[Haskell] Announcement: Fast linear programming with comfort-glpk and coinor-clp
I happily released two other numeric packages based on the comfort-array types. These are bindings to fast numeric linear programming solvers: https://hackage.haskell.org/package/comfort-glpk https://hackage.haskell.org/package/coinor-clp The first one is (another) binding to GLPK and the second one is a binding to COIN-OR/CLP. I guess this is the first Haskell binding to COIN-OR/CLP, at all. I found that the COIN-OR solver is not as simply structured as GLPK and the examples miss the simple use cases, but its performance is much better than that of GLPK and its interior point solver (Method.initialBarrierSolve) just works, in contrast to the one of GLPK. Warm start of solvers is supported by according monadic interfaces. Both packages use the same types to describe linear programming problems, thus you can describe your problem once and then simply choose the appropriate solver. The types are exported by the package linear-programming. The flexible array shapes provided by comfort-array help a lot to structure the problem variables. This saves you from the need to manually work with integer indices. You can concatenate array shapes with (::+) and establish Cartesian products with (,) and define array shapes that are compatible with nested tuples (e.g. Shape.NestedTuple ((X,X),(X,X,X))) or define arrays with indices of any Enum type (Shape.Enumeration). ___ Haskell mailing list Haskell@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell
Re: [Haskell-cafe] Decorating exceptions with backtrace information
On Fri, 8 May 2020, Ben Gamari wrote: Henning Thielemann writes: We are talking about the HasCallStack stack traces, yes? How is their emission addressed by extending exceptions with stack traces? HasCallStack stack traces are one type of backtrace that the proposal supports. However, it's not the only (nor is it even the most useful sort, in my opinion). Other mechanisms include cost center stacks from the cost-center profiler and native stack unwinding. Interesting. That's a completely new thing. * Developers cannot easily produce stack traces do debug unintended exceptions. What are "unintended exceptions"? What is an example of an "unintended exception"? For instance, * Somewhere deep in my code a colleague used `fromJust` due to a miscommunicated invariant That's a programming error. * Somewhere in my system a `writeFile "tmp" $ repeat 'a'` failed due to filling the disk Hm, that's also a programming error, but it ends in an IO exception. If it would not end in an IO exception (e.g. writing to /dev/null) it would go to an infinite loop. Anyway, it is a programming error. However it is an unchecked one. That is, there is no warranty that you can catch it by a debugger. So I do not think you can achieve much with callstacks here. * Somewhere in my system I have a partial pattern match in a module which was compiled without -Wall Programming error and btw. before thinking about a GHC extension I would enable -Wall ... * Somewhere in my system I `div` by zero due to lack of input validation Programming error * I use a record selector on a sum. Programming error * A logic error results in an assertion failure deep in my program, but it's unclear which path my program took to arrive at the assertion Sounds like Programming error This list could go on and on... From your list of examples I deduce that the proposal is about programming errors. But we have HasCallStack for that one. How does the proposal improve or alter the HasCallStack solution? And how does it relate to the IO exception system with hierarchical exceptions and SomeException and so on? Currently the proposal does not cover asynchronous exceptions but it wouldn't be particularly hard to extend it in this direction. This would allow far better reporting of heap/stack overflows and MVar deadlocks (which are particularly hard to debug at the moment). Hm, what kind of heap or stack overflow are you thinking of? A stack overflow sounds like unlimited recursion and thus like a programming error. In contrast to that, a program must be prepared for a failure of "malloc". Memory exhaustion is an IO exception, it should be explicit in the type. Are MVar deadlocks always detected by the runtime system? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Decorating exceptions with backtrace information
On Fri, 8 May 2020, Ben Gamari wrote: We can debate whether partial functions like `fromJust` should exist; however, the fact of the matter is that they do exist and they are used. That's not my point. I say: fromJust on Nothing is a programming error, ok. We must debug this. HasCallStack helps here. However, it does not have to do with exceptions or with the proposals as I understand them. Furthermore, even `base`'s own IO library (e.g. `openFile`) uses synchronous exceptions to report errors. Right. I say: Such exceptions are part of the public interface and should be expressed in types. If you encounter any problems when not doing this, I would first try to solve the problem with exceptions explicit in the type. E.g. Haddock for openFile says: This operation may fail with: * isAlreadyInUseError ... * isDoesNotExistError ... * isPermissionError ... Thus the type should be: openFile :: (AlreadyInUseException e, DoesNotExistException e, PermissionException e) => FilePath -> IOMode -> ExceptT e IO Handle Perhaps this helps to shed some light on the motivation? Unfortunately no. I only see the immortal confusion about (programming) errors vs. (IO) exceptions. And I think that part of this confusion is that IO exceptions in 'base' are hidden in the IO type and that there are hybrid functions like 'throw' that can be called like 'error' but they cause IO exceptions that can be caught by 'catch'. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Decorating exceptions with backtrace information
On Fri, 8 May 2020, Niklas Hambüchen wrote: What are "unintended exceptions"? What is an example of an "unintended exception"? A recent example from my production server: hPutBuf: resource vanished (Broken pipe) Ok, I lookup the Haddock comment of hPutBuf and it says: "This operation may fail with: * ResourceVanished if the handle is a pipe or socket, and the reading end is closed." That is, ResourceVanished is part of the public interface and in no way unexpected (or what "unintended" may be). I would prefer to make this explicit in the type of hPutBuf: hPutBuf :: (ResourceVanishedException e) => Handle -> Ptr a -> Int -> ExceptT e IO () Now, what do you intend to do with the call-stack? Isn't it something you can attach to the e value?___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Decorating exceptions with backtrace information
On Fri, 8 May 2020, Niklas Hambüchen wrote: On 5/8/20 7:32 PM, Henning Thielemann wrote: Can someone please give me examples where current state lacks * Currently stack traces are not printed, so users cannot forward them to the developer, even if both the users and the developers would like that. We are talking about the HasCallStack stack traces, yes? How is their emission addressed by extending exceptions with stack traces? * Developers cannot easily produce stack traces do debug unintended exceptions. What are "unintended exceptions"? What is an example of an "unintended exception"?___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Decorating exceptions with backtrace information
On Fri, 8 May 2020, Niklas Hambüchen wrote: On 5/8/20 5:37 PM, Henning Thielemann wrote: a callstack is not useful for a user. Call stacks have been very useful to me as a user of non-Haskell tools so far, because they are excellent for attaching to bug reports and usually led to developers fixing my problems faster. This confirms that they are not for you, but you only forward them to the developer. Can someone please give me examples where current state lacks and how they are addressed by the proposal(s)?___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Decorating exceptions with backtrace information
There seem to be multiple beginnings of the discussion. What is currently discussed? If someone says "exceptions" and "backtrace" in one sentence, I suspect like many times before, that again confusion of the concepts of exceptions and errors is ahead. Errors already support call stacks. Why should exceptions get them, too? Exceptions should carry information that is useful for a user, but a callstack is not useful for a user. I can imagine that it would be helpful for the user to get a stacked exception information like: Parse error on line 42, column 23 while reading file "foo/bar" while traversing directory "blabla" But since you refer to the CallStack feature of GHC, this seems not to be addressed in the proposals. On Fri, 8 May 2020, Carter Schonwald wrote: I have no doubt such a mechanism would have saved me many hours of debugging exceptions in Haskell systems I've worked on in the past. If you must debug exceptions, then this sounds like exceptions were abused for programming errors. Ben writes in: http://www.well-typed.com/blog/2020/04/dwarf-3/ "Unfortunately, the untyped nature of Haskell exceptions complicates the migration path for existing code." Actually, it only proves again, that it was wrong from the beginning to hide information about potential exceptions in the IO monad instead of making them explicit via ExceptionalT, ExceptT or the like. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
[Haskell] Announce: comfort-array, lapack
I like two announce two of my packages: 1. comfort-array http://hackage.haskell.org/package/comfort-array It provides Boxed and Storable arrays with very liberal shape definitions. You may use ranges of indices like in 'array' or zero-based indexing like in 'repa', but you can also use arbitrary index Sets, enumerations, concatenation of arrays and more. E.g. an array with (Shape.Enumeration Ordering) has three elements with indices LT, EQ, GT. 2. lapack http://hackage.haskell.org/package/lapack A high-level interface to the numerical Linear Algebra package LAPACK. It is based on comfort-array, which means that a vector can have a rich structure. E.g. matrix vector multiplication has the signature: (#*|) :: Matrix.General height width a -> Vector width a -> Vector height a Thus, a 'Matrix.General (Shape.Enumeration Ordering) (h,w) a' would map a rectangular array with dimensions h and w to a three-element vector with indices LT, EQ, GT. The LAPACK interface provides solvers for simultaneous linear equations, linear least-squares problems, eigenvalue and singular value problems for square, triangular, symmetric, Hermitian, banded and banded Hermitian matrices, as LAPACK supports them. For a motivating example refer to: http://code.henning-thielemann.de/bob2019/main.pdf ___ Haskell mailing list Haskell@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell
[Haskell] GHC 8.4.1 released
So far only announced on Haskell-Cafe, but not the Haskell mailing list: http://mail.haskell.org/haskell-cafe/2018-March/128730.html ___ Haskell mailing list Haskell@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell
Re: TDNR without new operators or syntax changes
On Sun, 22 May 2016, Jeremy . wrote: 1. If the compiler encounters a term f a, and there is more than one definition for f in scope (after following all of the usual rules for qualified imports); 2. And exactly one of these definitions matches the type of a (or the expected type of f if given); 3. Then this is the definition to use. I know people are unhappy with Haskell's records and module system, but I still think that's because these language features are not used properly. Type classes are the tool to write generic code and reduce combinatoric explosion of functions and modules are a way to collect functions per type. Following this principle you give function names that make sense together with the module name like File.write or Channel.write. Then there is no need for the compiler to disambiguate unqualified identifiers and you keep the type and the module issues separated. Today, if you stick to the unqualified style, and I guess you want to import modules without explicit identifier list, too, then your code can break whenever the imported modules add identifiers. In order to prevent this you have to use tight package import version bounds in your Cabal file. Your proposal would not solve this problem. Type-driven name resolution may disambiguate identifiers in some case but not in all ones, thus you still need to use tight version bounds. The proposal seems to be a big complication. The compiler can no longer emit a message: "Type of function f mismatch", but it has to emit "If f means A.f, then the type error would be ..., but if it means B.f, then the type error would be ..." Or even worse: "If f means A.f and g means C.g, then the type error would be ... if f means B.f and g means C.g ... or f means A.f and g means D.g ..." The proposal also is more error-prone, because if you make a type-error this could be shadowed by a function in scope with a type that matches accidentally. A function with a very generic type and a generic name might be such an accidental match. That said, the more complicated the proposals become the more one should reconsider about whether one runs in the right direction. I think this is the case here. The simple answer could be: Switch to a cleaner coding style!___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Warn about unwanted instances in a modular way
I like to propose the following way to warn about instances that are
unwanted by some programmers. First step is to mark the instances at their
definition site like so:
{-# WARN_INSTANCE tuple #-}
instance Foldable ((,) a) where ...
