Re: getWorkingDirectory/changeWorkingDirectory
How does it differ to getCurrentDirectory/setCurrentDirectory in System.Directory? On 4 December 2013 14:38, Benjamin Franksen benjamin.frank...@helmholtz-berlin.de wrote: Module System.Posix.Directory of the unix package defines getWorkingDirectory :: IO FilePath changeWorkingDirectory :: FilePath - IO () I believe the functionality is quite portable and not limited to unix-like systems. I know that e.g. Windows has chdir and getcwd. Module Filesystem of the system-fileio package has getWorkingDirectory :: IO FilePath setWorkingDirectory :: FilePath - IO () I propose to add these functions to System.Environmant or maybe System.Directory. Rationale: (1) This is standard functionality that should at least be in the Haskell Platform, if not in the standard libraries. (2) I would like to avoid depending on an extra package just to have these two very basic functions available in a OS independent way. (3) system-fileio.Filesystem does not seem to be the right place for this. The last point may be arguable, but the first two are plain common sense IMO. Cheers Ben -- Make it so they have to reboot after every typo. ? Scott Adams ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Anonymous records. A solution to the problems of record-system.
So basically, TRex?
On 14 October 2013 18:13, Nikita Volkov nikita.y.vol...@gmail.com wrote:
Anonymous records. A solution to the problems of record-system.
The current record system is notorious for three major flaws:
It does not solve the namespacing problem. I.e., you cannot have two records
sharing field names in a single module. E.g., the following won't compile:
data A = A { field :: String }
data B = B { field :: String }
It's partial. The following code will result in a runtime error:
data A = A1 { field1 :: String } | A2 { field2 :: String }
main = print $ field1 $ A2 abc
It does not allow you to use the same field name for different types across
constructors:
data A = A1 { field :: String } | A2 { field :: Int }
This proposal approaches all the problems above and also a fourth one, which
is unrelated to the current record system: it allows one to avoid
declaration of intermediate types (see details below).
Gentlemen, I want you to meet,
Anonymous Records
When a record-syntax is used in Haskell it's almost always a
single-constructor ADT. A question rises then: why use ADT when you don't
need its main feature (i.e., the multiple constructors)? This main feature
is actually the root of the second and the third problem of record-syntax
from the list above. In such situations one doesn't actually need ADT, but
something more like a tuple with ability to access its items by name. E.g.:
f :: (a :: Int, b :: String) - String
f rec = rec.b ++ show rec.a
application:
f (a = 123, b = abc)
So now you think Okay, but how about naming it?. Well, not a problem at
all - use the existingtype-construct:
type TheRecord = (a :: Int, b :: String)
Now, about the avoidance of intermediate types:
type Person = (name :: String, phone :: (country :: Int, area :: Int, number
:: Int))
See? No need to declare separate types for inner values. But, of course, if
you need, you still can:
type Phone = (country :: Int, area :: Int, number :: Int)
type Person = (name :: String, phone :: Phone)
We can nicely access the deeply nested fields, e.g.:
personCountryCode :: Person - Int
personCountryCode person = person.phone.country
Okay. What about the type ambiguity? E.g., in the following the Person is
actually the same type asCompany:
type Person = (name :: String, phone :: Phone)
type Company = (name :: String, phone :: Phone)
Easily solvable with a help of newtype:
newtype Person = Person (name :: String, phone :: Phone)
newtype Company = Company (name :: String, phone :: Phone)
What about ADTs? Again, easy:
data Product = Tea (brand :: Company)
| Milk (brand :: Company, fatness :: Float)
Now, the beautiful fact:
This solution does not conflict with any existing feature of Haskell! As the
examples show, it easily fits into the language as an extension. It can
peacefully coexist with the existing record system of ADTs. Hence a complete
backwards compatibility with old codebase. There's also a potential for many
other additional features.
Links
Source of this proposal.
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Re: [Haskell-cafe] Store type-class polymorphic values generically
Wait... what do you mean Core cannot generate new names to be exported. I meant if I add a new name in the Core transformation, that doesn't change the module's export list as seen by everything outside that module. Which makes sense, it just means I have to change my approach. Maybe you mean that you want your plugin to transform module M( f ) where f = e into module M( f_ ) where f_ = ...f... f = e No, I meant that module M(f) where f = e should be come module M (f, f_) where f = readRefOf f_; f_ = makeSomeRef e In other words, the API is only changed in that an additional binding has been exported for each top-level definition to which you can write (only of the correct type) a new definition. This is something that you could do manually, write it by hand, but I want it automatic for any module I load into GHCi! That seems pretty drastic, because now the programmer's API for the module has changed. Are you sure you don't want to do this module M( f ) wehre f_ = e f = ...f_... by renaming the existing f with some local name. Sure -- but both need to be exported otherwise you can't update the definition of `f` by writing to `f_`. With both, all other modules (and the module itself) just refer to `f' as they normally would, it's just that `f` gets its definition from some kind of mutable cell. I discussed with Daniel Peebles an approach to this with the new kind polymorphic Typeable landing in GHC 7.8, in which I could safely write functions in and out with Fun from HList: http://code.haskell.org/~aavogt/HList/docs/HList/Data-HList-FakePrelude.html#t:Fun Hypothetically I can use bog standard Typeable deriving for that type, and actually use Data.Dynamic to store all functions, using fromDynamic :: a - Maybe safe coercion. Don't get me wrong, I don't want the plugin to break any APIs or do anything unsafe (beyond using unsafePerformIO to hold a Map Name Dynamic or so), I just want in-place update of IO-ish actions. I'm compiling GHC from Git at the moment to see if this approach is worthwhile. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Compiling arbitrary Haskell code
Is there a definitive list of things in GHC that are unsafe to _compile_ if I were to take an arbitrary module and compile it? E.g. off the top of my head, things that might be dangerous: * TemplateHaskell/QuasiQuotes -- obviously * Are rules safe? * #includes — I presume there's some security risk with including any old file? * FFI -- speaks for itself I'm interested in the idea of compiling Haskell code on lpaste.org, for core, rule firings, maybe even Th expansion, etc. When sandboxing code that I'm running, it's really easy if I whitelist what code is available (parsing with HSE, whitelisting imports, extensions). The problem of infinite loops or too much allocation is fairly straight-forwardly solved by similar techniques applied in mueval. SafeHaskell helps a lot here, but suppose that I want to also allow TemplateHaskell, GeneralizedNewtypeDeriving and stuff like that, because a lot of real code uses those. They only seem to be restricted to prevent cheeky messing with APIs in ways the authors of the APIs didn't want -- but that shouldn't necessarily be a security—in terms of my system—problem, should it? Ideally I'd very strictly whitelist which modules are allowed to be used (e.g. a version of TH that doesn't have runIO), and extensions, and then compile any code that uses them. I'd rather not have to setup a VM just to compile Haskell code safely. I'm willing to put some time in to investigate it, but if there's already previous work done for this, I'd appreciate any links. At the end of the day, there's always just supporting a subset of Haskell using SafeHaskell. I'm just curious about the more general case, for use-cases similar to my own. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Compiling arbitrary Haskell code
On 12 October 2013 01:19, Johan Tibell johan.tib...@gmail.com wrote: Whatever guarantees GHC offers (e.g. using Safe Haskell), I would always run things like these in a sandbox. It's much better for security to dissallow everything and then whitelist some things (e.g. let the sandbox communicate with the rest of the world in some limited way) than the other way around. Yeah, the impression I'm getting is that compiling pretty much anything other than simple expressions (a la lambdabot) is that all bets are off. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: carriage returns on Windows from quasi-quotes
They're on Windows? On 5 October 2013 01:36, Greg Weber g...@gregweber.info wrote: A Windows user rerported using Data.Text.IO.writeFile to write out quasi-quoted text. writeFile automatically translates '\r' to \r\n, so the user ended up writing out \r\r\n to a file. Haskell seems to be adopting the policy or removing '\r' from Haskell land. Is there any reason why quasi-quotes should not automatically strip carriage returns? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Store type-class polymorphic values generically
On 4 October 2013 10:56, Heinrich Apfelmus apfel...@quantentunnel.de wrote: In particular, the Locker stores arbitrary values like Dynamic , except that values are extracted and removed with the help of a Key . This gets rid of the Typeable constraint. lock :: Key a - a - Locker I can't pass anything with class constraints to that. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using lenses
On 3 October 2013 10:57, Roman Cheplyaka r...@ro-che.info wrote: An interesting use case is my time-lens library. http://hackage.haskell.org/package/time-lens-0.3/docs/Data-Time-Lens.html You can do things like modL minutes (+5) (TimeOfDay 16 57 13) 17:02:13 But one has to be somewhat lenient about the lens laws here. Relatedly the thyme package (really fast time implementation) provides lenses for all its data types: http://hackage.haskell.org/package/thyme ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Store type-class polymorphic values generically
It's very easy to state this problem without enough details and mislead people into providing a solution for a different problem, so I'll try to include all the information and use-case. I need a function that can store a value in a concrete opaque type. I know the type of the value when I store it, and I know the type of the value when I extract it, insofar as I know the type inclusive of a class constraint context. But the container must store many different things at once. Given that I know the type of the thing when I store it and when I extract it, there ought to be a “safe’ way to do this, in the same way that Data.Dynamic is “safe”. The use-case is I want to store a table of IO-like actions in an opaque like [(Name,Dynamic)] and I write into it statically, e.g. in GHCi. The reason is due to this approach: go_ref = newIORef go_ go_ = putStrLn Hello, World! go = do go' - liftIO $ readIORef go_ref go' main = forkIO $ forever $ go then in GHCi I writeIORef go_ (putStrLn What's up?) then go will now start printing What's up? This works now, I can do this presently. However, I want to write this as a core-to-core translation as a ghc-plugin. I want the definition go = putStrLn Hello World! to be translated to what I wrote above. Core cannot generate new names to be exported from a module, so go_ is now gone. So how does the `go' function read and write the IORef? With a table: table = unsafePerformIO $ newIORef [(go,Dynamic go_ref)] Hurrah! I can now put table in some module like DynamicUpdate.table and then read/write to it from Core in the generated definition of go. Done. But how do I update it from the GHCi REPL? What follows is where I'm stuck. So with Data.Dynamic, I have: toDyn :: Typeable a = a - Dynamic With toDyn I can store concrete values and functions and then extract them: λ fmap ($ 12) (fromDynamic (toDyn ((*2) :: Int - Int)) :: Maybe (Int - Int)) Just 24 But the problem with toDyn is that it can only store concrete values due to the Typeable constraint. So then I turn to existentials and unsafeCoerce: λ data Anything = forall a. Anything a λ let x = Anything id λ case x of Anything (unsafeCoerce - (id' :: Int - Int)) - id' 123 123 Great, I was able to store a value which contained non-concrete types. But now consider the case of a value with type-class polymorphic type in it: y = Anything (print :: Show a = a - IO ()) Which cannot be type checked, because the Show instance is ambiguous. So you might propose to use rank-N types, like this: data Anything = Anything (Show a = a - IO ()) Now I can store print in there happily. But now the type is not Anything, it's not generic anymore. Maybe I want to store `print', maybe I want to store `readLn'. Dead end. I don't want to have to generate existential wrappers for all functions I might possibly want to store. The support of Constraints in this page http://blog.omega-prime.co.uk/?p=127 makes me think that it's still possible. It would be cool to somehow store a tuple of the dictionary of the constraint and the value itself and then I'd later be able to extract it. But I'm finding it difficult developing anything even simple. Any ideas/help appreciated! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HTML framework for web-ui
