm' is the monad in which it is being sampled. They are allowed to differ so that random variables can be given more general types. If they had to be the same, the RVar would have to carry around the monad in which it would eventually be sampled (and would incidentally be granted access to all its capabilities via Control.Monad.Trans.lift, which would be undesirable). It would also restrict the monads in which the RVar could be sampled. With this scheme, one RVar/RVarT can be sampled in many monads if desired (and I have used this ability more than once in real code). Finally, some may still wonder why there is a monad transformer here at all - a plain RVar would already be sampleable in any monad that can feed it some random data. Originally that's what the library had, but a kind and perceptive contributor (Reiner Pope) rectified that. As a result, the same framework supports some really nifty tricks, most importantly the ability to define random processes reusing all the existing definitions of random variables. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Issue with connectTo function in network package
Hi all, I had an issue where using the connectTo [1] function would fail to connect to localhost if my wireless card was turned off. The moment I turned on my wireless connection it worked. But if I use connectTo with 127.0.0.1 [2] with my network off it works. I confirmed that localhost' resolves to 127.0.0.1 by pinging localhost from command line with the Internet off. Is this a bug in connectTo? -deech [1] connectTo localhost (PortNumber some_number) [2] connectTo 127.0.0.1 (PortNumber some_number) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal -j
On Thu, Jun 3, 2010 at 3:05 PM, Don Stewart d...@galois.com wrote: wasserman.louis: What, if anything, stands in the way of parallelizing Cabal installs, make -j style? Parallelizing ghc --make http://vimeo.com/6572966 Something I wondered from watching that talk, rather than trying to make ghc run concurrently internally, can we just have --make, when faced with multiple possibilities, pick the first one without a 'ModuleName.working' file, create such a working file, and then go to? Then you can run 'ghc --make X.hs ; ghc --make X.hs ; ...'. In fact, isn't that what make -j already does? I could try it with the old style 'ghc -M' and pure makefile, but it turns out to be a lot of work to figure out what packages to include and tangle out the right .o files and whatnot, work that --make does for me. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: random-fu 0.1.0.0
On Jun 3, 2010, at 6:40 PM, mo...@deepbondi.net wrote:
If anyone knows a way this could be done while still allowing general
functions to be mapped over RVars, I'd love to hear about it. My
suspicion though is that it is not possible. It would be a very
similar
problem to computing the inverse of a function since the PDF is a
measure
of the size of the preimage of an event in the probability space (if
I'm
putting all those words together correctly ;)).
We don't necessarily have to compute the inverse of the distribution
via sampling to do it. It can be done algebraically, in terms of the
convolution operator. Since the types are enumerated, wouldn't
something like... work?
-- A set and binary operation. We have an algebra. I like the J for
'join'.
-- With this algebra, we can use the real-complex analytical methods to
-- interpret the terms later, if we want to actually reify a
Distribution
-- instance as a Real (Float, Double) function.
data DistributionJ a = UniformDistribution Uniform a
| ...
| ExponentialDistribution Exponential a
| DistributionJ a `Convolve` (DistributionJ a)
-- I hope I understand the semantics for the PromptT monad.
newtype RVarT m a = RVarT { unRVarT :: PromptT (Prim,
DistributionJ) m a }
I guess threading fst and snd in all the low level computations is
inelegant, but it's a step closer.___
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