{-# WARN_INSTANCE tuple #-}
instance Functor ((,) a) where ...
{-# WARN_INSTANCE tuple #-}
instance Foldable ((,,) a b) where ...
{-# WARN_INSTANCE tuple #-}
instance Functor ((,,) a b) where ...
This way, all the above instances are collected in an instance group
labelled 'tuple'. At the use sites we introduce a GHC warning option like
-fwarn-instance=tuple. This warns about any place where any of the 'tuple'
instances is used. We can either place
GHC-Options: -fwarn-instance=tuple
in a Cabal package description in order to issue warnings in a whole
package or we can put
{-# OPTIONS_GHC -fwarn-instance=tuple #-}
at the top of a module in order to enable the warning per module.
Another candidate for an instance group might be 'numeric' for numeric
instances of functions and tuples in the NumInstances package.
What does it mean to use an instance? I would say, if omitting an instance
X Y would lead to a "missing instance" type error at place Z in a module,
then instance X Y is used at place Z.
There might be an even more restrictive option like:
-fforbid-instance=tuple
This would not only warn about an instance usage, but it would cause a
type error. Essentially it should treat all 'tuple' instances as if they
were not defined. (Other instances might depend on 'tuple' instances and
if the 'tuple' instances weren't there the compiler would not even reach
the current module. I do not know, whether this case needs special
treatment. We might require that any instance depending on 'tuple' must be
added to the 'tuple' group as well or it might be added automatically.)
The advantage of a type error is that we see all problems from 'tuple'
instances also in the presence of other type errors. Warnings would only
show up after a module is otherwise type correct.
This solution requires cooperation of the instance implementor. Would that
work in practice? Otherwise we must think about ways to declare instance
groups independently from the instance declaration and we get the problem
of bringing the instance group names into the scope of the importing
module.
A separate discussion must be held on whether -fwarn-instance=tuple should
be part of -Wall. I think that people should be warned about 'tuple'
instances early because they won't expect that there is a trap when using
'length' and 'maximum' and so on.
One might also think about generalizations, e.g. whether
{-# WARN_INSTANCE tuple, functor #-}
should be allowed in order to put an instance in several groups or whether
there should be a way to compose a group from subgroups.
Another topic would be a form of instance group disambiguation. Instance
groups might be qualified with module or package names. I think package
names are more appropriate, like so:
-fwarn-instance=base:tuple
___
Glasgow-haskell-users mailing list
Glasgow-haskell-users@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: suppress warning "Defined but not used: type variable ‘x’" in GHC-8.0
On Mon, 11 Jan 2016, Richard Eisenberg wrote: On Jan 9, 2016, at 6:44 PM, Henning Thielemann <lemm...@henning-thielemann.de> wrote: instance (Natural n) => Num.Integer (Un n) where type Repr (Un _n) = Unary GHC-7.6.3 and GHC-7.4.2 complain: Type indexes must match class instance head Found `Un _n' but expected `Un n' In the type synonym instance declaration for `Num.Repr' In the instance declaration for `Num.Integer (Un n)' GHC-7.8.4, GHC-7.10.3 and GHC-8.0 are happy with the difference. I'm surprised this is accepted at all. Looks like hogwash to me. I think you should post a bug report. Ok, but then GHC must not warn about the unused argument of Repr. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
suppress warning "Defined but not used: type variable ‘x’" in GHC-8.0
GHC-8.0 emits several new warnings of this kind: Defined but not used: type variable ‘x’ for declarations like type instance Snd x y = y Enthusiastically, I started to replace unused type function arguments by underscores, only to find out that older GHC versions do not accept that. With what option can I disable this warning? Or can it be removed from -Wall for now?___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: suppress warning "Defined but not used: type variable ‘x’" in GHC-8.0
On Sat, 9 Jan 2016, Carter Schonwald wrote: Have you tried _x instead? Ah, this solves the problem! Almost. I have an instance like this one: instance (Natural n) => Num.Integer (Un n) where type Repr (Un _n) = Unary GHC-7.6.3 and GHC-7.4.2 complain: Type indexes must match class instance head Found `Un _n' but expected `Un n' In the type synonym instance declaration for `Num.Repr' In the instance declaration for `Num.Integer (Un n)' GHC-7.8.4, GHC-7.10.3 and GHC-8.0 are happy with the difference. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: Optimization of IORefs and STRefs - comparison to g++
How about just using alloca, peek and poke - like C guys do in order to get C's speed? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: [Haskell] [Haskell-beginners] DOOM rewritten in the Haskell programming language.
On Mon, 7 Dec 2015, Patrick Redmond wrote: I'd also like to show support and participate in building this out if work is needed. Contact me when/if that happens! haskell@haskell.org is an announcement list. Please continue discussion in haskell-cafe etc. ___ Haskell mailing list Haskell@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell
Re: [Haskell-cafe] record field names vs. -fwarn-unused-binds
On Tue, 3 Nov 2015, Evan Laforge wrote: I can work around by putting underscores on field names I haven't used yet, but it's a hassle to go edit them when I want to use them. I do it this way and I do not consider it a work-around. The underscore is just the shortest way to say that a record field name is not used. It's shorter than any pragma could be. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: [Haskell] There has been discussion on matrix operations and cache thrashing; does management think using Haskell would lead to cash thrashing?
On Mon, 16 Mar 2015, KC wrote: There has been discussion on matrix operations and cache thrashing; does management think using Haskell would lead to cash thrashing? What could change management's mind? Unfortunately I don't understand the question, but in any case I think that better fits to haskell-c...@haskell.org than haskell@haskell.org ___ Haskell mailing list Haskell@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell
Re: [Haskell] Constraint Satisfaction Problem
On Wed, 4 Mar 2015, K Sai Anirudh wrote: Hello, I tried to solve simple constraint satisfaction problem. This is my code http://pastebin.com/VAaRYSEA ; . This gives solution for present list of domains, but when I change the domain of 'd' in the list 'ld' then I get error. I think the error is in line 52. I indexed the first value, but I tried filtering the results where all the variables are assigned and I get error. I think this fits better to Haskell Cafe haskell-c...@haskell.org where I send this reply, too.___ Haskell mailing list Haskell@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell
Re: [Haskell] Rank-N types with (.) composition
On Tue, 10 Feb 2015, Tyson Whitehead wrote: I came across something that seems a bit strange to me. Here is a simplified version (the original was trying to move from a lens ReifiedFold to a lens-action ReifiedMonadicFold) You are on Haskell@haskell.org here. Could you please move to haskell-cafe? ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell] ANN: patch-image
Right after the announcement of the latest version of Accelerate I like to announce an application build using that framework: patch-image assembles a big image from several overlapping parts. http://hackage.haskell.org/package/patch-image Now, let me extract the beginning of the docs: Compose a collage from overlapping image parts. In contrast to Hugin, this is not intended for creating panoramas from multiple photographies, but instead is specialised to creating highly accurate reconstructions of flat but big image sources, like record covers, posters or newspapers. It solves the problem that your scanner may be too small to capture a certain image as a whole. . This is the workflow: Scan parts of an image that considerably overlap. They must all be approximately oriented correctly. The program uses the overlapping areas for reconstruction of the layout of the parts. If all parts are in the directory @part@ then in the best case you can simply run: . patch-image --output=collage.jpeg part/*.jpeg . If you get blurred areas, you might enable an additional rotation correction: . patch-image --finetune-rotate --output=collage.jpeg part/*.jpeg Currently it depends on CUDA although this is not strictly necessary. ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[haskell art] HaL-9 registration open
A message for German Haskell users follows: HaL ist ein lokaler Haskell-Workshop mit überregionaler Bedeutung, der nun bereits das 9. Mal stattfindet. Dieses Jahr laden wir für den 20. Juni ins Institut für Informatik an der Martin-Luther-Universität Halle-Wittenberg ein. Das Programm für HaL-9 kann man herunterladen von: http://code.haskell.org/hal/09-2014/druck/programm.pdf Es wird noch kleinere Änderungen und Erweiterungen geben. Das endgültige Programm werden wir beim Empfang austeilen. Anmelden kann man sich unter: http://sim.mathematik.uni-halle.de:8080/hal9/ Anmeldeschluss ist 2014-06-11. Frühes Anmelden sichert Plätze in den beliebtesten Tutorien! Viele Grüße Henning Thielemann -- Read the whole topic here: Haskell Art: http://lurk.org/r/topic/6sT8bnDabQ3yRxF8plXb9z To leave Haskell Art, email haskell-...@group.lurk.org with the following email subject: unsubscribe
[Haskell] HaL-9 registration open
A message for German Haskell users follows: HaL ist ein lokaler Haskell-Workshop mit überregionaler Bedeutung, der nun bereits das 9. Mal stattfindet. Dieses Jahr laden wir für den 20. Juni ins Institut für Informatik an der Martin-Luther-Universität Halle-Wittenberg ein. Das Programm für HaL-9 kann man herunterladen von: http://code.haskell.org/hal/09-2014/druck/programm.pdf Es wird noch kleinere Änderungen und Erweiterungen geben. Das endgültige Programm werden wir beim Empfang austeilen. Anmelden kann man sich unter: http://sim.mathematik.uni-halle.de:8080/hal9/ Anmeldeschluss ist 2014-06-11. Frühes Anmelden sichert Plätze in den beliebtesten Tutorien! Viele Grüße Henning Thielemann ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell] Automated YouTube uploads