Threepenny is now ready for public consumption, FIW. On 23 May 2013 08:34, Vlatko Basic vlatko.ba...@gmail.com wrote: Hi Heinrich, Looks simple and interesting. I browsed the git, but not much docs yet. Just examples, or have I looked at wrong places? I see that API is still under heavy design. When do you expect the API might stabilize? (BTW, examples in Readme do not work.) vlatko Vlatko Basic wrote: I'd like to start using web pages as the UI for apps. I found out for yesod, snapp and happstack as the candidates. Would you recommend any of them as better for app ui (not classical web pages)? Or maybe another one? Not sure if that's what you are looking for, but with help from Daniel Austin, I'm currently working on a small GUI library that use the web browser to display GUI elements. https://github.com/HeinrichApfelmus/threepenny-gui It's derived from Chris Done's former Ji project. It's not quite ready for public consumption yet, but any feedback is appreciated, of course. Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] inv f g = f . g . f
Anyone ever needed this? Me and John Wiegley were discussing a decent name for it, John suggested inv as in involution. E.g. inv reverse (take 10) inv reverse (dropWhile isDigit) trim = inv reverse (dropWhile isSpace) . dropWhile isSpace That seems to be the only use-case I've ever come across. There's also this one: co f g = f g . g which means you can write trim = co (inv reverse) (dropWhile isSpace) but that's optimizing an ever rarer use-case. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] Spam on the Haskell wiki
Anyone ran SpamAssassin on the offending content created by the spammers? I've been using it on hpaste and it's been very effective at cutting out the crap. On 4 August 2012 19:15, Gwern Branwen gwe...@gmail.com wrote: On Fri, Aug 3, 2012 at 10:34 PM, damodar kulkarni kdamodar2...@gmail.com wrote: So, another doubt, if detecting spam is trivial, then why not just send the detected spam to trash directly without any human inspection? This may mean some trouble for the posters due to false positives; but the moderator's job can be reduced to some extent. Which is pretty much what this whole thread is about: asking that the sysadmins Do Something about this trivial yet overwhelming spam. -- gwern http://www.gwern.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: How to fix DatatypeContexts?
Why not this?
data Pair = forall a. Eq a = Pair {x::a, y::a}
equal :: Pair - Bool
equal (Pair x y) = x == y
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Re: How to fix DatatypeContexts?
Hm, also, with equality constraints you can make the type parametrized, too:
data Pair a' = forall a. (a ~ a', Eq a) = Pair {x::a, y::a}
equal :: Pair a - Bool
equal (Pair x y) = x == y
On 18 July 2013 13:00, Christopher Done chrisd...@gmail.com wrote:
Why not this?
data Pair = forall a. Eq a = Pair {x::a, y::a}
equal :: Pair - Bool
equal (Pair x y) = x == y
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Re: How to fix DatatypeContexts?
Good point, classic use-case for GADTs.
On 18 July 2013 13:11, Sjoerd Visscher sjo...@w3future.com wrote:
I'd use GADT syntax for this:
{-# LANGUAGE GADTs #-}
data Pair a where Pair :: Eq a = {x::a, y::a} - Pair a
Sjoerd
On Jul 18, 2013, at 1:05 PM, Christopher Done chrisd...@gmail.com wrote:
Hm, also, with equality constraints you can make the type parametrized,
too:
data Pair a' = forall a. (a ~ a', Eq a) = Pair {x::a, y::a}
equal :: Pair a - Bool
equal (Pair x y) = x == y
On 18 July 2013 13:00, Christopher Done chrisd...@gmail.com wrote:
Why not this?
data Pair = forall a. Eq a = Pair {x::a, y::a}
equal :: Pair - Bool
equal (Pair x y) = x == y
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Re: Why is GHC so much worse than JHC when computing the Ackermann function?
JHC compiles to C and last time I tried this it looked very much like the
original C version:
http://www.reddit.com/r/haskell/comments/1bcru7/damn_lies_and_haskell_performance/c9689a3
This is the same thing. Compile with --tdir=/tmp/ajhc and then cat
/tmp/ajhc/main_code.c. Output should be like this:
static uint32_t A_STD
fW$__fMain_1__ack(gc_t gc,uint32_t v105553376,uint32_t v61835120)
{
if (0 == v105553376) {
return 1 + v61835120;
} else {
uint32_t v16;
uint32_t v22;
struct tup1 x2;
if (0 == v61835120) {
uint32_t v228308038 = (v105553376 - 1);
x2.t0 = v228308038;
x2.t1 = 1;
} else {
uint32_t v110947990;
uint32_t v215884490 = (v61835120 - 1);
uint32_t v62470112 = (v105553376 - 1);
v110947990 = fW$__fMain_1__ack(gc,v105553376,v215884490);
x2.t0 = v62470112;
x2.t1 = v110947990;
}
v22 = x2.t0;
v16 = x2.t1;
return fW$__fMain_1__ack(gc,v22,v16);
}
}
And it's as fast as C on my machine:
chris@midnight:~/Projects/me/ajhc$ time ./ack
65533
real 0m2.134s
user 0m2.124s
sys 0m0.000s
chris@midnight:~/Projects/me/ajhc$ gcc -O3 ack.c -o ack-c
ack.c: In function ‘main’:
ack.c:8:3: warning: incompatible implicit declaration of built-in function
‘printf’ [enabled by default]
chris@midnight:~/Projects/me/ajhc$ time ./ack-c
65533
real 0m2.255s
user 0m2.248s
sys 0m0.000s
chris@midnight:~/Projects/me/ajhc$
On 20 April 2013 10:55, Mikhail Glushenkov the.dead.shall.r...@gmail.comwrote:
Hi all,
This came up on StackOverflow [1]. When compiled with GHC (7.4.2
7.6.2), this simple program:
main = print $ ack 4 1
where ack :: Int - Int - Int
ack 0 n = n+1
ack m 0 = ack (m-1) 1
ack m n = ack (m-1) (ack m (n-1))
consumes all available memory on my machine and slows down to a crawl.
However, when compiled with JHC it runs in constant space and is about
as fast as the straightforward Ocaml version (see the SO question for
benchmark numbers).
I was able to fix the space leak by using CPS-conversion, but the
CPS-converted version is still about 10 times slower than the naive
version compiled with JHC.
I looked both at the Core and Cmm, but couldn't find anything
obviously wrong with the generated code - 'ack' is compiled to a
simple loop of type 'Int# - Int# - Int#'. What's more frustrating is
that running the program with +RTS -hc makes the space leak
mysteriously vanish.
Can someone please explain where the space leak comes from and if it's
possible to further improve the runtime of this program with GHC?
Apparently it's somehow connected to the stack management strategy,
since running the program with a larger stack chunk size (+RTS -kc1M)
makes the space leak go away. Interestingly, choosing smaller stack
chunk sizes (256K, 512K) causes it to die with an OOM exception:
$ time ./Test +RTS -kc256K
Test: out of memory (requested 2097152 bytes)
[1]
http://stackoverflow.com/questions/16115815/ackermann-very-inefficient-with-haskell-ghc/16116074#16116074
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[Haskell-cafe] Idea: Source maps for GHC's -pgmF
Here's an idea. For the -pgmF flag, because compile errors become really obscure and line numbers rendered unhelpful, why don't we use source maps as recently done for JavaScript in the browser? Info: https://wiki.mozilla.org/DevTools/Features/SourceMap https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit Here is an example I experimented with the Fay (Haskell→JS compiler): https://dl.dropbox.com/u/62227452/Screenshots/Screenshot%20from%202012-09-26%2000%3A48%3A01.png This shows the original source code and a backtrace of an exception thrown in JavaScript. We can use Mozilla/Google's format: http://hackage.haskell.org/package/sourcemap Though it's kind of an obscure format because it's aimed at being small, but if it's already been done, why not? Otherwise a simple JSON format is probably sufficient. It could be used both in GHC's compilation, pattern match exceptions, and even in debugger stepping, if desired. Provided with, e.g. -pgmFsm foo.map. This would make things like the XML mode or other syntactical extensions feel quite natural and not awkward in GHC's error messages. What say you, -pgmF users and GHC hackers? Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Associated types for number coercion
(But I get annoyed about having to convert between five string types (String, Text, lazy Text, ByteString, lazy ByteString), so maybe I'm just generally more bothered by the whole “not being able to just write the program” than others.) On 20 March 2013 00:22, Christopher Done chrisd...@gmail.com wrote: On 20 March 2013 00:05, Johan Tibell johan.tib...@gmail.com wrote: I prefer the current way (which is interestingly what Go chose as well). With implicit casts it's easy to shoot yourself in the foot e.g. when doing bit-twiddling. I don't think it's an either-or case, though, is it? I would use the magic implicitness when I don't care, like all the times I have to write fromIntegral because I have an Int here and an Integer there, and now I want to use them in a Double calculation, so my code ends up littered with fromIntegral, or fi. Elsewhere in the world, programmers just write arithmetic. When I would care, like in bit-twiddling, I would use the explicit conversions. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Some aggregation of Haskell content
As a follow up, here's an implementation: http://haskellnews.org/ More info here: http://www.reddit.com/r/haskell/comments/1ahgrn/haskell_news/c8xfp9s On 10 February 2013 18:22, Daniel Díaz Casanueva dhelta.d...@gmail.com wrote: I'm totally with this. Also, it is exhausting to check in so many places to see what's going on. I have been looking for this for a while. On Sun, Feb 10, 2013 at 10:41 AM, Christopher Done chrisd...@gmail.com wrote: Is there a page somewhere that aggregates all of Haskell's community output into one place? As a consumer of Haskell content I neither have the time nor inclination to follow haskell-cafe and other various mailing lists, the reddits, the google+ community, planet haskell, hackage releases, twitter, youtube and whatever other submission places I haven't heard of. I made this page for the Lojban community some years ago: http://jbotcan.org/hub/ Lojban doesn't have much community activity (tho this doesn't include mailing list posts), but Haskell's community is much larger and more active, it would be far more useful. I may write such a page for Haskell content, if not for the community then at least for myself, as I keep missing out on cool things because I didn't happen to check out that particular medium of exchange. For example, even this message will be lost on a thousand people who doesn't follow the mailing list but maybe follows G+ or reddit. Kind of like a Haskell Weekly news, except more like Haskell news right now or in some adjustable time frame. And the option to toggle between chronological order or categorized. Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- E-mail sent by Daniel Díaz Casanueva let f x = x in x ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ticking time bomb
Hey dude, it looks like we made the same project yesterday: http://www.reddit.com/r/haskell/comments/17njda/proposal_a_trivial_cabal_package_signing_utility/ Yours is nice as it doesn't depend on GPG. Although that could be a nice thing because GPG manages keys. Dunno. Another diff is that mine puts the .sig inside the .tar.gz, yours puts it separate. =) On 31 January 2013 09:11, Vincent Hanquez t...@snarc.org wrote: On 01/30/2013 07:27 PM, Edward Z. Yang wrote: https://status.heroku.com/incidents/489 Unsigned Hackage packages are a ticking time bomb. I agree this is terrible, I've started working on this, but this is quite a bit of work and other priorities always pop up. https://github.com/vincenthz/cabal https://github.com/vincenthz/cabal-signature My current implementation generate a manifest during sdist'ing in cabal, and have cabal-signature called by cabal on the manifest to create a manifest.sign. The main issue i'm facing is how to create a Web of Trust for doing all the public verification bits. -- Vincent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: How to get started with a new backend?
The trac claims that ghc can compile itself to C so that only standard gnu C tools are needed to build an unregistered compiler. Wait, it can? Where's that? On 28 January 2013 02:15, Jason Dagit dag...@gmail.com wrote: I would like to explore making a backend for .NET. I've done a lot of background reading about previous .NET and JVM attempts for Haskell. It seems like several folks have made significant progress in the past and, with the exception of UHC, I can't find any code around the internet from the previous efforts. I realize that in total it's a huge undertaking and codegen is only one of several significant hurdles to success. I would like to get a very, very, very simple translation working inside GHC. If all I can compile and run is fibonacci, then I would be quite happy. For my first attempt, proof of concept is sufficient. I found a lot of good documentation on the ghc trac for how the compilation phases work and what happens in the different parts of the backend. The documentation is excellent, especially compared to other compilers I've looked at. When I started looking at how to write the code, I started to wonder about the least effort path to getting something (anything?) working. Here are some questions: * Haskell.NET seems to be dead. Does anyone know where their code went? * Did lambdavm also disappear? (JVM I know, but close enough to be useful) * Would it make sense to copymodify the -fvia-C backend to generate C#? The trac claims that ghc can compile itself to C so that only standard gnu C tools are needed to build an unregistered compiler. Could I use this trick to translate programs to C#? * What stage in the pipeline should I translate from? Core? STG? Cmm? * Which directories/source files should I look at to get familiar with the code gen? I've heard the LLVM codegen is relatively simple. * Any other advice? Thank you in advance! Jason ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] HaskellDB-HDBC-PostgreSQL installation problem
Tricky. For what it's worth, if you can't figure this out in the end, you could perhaps use my pgsql-simple which is implemented in pure haskell: https://github.com/chrisdone/pgsql-simple It's been in use on hpaste.org for about 2 years. On 9 January 2013 14:44, Johannes.Reiher johannes.rei...@fh-zwickau.de wrote: Hello Community, I have a problem installing the HaskellDB-HDBC-PostgreSQL package with cabal. I'm using Haskell Platform in Windows and I tried to install this package, but there was the error could not find pq library. So I tried to install libpq wich includes pq but there was another error: this package needs a unix installation. Is there any way to install pq on Windows or get the HaskellDB-HDBC-PostgreSQL in another way? Thanks for your advice Johannes Reiher ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] help diagnosing space leak with IORef/STRef, just incrementing a million times.
A similar use-case and same solution with IORefs:
http://hpaste.org/diff/80055/80058 Guess which one threw a
stackoverflow and which one ran indefinitely when given a few hundred
million lines of input.
On 7 January 2013 07:35, Albert Y. C. Lai tre...@vex.net wrote:
On 13-01-07 12:12 AM, Thomas Hartman wrote:
I have a space leak in a function that increments a number inside
IORef or STRef (either lazy or strict).
IORef and STRef operations do not automatically evaluate contents.
writeIORef r (x + 1) simply stores a pointer to the expression (thunk) x
+ 1 into the mutable cell. readIORef just reports back a pointer.
modifyIORef just calls readIORef and writeIORef. No evaluation throughout.
modifyIORef incr where
incr !x = x + 1
does not make a difference because it is just writeIORef r (incr x)),
i.e., simply stores a pointer to the expression (thunk) incr x into the
mutable cell. The whole process doesn't even care about how many bangs are
in incr.
(It is illuminating to consider how const True (incr x) does not evaluate
x. A pointer to True and a pointer to incr x are passed to const, then
const throws away the latter without even looking. See also const True
undefined. One day, you will thank writeIORef r undefined; I certainly
did.)
Same for both Data.STRef.Strict and Data.STRef.Lazy. They do not mean what
you think. Here is what they mean:
Data.STRef.Strict means what Control.Monad.ST.Strict means
Data.STRef.Lazy means what Control.Monad.ST.Lazy means
Control.Monad.ST.Strict means that the following hangs:
x = head (runST list) where
list :: ST s [Bool]
list = do {xs - list; return (True : xs)}
Control.Monad.ST.Lazy means that the above terminates and gives the answer
True.
(Up to this point, same story for Control.Monad.State.Strict and
Control.Monad.State.Lazy.)
I still have not understood Control.Monad.ST.Lazy enough to articulate its
full semantics, but I have some more examples to show what it does:
http://hpaste.org/63925
By understanding what Lazy in Control.Monad.ST.Lazy means, you also see
what Strict does *not* mean.
In IO or Control.Monad.ST.Strict, use
let y = x+1 in y `seq` write[IO/ST]Ref r y
to expedite the evaluation of x+1. Using the same idea, you may write your
own modify[IO/ST]RefNOW to evaluate while updating.
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[Haskell-cafe] Documentation operator
Hello chums,
I've been playing around with an idea, something that has obvious pros
and cons, but I'll sell it to you because there might be some positive
ideas out of it. Consider the following operator:
{-# LANGUAGE TypeOperators, DataKinds, KindSignatures #-}
module Docs where
import GHC.TypeLits
type a ? (sym :: Symbol) = a
First I'll describe how I'd want to use this and then what I think
are the advantages and disadvantages.
I call this (?) operator “the documentation operator”, to be used for:
* Things that either don't belong or can't be encoded in the type
system, or for things need to be in English.
* Things that cannot be encoded in Haddock.
The simple case of ye olde days:
-- | Lorem ipsum dolor sit amet. Suspendisse lacinia nibh et
-- leo. Aenean auctor aliquam dapibus.
loremIpsum :: Int - Int - String
Which has since been somewhat evolved into:
loremIpsum :: Int-- ^ Lorem ipsum dolor sit amet.
- Int-- ^ Suspendisse lacinia nibh et leo.
- String -- ^ Aenean auctor aliquam dapibus.
But could now be written:
loremIpsum :: Int? Lorem ipsum dolor sit amet.
- Int? Suspendisse lacinia nibh et leo.
- String ? Aenean auctor aliquam dapibus.
Here is a contrived case I'll use later on:
data Person = Person
describeAge :: Int ? an age - String ? description of their
elderliness
describeAge n = undefined
personAge :: Person ? a person - Int ? their age
personAge = undefined
One could also encode previously informal specifications more formally,
so that
-- | The action 'hFlush' @hdl@ causes any items buffered for output
-- in handle @hdl@ to be sent immediately to the operating system.
--
-- This operation may fail with:
--
-- * 'isFullError' if the device is full;
--
-- * 'isPermissionError' if a system resource limit would be exceeded.
--It is unspecified whether the characters in the buffer are
discarded
--or retained under these circumstances.
hFlush :: Handle - IO ()
hFlush handle = wantWritableHandle hFlush handle flushWriteBuffer
with
type Throws ex (docs :: Symbol) = docs
could now be written
hFlush :: Handle ? flush buffered items for output on this handle -
IO ()
? Throws IsFullError if the device is full
? Throws IsPermissionError
if a system resource limit would be exceeded. It is \
\unspecified whether the characters in the buffer are \
\discarded or retained under these circumstances.
hFlush handle = wantWritableHandle hFlush handle flushWriteBuffer
With this in place, in GHCi you get documentation lookup for free:
:t hFlush
hFlush
:: (Handle ? flush buffered items for output on this handle)
- (IO () ? Throws IsFullError if the device is full)
? Throws
IsPermissionError
if a system resource limit would be exceeded. It is
unspecified
whether the characters in the buffer are discarded or
retained
under these circumstances.
And you get function composition, or “documentation composition” for free:
:t describeAge . personAge
describeAge . personAge
:: (Person ? a person)
- String ? description of their elderliness
We could have a :td command to print it with docs, and otherwise docs
could be stripped out trivially by removing the ? annotations:
:t describeAge . personAge
describeAge . personAge
:: Person - String
:td describeAge . personAge
describeAge . personAge
:: (Person ? a person)
- String ? description of their elderliness
You could even add clever printing of such “documentation types”:
:t hFlush
hFlush
:: Handle — flush buffered items for output on this handle
- IO ()
Throws IsFullError if the device is full
Throws IsPermissionError if a system resource limit would be
exceeded. It is unspecified whether the characters in the buffer
are discarded or retained under these circumstances.