In case I did not announce it before - I wrote a set of two small programs that upload videos to YouTube. It is useful in two situations: 1. Upload a list of videos with metadata fetched from a spreadsheet. 2. Upload from a remote machine without a graphical browser. http://hackage.haskell.org/package/youtube You need 'curl' to be installed and you need to register for a YouTube developer key. ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: can't load .so/.DLL - undefined symbol
Am 17.03.2014 15:33, schrieb Henning Thielemann: Am 17.03.2014 10:22, schrieb Simon Marlow: package. Perhaps you have a copy of that module on the search path somewhere, or inside the alsa-seq package? This would confirm how I understood the linker message. Then I guess that compiling all packages at once in a single build dir with cabal was the problem. The command line was like: $ cabal install --builddir=/tmp/dist --with-ghc=ghc7.8.0.20140228 poll alsa-seq pkg1 pkg2 pkg3 ... After compiling the packages separately the problem has gone. I think I know what the problem was: 'poll' uses HSC as preprocessor, thus preprocessed files were stored in dist. This way the preprocessed source files were available to GHC when compiling 'alsa' and thus it was compiled again, but not registered in the 'alsa' package. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
[Haskell] HaL-9 - Call for Contributions
HaL ist ein lokaler Haskell-Workshop mit überregionaler Bedeutung, der nun bereits das 9. Mal stattfindet. Dieses Jahr laden wir für den 20. Juni ins Institut für Informatik an der Martin-Luther-Universität Halle-Wittenberg ein. Wir suchen Beiträge zu Haskell im Besonderen und der funktionalen Programmierung im Allgemeinen, aber auch Anknüpfungen an andere Programmierparadigmen. Dabei interessieren wir uns unter anderem für die Themenbereiche * Neues von Sprache, Bibliotheken, Werkzeugen, * Anwendungen von Kunst bis Industrie, * Lehre und Forschung an Schulen und Hochschulen. Die Beiträge können präsentiert werden als * Tutorium (etwa 90 min) * Vortrag (etwa 30 min) * Demonstration, künstlerische Aufführung Die Veranstaltungssprache ist Deutsch, nach Absprache auch Englisch. Presentations will be given in German but we can switch to English if requested. Bitte reichen Sie Kurzfassungen der Beiträge ein (max. 3 Seiten), die dem Programmkomitee eine Einschätzung ermöglichen, sowie eine knappe Zusammenfassung von etwa 100 Wörtern. Teilnehmer des Workshops sind Interessenten (keine Erfahrung mit Haskell oder funktionaler Programmierung), Anfänger (wenig Erfahrung) und Experten. Wir bitten die Vortragenden, die Zielgruppe des Beitrags anzugeben und die nötigen Vorkenntnisse zu beschreiben. Bei Tutorien sollen Teilnehmer auf eigenen Rechnern arbeiten. Bitte beschreiben Sie dazu die vorher zu installierende Software. Senden Sie die Beitragsvorschläge als PDF-Dokument bis zum 27. April 2014 an hal-commit...@iba-cg.de Wir werden Ihnen bis zum 9. Mai mitteilen, ob wir Ihren Beitrag in das Programm aufnehmen. Für das Organisationsteam Henning Thielemann ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: positive type-level naturals
Hi Iavor, Am 19.03.2014 22:27, schrieb Iavor Diatchki: I see two separate issues that show in what you describe, so it might be useful to discuss them separately: Thank you and Richard Eisenberg for the detailed explanations. For now, I have just fooled GHC by unsafeCoerceing dictionaries as suggested by Richard. A general comment: the function `withVec` is fairly tricky because it introduces vectors whose length is not known statically. This tends to require much more advanced tools because one has to do real mathematical reasoning about abstract values. Of course, sometimes there is no way around this, but on occasion one can avoid it. For example, in the expression `withVec 1 [2,3,4]` we know exactly the length of the vectors involved, so there is no reason to resort to using fancy reasoning. The problem is that Haskell's list notation does not tell us the length of the list literal. One could imagine writing a little quasi-quoter that will allow us to write things like `[vec| 1, 2, 3, 4]`, which would generate the correctly sized vector. Then you can append and manipulate these as usual and GHC will be able to check the types because it only has to work with concrete numbers. This is not a great program verification technique, but it certainly beats having to do it manually :-) For this problem I have a simple solution. I think that the infix list syntax is underrated. If you are used to write 1:2:3:4:[], then you have no problem writing: x = 1:.2:.3:.4:.End with data OneMore f a = a :. f a data End a = End Then x has type (OneMore (OneMore (OneMore (OneMore End))) a) and GHC can easily derive the static list length from it. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: can't load .so/.DLL - undefined symbol
Am 17.03.2014 10:22, schrieb Simon Marlow: On 11/03/2014 22:11, Henning Thielemann wrote: I am trying to understand the following linker message. I have started GHCi, loaded a program and try to run it: Main main ... Loading package poll-0.0 ... linking ... done. Loading package alsa-seq-0.6.0.3 ... can't load .so/.DLL for: /var/cabal/lib/x86_64-linux-ghc-7.8.0.20140228/alsa-seq-0.6.0.3/libHSalsa-seq-0.6.0.3-ghc7.8.0.20140228.so (/var/cabal/lib/x86_64-linux-ghc-7.8.0.20140228/alsa-seq-0.6.0.3/libHSalsa-seq-0.6.0.3-ghc7.8.0.20140228.so: undefined symbol: alsazmseqzm0zi6zi0zi3_SystemziPosixziPoll_zdfStorableFd_closure) I assume that GHCi wants to say the following: The instance Storable Fd defined in module System.Posix.Poll cannot be found in the shared object file of the alsa-seq package. That's certainly true because that module is in the package 'poll' and not in 'alsa-seq'. But 'alsa-seq' imports 'poll'. What might be the problem? It seems to have the idea that System.Posix.Poll is part of the alsa-seq package. Perhaps you have a copy of that module on the search path somewhere, or inside the alsa-seq package? This would confirm how I understood the linker message. Then I guess that compiling all packages at once in a single build dir with cabal was the problem. The command line was like: $ cabal install --builddir=/tmp/dist --with-ghc=ghc7.8.0.20140228 poll alsa-seq pkg1 pkg2 pkg3 ... After compiling the packages separately the problem has gone. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
type-level induction on Nat
Am 16.03.2014 09:40, schrieb Christiaan Baaij: To answer the second question (under the assumption that you want phantom-type style Vectors and not GADT-style): That works, someNatVal was the missing piece. Now the natural next question is how to perform type-level induction on Nat. This page mentions the Nat1 type, a unary representation of natural numbers: https://ghc.haskell.org/trac/ghc/wiki/TypeNats/MatchingOnNats Since the unary natural number kind so ubiquituous in examples, is there a recommended module to import it from, which also contains the injectivity magic of FromNat1? I cannot see it in: http://hackage.haskell.org/package/base-4.7.0.0/candidate/docs/GHC-TypeLits.html although it seems to have been there: http://co-dan.github.io/base-docs/src/GHC-TypeLits.html ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: type-level induction on Nat
Am 16.03.2014 11:29, schrieb Henning Thielemann: Since the unary natural number kind so ubiquituous in examples, is there a recommended module to import it from, which also contains the injectivity magic of FromNat1? I cannot see it in: http://hackage.haskell.org/package/base-4.7.0.0/candidate/docs/GHC-TypeLits.html although it seems to have been there: http://co-dan.github.io/base-docs/src/GHC-TypeLits.html Nat1 was removed here: https://github.com/ghc/packages-base/commit/5eaba365ff2354d3231f049866964d25f245ede2 but commit message does not tell where it was moved. :-( Obviously it was not moved to singletons. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
positive type-level naturals
Am 16.03.2014 09:40, schrieb Christiaan Baaij:
To answer the second question (under the assumption that you want
phantom-type style Vectors and not GADT-style):
Now I like to define non-empty vectors. The phantom parameter for the
length shall refer to the actual vector length, not to length-1, for
consistency between possibly empty and non-empty vectors.
I have modified your code as follows:
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE TypeFamilies #-}
module PositiveNat where
import Data.Proxy (Proxy(Proxy))
import GHC.TypeLits
(Nat, SomeNat(SomeNat), KnownNat, someNatVal, natVal,
type (=), type (+))
data Vector (n :: Nat) a = Vector a [a]
withVector ::
forall a b.
a - [a] -
(forall n . (KnownNat n, 1=n) = Vector n a - b) - b
withVector x xs f =
case someNatVal $ toInteger $ length xs of
Nothing - error static/dynamic mismatch
Just (SomeNat (_ :: Proxy m)) - f (Vector x xs :: Vector (m+1) a)
vecLen :: forall n . KnownNat n = Vector n Integer - Integer
vecLen _ = natVal (Proxy :: Proxy n)
-- withVector vecLen [1,2,3,4]
-- 4
GHC-7.8 complains with:
PositiveNat.hs:23:40:
Could not deduce ((1 GHC.TypeLits.=? (n + 1)) ~ 'True)
from the context (KnownNat n)
bound by a pattern with constructor
SomeNat :: forall (n :: Nat). KnownNat n = Proxy n -
SomeNat,
in a case alternative
at PositiveNat.hs:23:13-34
In the expression: f (Vector x xs :: Vector (m + 1) a)
In a case alternative:
Just (SomeNat (_ :: Proxy m))
- f (Vector x xs :: Vector (m + 1) a)
In the expression:
case someNatVal $ toInteger $ length xs of {
Nothing - error static/dynamic mismatch
Just (SomeNat (_ :: Proxy m))
- f (Vector x xs :: Vector (m + 1) a) }
How can I convince GHC that n+1 is always at least 1?
When I remove the (1=n) constraint, I still get:
PositiveNat.hs:23:40:
Could not deduce (KnownNat (n + 1)) arising from a use of ‘f’
from the context (KnownNat n)
bound by a pattern with constructor
SomeNat :: forall (n :: Nat). KnownNat n = Proxy n -
SomeNat,
in a case alternative
at PositiveNat.hs:23:13-34
In the expression: f (Vector x xs :: Vector (m + 1) a)
In a case alternative:
Just (SomeNat (_ :: Proxy m))
- f (Vector x xs :: Vector (m + 1) a)
In the expression:
case someNatVal (toInteger (length xs)) of {
Nothing - error static/dynamic mismatch
Just (SomeNat (_ :: Proxy m))
- f (Vector x xs :: Vector (m + 1) a) }
That is, I also have to convince GHC, that if (KnownNat n) then (n+1) is
also KnownNat. How to do that?