Unfortunately it doesn't work with monadic composition, of course.
So here are the advantages:
* You get parsing for free (and anyone using haskell-src-exts).
* You get checking for free (i.e. GHC can check that IsFullError exists
for you).
* You get a continuity of documentation through your operations
including composition.
* You can extend the documentation language easily by just defining
some types (like the Throws I used above). SeeMore, Author,
Deprecated, etc. Whatever.
* You can print out some helpful looking documentation in GHCi based on
these simple types.
* There's no longer this informal it might throw this exception kind
of pros we're forced to write.
* It could also be used for annotations other than pure documentation,
including testing. E.g. add a Testable property and then your test
[Haskell-cafe] ANNOUNCE: haskell-docs - Given a module name and a name, it will find and display the documentation of that name.
Ahoy hoy, Just thought I'd announce a tool I whipped up these evening to take a module name and a name and output the installed Haddock documentation for it. Examples with my GHCi session: λ :doc Data.List.Split split Split a list according to the given splitting strategy. This is how to run a Splitter that has been built using the other combinators. λ :doc Control.Concurrent.MVar swapMVar Take a value from an MVar, put a new value into the MVar and return the value taken. This function is atomic only if there are no other producers for this MVar. λ :doc Data.List sort Ambiguous module, belongs to more than one package: base haskell2010-1.1.0.1 Continuing anyway... Package: base The sort function implements a stable sorting algorithm. It is a special case of sortBy, which allows the programmer to supply their own comparison function. Please have a play with it, the package is at: http://hackage.haskell.org/package/haskell-docs It has installation instructions. Feel free to share any issues that you have, either here, or on the Github page: https://github.com/chrisdone/haskell-docs There are some issues to do with versioning that I'm not sure how to solve in a standard way. The obvious next step is to have a -package-conf flag so that it can be used with cabal-dev. The wizards on #haskell are currently thinking of a way to avoid having to write the module name and just use what's in scope. Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: UHC-like JavaScript backend in GHC
On 13 November 2012 16:33, J. Stutterheim j.stutterh...@me.com wrote: Yes, I did check out other work that's been done in this area, albeit only briefly. Unless I've overlooked it (which is very much possible), none of the other solutions (except Fay) support an FFI that bridges the gap between JS's OO and the functional world, like our JS-like language in the foreign imports. In real-life situations, where you want to get rid of writing JS entirely, but still might want to use existing JS libraries such as jQuery, this feature is essential. Just a small point, but Fay's FFI differs from UHC/GHC's in that it natively supports String/Double and functions without needing wrappers and conversions from CString or whatnot. E.g. you write addClassWith :: (Double - String - Fay String) - JQuery - Fay JQuery addClassWith = ffi %2.addClass(%1) and you're already ready to use it. If I recall in UHC last I tried, I had to do some serializing/unserializing for the string types, and make a wrapper function for the callback. Whether it makes any sense for a UHC/GHC-backend to behave like this, I don't know. But people really like it. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: UHC-like JavaScript backend in GHC
You also need an accomplice web server to host the JS file containing the JavaScript for the web worker to run. I don't see how you can fork threads without such support. On 13 November 2012 20:53, Luite Stegeman stege...@gmail.com wrote: Does/can cabal-install support GHCJS? I suppose that's a minor advantage of extending GHC itself; you get cabal support almost for free. Yes. There are two GHCJS installation options. One is the standalone option that includes wrappers for cabal and ghc-pkg. You use `ghcjs-cabal` to install packages, see the result with `ghcjs-pkg list`. The standalone compiler can be installed with cabal-install, but it does require you to run `ghcjs-boot` in a configured GHC source tree, to install the core libraries (ghc-prim, base, integer-gmp). The alternative is the integrated compiler, where you completely replace your existing GHC with one that can output Javascript. You don't get separate package databases this way. How big are the JS files generated with either the new or the old code generator? I recall there was a HS - JS effort out there that generated huge JS files. UHC's output is relatively compact and doesn't grow as fast with bigger programs. Relatively big for the new generator because I haven't focused on this yet. The generated code has lots of redundant assignments that can be weeded out later with a dataflow analysis pass. The old generator is a bit more compact (similar to haste compiler). Both versions have a function-level linker that only includes functions that are actually used. WebWorkers is quite limited indeed. I'm not yet sure how the serialisation might complicate matters, but it seems that WebWorkers is only really a possible backend for `fork`, and not `forkIO`. For one, you cannot serialize closures, so it will probably be similar to the restrictions in Cloud Haskell in that you can only call top-level things on the other side (Unless you don't use Javascript closures for your Haskell closures, the new GHCJS generator can actually move closures to a WebWorker, at least in theory, it's not yet implemented) luite ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: GADTs in the wild
On 18 August 2012 20:57, Bertram Felgenhauer bertram.felgenha...@googlemail.com wrote: The natural encoding as a GADT would be as follows: data Command result where GetFoo :: Double - Command Foo PutFoo :: String - Command Double Right, that's exactly what I wrote at the end of my email. And then indeed dispatch would be `dispatch :: Command a - Snap a`. But how do you derive an instance of Typeable and Read for this data type? The Foo and the Double conflict and give a type error. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: GADTs in the wild
Funny, I just solved a problem with GADTs that I couldn't really see how
to do another way.
The context
===
In a fat-client web app (like GMail) you have the need to send requests
back to the server to notify the server or get information back, this is
normally transported in JSON format. For a Haskell setup, it would be:
JavaScript (Client) → JSON → Haskell (Server)
I made Fay, a Haskell subset that compiles to JavaScript to displace
JavaScript in this diagram and now it's:
Haskell (Client) → JSON → Haskell (Server)
Three problems to solve
===
There are three problems that I wanted to solve:
1. Make serialization just work, no writing custom JSON instances or
whatnot. That problem is solved. So I can just write:
get some-request $ \(Foo bar mu) - …
2. Share data type definitions between the client and server code. That
problem is solved, at least I have a solution that I like. It's like
this:
module SharedTypes where
… definitions here …
module Client where
import SharedTypes
module Server where
import SharedTypes
Thus, after any changes to the data types, GHC will force the programmer
to update the server AND the client. This ensures both systems are in
sync with one-another. A big problem when you're working on large
applications, and a nightmare when using JavaScript.
3. Make all requests to the server type-safe, meaning that a given
request type can only have one response type, and every command which is
possible to send the server from the client MUST have a response. I have
a solution with GADTs that I thing is simple and works.
The GADTs part
==
module SharedTypes where
I declare my GADT of commands, forcing the input type and the return
type in the parameters. The Foreign instance is just for Fay to allow
things to be passed to foreign functions.
-- | The command list.
data Command where
GetFoo :: Double - Returns Foo - Command
PutFoo :: String - Returns Double - Command
deriving Read
instance Foreign Command
Where `Returns' is a simple phantom type. We'll see why this is
necessary in a sec.
-- | A phantom type which ensures the connection between the command
-- and the return value.
data Returns a = Returns
deriving Read
And let's just say Foo is some domain structure of interest:
-- | A foobles return value.
data Foo = Foo { field1 :: Double, field2 :: String, field3 :: Bool }
deriving Show
instance Foreign Foo
Now in the Server module, I write a request dispatcher:
-- | Dispatch on the commands.
dispatch :: Command - Snap ()
dispatch cmd =
case cmd of
GetFoo i r - reply r (Foo i Sup? True)
Here is the clever bit. I need to make sure that the response Foo
corresponds to the GetFoo command. So I make sure that any call to
`reply` must give a Returns value. That value will come from the nearest
place; the command being dispatched on. So this, through GHC's pattern
match exhaustion checks, ensures that all commands are handled.
-- | Reply with a command.
reply :: (Foreign a,Show a) = Returns a - a - Snap ()
reply _ = writeLBS . encode . showToFay
And now in the Client module, I wanted to make sure that GetFoo can only
be called with Foo, so I structure the `call` function to require a
Returns value as the last slot in the constructor:
-- | Call a command.
call :: Foreign a = (Returns a - Command) - (a - Fay ()) - Fay ()
call f g = ajaxCommand (f Returns) g
The AJAX command is a regular FFI, no type magic here:
-- | Run the AJAX command.
ajaxCommand :: Foreign a = Command - (a - Fay ()) - Fay ()
ajaxCommand =
ffi jQuery.ajax({url: '/json', data: %1,\
dataType: 'json', success : %2 })
And now I can make the call:
-- | Main entry point.
main :: Fay ()
main = call (GetFoo 123) $ \(Foo _ _ _) - return ()
Summary
===
So in summary I achieved these things:
* Automated (no boilerplate writing) generation of serialization for
the types.
* Client and server share the same types.
* The commands are always in synch.
* Commands that the client can use are always available on the server
(unless the developer ignored an incomplete-pattern match warning, in
which case the compiler did all it could and the developer deserves
it).
I think this approach is OK. I'm not entirely happy about reply r. I'd
like that to be automatic somehow.
Other approaches / future work
==
I did try with:
data Command a where
GetFoo :: Double - Command Foo
PutFoo :: String - Command Double
But that became difficult to make an automatic decode instance. I read
some suggestions by Edward Kmett:
http://www.haskell.org/pipermail/haskell-cafe/2010-June/079402.html
But it looked rather hairy to do in an automatic way. If anyone has any
improvements/ideas to achieve this, please let me know.
Re: GADTs in the wild
Oh, I went for a walk and realised that while I started with a GADT, I
ended up with a normal Haskell data type in a fancy GADT dress. I'll
get back to you if I get the GADT approach to work.
On 17 August 2012 15:14, Christopher Done chrisd...@gmail.com wrote:
Funny, I just solved a problem with GADTs that I couldn't really see how
to do another way.
The context
===
In a fat-client web app (like GMail) you have the need to send requests
back to the server to notify the server or get information back, this is
normally transported in JSON format. For a Haskell setup, it would be:
JavaScript (Client) → JSON → Haskell (Server)
I made Fay, a Haskell subset that compiles to JavaScript to displace
JavaScript in this diagram and now it's:
Haskell (Client) → JSON → Haskell (Server)
Three problems to solve
===
There are three problems that I wanted to solve:
1. Make serialization just work, no writing custom JSON instances or
whatnot. That problem is solved. So I can just write:
get some-request $ \(Foo bar mu) - …
2. Share data type definitions between the client and server code. That
problem is solved, at least I have a solution that I like. It's like
this:
module SharedTypes where
… definitions here …
module Client where
import SharedTypes
module Server where
import SharedTypes
Thus, after any changes to the data types, GHC will force the programmer
to update the server AND the client. This ensures both systems are in
sync with one-another. A big problem when you're working on large
applications, and a nightmare when using JavaScript.