___
Glasgow-haskell-users mailing list
Glasgow-haskell-users@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: positive type-level naturals
Am 16.03.2014 13:48, schrieb Dan Frumin: This is just a wild guess, but is there a possibility that (1+n) will produce less complaints than (n+1)? unfortunately no ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: positive type-level naturals
Am 16.03.2014 14:35, schrieb Carter Schonwald: You can't with type lits. The solver can only decide concrete values :( I hoped that with type-level natural numbers all my dreams would become true. :-) I'd be also happy if I could manually provide the proof for 1=n+1 and more complicated statements like n+n=2*n and n0 m0 = n*m0. You'll have to use a concrete peano Nats type instead. That is, I may as well stay with the existing type-level number packages? I've been toying with the idea that the type lits syntax should be just that, a type level analogue of from integer that you can give to user land types, but I'm not going to suggest that till 7.8 is fully released. Seems reasonable. By the way, is the GHC Nat kind defined by data promotion or is it a special kind with an efficient internal representation? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: positive type-level naturals
Am 16.03.2014 20:02, schrieb Carter Schonwald: respectfully, The current typeLits story for nats is kinda a fuster cluck to put it politely . We have type lits but we cant use them (well, we can't compute on them, which is the same thing). For the past 2 years, every ghc release cycle, I first discover, then have to communicate to everyone else you can't compute on type lits. A minimal invasive solution would be to provide a kind for unary type level numbers and type functions that convert between Unary and Nat. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
importing (=) from GHC.TypeLits
I want to import Nat and type-level (=) from GHC.TypeLits: import GHC.TypeLits (Nat, (=)) Nat is found this way, but (=) is not: Module ‘GHC.TypeLits’ does not export ‘(=)’ What is the trick? The doc only shows the anonymous import: http://www.haskell.org/ghc/docs/7.8.1-rc2/html/users_guide/promotion.html ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
converting type-level natural numbers to data-level
Am 15.03.2014 18:13, schrieb adam vogt: http://www.haskell.org/ghc/docs/7.8.1-rc2/html/users_guide/syntax-extns.html#explicit-namespaces is the trick Great, this works! Now I run into the next problem: How can I convert a type-level natural number into a data-level number? The Trac-Wiki mentions singletons: https://ghc.haskell.org/trac/ghc/wiki/TypeNats/Basics and the base package of GHC-7.6 exports the Sing class: http://hackage.haskell.org/package/base-4.6.0.1/docs/GHC-TypeLits.html but it seems to have gone in GHC-7.8. :-( ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
converting data-level natural numbers to type-level
Am 15.03.2014 19:17, schrieb Erik Hesselink: I think most of the singletons stuff has been moved to the 'singletons' package [0]. Yes, that's it. It means that all Nat related functionality in 'singletons' can be implemented using GHC.TypeLits - interesting. Using the library I succeeded to convert type-level Nats to data-level Integer. Now I need the other way round. I want to implement: withVector :: [a] - (forall n. (KnownNat n) = Vector n a - b) - b I want to have the (KnownNat n) constraint, since I want to call 'sing' within the continuation and this requires (KnownNat n). I guess, in order to implement withVector I need toSing, but this one does not give me a (KnownNat n). :-( Thus I have two questions: What is the meaning of KnownNat and how can I implement withVector? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
[Haskell] HaL-9 - regional Haskell meeting in Halle/Saale, Germany, 2014-06-20 - Save the date
Save the date for our local Haskell meeting in Halle/Saale, Germany, presenting tutorials, talks, demonstrations ... everything you like. Workshop language is German (mainly), and English (by request). Switching to German: - Was: Haskell-Treffen HaL-9 Wann: Freitag, 2014-06-20 Wo: Institut für Informatik an der Martin-Luther-Universität in Halle an der Saale Der offizielle Aufruf zum Einreichen von Beiträgen folgt demnächst. Mit besten Grüßen Henning Thielemann ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
GHC-7.8 warning on rules that may not fire
With GHC-7.8 I get lots of warnings like src/Foo/Bar.hs:215:6: Warning: Rule foo may never fire because ‘bar’ might inline first Probable fix: add an INLINE[n] or NOINLINE[n] pragma on ‘bar’ So far I thought that rewrite RULES always have precedence to INLINE. Has this changed? I hesitate to follow the advice of adding phase numbers in bracket because I consider these phase numbers a quite fragile and non-modular solution (like precedence numbers for infix operators). I have found: https://ghc.haskell.org/trac/ghc/wiki/Plugins/Phases Is this still considered for future developments? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: GHC-7.8 warning on rules that may not fire
Am 14.03.2014 18:05, schrieb Simon Peyton Jones: You may think they are fragile, but not as fragile as saying nothing and hoping for the best, which is *super*-fragile. You can't rely on rules to take priority, because the rule only fires if it matches, and it may only match if some other inlining has taken place. (We tried that originally.) Ok, how shall I choose n in INLINE[n]? Is there a meaning of the phase numbers? I guess it is important to adhere to some conventions in order to work together with other libraries. If I understand correctly I can alter the number of phases with the -fsimplifier-phases option - how can I choose phase numbers for INLINE that are universally reasonable? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
can't load .so/.DLL - undefined symbol
I am trying to understand the following linker message. I have started GHCi, loaded a program and try to run it: Main main ... Loading package poll-0.0 ... linking ... done. Loading package alsa-seq-0.6.0.3 ... can't load .so/.DLL for: /var/cabal/lib/x86_64-linux-ghc-7.8.0.20140228/alsa-seq-0.6.0.3/libHSalsa-seq-0.6.0.3-ghc7.8.0.20140228.so (/var/cabal/lib/x86_64-linux-ghc-7.8.0.20140228/alsa-seq-0.6.0.3/libHSalsa-seq-0.6.0.3-ghc7.8.0.20140228.so: undefined symbol: alsazmseqzm0zi6zi0zi3_SystemziPosixziPoll_zdfStorableFd_closure) I assume that GHCi wants to say the following: The instance Storable Fd defined in module System.Posix.Poll cannot be found in the shared object file of the alsa-seq package. That's certainly true because that module is in the package 'poll' and not in 'alsa-seq'. But 'alsa-seq' imports 'poll'. What might be the problem? It's a rather big example that fails here, whereas the small examples in alsa-seq package work. Thus I first like to know what the message really means, before investigating further. I installed many packages at once with cabal-install using a single build directory, like: $ cabal install --builddir=/tmp/dist --with-ghc=ghc7.8.0.20140228 poll alsa-seq pkg1 pkg2 pkg3 ... ? Can this cause problems? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
[Haskell] ANN: unicode-0.0
The first announcement this year: The 'unicode' package contains functions for construction of various characters like: * block graphic elements * frame elements * fractions * subscript and superscript characters http://hackage.haskell.org/package/unicode The package is simple Haskell 2010. For example usage see the included 'visualize' example, buildable with 'cabal install -fbuildExamples', and http://code.haskell.org/~thielema/set-cover/example/Domino.hs ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell] Haskell can sing
Hi all, it's again Advent time and I took the opportunity to program another song for you. Those who liked last year's songs [1,2,3] may also be interested in the new one: http://www.youtube.com/watch?v=0EQCgi5qa3E Alta trinita beata It employs the great Haskell live sequencer and a new speech synthesizer that I developed with Haskell and LLVM. You find additional information in the video description. Best, Henning [1] http://www.haskell.org/pipermail/haskell/2012-December/023591.html [2] http://www.youtube.com/watch?v=-fmxHM69zgI [3] http://www.youtube.com/watch?v=O5k0wUh0lj8 ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell-cafe] Richard Bird and the fast nub function
In Richard Bird's Functional Pearls in Algorithm Design there is chapter 10 Removing duplicates which is about a fast and sorting variant of 'nub'. After reading the introduction of the chapter I answered mentally Set.toAscList . Set.fromList - next chapter please. However after the introduction eight pages follow that develop an efficient algorithm for the problem. I suspected there might be the additional difficulty of not using the standard Set type, however on page 70 the common Set API is imported. In the final remarks of the chapter Bird writes: A nagging doubt remains that there might be a much simpler solution to such a simply stated problem. But so far I have not been able to find one. Now I am lost. Can someone tell me, how the task differs from what Set.toAscList . Set.fromList does? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANN: Cabal v1.18.0 released
On Wed, 4 Sep 2013, Johan Tibell wrote: * GHCi support. It's now much easier to use ghci when developing your packages, especially if those packages require preprocessors (e.g. hsc2hs). That's a great feature! How can I configure Cabal to start ghci with certain options? I like to enable more warnings. I could not find a documentation for the Cabal config file. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell] ANN: set-cover solves Sudoku, Soma cube, 8 Queens etc.
I have prepared the package set-cover for solving exact set cover problems. It includes example programs for solving Sudoku, 8 Queens, Soma Cube, Tetris Cube, Cube of L's, and Logika's Baumeister puzzle. Please refer to these examples for learning how the library works. The solver is generic with respect to the representation of sets. You may either use the high-level Set type from containers package or low-level bit vectors. http://hackage.haskell.org/package/set-cover The package is simple Haskell 2010. ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [Haskell-cafe] sequence causing stack overflow on pretty small lists
On Tue, 27 Aug 2013, John Lato wrote: [1] Most people are physically incapable of reading documents that explain why what they want to do won't work. Even if people did read the documentation, I suspect that the people most in need of the information would be the least likely to understand how it applies to their situation. Plus: I don't expect that programmers read the documentation of 'sequence' and 'mapM' again every time they use the function. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Extending Type Classes
The problem of refinement of type classes annoys me from time to time when I work on the NumericPrelude. It is an experimental type class hierarchy for mathematical types. Sometimes a new data type T shall be implemented and it turns out that you can implement only a part of all methods of a certain class. Then a natural step is to split the class into two classes A and B: 'A' contains the methods we can implement for T and 'B' contains the remaining methods and 'B' is a sub-class of 'A'. First, this means that all client code has to be rewritten. Second, code for instances becomes very lengthy, because over the time code tends to contain one instances for every method. However the many small instances actually carry information: Every instance has its specialised constraints. E.g. you would certainly try to use only Applicative constraints in an Applicative instance and not Monad constraints. However, if there is a way to define Applicative and Monad instances in one go, the Applicative instance may get Monad constraints. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GHC and backwards compatibility
If you use $ cabal install --constraint=array installed then cabal-install is forced to use the installed version of array. If a package conflicts with this version, then it will report the conflicting packages. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Renumbered mailing list posts
Am 10.08.2013 21:48, schrieb Austin Seipp: Henning, Thanks for the report. I'm currently investigating this, and think it should be possible to keep all of the old URLs intact. Thank you! This would be really really great! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Renumbered mailing list posts
Recently I found that links from Google search results to archive Haskell-Cafe messages are invalid. The messages are still there, but got a different number. E.g. the search result says: http://www.haskell.org/pipermail/haskell-cafe/2011-February/089455.html But the message is at http://www.haskell.org/pipermail/haskell-cafe/2011-February/088146.html Also links from Haskell-Wiki articles to the Haskell-Cafe archive are invalid now. This is very very very bad, since I used tons of such URLs in Wiki articles and it is very hard to find the message I referred to, if the URL does not work anymore. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANN: Monad.Reader Issue 22
On Wed, 7 Aug 2013, Edward Z. Yang wrote: I am pleased to announce that Issue 22 of the Monad Reader is now available. http://themonadreader.files.wordpress.com/2013/08/issue22.pdf Issue 22 consists of the following two articles: * Generalized Algebraic Data Types in Haskell by Anton Dergunov * Error Reporting Parsers: a Monad Transformer Approach by Matt Fenwick and Jay Vyas * Two Monoids for Approximating NP-Complete Problems by Mike Izbicki That is, there are three kinds of Haskellers: The ones who can count and the others who cannot. :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] [ANN] Initial release of the threepenny-gui library, version 0.1.0.0
On Sun, 21 Jul 2013, Sergey Mironov wrote: Hi, I have a Path problem when installing threepenny-gui from Hackage. Probably somtething trivial. I have written a small script cabal-upload that tries to compile a package before uploading it to Hackage. That helps to assert that all required files are registered in the cabal file. http://hackage.haskell.org/package/cabal-scripts ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
nightly builds: empty directory
The page http://www.haskell.org/ghc/download refers to directories for the nightly builds, that are actually empty: http://www.haskell.org/ghc/dist/current/dist/ http://www.haskell.org/ghc/dist/stable/dist/ :-( ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell] recursion patterns?