3. Make all requests to the server type-safe, meaning that a given
request type can only have one response type, and every command which is
possible to send the server from the client MUST have a response. I have
a solution with GADTs that I thing is simple and works.
The GADTs part
==
module SharedTypes where
I declare my GADT of commands, forcing the input type and the return
type in the parameters. The Foreign instance is just for Fay to allow
things to be passed to foreign functions.
-- | The command list.
data Command where
GetFoo :: Double - Returns Foo - Command
PutFoo :: String - Returns Double - Command
deriving Read
instance Foreign Command
Where `Returns' is a simple phantom type. We'll see why this is
necessary in a sec.
-- | A phantom type which ensures the connection between the command
-- and the return value.
data Returns a = Returns
deriving Read
And let's just say Foo is some domain structure of interest:
-- | A foobles return value.
data Foo = Foo { field1 :: Double, field2 :: String, field3 :: Bool }
deriving Show
instance Foreign Foo
Now in the Server module, I write a request dispatcher:
-- | Dispatch on the commands.
dispatch :: Command - Snap ()
dispatch cmd =
case cmd of
GetFoo i r - reply r (Foo i Sup? True)
Here is the clever bit. I need to make sure that the response Foo
corresponds to the GetFoo command. So I make sure that any call to
`reply` must give a Returns value. That value will come from the nearest
place; the command being dispatched on. So this, through GHC's pattern
match exhaustion checks, ensures that all commands are handled.
-- | Reply with a command.
reply :: (Foreign a,Show a) = Returns a - a - Snap ()
reply _ = writeLBS . encode . showToFay
And now in the Client module, I wanted to make sure that GetFoo can only
be called with Foo, so I structure the `call` function to require a
Returns value as the last slot in the constructor:
-- | Call a command.
call :: Foreign a = (Returns a - Command) - (a - Fay ()) - Fay ()
call f g = ajaxCommand (f Returns) g
The AJAX command is a regular FFI, no type magic here:
-- | Run the AJAX command.
ajaxCommand :: Foreign a = Command - (a - Fay ()) - Fay ()
ajaxCommand =
ffi jQuery.ajax({url: '/json', data: %1,\
dataType: 'json', success : %2 })
And now I can make the call:
-- | Main entry point.
main :: Fay ()
main = call (GetFoo 123) $ \(Foo _ _ _) - return ()
Summary
===
So in summary I achieved these things:
* Automated (no boilerplate writing) generation of serialization for
the types.
* Client and server share the same types.
* The commands are always in synch.
* Commands that the client can use are always available on the server
(unless the developer ignored an incomplete-pattern match warning, in
which case the compiler did all it could and the developer deserves
it).
I think this approach is OK. I'm not entirely happy about reply r. I'd
like that to be automatic somehow.
Other approaches / future work
==
I did try with:
data Command a where
GetFoo :: Double - Command Foo
[Haskell-cafe] GHC type error pretty printing
Is it me or is this output not right? The \ syntax doesn't indicate a newline. chris@midnight:~$ ghci GHCi, version 7.4.2: 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 abc\n123 :: () interactive:2:1: Couldn't match expected type `()' with actual type `[Char]' In the expression: abc\ \123 :: () In an equation for `it': it = abc\ \123 :: () ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Why GHC doesn't warn about LHS nullary-constructor pattern bindings?
In your case the Nothing is unused so will never be a problem. Perhaps more worrying: foo :: Int - Int foo n = x + 1 where Just x = Nothing This gives no warnings. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Haskell's type inference considered harmful [Re: [Haskell] A riddle...]
On 17 July 2012 09:27, Andreas Abel andreas.a...@ifi.lmu.de wrote: 1. Haskell's type inference is NON-COMPOSITIONAL! In the riddle below, I am defining two things f (rgbliste) and g (farbliste). Even though they are not strongly connected, but g comes after f in the definition order, the code of g influences the type of f. THAT'S WRONG! :-( Bindings at the same level in Haskell are mutually recursive. Order of declaration does not matter. These two terms are unified by the type system. So I'm not sure what you expect to happen here. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is the surefire way to handle all exceptions and make sure the program doesn't fail?
On 17 July 2012 22:10, Bardur Arantsson s...@scientician.net wrote: On 07/17/2012 08:34 AM, Yifan Yu wrote: I can only tell if I browse the source code. So the question is, how can I determine all the exceptions that can be thrown by a given function? Look at its source. Not sure that's the most productive comment. ;-P ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: How to describe this bug?
Depends what the real offending code is. For example, if it contains unsafePerformIO then it's not a bug. On 10 July 2012 12:42, Sönke Hahn sh...@cs.tu-berlin.de wrote: Hi! I've discovered a strange bug that violates simple equational reasoning. Basically, something similar to this: let a = f x in a == f x evaluates to False. I'd like to report this on ghc-trac, but I realised, that I don't know a good name for behaviour like this. Is there one? Broken referential transparency, perhaps? Thanks, Sönke ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Call to arms: lambda-case is stuck and needs your help
I like \case as is proposed. It seems the least controversial one and there's curry (\case ) for two-args, but even that seems a rare case. For what it's worth, I like the idea of omission being partiality, as in case of and if then. It seems perfectly natural to me, I don't need a \ to tell me that an expression will result in a function. But some do. So I'll go along with and vote for \case. The lack of a lambda case is one of the few legitimate complaints I have about Haskell's syntax so it would be marvey to see it in GHC. P.S. \if then … else …? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Call to arms: lambda-case is stuck and needs your help
I like \case as is proposed. It seems the least controversial one and there's curry (\case ) for two-args, but even that seems a rare case. For what it's worth, I like the idea of omission being partiality, as in case of and if then. It seems perfectly natural to me, I don't need a \ to tell me that an expression will result in a function. But some do. So I'll go along with and vote for \case. The lack of a lambda case is one of the few legitimate complaints I have about Haskell's syntax so it would be marvey to see it in GHC. P.S. \if then … else …? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Template-haskell loading packages
'Ello, I'm using TH in a big project and whenever TH starts-up in the GHC (6.4.2) compilation process it loads a number of packages: [119 o 119] Compiling Main ( src/Main.hs, dist/build/eudl/eudl-tmp/Main.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package array-0.4.0.0 ... linking ... done. Loading package strict-0.3.2 ... linking ... done. Loading package split-0.1.4.3 ... linking ... done. Loading package safe-0.3.3 ... linking ... done. Loading package bytestring-0.9.2.1 ... linking ... done. Loading package deepseq-1.3.0.0 ... linking ... done. Loading package containers-0.4.2.1 ... linking ... done. Loading package binary-0.5.1.0 ... linking ... done. Loading package cereal-0.3.5.2 ... linking ... done. Loading package entropy-0.2.1 ... linking ... done. Loading package largeword-1.0.1 ... linking ... done. Loading package tagged-0.4.2.1 ... linking ... done. Loading package crypto-api-0.10.2 ... linking ... done. Loading package pureMD5-2.1.0.3 ... linking ... done. Loading package dlist-0.5 ... linking ... done. Loading package old-locale-1.0.0.4 ... linking ... done. Loading package data-default-0.4.0 ... linking ... done. Loading package pretty-1.1.1.0 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package utf8-string-0.3.7 ... linking ... done. Loading package printf-mauke-3000.0.5.0.1 ... linking ... done. Loading package haskell-lexer-1.0 ... linking ... done. Loading package pretty-show-1.2 ... linking ... done. Loading package parallel-3.2.0.3 ... linking ... done. Loading package transformers-0.2.2.0 ... linking ... done. Loading package mtl-2.0.1.0 ... linking ... done. Loading package text-0.11.2.1 ... linking ... done. Loading package parsec-3.1.3 ... linking ... done. Loading package unix-2.5.1.1 ... linking ... done. Loading package network-2.3.0.14 ... linking ... done. Loading package old-time-1.1.0.0 ... linking ... done. Loading package HTTP-4000.2.3 ... linking ... done. Loading package base64-bytestring-0.1.1.1 ... linking ... done. Loading package blaze-builder-0.3.1.0 ... linking ... done. Loading package blaze-html-0.4.3.4 ... linking ... done. Loading package filepath-1.3.0.0 ... linking ... done. Loading package directory-1.1.0.2 ... linking ... done. Loading package syb-0.3.6.1 ... linking ... done. Loading package hs-bibutils-4.12 ... linking ... done. Loading package json-0.5 ... linking ... done. Loading package pandoc-types-1.9.1 ... linking ... done. Loading package time-1.4 ... linking ... done. Loading package xml-1.3.12 ... linking ... done. Loading package citeproc-hs-0.3.4 ... linking ... done. Loading package extensible-exceptions-0.1.1.4 ... linking ... done. Loading package regex-base-0.93.2 ... linking ... done. Loading package regex-pcre-builtin-0.94.2.1.7.7 ... linking ... done. Loading package highlighting-kate-0.5.1 ... linking ... done. Loading package process-1.1.0.1 ... linking ... done. Loading package random-1.0.1.1 ... linking ... done. Loading package tagsoup-0.12.6 ... linking ... done. Loading package temporary-1.1.2.3 ... linking ... done. Loading package texmath-0.6.0.6 ... linking ... done. Loading package digest-0.0.1.1 ... linking ... done. Loading package zlib-0.5.3.3 ... linking ... done. Loading package zip-archive-0.1.1.8 ... linking ... done. Loading package pandoc-1.9.4.1 ... linking ... done. Loading package convertible-1.0.11.1 ... linking ... done. Loading package HDBC-2.3.1.1 ... linking ... done. Loading package HDBC-postgresql-2.3.2.1 ... linking ... done. Loading package haskelldb-2.1.3 ... linking ... done. Loading package haskelldb-hdbc-2.1.0 ... linking ... done. Loading package haskelldb-hdbc-postgresql-2.1.0 ... linking ... done. Loading package QuickCheck-2.4.2 ... linking ... done. Loading package has-0.5.0.1 ... linking ... done. Loading package feed-0.3.8 ... linking ... done. Loading package MonadCatchIO-mtl-0.3.0.4 ... linking ... done. Loading package xhtml-3000.2.1 ... linking ... done. Loading package cgi-3001.1.8.2 ... linking ... done. Loading package fastcgi-3001.0.2.3 ... linking ... done. Loading package ranges-0.2.4 ... linking ... done. Loading package email-validate-0.2.8 ... linking ... done. Loading package digestive-functors-0.2.0.0 ... linking ... done. Loading package digestive-functors-blaze-0.2.1.0 ... linking ... done. Loading package curl-1.3.7 ... linking ... done. Loading package csv-0.1.2 ... linking ... done. Loading package MonadRandom-0.1.6 ... linking ... done. Loading package HUnit-1.2.4.3 ... linking ... done. Loading package hslogger-1.1.5 ... linking ... done. Loading package regex-posix-0.95.2 ... linking ... done. Loading package regex-compat-0.95.1 ... linking ... done. Loading package MissingH-1.1.1.0 ... linking ... done. Loading package ConfigFile-1.1.1 ... linking ... done. The TH is declared in a separate module, e.g.
Re: [Haskell-cafe] Long-running request/response protocol server using enumerator/iterator/iterIO/pipes/conduits/...
On 26 June 2012 21:22, Nicolas Trangez nico...@incubaid.com wrote: Might sound easy (and actually it's pretty easy in most other languages I know, including an OCaml implementation), yet I fail to figure out how to get this done using some enumerator-style library. Well, it's easy in Haskell, too. Just use the standard libraries. If you want to mess around with these still-in-research iteratees and eumerators for the composability then go for it, but when it's hard or weird, you can't really blame that on the language. :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How do people still not understand what FP is about? What are we doing wrong?
On 18 June 2012 22:28, Ertugrul Söylemez e...@ertes.de wrote: You just have to live with the fact that there will always be a small percentage of retarded people. It's best to just ignore them. Well, they're not stupid. Just very stubborn. Like most programmers. Stupid people can be taught to be smarter, stubborn people don't want to be taught. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Noticed this change about infix decls in GHC 7.4.2
So I have some module, in a work project that I'm portnig from GHC 6.12.3 to GHC 7.4.2, module Data.Monoid.Operator where import Data.Monoid (++) :: Monoid a = a - a - a (++) = mappend infixr 5 ++ This compiles happily on GHC 6.12.3, but on 7.4.2 says: src/Data/Monoid/Operator.hs:9:10: Ambiguous occurrence `++' It could refer to either `Data.Monoid.Operator.++', defined at src/Data/Monoid/Operator.hs:8:1 or `Prelude.++', imported from `Prelude' at src/Data/Monoid/Operator.hs:3:8-27 (and originally defined in `GHC.Base') It seems that it used to assign higher priority to the declared thing in the current module over the imported one. Is this intentional? I'd suspect not, given that if I comment the binding out: -- (++) :: Monoid a = a - a - a -- (++) = mappend I get: src/Data/Monoid/Operator.hs:9:10: The fixity signature for `++' lacks an accompanying binding (The fixity signature must be given where `++' is declared) Which seems to contradict the previous error message. Bug? Ciao! P.S. Yes, I know I can fix this by not importing Prelude. P.P.S Yes, I know there's a or + defined now, but I prefer (++), thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Current uses of Haskell in industry?
On 14 June 2012 02:00, Chris Smith cdsm...@gmail.com wrote: It turns out I'm filling in for a cancelled speaker at a local open source user group, and doing a two-part talk, first on Haskell and then Snap. For the Haskell part, I'd like a list of current places the language is used in industry. I recall a few from Reddit stories and messages here and other sources, but I wonder if anyone is keeping a list. The wiki goes without saying I suppose: http://www.haskell.org/haskellwiki/Haskell_in_industry We use it for web dev here at CREATE-NET. Two public facing sites: http://confy.eai.eu/ -- For paper submission/review (like EasyChair). About 17K lines of Haskell, 20K of JS (actually some pages are Haskell compiled to JavaScript with my compiler). Couple hundred lines of Java. It was supposed to be released open source last year but you know what corporations are like. http://eudl.eu/content -- A digital archive, like IEEEXplore or ACM digital library. Not so big, about 11K lines of Haskell. Both have lots of internal-only features, IEEE/ACM/Springer communication stuff. Maybe I should add to the wiki list. Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: scrobble-0.1.0.1: Scrobbling server
Heyo, If you use Last.fm/Libre.fm you might be interested in running your own local scrobbling server in Haskell. $ cabal update $ cabal install scrobble $ scrobble-server 8910 Source is here with further instructions for audio players and such: https://github.com/chrisdone/scrobble Exactly what the server does with the scrobbles it receives is purely up to you, use it as a library and do as you please. Personally I might work on a Last.fm replacement, at least as far as the statistics/reporting generation goes. Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: stylish-haskell 0.2
Excellent, I'll check these new features work in haskell-mode when I get home. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Explicit calls to the garbage collector.
I would also be interested to know this. A web server is an example of a Haskell program that could force garbage collection at the end of every request reply, especially a multi-threaded server where the memory use is localized to threads. For long-running applications, a GC at this point would be nice. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: default instance for IsString
Pretty sure it does default to String, anyway:
{-# LANGUAGE OverloadedStrings #-}
main = print (show Hello!)
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Re: [Haskell-cafe] strange GHCi type inference behavior involving map and partially applied functions
On 16 April 2012 01:44, Ting Lei tin...@hotmail.com wrote: Kind of a newbie question, how can I automatically turn on NoMonomorphismRestriction using emacs mode for haskell? I know there is the :set command, but I don't want to do it every time I start up emacs. You can just add it to your ~/.ghci or the .ghci file of your project directory. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A Modest Records Proposal
On 2 April 2012 14:41, Michael Snoyman mich...@snoyman.com wrote: import Data.Time main = do now - getCurrentTime let (_, month, day) = toGregorian $ utctDay now putStrLn $ if month == 4 day == 1 then It's a joke else It's real import Data.Time main = do now - getCurrentTime let (_, month, day) = toGregorian $ utctDay now putStrLn $ if month == 4 day == 1 then It's a joke else It's real. (This output is not a joke. But run this program again to be sure.) ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] A Modest Records Proposal
On 2 April 2012 14:41, Michael Snoyman mich...@snoyman.com wrote: import Data.Time main = do now - getCurrentTime let (_, month, day) = toGregorian $ utctDay now putStrLn $ if month == 4 day == 1 then It's a joke else It's real import Data.Time main = do now - getCurrentTime let (_, month, day) = toGregorian $ utctDay now putStrLn $ if month == 4 day == 1 then It's a joke else It's real. (This output is not a joke. But run this program again to be sure.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A Modest Records Proposal
I actually read the first couple paragraphs and thought “sounds interesting I'll read it later”. After reading it properly, I lol'd. After some initial feedback, I'm going to create a page for the Homotopy Extensional Records Proposal (HERP) on trac. There are really only a few remaining questions. 1) Having introduced homotopies, why not go all the way and introduce dependent records? In fact, are HERP and Dependent Extensional Records Proposal (DERP) already isomorphic? My suspicion is that HERP is isomorphic, but DERP is not. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] ANNOUNCE: fast-tags-0.0.1
On 1 April 2012 00:23, Evan Laforge qdun...@gmail.com wrote: Two of them use haskell-src which means they can't parse my code. Two more use haskell-src-exts, which is slow and fragile, breaks on partially edited source, and doesn't understand hsc. For what it's worth: * As you say below, HSC is easily dealth with by ignoring # lines. * haskell-src-exts is not slow. It can parse a 769 module codebase racking up to 100k lines of code in just over a second on my machine. That's good. Also, I don't think speed of the individual file matters, for reasons I state below. * Broken source is not a big issue to me. Code is written with a GHCi session on-hand; syntactic issues are the least of my worries. I realise it will be for others. The problem with haskell-src-exts is that it refuses to parse expressions for which it cannot reduce the operator precedence, meaning it can't parse any module that uses a freshly defined operator. The reason I don't think individual file performance matters is that the output can be cached. There's also the fact that if I modify a file, and generate tags, I'm likely editing that file presently, and I'm not likely to need jumping around which tags provides. Then there's the venerable hasktags, but it's buggy and the source is a mess. I fixed a bug where it doesn't actually strip comments so it makes tags to things inside comments, but then decided it would be easier to just write my own. Hasktags is hardly buggy in my experience. The comments bug is minor. But I agree that the codebase is messy and would be better handled as Text. But again, speed on the individual basis isn't a massive issue here. fast-tags is fast because it has a parser that's just smart enough to pick out the tags. It can tagify my entire 300 module program in about a second. Unfortunately there appears to be a horrific problem with it, as the log below shows: $ time (find . -name '*.hs' | xargs hasktags -e) real0m1.573s user0m1.536s sys 0m0.032s $ cabal install fast-tags --reinstall --ghc-options=-O2 Resolving dependencies... Configuring fast-tags-0.0.2... Preprocessing executables for fast-tags-0.0.2... Building fast-tags-0.0.2... [1 of 1] Compiling Main ( src/Main.hs, dist/build/fast-tags/fast-tags-tmp/Main.o ) Linking dist/build/fast-tags/fast-tags ... Installing executable(s) in /home/chris/.cabal/bin $ time (find . -name '*.hs' | xargs fast-tags) ^C real10m39.184s user0m0.016s sys 0m0.016s $ I cancelled the program after ten minutes. The CPU was at 100% and memory usage was slowly climbing, but only slowly. It's not an infinite loop, however. If I delete the tags file and restrict the search to only the src directory, it completes earlier, but gets slower. $ time (find src -name '*.hs' | xargs hasktags -e) real0m0.113s user0m0.112s sys 0m0.008s $ time (find src -name '*.hs' | xargs fast-tags) real0m0.136s user0m0.120s sys 0m0.020s $ time (find src -name '*.hs' | xargs fast-tags) real0m0.250s user0m0.244s sys 0m0.012s So there appears to be an exponential component to the program. E.g. $ time (find . -name '*.hs' | xargs fast-tags) ./lib/text-0.11.1.5/tests/benchmarks/src/Data/Text/Benchmarks/Pure.hs:435: unexpected end of block after data * = ./lib/split-0.1.2.3/Data/List/Split/Internals.hs:68: unexpected end of block after data * = ./lib/QuickCheck-2.4.1.1/Test/QuickCheck/Function.hs:51: unexpected end of block after data * = real0m26.993s user0m26.590s sys 0m0.324s If I try to run again it hangs again. I expect it's somewhere around sort/merge/removeDups. This is on GHC 7.2.1. But it's also incremental, so it only needs to do that the first time. For what it's worth to anybody using hasktags, I've added this to hasktags: https://github.com/chrisdone/hasktags/commits/master I save the file data as JSON. I tried using aeson but that's buggy: https://github.com/bos/aeson/issues/75 At any rate, it should cache the generated tags rather than the file data, but I'd have to restructure the hasktags program a bit and I didn't feel like that yet. hasktags has no problem with this codebase: $ time (find . -name '*.hs' | xargs hasktags --cache) real0m1.512s user0m1.420s sys 0m0.088s and with the cache generated, it's half the time: $ time (find . -name '*.hs' | xargs hasktags --cache) real0m0.780s user0m0.712s sys 0m0.072s I have vim's BufWrite autocommand bound to updating the tags every time a file is written, and it's fast enough that I've never noticed the delay. It understands hsc directly (that's trivial, just ignore the # lines) so there's no need to run hsc2hs before tagifying. The result is tags which are automatically up to date all the time, which is nice. This is the use-case I (and the users who have notified me of it) have with Emacs in haskell-mode. If people care about lhs and emacs tags then it wouldn't be hard to support
Re: [Haskell-cafe] A Modest Records Proposal
I actually read the first couple paragraphs and thought “sounds interesting I'll read it later”. After reading it properly, I lol'd. After some initial feedback, I'm going to create a page for the Homotopy Extensional Records Proposal (HERP) on trac. There are really only a few remaining questions. 1) Having introduced homotopies, why not go all the way and introduce dependent records? In fact, are HERP and Dependent Extensional Records Proposal (DERP) already isomorphic? My suspicion is that HERP is isomorphic, but DERP is not. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: fast-tags-0.0.1
By the way, I'm assuming that this library isn't an April Fools joke by making a library called “fast” with explosive O(n²) time problems. :-P ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] for = flip map
Similar proposal here: http://www.reddit.com/r/haskell/comments/qy990/suggestion_for_flip_map/ It seems generally favorable. Might as well generalize it though and have flip fmap. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] for = flip map
On 28 March 2012 22:05, Matthew Steele mdste...@alum.mit.edu wrote: Doesn't for already exist, in Data.Traversable? Except that for = flip traverse. Traverse doesn't fit the type of fmap, it demands an extra type constructor: traverse :: (Traversable t,Applicative f) = (a - f b) - t a - f (t b) fmap :: Functor f = (a - b) - f a - f b Note the (a - f b) instead of (a - b). E.g. fmap :: (a - b) - [a] - [b] can't be expressed with traverse, you can only get this far: traverse :: (a - [b]) - [a] - [[b]] Unless I'm missing something. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What happened with goa package repo?