On Wed, 15 May 2013, 7stud wrote: Well, my question does not meet the standards for a question at stackoverflow: (I am a haskell beginner) Then you might want to post your question to haskell-beginners mailing list. Is one solution more efficient than the other? I believe my solution is tail recursive, but it's my understanding that compilers can now optimize just about anything into tail recursion. The first solution works for infinite lists and the second one does not. It's really like foldr vs. foldl. ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell-cafe] meaning of referential transparency
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 reference and transparency in a dictionary, but I don't know why these words were chosen as name for this defined property. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] closed world instances, closed type families
Recently I needed to define a class with a restricted set of instances.
After some failed attempts I looked into the DataKinds extension and in
Giving Haskell a Promotion I found the example of a new kind Nat for
type level peano numbers. However the interesting part of a complete case
analysis on type level peano numbers was only sketched in section 8.4
Closed type families. Thus I tried again and finally found a solution
that works with existing GHC extensions:
data Zero
data Succ n
class Nat n where
switch ::
f Zero -
(forall m. Nat m = f (Succ m)) -
f n
instance Nat Zero where
switch x _ = x
instance Nat n = Nat (Succ n) where
switch _ x = x
That's all. I do not need more methods in Nat, since I can express
everything by the type case analysis provided by switch. I can implement
any method on Nat types using a newtype around the method which
instantiates the f. E.g.
newtype
Append m a n =
Append {runAppend :: Vec n a - Vec m a - Vec (Add n m) a}
type family Add n m :: *
type instance Add Zero m = m
type instance Add (Succ n) m = Succ (Add n m)
append :: Nat n = Vec n a - Vec m a - Vec (Add n m) a
append =
runAppend $
switch
(Append $ \_empty x - x)
(Append $ \x y -
case decons x of
(a,as) - cons a (append as y))
decons :: Vec (Succ n) a - (a, Vec n a)
cons :: a - Vec n a - Vec (Succ n) a
The technique reminds me on GADTless programming. Has it already a name?
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] closed world instances, closed type families
On Tue, 2 Apr 2013, Daniel Peebles wrote: It seems very similar to Ryan Ingram's post a few years back (pre-TypeNats): http://www.haskell.org/pipermail/haskell-cafe/2009-June/062690.html The main difference is that he introduces the knowledge about zero vs. suc as a constraint, and you introduce it as a parameter. In fact, his induction function (which is probably what I'd call it too) is almost identical to your switch. The answer to his post by Miguel Mitrofanov contains a caseNat that is exactly my 'switch'. I see I am four years late. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANN: psqueue-benchmarks - benchmarks of priority queue implementations
On Fri, 29 Mar 2013, Niklas Hambüchen wrote: (This is a slightly detailed email. If you are the maintainer of one of the packages benchmarked here, you might want to read it though.) Could you please put your experiences the Wiki? This would help others to choose a package. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANN: psqueue-benchmarks - benchmarks of priority queue implementations
On Fri, 29 Mar 2013, Louis Wasserman wrote: Bearing in mind that I haven't looked at this in several years... Why did you switch from queuelike to pqueue? Because I liked the API better? Could you put the code up somewhere manageable (repo)? I had it up on darcs, but since that's not there any more, I don't have any more source history than you do. Was it on code.haskell.org? Then it might have been moved to a non-web directory after the last attack 2011. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANN: psqueue-benchmarks - benchmarks of priority queue implementations
On Fri, 29 Mar 2013, Niklas Hambüchen wrote: On 29/03/13 20:14, Henning Thielemann wrote: Was it on code.haskell.org? Then it might have been moved to a non-web directory after the last attack 2011. Does that mean the repo is still there without web access I assume that. or gone? If the original author has not deleted it, then it should still be somewhere: http://www.haskell.org/pipermail/haskell-cafe/2011-February/089352.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANN: monad-bool 0.1
On Tue, 22 Jan 2013, John Wiegley wrote: Use 'onlyIf' with AndM and AndMT to guard later statements, which are only evaluated if every preceding 'onlyIf' evaluates to True. For example: foo :: AndM Int foo = do onlyIf (True == True) return 100 onlyIf (True == True) return 150 onlyIf (True == False) return 200 When run with `evalAndM foo (-1)` (where (-1) provides a default value), 'foo' returns 150. Does the And monad fulfill the monad laws? In a proper monad an interim (return x) (without a '-') is a no-op. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] Silent error
On Mon, 21 Jan 2013, mip...@meta.ua wrote: The program looks like this: --*** factorial :: Int-Int factorial n = product [1..n] main = do print $ factorial 50 --*** And that yields 0 (no errors). Is it a bug or feature? :) This question is certainly better posted to haskell-cafe. The answer is: Int has limited bitsize (32 ord 64 bit depending on your machine), thus it computes factorial modulo 2^32 or 2^64. You can get the correct result by replacing Int by Integer. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell] Importing Repa library
On Thu, 3 Jan 2013, Емануела Моллова wrote: Hello! :) I think you should better post your question to haskell-c...@haskell.org. Then I put this script import qualified Data.Array.Repa as R :m +Data.Array.Repa Z into the file file.hs, This is GHCi syntax, but it is not a valid Haskell module as indicated by the .hs filename extension. opened WinGHCi and loaded the file, and then evaluated it, but what I get is: Could not find module `Data.Array.Repa' Perhaps you meant Data.Array.Base (from array-0.4.0.0) Data.Array.IO (from array-0.4.0.0) Data.Array.ST (from array-0.4.0.0) Use -v to see a list of the files searched for. Failed, modules loaded: none. I wonder why it loads file.hs at all. I would expect that it gives a syntax error. Also ghc-pkg list repa says: WARNING: cache is out of date: C:/Program Files/Haskell Platform/2012.4.0.0\lib\package.conf.d\package.cache use 'ghc-pkg recache' to fix. C:/Program Files/Haskell Platform/2012.4.0.0\lib\package.conf.d: C:\Users\Faery\AppData\Roaming\ghc\i386mingw32-7.4.2\package.conf.d: Since 'repa' is not listed, it was not installed successfully. This would be consistent with the Could not find module message of GHCi. You may post the output of the 'cabal install repa' run. ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [Haskell-cafe] [Haskell] Importing Repa library
On Thu, 3 Jan 2013, Емануела Моллова wrote: Hello! :) I think you should better post your question to haskell-cafe@haskell.org. Then I put this script import qualified Data.Array.Repa as R :m +Data.Array.Repa Z into the file file.hs, This is GHCi syntax, but it is not a valid Haskell module as indicated by the .hs filename extension. opened WinGHCi and loaded the file, and then evaluated it, but what I get is: Could not find module `Data.Array.Repa' Perhaps you meant Data.Array.Base (from array-0.4.0.0) Data.Array.IO (from array-0.4.0.0) Data.Array.ST (from array-0.4.0.0) Use -v to see a list of the files searched for. Failed, modules loaded: none. I wonder why it loads file.hs at all. I would expect that it gives a syntax error. Also ghc-pkg list repa says: WARNING: cache is out of date: C:/Program Files/Haskell Platform/2012.4.0.0\lib\package.conf.d\package.cache use 'ghc-pkg recache' to fix. C:/Program Files/Haskell Platform/2012.4.0.0\lib\package.conf.d: C:\Users\Faery\AppData\Roaming\ghc\i386mingw32-7.4.2\package.conf.d: Since 'repa' is not listed, it was not installed successfully. This would be consistent with the Could not find module message of GHCi. You may post the output of the 'cabal install repa' run. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell] Haskell from Glorious Kingdom
Hi Haskellers, since it is Advent time you might like to listen to a song that I programmed and performed with the Haskell Live-Sequencer [1]: http://www.youtube.com/watch?v=O5k0wUh0lj8 and you might want to check the Live-Sequencer, too. The Live-Sequencer allows to compose songs in Haskore style interactively. The most important feature is that you may alter the running program/song and that you can do so together with many people via network. Best, Henning [1] http://www.haskell.org/haskellwiki/Live-Sequencer ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [Haskell] Status of Haskell'?