On 26 March 2012 07:24, Dmitry Malikov malikov@gmail.com wrote: Cloning into bare repository '/usr/portage/distfiles/egit-src/goa.git'... fatal: The remote end hung up unexpectedly * ERROR: dev-haskell/goa- failed (unpack phase): * git-2_initial_clone: can't fetch from git://github.com/chrisdone/goa.git https://github.com/chrisdone/goa returns 404. So it seems like Chris dropped that repo. Did someone have clone of it? It will be nice to put it back on github. This has been entirely unmaintained for some time. The repo is up there now, but I haven't used it or maintained it in nearly a year. Please clone this if you want the commits, but otherwise it is available on hackage. I will remove it eventually. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: GHCi and line numbers (with ghc-7.4.1)
On 22 March 2012 12:13, Simon Marlow marlo...@gmail.com wrote:
On 20/03/2012 20:12, Simon Hengel wrote:
They are now incremented with each evaluated expression.
Why *are* they incremented with each evaluation? Surely the only use
for line numbers would be in multi-line statements:
:{
Prelude| do x - [1..10]
Prelude| return y
Prelude| :}
interactive:6:11: Not in scope: `y'
Would it not make more sense to have
interactive:2:11: Not in scope: `y'
as it would do if compiling the file in a source file? From the older
GHCs, this always gives 1, indicating that multi-line statements are
somehow parsed and collapsed before being compiled, or maybe the line
number was just hard coded to 1.
FWIW, in my Emacs mode (making good progress on adding to
haskell-mode) I use the column number in the REPL to highlight on the
line where the problem is (e.g. here
http://chrisdone.com/images/hs-repl-error-demo.png), for GHC 7.* with
proper multi-line support I will automatically wrap any multi-line
expressions entered in the REPL in :{ and :}, it would be cool for
line numbers in errors to be useful for that. (Arguably we should be
using the GHC API and Scion or something like it, but these change
quite often and are hard to support whereas interfacing with GHCi is
quite stable across around seven releases and just works.)
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Re: String != [Char]
On 17 March 2012 05:30, Tony Morris tonymor...@gmail.com wrote: Do you know if there is a good write-up of the benefits of Data.Text over String? I'm aware of the advantages just by my own usage; hoping someone has documented it rather than in our heads. Good point, it would be good to collate the experience and wisdom of this decision with some benchmark results on the HaskellWiki as The Place to link to when justifying it. ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: [Haskell-cafe] In Haskell, because of the fine layers of abstraction that are possible, it pays to hone one's critical thinking skills.
Are you creating these posts by accident or what's the point of them? They are completely devoid of a message body. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] In Haskell, because of the fine layers of abstraction that are possible, it pays to hone one's critical thinking skills.
On 17 March 2012 22:09, Brandon Allbery allber...@gmail.com wrote: I think KC is simply unfamiliar with mail clients, and is putting what is intended to be the body in the subject line. Possibly. If that's the case I'm sorry KC if any offense was caused with my blunt words. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Open-source projects for beginning Haskell students?
On 16 March 2012 21:28, Brent Yorgey byor...@seas.upenn.edu wrote: So I'd like to do it again this time around, and am looking for particular projects I can suggest to them. Do you have an open-source project with a few well-specified tasks that a relative beginner (see below) could reasonably make a contribution towards in the space of about four weeks? I'm aware that most tasks don't fit that profile, but even complex projects usually have a few simple-ish tasks that haven't yet been done just because no one has gotten around to it yet. I have a bunch of small Haskell projects and I would enjoy helping someone contribute to them. The problem would be finding projects that are actually interesting to a student. The only ones I can think of, that are trivial to work on, are: * https://github.com/chrisdone/freenect Requires a Kinect device (your students have X-Box right?). This is my Kinect interface. Who doesn't love devices with video and depth perception? Currently it only supports depth perception, as that's all I wanted from it, but one could fairly straight-forwardly add video support. This would require some mentoring and helping along as it requires not only Haskell knowledge, but it needs some C code and using the FFI. It took me a weekend to figure out and write the depth perception part, with help a newbie could tackle video within four weeks. Alternatively -- there's also the opportunity to write some simple motion detection stuff with the existing code. * https://github.com/chrisdone/stepeval This is benmachine's project to evaluate Haskell in steps. It's currently on hpaste.org, but it's rather incomplete. Fleshing this out to support more syntax would be nice. Not sure if this is actually interesting to anyone else. But it's a good way to solidify your understanding of Haskell's evaluation model and syntax, maybe. * https://github.com/chrisdone/css Making this very trivial CSS library well-typed could be easy and useful. * https://github.com/chrisdone/wordnik A little interface to the Wordnik online dictionary service. I kinda started this but didn't finish it. Once done though we can send it to Wordnik and they'll for sure stick it on their libraries page. * https://github.com/chrisdone/amelie (hpaste.org) The only one that is relevant to the Haskell community, but I don't have any features that need doing on it, as far as I'm aware. I think the code is fairly easy to grok, though. Could be an opportunity for adding some feature, and it'll be used by a fair chunk of the Haskell community. * https://github.com/chrisdone/pgsql-simple The PostgreSQL library that amelie uses, it's a raw tcp/ip socket interface to the server, fairly trivial and yet interesting (to me) and useful. Needs more authentication methods, and I have some opportunities for optimizing some things. Tests and benchmarks for it would be good too, and probably easy to write. * https://github.com/chrisdone/hulk My IRC server that we use at work could do with a better logging mechanism than a file full of JSON. Probably a DB backend. I don't know if any student would care at all about such a project. Yeah… I don't really work on interesting projects, I won't bother listing the rest. Nor are they a big deal for the community. I'm sure the Hackage2 guys can do with some help. The ecosystem of Yesod, Happstack and Snap always has a bunch of libraries that could do with some fleshing out, I'd estimate. Another idea might be hacking on Leksah, which can always have more features. Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Functional programming podcast
On 15 March 2012 06:53, Clint Moore cl...@ivy.io wrote: We're closing in on a month since this post. Did everyone decide to do their own thing, do nothing, or ? Ah, I'd been traveling after posting this and then settling back in work, this remains on my TODO list in my organizer. I have no plans laid out, it's something I've wanted for some time and this post is the “Hey guys what if?” We should continue—my time zone is UTC+1, I am usually free within 19-23:00 with varying degrees of freeness. Friday and the rest of the weekend is better. We could try out G+ hangout and or I can setup a Mumble on hpaste.org. These are good for group chats, and if the quality isn't too great we can each record locally also and synchronize the audio later. Anyway, must dash. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: How to work around GHC bug
On 14 March 2012 15:08, Ozgur Akgun ozgurak...@gmail.com wrote: On 14 March 2012 13:51, Volker Wysk p...@volker-wysk.de wrote: import System main = do [a] - getArgs putStrLn (show a) a here is already of type String. If you don't call show on it, it'll do the expected thing. He means that the UTF-8 encoded string passed to the program should be decoded into unicode points into Chars. So putStrLn (length a) should be 1 were it decoded, but it's actually 2. You can't use this string properly, there is no Char containing the ä. See? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Prettier pretty-printing of data types?