On Sat, 1 Dec 2012, Gábor Lehel wrote: On Fri, Nov 30, 2012 at 11:06 PM, Nate Soares n...@so8r.es wrote: +1. I agree generally with Gabor's points -- GHC is in the drivers seat. But at some point we should take a look at all the things GHC has made that did pay off and that are good and make them official. I'd very much like to see that endorsement happen soon, even if it's not aggressive. Well, I'm not so sure it's a great idea to just bake what GHC does at this moment (for any particular extension) into the standard without really thinking about it. Even then, you have to figure out, in great detail, what GHC does, and write it all down! That's not negligible effort, either. And the alternative is to also publicly discuss and hash all of it out down to the little tiny gritty stuff. But wanting to write a new standard (big effort!) just to get rid of some pragmas and make people feel better (small payoff!) feels like a mismatch to me. In my opinion it is a good thing if people feel bad about a lot of LANGUAGE pragmas at top of their modules. For me the number of LANGUAGE pragmas is a (reciprocal) measure of how much effort the programmer invested in cleaning up the code. In the past I removed a lot of FlexibleInstances, FlexibleContexts, UndecidableInstances, TypeSynonymInstances, PatternGuards and _improved_ the code this way. The need for generalized instances is often caused by badly designed classes or types. For me many extensions are a way to get a working implementation quickly from which I can derive a simpler one by throwing out extensions successively. I would also like to tell students that if they need to enable language extensions (or specific set of extensions) then they are solving a task in a too complicated way. I like to support Gábors arguments. We should have multiple implementations before standardization. E.g. I remember how TypeFamilies have evolved over the time or how the interaction of the forall quantifier with ($) changed between versions of GHC - how can we get confidence that GHC implemented these features in the most reasonable way? ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [haskell-llvm] fatal error with ghci and llvm
On Fri, 23 Nov 2012, José Romildo Malaquias wrote: When experimenting with the module LLVM.Core in GHCi on my gentoo linux system, I have got a fatal error: $ ghci GHCi, version 7.6.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude :m + LLVM.Core Prelude LLVM.Core IntEQ Loading package llvm-base-3.0.1.0 ... GHCi runtime linker: fatal error: I found a duplicate definition for symbol LLVMAddAlwaysInlinerPass whilst processing object file /usr/lib64/llvm/libLLVMipo.a This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry. There are problems with the configure procedure of llvm-base. The configure file fetches the llvm-base.buildinfo.in file and replaces the variables with informations for your system. The result ends up in ~/.ghc/your-ghc-version/package.conf.d/llvm-base-3.0.0.1-some-hash.conf You may post the content of this file for further diagnostics. You said earlier that you use a custom path for llvm. Maybe you have conflicts between two versions, one in /usr/lib and one in /usr/local/lib? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] mtl-2.1 severly broken, cabal needs blacklisting
On Wed, 14 Nov 2012, Jean-Philippe Bernardy wrote: On Tue, Nov 13, 2012 at 11:39 PM, Andreas Abel andreas.a...@ifi.lmu.de wrote: On 13.11.12 11:13 PM, Jean-Philippe Bernardy wrote: Blacklisting equals releasing a bugfix. Not quite. I propose to *define* blacklisting as such. package-X.Y.Z.W is blacklisted if there exists package-X.Y.Z.V where V W (maybe I'm off by one position in the version number scheme here, but you get the idea) This rule is correct for packages following the Package Versioning Policy. Currently cabal-install and Cabal make no assumptions about the employed versioning scheme. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] mtl-2.1 severly broken, cabal needs blacklisting
On Tue, 13 Nov 2012, Bas van Dijk wrote: On 13 November 2012 17:27, Andreas Abel andreas.a...@ifi.lmu.de wrote: This calls for a means of blacklisting broken or malicious packages. cabal update should also pull a blacklist of packages that will never be selected by cabal install (except maybe by explicit user safety overriding). Maybe we can use the existing preferred-versions file that cabal-install uses: http://hackage.haskell.org/packages/archive/preferred-versions It is also possible to deprecate a package. Is it possible to deprecate a single version? I'm afraid that the user is also not warned if he installs a deprecated package. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: data-dword: Long binary words from short ones
On Thu, 11 Oct 2012, Mikhail Vorozhtsov wrote: I'm pleased to announce my new little library, data-dword[1]. It provides Template Haskell utilities for defining binary word data types from low and high halves, e.g. data Word96 = Word96 Word32 Word64 -- strictness is configurable data Int96 = Int96 Int32 Word64 What is the advantage over 'largeword' which does the same with plain Haskell 98? http://hackage.haskell.org/package/largeword ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] total Data.Map.! function
Hi Joachim, On Wed, 5 Oct 2012, Joachim Breitner wrote: On Wed, 3 Oct 2012, Henning Thielemann wrote: I wondered whether there is a brilliant typing technique that makes Data.Map.! a total function. That is, is it possible to give (!) a type, such that m!k expects a proof that the key k is actually present in the dictionary m? How can I provide the proof that k is in m? Same question for 'lab' (import Data.Graph.Inductive(lab)). That is, can there be a totalLab, with (totalLab gr = fromJust . lab gr) that expects a proof that the node Id is actually contained in a graph? I think it is possible to do this using the same trick that ST is using, i.e. rank 2 types. The problem is that this code is likely to be unwieldy to use, as the variable needs to change with every change to the map – but I guess if you create your map once and then use it in various places without modification, this can actually work. Thank you for your detailed answer! I thought about such a tagging method but was missing your idea of updating tags of existing keys in order to reflect the knowledge about newly added keys. Your solution will certainly work for the set of methods you have implemented. All of your methods extend the set of keys or preserve it. But what about deletion? The certificate that key k is contained in a Map must be invalidated by the deletion of k. How could I add this to your approach? Maybe I should track the operations applied to the keys of a map and provide algebraic simplifications, like so: insert :: Ord k = Tagged s k - v - Tagged m (Map k v) - Tagged (Insert s m) (Map k v) lookup :: Ord k = Tagged s k - Tagged (Insert s m) (Map k v) - v -- * example simplifications commuteInsert :: Tagged (Insert s0 (Insert s1 m)) (Map k v) - Tagged (Insert s1 (Insert s0 m)) (Map k v) simplifyInsertInsert :: Tagged (Insert s (Insert s m)) (Map k v) - Tagged (Insert s m) (Map k v) simplifyInsertDelete :: Tagged (Insert s (Delete s m)) (Map k v) - Tagged (Insert s m) (Map k v) simplifyDeleteInsert :: Tagged (Delete s (Insert s m)) (Map k v) - Tagged (Delete s m) (Map k v) example = lookup k0 $ commuteInsert $ insert k1 for $ insert k0 bar m I also thought about something like the exceptions trick. That is, a context like (ContainsKeyA k, ContainsKeyB k) = Map k x might tell that certain keys are in the Map. However, this would not only mean that I need a type class for every insertion, it would also not work reliably for deletion. If keyA = keyB, then deletion of keyA must also remove the ContainsKeyB constraint. :-( ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] total Data.Map.! function
I wondered whether there is a brilliant typing technique that makes Data.Map.! a total function. That is, is it possible to give (!) a type, such that m!k expects a proof that the key k is actually present in the dictionary m? How can I provide the proof that k is in m? Same question for 'lab' (import Data.Graph.Inductive(lab)). That is, can there be a totalLab, with (totalLab gr = fromJust . lab gr) that expects a proof that the node Id is actually contained in a graph? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Call to arms: lambda-case is stuck and needs your help (fwd)
I want to vote, too. I am ok with all of case of \case \of \case of For me single arguments are enough. We already have this restriction for 'case' and I can work around it simply by wrapping arguments in pairs temporarily (cf. curry $ \case ...). I vote against LambdaIf, since if-then-else is already unnecessary and can be written by ifThenElse, and LambdaIf is just ifThenElse with different parameter order. I vote against MultiCaseIf since it can be simply achieved by ifThenElse b1 a1 $ ifThenElse b2 a2 $ ifThenElse b3 a3 $ a4 http://www.haskell.org/haskellwiki/Case ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Why GHC doesn't warn about LHS nullary-constructor pattern bindings?
On Thu, 19 Jul 2012, Herbert Valerio Riedel wrote: Recently, I was a bit suprised that GHC didn't warn about useless `where` definitions such as the following when using `-Wall` (and I couldn't find a respective warning GHC CLI flag which would have enabled reporting a warning in this case -- unless I missed it) module Foo where foo :: Int - Int foo n = n + 1 where Nothing = Just n I think that where x@Nothing = Just n could be useful, if 'x' is evaluated somewhere. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] [Haskell] A riddle...
On Mon, 16 Jul 2012, Felipe Almeida Lessa wrote: On Mon, Jul 16, 2012 at 12:33 PM, Vo Minh Thu not...@gmail.com wrote: It seems like the infered type (and thus bounds) is different when you force the result to be a Color or not. Just give explicit type signatures and conversion functions. Actually, just *always* give explicit type signatures. Additionally, always compile with '-Wall' and follow the warnings. This way GHC will also warn about missing type signatures and it will even suggest type signatures. (and use haskell-cafe for riddles, please :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Sifflet type checker
On Mon, 9 Jul 2012, gdwe...@iue.edu wrote: data Type = TypeVar TypeVarName -- named type variable | TypeCons TypeConsName [Type] -- constructed type deriving (Eq) Do you still think my type checker would be useful to you, or to Haskellers generally? I see. Then it is probably not very useful for me. :-( [1] http://www.youtube.com/watch?v=sXywCHR9WwE Ah, I enjoyed the performance! Nice to hear that you like it! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANNOUNCE: Sifflet visual programming language, release 2.0.0.0
On Thu, 5 Jul 2012, gdwe...@iue.edu wrote: Sifflet and sifflet-lib 2.0.0.0, now available on Hackage! This version introduces a type checker and partial support for higher order functions in Sifflet, the visual, functional programming language and support system for students learning about recursion. You have implemented your own type-checker, right? I plan to add a type-checker to our live-sequencer project. [1] So far I have thought about using the Helium type checker but I have not done it so far. If you want to make your type-checker useful for other projects, you may put it into a separate package without the hard to install dependencies on cairo and glib. [1] http://www.youtube.com/watch?v=sXywCHR9WwE ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANNOUNCE: lens-family-th 0.1.0.0
On Sat, 7 Jul 2012, rocon...@theorem.ca wrote:
On Fri, 6 Jul 2012, Dan Burton wrote:
Following the announcement of lens-family, I'm pleased to announce
lens-family-th 0.1.0.0, a Template Haskell library supplying macros to
generate
lens-family lenses for fields of data types declared with record syntax.
Be warned that currently, type signatures are *not* generated alongside the
lens definitions. Type inference should correctly determine the type of the
generated lenses, but I have structured the library code so that in the
future, type signatures can also be generated. Patches welcome!
http://hackage.haskell.org/package/lens-family-th
I cannot help but wonder if it is better to *not* generate type signatures
(or at least have an option not to).
In data-accessor-template we generate type signatures, also because it
avoids warnings for missing type signatures. However it needed some
fine-tuning before it worked in all cases.
At the moment one can write:
import Lens.Family2.Stock
import Lens.Family2.TH
data Foo a = Foo { _bar :: Int, _baz :: a }
deriving (Show, Read, Eq, Ord)
$(mkLenses ''Foo)
-- | My documentation for the 'bar' lens.
bar :: Lens (Foo a) Int
-- | My documentation for the 'baz' lens.
baz :: LensFamily (Foo a) (Foo a') a a'
I don't know if it is possible to add haddock to functions whose type
signatures are generated by template haskell.
Could the documentation be an argument of mkLenses?
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANNOUNCE: lens-family-th 0.1.0.0
On Sat, 7 Jul 2012, Dan Burton wrote: Could the documentation be an argument of mkLenses? Does haddock run on the template-haskell expanded code? TH macros must have type Q [Dec]. Dec has no constructor for comments, with the exception of pragmas. This might be feature request worthy, though it is a rather strange case to want to generate comments via a macro. Alternatively, Haddock allows you to document functions in the export list. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] [ANN] GenCheck - a generalized property-based testing framework
On Tue, 19 Jun 2012, Jacques Carette wrote: Its main novel features are: * introduces a number of /testing strategies/ and /strategy combinators/ * introduces a variety of test execution methods * guarantees uniform sampling (at each rank) for the random strategy * guarantees both uniqueness and coverage of all structures for the exhaustive strategy * introduces an /extreme/ strategy for testing unbalanced structures * also introduces a /uniform/ strategy which does uniform sampling along an enumeration * allows different strategies to be mixed; for example one can exhaustively test all binary trees up to a certain size, filled with random integers. * complete separation between properties, generators, testing strategies and test execution methods This sounds very interesting to me since I had a lot of trouble with changed test case distributions when switching from QuickCheck-1 to QuickCheck-2. It was mainly that tested numbers became much bigger in QuickCheck-2 and if I used the numbers as size of lists, then tests could not be run in reasonable time anymore. Thus I think more control over test-case generation is necessary. QuickCheck is Haskell-98 and thus is very portable. I see that GenCheck needs some more extensions - type families, multi-parameter type classes, what else? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] relocation R_X86_64_PC32 against undefined symbol
Just for the record: I compiled with GHC and got the linker error: /usr/bin/ld: dist/build/.../Module.dyn_o: relocation R_X86_64_PC32 against undefined symbol `..._xyz1_closure' can not be used when making a shared object; recompile with -fPIC Problem was that I forgot to declare Module in the Cabal description. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] converting functional dependencies to type families
On Mon, 11 Jun 2012, Simon Peyton-Jones wrote: Thanks. I've linked to it from http://www.haskell.org/haskellwiki/GHC/Type_families#Frequently_asked_questions Thank you! I already added this and another link to a new See also section below. Which one shall we maintain? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] converting functional dependencies to type families
On Thu, 7 Jun 2012, Simon Peyton-Jones wrote: Very useful! Maybe worth turning into a page on the Haskell wiki? I created one: http://www.haskell.org/haskellwiki/Functional_dependencies_vs._type_families ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell] HaL7: Haskell-Treffen in Halle/Saale, Freitag 2012-07-13
For our German readers: Es ist wieder so weit: Am Freitag, 13. Juli laden wir zum 7. Haskell-Treffen HaL ein, diesmal nach Halle an der Saale. Wir bieten eine bunte Mischung aus Tutorien zum Mitmachen, Vortraegen zum Anhoeren und Gelegenheiten zum Fachsimpeln, theoretisches wie praktisches, ernstes wie heiteres. Das Programm im Schnelldurchlauf ist: vormittags 6 Tutorien 09:30 - 11:00 snap repa schule 11:30 - 13:00 reactive generics liveseq nachmittags 4 Vortraege 14:30 - 15:15 Dorn: Schule 15:15 - 16:00 Voigtlaender: ADP 16:30 - 17:15 Goergens: XenClient 17:15 - 18:00 Eijkel: Hommage sonstiges: 09:00 - 11:30 Installationshilfen 11:00 - 11:30 Kaffeepause 13:00 - 14:30 Mittagspause 16:00 - 16:30 Kaffeepause 19:00 - Ende Abendessen und Fachsimpelei im Restaurant Die Details finden Sie hier: http://iba-cg.de/hal7.html und die Anmeldung da: http://sim.mathematik.uni-halle.de:8080/hal7/ Bitte melden Sie sich bis zum 4. Juli an. Wir freuen uns auf Ihr zahlreiches Erscheinen! für das Programmkomitee Henning Thielemann ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell-cafe] HaL7: Haskell-Treffen in Halle/Saale, Freitag 2012-07-13
For our German readers: Es ist wieder so weit: Am Freitag, 13. Juli laden wir zum 7. Haskell-Treffen HaL ein, diesmal nach Halle an der Saale. Wir bieten eine bunte Mischung aus Tutorien zum Mitmachen, Vortraegen zum Anhoeren und Gelegenheiten zum Fachsimpeln, theoretisches wie praktisches, ernstes wie heiteres. Das Programm im Schnelldurchlauf ist: vormittags 6 Tutorien 09:30 - 11:00 snap repa schule 11:30 - 13:00 reactive generics liveseq nachmittags 4 Vortraege 14:30 - 15:15 Dorn: Schule 15:15 - 16:00 Voigtlaender: ADP 16:30 - 17:15 Goergens: XenClient 17:15 - 18:00 Eijkel: Hommage sonstiges: 09:00 - 11:30 Installationshilfen 11:00 - 11:30 Kaffeepause 13:00 - 14:30 Mittagspause 16:00 - 16:30 Kaffeepause 19:00 - Ende Abendessen und Fachsimpelei im Restaurant Die Details finden Sie hier: http://iba-cg.de/hal7.html und die Anmeldung da: http://sim.mathematik.uni-halle.de:8080/hal7/ Bitte melden Sie sich bis zum 4. Juli an. Wir freuen uns auf Ihr zahlreiches Erscheinen! für das Programmkomitee Henning Thielemann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] converting functional dependencies to type families
Hi all, when I reported a typechecker performance problem related to functional dependencies http://hackage.haskell.org/trac/ghc/ticket/5970 I promised to try to convert from functional dependencies to type families. Thus I converted my code and the llvm package to type-families: http://code.haskell.org/~thielema/llvm-tf/ Here are some of my experiences: == Advantages of TypeFamilies == * Speed For what I did the type families solution was considerably faster than the functional dependencies code at least in GHC-7.4.1. Thus the bug in ticket 5970 does no longer hurt me. (In GHC-6.12.3 the conversion to type families made the compilation even slower.) * Anonymous type function values One of the most annoying type classes of the llvm package was the IsSized class: class (LLVM.IsType a, IsPositive size) = IsSized a size | a - size where size is a type-level decimal natural number. Many llvm functions require that an LLVM type has a size where the particular size is not important. However, I always have to name the size type. I also cannot get rid of it using a subclass, like class (IsSized a size) = IsAnonymouslySized a where The 'size' type is somehow sticky. The conversion of this type class to type families is straightforward: class (IsType a, PositiveT (SizeOf a)) = IsSized a where type SizeOf a :: * Now I have to use SizeOf only if needed. I can also easily define sub-classes like class (IsSized a) = C a where * No TypeSynonymInstances At the right hand side of a 'type instance' I can use type synonyms like type instance F T = String without the TypeSynonymInstance extension. This feels somehow more correct than refering to a type synonym in a class instance head like in instance C T String where The compiler does not need to analyze String in order to find the correct instance. * No FlexibleInstances The same applies to instance C (T a) (A (B a)) which is a flexible instance that is not required for type instance F (T a) = A (B a) * No MultiParamTypeClass, No UndecidableInstances I have some type classes that convert a type to another type and a tuple of types to another tuple of types where the element types are converted accordingly. With functional dependencies: class MakeValueTuple haskellTuple llvmTuple | haskellTuple - llvmTuple where instance (MakeValueTuple ha la, MakeValueTuple hb lb) = MakeValueTuple (ha,hb) (la,lb) The class is a multi-parameter type class and the instance is undecidable. This is much simpler with type families: class MakeValueTuple haskellTuple where type ValueTuple haskellTuple :: * instance (MakeValueTuple ha, MakeValueTuple hb) = MakeValueTuple (ha,hb) where type ValueTuple (ha,hb) = (ValueTuple ha, ValueTuple hb) Thus summarized: Type families may replace several other type extensions. If I ignore the associated type functions then many classes become Haskell 98 with Haskell 98 instances. This is good because those instances prevent instance conflicts with other non-orphan instances. == Disadvantage of TypeFamilies == * Redundant instance arguments I have to write the type arguments both in the instance head and in the function argument. This is especially annoying in the presence of multi-parameter type classes with bidirectional dependencies. E.g. class (a ~ Input parameter b, b ~ Output parameter a) = C parameter a b where type Input parameter b :: * type Output parameter a :: * process :: Causal p (parameter, a) b instance (...) = C (FilterParam a) v (FilterResult v) where type Input (FilterParam a) (FilterResult v) = v type Output (FilterParam a) v = FilterResult v With functional dependencies it was: class C parameter a b | parameter a - b, parameter b - a where process :: Causal p (parameter, a) b instance (...) = C (FilterParam a) v (FilterResult v) where * Bidirectional dependencies In GHC-6.12.3 it was not possible to write class (a ~ Back b, b ~ Forth a) = C a b where Fortunately, this is now allowed in GHC-7. But bidirectional dependencies are still cumbersome to work with as shown in the example above. * Equality constraints are not supported for newtype deriving Not so important, just for completeness: http://hackage.haskell.org/trac/ghc/ticket/6088 == Confusions == * Upper case type function names Why are type function names upper case, not lower case? They are not constructors after all. Maybe this is one reason, why I forget from time to time that type functions are not injective. Sure, lower-case type variables are implicitly forall quantified in Haskell 98. In the presence of lower-case type functions we would need explicit forall quantification. * Why can associated types not be exported by C(AssocType) syntax? Why must they be exported independently from the associated class? * FlexibleContexts The context (Class (TypeFun a)) requires
Re: [Haskell] Creating a factorial function in GHC
On Wed, 9 May 2012, Angus Comber wrote: I am trying to create a factorial function in GHC. I am following the online learnyouahaskell.com book (specifically types-and-typeclasses page). Bear in mind this is my day 1 of learning Haskell. Then beginn...@haskell.org might be a better place to ask, since haskell@haskell.org is for announcements. The book suggests: factorial :: Integer - Integer factorial n = product [1..n] But if I enter first line then press Enter I see: interactive:1:1 Not in scope: 'factorial' What am I doing wrong? The code you entered is intended to be the content of a text file that can be loaded into GHCi or Hugs. If you want to write it immediately into GHCi you may write: Prelude let factorial :: Integer - Integer; factorial n = product [1..n] ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell] HaL-7, 2012-07-13, Call for submissions
Call for submissions and Save the date for our local Haskell Workshop in Halle/Saale, Germany. Tutorials, talks, demonstrations ... everything welcome. Workshop language is German (mainly), and English (by request). Submission deadline: May, 21, Workshop date: June, 22 Workshop homepage: http://iba-cg.de/hal7.html The complete call in German: - Aufruf zum Einreichen von Beiträgen und Hinweis zum Vormerken des Termins Was: Haskell-Treffen HaL-7 Wann: Freitag, 13.07.2012 Wo: Institut für Informatik an der Martin-Luther-Universität in Halle an der Saale Wir suchen Vorträge zu Haskell im Besonderen und der funktionalen Programmierung im Allgemeinen, zum Beispiel zu den Themen * Neues von Sprache, Bibliotheken, Werkzeugen, * Anwendungen von Kunst bis Industrie, * Lehre an Schulen und Hochschulen, gerne aber auch zu anderen Themen. Die Beiträge können präsentiert werden als * Tutorium (60 .. 90 min) * Vortrag (30 min) * Demonstration, künstlerische Aufführung Die Veranstaltungssprache ist Deutsch, in begründeten Ausnahmen Englisch. Presentations will be given in German but we can switch to English if requested. Bitte reichen Sie Kurzfassungen der Beiträge ein (2 bis 4 Seiten), die dem Programmkomitee eine Einschätzung ermöglichen. Die Kurzfassung soll mit einer Zusammenfassung (10 Zeilen) beginnen und einem Literaturverzeichnis enden. Teilnehmer des Workshops sind Interessenten (keine Erfahrung mit Haskell/FP), Anfänger (wenig Erfahrung) und Experten. Wir bitten die Vortragenden, die Zielgruppe des Beitrags anzugeben und die nötigen Vorkenntnisse zu beschreiben. Bei Tutorien sollen Teilnehmer auf eigenen Rechnern arbeiten. Bitte beschreiben Sie dazu die vorher zu installierende Software. Schicken Sie Beitragsvorschläge als PDF-Dokument bis zum 21.05.2012 per Mail an hal-committee at iba-cg punkt de oder an ein Mitglied des Programmkomitees. Programmkomitee * Henning Thielemann - Univ. Halle (Vorsitzender), * Petra Hofstedt - BTU Cottbus, * Alf Richter - iba CG Leipzig, * Uwe Schmidt - FH Wedel, * Janis Voigtländer - Univ. Bonn, * Johannes Waldmann - HTWK Leipzig. Mit besten Grüßen Henning Thielemann ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [Haskell] HaL-7, 2012-07-13, Call for submissions
On Mon, 23 Apr 2012, Henning Thielemann wrote: Call for submissions and Save the date for our local Haskell Workshop in Halle/Saale, Germany. Tutorials, talks, demonstrations ... everything welcome. Workshop language is German (mainly), and English (by request). Submission deadline: May, 21, Arrg, this was the wrong date: Workshop date: June, 22 The correct one is July, 13 ! Workshop homepage: http://iba-cg.de/hal7.html The complete call in German: - Aufruf zum Einreichen von Beiträgen und Hinweis zum Vormerken des Termins Was: Haskell-Treffen HaL-7 Wann: Freitag, 13.07.2012 Wo: Institut für Informatik an der Martin-Luther-Universität in Halle an der Saale Wir suchen Vorträge zu Haskell im Besonderen und der funktionalen Programmierung im Allgemeinen, zum Beispiel zu den Themen * Neues von Sprache, Bibliotheken, Werkzeugen, * Anwendungen von Kunst bis Industrie, * Lehre an Schulen und Hochschulen, gerne aber auch zu anderen Themen. Die Beiträge können präsentiert werden als * Tutorium (60 .. 90 min) * Vortrag (30 min) * Demonstration, künstlerische Aufführung Die Veranstaltungssprache ist Deutsch, in begründeten Ausnahmen Englisch. Presentations will be given in German but we can switch to English if requested. Bitte reichen Sie Kurzfassungen der Beiträge ein (2 bis 4 Seiten), die dem Programmkomitee eine Einschätzung ermöglichen. Die Kurzfassung soll mit einer Zusammenfassung (10 Zeilen) beginnen und einem Literaturverzeichnis enden. Teilnehmer des Workshops sind Interessenten (keine Erfahrung mit Haskell/FP), Anfänger (wenig Erfahrung) und Experten. Wir bitten die Vortragenden, die Zielgruppe des Beitrags anzugeben und die nötigen Vorkenntnisse zu beschreiben. Bei Tutorien sollen Teilnehmer auf eigenen Rechnern arbeiten. Bitte beschreiben Sie dazu die vorher zu installierende Software. Schicken Sie Beitragsvorschläge als PDF-Dokument bis zum 21.05.2012 per Mail an hal-committee at iba-cg punkt de oder an ein Mitglied des Programmkomitees. Programmkomitee * Henning Thielemann - Univ. Halle (Vorsitzender), * Petra Hofstedt - BTU Cottbus, * Alf Richter - iba CG Leipzig, * Uwe Schmidt - FH Wedel, * Janis Voigtländer - Univ. Bonn, * Johannes Waldmann - HTWK Leipzig. Mit besten Grüßen Henning Thielemann ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell-cafe] HaL-7, 2012-07-13, Call for submissions
Call for submissions and Save the date for our local Haskell Workshop in Halle/Saale, Germany. Tutorials, talks, demonstrations ... everything welcome. Workshop language is German (mainly), and English (by request). Submission deadline: May, 21, Workshop date: July, 13 Workshop homepage: http://iba-cg.de/hal7.html The complete call in German: - Aufruf zum Einreichen von Beiträgen und Hinweis zum Vormerken des Termins Was: Haskell-Treffen HaL-7 Wann: Freitag, 13.07.2012 Wo: Institut für Informatik an der Martin-Luther-Universität in Halle an der Saale Wir suchen Vorträge zu Haskell im Besonderen und der funktionalen Programmierung im Allgemeinen, zum Beispiel zu den Themen * Neues von Sprache, Bibliotheken, Werkzeugen, * Anwendungen von Kunst bis Industrie, * Lehre an Schulen und Hochschulen, gerne aber auch zu anderen Themen. Die Beiträge können präsentiert werden als * Tutorium (60 .. 90 min) * Vortrag (30 min) * Demonstration, künstlerische Aufführung Die Veranstaltungssprache ist Deutsch, in begründeten Ausnahmen Englisch. Presentations will be given in German but we can switch to English if requested. Bitte reichen Sie Kurzfassungen der Beiträge ein (2 bis 4 Seiten), die dem Programmkomitee eine Einschätzung ermöglichen. Die Kurzfassung soll mit einer Zusammenfassung (10 Zeilen) beginnen und einem Literaturverzeichnis enden. Teilnehmer des Workshops sind Interessenten (keine Erfahrung mit Haskell/FP), Anfänger (wenig Erfahrung) und Experten. Wir bitten die Vortragenden, die Zielgruppe des Beitrags anzugeben und die nötigen Vorkenntnisse zu beschreiben. Bei Tutorien sollen Teilnehmer auf eigenen Rechnern arbeiten. Bitte beschreiben Sie dazu die vorher zu installierende Software. Schicken Sie Beitragsvorschläge als PDF-Dokument bis zum 21.05.2012 per Mail an hal-committee at iba-cg punkt de oder an ein Mitglied des Programmkomitees. Programmkomitee * Henning Thielemann - Univ. Halle (Vorsitzender), * Petra Hofstedt - BTU Cottbus, * Alf Richter - iba CG Leipzig, * Uwe Schmidt - FH Wedel, * Janis Voigtländer - Univ. Bonn, * Johannes Waldmann - HTWK Leipzig. Mit besten Grüßen Henning Thielemann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANNOUNCE: notcpp-0.0.1
On Fri, 13 Apr 2012, Ben Millwood wrote: But I never liked using CPP: it completely defeats haskell-src-exts and hence things like SourceGraph, and anyway it's not designed for Haskell and doesn't at all understand its structure, or fit with its syntax. With a little thought, I wondered if creative use of template haskell might not achieve the same goal. It turned out it did, and emboldened with this knowledge I set out to write a new package making this technique available to others. I never liked CPP in Haskell, too. The problem is: I also do not like Template Haskell. :-) Whereever possible I use a Cabal flag and a conditional Hs-Source-Dirs. http://www.haskell.org/haskellwiki/Cabal/Developer-FAQ#Adapt_to_different_systems_without_CPP ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] Higher types in contexts
moved to haskell-cafe On Mon, 5 Mar 2012, Barney Hilken wrote: Is there any deep reason why I can't write a polymorphic type in a context? I think the record update problem can be (sort of) solved if you could write: class Has r Rev (forall a. [a] - [a]) = HRClass r where setHRClass :: (forall a.[a] - [a]) - r - r but polymorphic types are not allowed in contexts. Is this one of the problems SPJ considers Hard or is it a feasible extension? I don't know what you want to do, but you may wrap the (forall a. [a] - [a]) in an existential type: data ListFunc = forall a. ListFunc ([a] - [a]) class Has r Rev ListFunc = HRClass r where setHRClass :: ListFunc - r - r ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell] Support tools for development with Cabal and Darcs
I have uploaded three packages to Hackage that shall simplify maintaining cabal packages under darcs revision control. They simplify tasks like uploading packages after some tests, cabal version handling, compiling multiple local packages in the right order, replacing identifiers in multiple files, renaming modules. * http://hackage.haskell.org/package/darcs-scripts * http://hackage.haskell.org/package/cabal-scripts * http://hackage.haskell.org/package/cabal-sort ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [Haskell-cafe] [Haskell] Support tools for development with Cabal and Darcs
On Fri, 10 Feb 2012, Duncan Coutts wrote: Would you mind giving me a breif explanation of the compiling multiple local packages in the right order feature? I'd like to understand what is missing in cabal-install in this respect. Currently with cabal-install you can say: cabal install ./a ./b ./c and it will install the packages in those directories in the right order. (It is also possible to list other install targets including local and remote tarballs, and of course packages from hackage). I believe that the first version of cabal-sort is older than this cabal-install feature. Nonetheless, cabal-sort can be used for other purposes, too. E.g. you can use plain Cabal installation, when 'cabal install' does not work due to problems in constraint solving. You can upload packages in topologically sorted order to Hackage, such that building on Hackage works correctly. Is this also done by cabal-install's upload command? You can also use cabal-sort for stepping into package directories and do some manual updates before installing. However, I will add references to the new cabal-install features in the documentation of cabal-sort. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] Support tools for development with Cabal and Darcs
On Fri, 10 Feb 2012, Duncan Coutts wrote: I wonder if you have any suggestions for UI changes/improvements for cabal-install for working with related sets of local packages (something it's fairly weak on at the moment). Are there things in cabal-sort you think we should just lift directly into cabal-install or variations etc? Sure, you can add a command 'sort' that outputs the given packages in topologically sorted order. :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] Support tools for development with Cabal and Darcs
On Fri, 10 Feb 2012, Henning Thielemann wrote: On Fri, 10 Feb 2012, Duncan Coutts wrote: I wonder if you have any suggestions for UI changes/improvements for cabal-install for working with related sets of local packages (something it's fairly weak on at the moment). Are there things in cabal-sort you think we should just lift directly into cabal-install or variations etc? Sure, you can add a command 'sort' that outputs the given packages in topologically sorted order. :-) I missed something: The reason for the current upload was a new cabal-sort feature that emits the package dependencies as a Makefile in order to allow building packages in parallel using 'make -j'. Of course, a '--jobs' option would also be a nice addition to 'cabal install'. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANNOUNCE multiarg - parser combinators for command line parsing
On Sun, 29 Jan 2012, Simon Meier wrote: I'm currently using Neil Mitchell's cmdargs package [1]. How does your package compare to that? Last time I checked cmdargs it was not referential transparent. Is multiarg better in this respect? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] black Wikipedia (Was: PhD program at Portland State accepting applications)
On Wed, 18 Jan 2012, Nathan Collins wrote: - Portland is a very popular US city, known for beer, bikes, music, and street food: http://en.wikipedia.org/wiki/Portland_Oregon (wikipedia is blacked out today) Maybe it is only a JavaScript trick. In Firefox (with JavaScript) I see the complete a page before it is overwritten by the protest page. In Konqueror of KDE 3 (with and without JavaScript) I can read the Wiki pages without problems. Edit however is really disabled. Sometimes I am glad to have the old technology available. :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] black Wikipedia
On Wed, 18 Jan 2012, Andrew Butterfield wrote: Just add ?banner=none to the url if you really have to read the page Maybe the intention was to demonstrate that censorship (in this case self-censorship) is mostly a problem for average users but not for advanced users. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