Maybe an Emacs script to expand the nodes nicely: http://www.youtube.com/watch?v=6ofEZQ7XoEA I don't find mere pretty printing that useful compared to the “expanding” paradigm I'm used to in Chrome and Firebug. To try it just M-x eval-buffer on these two files, http://www.emacswiki.org/emacs/download/peg.el https://raw.github.com/chrisdone/haskell-emacs/master/src/hs-show.el then make some fresh empty buffer with some demo Show output code: BinJab 1 (Biny 2 Leaf Leaf) (Binpo 3 Leaf Leaf) (Binamr 3 Leaf (Lalar 3 Leaf Leaf)) and try, maybe, M-: (hs-show-replace (point-min) (point-max)) you should get “BinJab”, and then clicking it will give you more until you have: http://i.imgur.com/a7rvz.png The parser is of course a PEG parser within elisp so it kind of sucks for large data structures (limited by Elisp's stack, and is super slow). My haskell-emacs package has it in the REPL but I want to replace this parser with a haskell-src-exts→sexp utility to make it faster and more reliable. If anyone wants to replace the parser (and indeed the shower) as described, I'd be very happy as this is a Super Nice feature and indispensable in the REPL with “real” data. Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type classes for converting to Text and String
On 8 March 2012 10:53, Simon Hengel s...@typeful.net wrote: When writing library code that should work with both String and Text I find my self repeatedly introducing classes like: class ToString a where toString :: a - String class ToText a where toText :: a - Text Text is already an instance of IsString which provides IsString. I've defined ToString in my own projects though, it would be nice for it to be defined somewhere (Data.String maybe?). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] The (!) operation
‘Ello. Is there a generalization of this operator? It's all over the place, it's basically (!) :: (Monad m, Indexed collection index value) = index - container - m value We have `(!!)` on lists, `(!)` on maps, vectors, json objects, … (doesn't seem there's one for bytestring) (Though I seem to recall the monadic return value being frowned upon but I don't recall why.) Thoughts? Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The (!) operation
On 8 March 2012 18:32, Anthony Cowley acow...@seas.upenn.edu wrote: Perhaps Data.Key meets your needs? http://hackage.haskell.org/packages/archive/keys/2.1.2/doc/html/Data-Key.html Ah, perhaps indeed. Thanks! On 8 March 2012 19:12, Francesco Mazzoli f...@mazzo.li wrote: The type signature that you wrote is very generic and doesn't help in introducing effects while retrieving the indexed value, which I imagine is what you wanted to do. Because Maybe is already a monad and it's nice to fail in the monad of choice, e.g. if I'm in the list monad I get empty list instead, or if I'm in the Result monad from JSON it'll fail in there. ‘Course fail is suboptimal and MonadError might be better. I guess you could define a type family for the monad type as well, e.g.: type family Index f type family IndexMonad f :: * - * class Functor f = Indexed f where index :: Index f - f a - (IndexMonad f) (Maybe a) Right, that sounds interesting, similar to Data.Key above! It seems like a type family is a good approach. I'll try this keys library out. Grazie mille, a dopo… ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The (!) operation
On 8 March 2012 21:43, Brent Yorgey byor...@seas.upenn.edu wrote: ‘Course fail is suboptimal and MonadError might be better. Monads have nothing to do with failure. Instead of Monad you would want to use something like MonadZero or MonadError. Yeah that's what I said. GOSH. /NapoleanDynamite However, these are also suboptimal because in monads which carry extra information about the failure (i.e. anything other than [] or Maybe), the lookup function now has to make up an error message, when it almost certainly it doesn't know enough to give a good one. Good point! I had sort of felt this way regarding the monadic return in the past, but thought there might be some hidden wisdom behind the idea that I hadn't seen, and why it was in some base libraries some time back. Hadn't paid much attention to it, though. Indeed, the lookup function can't show the key to provide a useful exception message. Another problem, even if you make it like lookup :: MonadError (LookupError key) m = key - collection - m a, there's still the problem that the error isn't polymorphic in the same monad, so if lookup throws e :: LookupError the whole monad needs to be that because the functional dep is m - e. Making MonadError kinda pointless. MonadZero gives no information and can't be handled trivially like Maybe, too. This is why the use of Maybe is encouraged: Maybe is the *initial* instance of MonadZero, so you can map from it to failure in whatever monad you happen to be using. Instead of being an annoyance this is encouraged style, because in doing the conversion *you* get to pick a meaningful error message. Good points. I already use the fromMaybe style for this with lookup and such-like. Thanks for clarifying some things! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Summer of Code idea: Haskell Web Toolkit
I might as well chime in on this thread as it is relevant to my interests. I made a write up on a comparison of HJScript (JavaScript EDSL) and my Ji (control browser from Haskell) library: https://github.com/chrisdone/ji HJScript is OK, hpaste.org uses it here: https://github.com/chrisdone/amelie/blob/master/src/Amelie/View/Script.hs output here: http://hpaste.org/js/amelie.js Mini-summary of my experience: You're still stuck with JS semantics, and it can be a little odd when you confuse what level of code (JS or HS) you're working at, but at least it works right now and can be well-typed. The library needs a bit of an overhaul, the GADT of HJavaScript is simply flawed (take a brief look and you can see it can express totally invalid JS in the syntax tree and the pretty printer breaks operator/parens), but HJScript sorts the latter out, and I would make all HJScript's functions generic upon MonadJS or something, if you want a reader transformer or whatnot (i.e. to carry around some state, a JS object), it breaks down with any higher-order combinators taking actions as arguments. I also had some problems making things generic AND type-accurate, but I don't recall them well enough now. Problems aside, At Least It's Partially Well Typed. I tried UHC out recently, made a little API for the canvas tag and drew some pretty things. Had a little trouble with timers, though… the callback for the timer /worked/, but the alert[1] printed the same thing every time, as if the thunk forcing is somehow broken. I looked at the outputted code but couldn't quite grok what was wrong with it. Didn't get more time to investigate why. It may just be my code but it looks sound to me, though I'm mostly winging it with the HTML5 part. Anyway, look forward to watching ideas and work in this area. Ciao! [1]: module Main where import Control.Monad import Language.UHC.JScript.Assorted import Language.UHC.JScript.W3C.HTML5 import Language.UHC.JScript.ECMA.String import Language.UHC.JScript.ECMA.Date import Language.UHC.JScript.Types import Language.UHC.JScript.Primitives import Data.IORef main = do doc - document bodies - documentGetElementsByTagName doc (toJS canvas) body - nodeListItem bodies 0 ctx - getContext body 2d setFillStyle ctx rgb(200,0,0) start - newIORef 0 setInterval 1000 $ do st - readIORef start forM_ [st..st+30] $ \i - do let ir = fromIntegral i fillRect ctx (20 + 10*round (sin ir)) (i*10) 2 2 writeIORef start (st + 1) alert (show st) return () In HTML5.hs: data Timer foreign import jscript setInterval(%*) _setInterval :: FunPtr (IO ()) - Int - IO Timer foreign import jscript wrapper makeIntervalCallback :: IO () - IO (FunPtr (IO ())) setInterval delay haskellCallback = do jsCallback - makeIntervalCallback haskellCallback _setInterval jsCallback delay ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Summer of Code idea: Haskell Web Toolkit
On 7 March 2012 06:14, Bardur Arantsson s...@scientician.net wrote:
We get the output
function (param0_0){var var_1 = true;return var_1;}(3);
But this is invalid syntax in JavaScript, and should really be
(function (param0_0){var var_1 = true;return var_1;})(3);
Right, that's one of the ones I picked up in HJavascript. Didn't
realise (or remember) it was present in HJScript, supposing that it
had its own pretty printer. Other stuff like this is present in the
HJavascript GADT.
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Re: [Haskell-cafe] ANNOUNCE: HaskellDB 2.0: Scrap your SQL strings
On 21 February 2012 11:51, Mats Rauhala mats.rauh...@gmail.com wrote: You mentioned that haskelldb was the first library where you weren't forced to break the abstraction. Do you have a solution to a situation where you might want to retrieve the last inserted id after an insert? That's a case where I would consider modifying haskelldb-hdbc-postgresql, for example, to export an insertReturningId or whatever, because some other engines don't support returning an ID, and it wouldn't make sense to return Maybe Int or error for the ones that don't support it. This way it's well-typed. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Functional programming podcast
Show of hands, who would be interested in working on a podcast weekly or biweekly and what would you like to provide? Light banter is an acceptable answer. Some points that might be covered on such a podcast might be: * Latest FP conferences/hackathons/etc * Competitions * Interesting papers (new, or old and dug up) * Interesting blog posts or stackoverflow questions * New and interesting libraries/tech released * Developments in the communities, funding, business developments * Interviews with prominent FP chappies This bleeds over a little with Haskell Weekly News, but it's more like FP weekly interesting stuff, and therefore there would be a lot more news to pack in. It would be something to listen to while you're walking to work with your ipod. On 21 February 2012 15:55, Mats Rauhala mats.rauh...@gmail.com wrote: On 15:15 Tue 21 Feb , Christopher Done wrote: I recently thought it would be Pretty Cool to make an FP podcast, sort of a spoken Haskell Weekly News but covering all FP, blogs, packages, conferences, papers, standards, mailing lists, even stackoverflow, whatever's interesting in FP. We could use Gtalk or Mumble (both quite high quality audio) to conduct it and cut it up in audacity. I for one would be an interested listener ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Functional programming podcast
With permission I forward that Justin has offered to help cutting it up and would also be on it. On 22 February 2012 04:39, serialhex serial...@gmail.com wrote: So I'm not a very good haskell (or fp) programmer, though I wouldn't mind doing the audio splicing (which I've done amore than a bit of) or even being on the podcast myself - though like I said, right now I'm better at theory than practice, and I'm still learning theory! So as a good host or regular speaker I'm not sure id do so well, but I am willing to do what I can to get this off the ground! Justin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] podcast?
I recently thought it would be Pretty Cool to make an FP podcast, sort of a spoken Haskell Weekly News but covering all FP, blogs, packages, conferences, papers, standards, mailing lists, even stackoverflow, whatever's interesting in FP. We could use Gtalk or Mumble (both quite high quality audio) to conduct it and cut it up in audacity. On 21 February 2012 15:00, Mats Rauhala mats.rauh...@gmail.com wrote: On 09:05 Wed 15 Feb , serialhex wrote: Does anybody know of any good haskell/fp podcasts out there? i dont know if my googling skillz are just failing me, but i can't seem to find anything. thanks all! hex Out of my head I can think of ThinkRelevance podcast at http://thinkrelevance.com/blog/tags/podcast ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Munich Haskell Meeting Tonight
Eh, I was in munich last month for a week. If you announce future meetings here I might make it up there. It's a ~4 hour trip. Ciao! 2011/9/29 Dr. Heinrich Hördegen hoerde...@funktional.info: Sorry for the bad subject... Here comes my announcement again: Hi everybody, this evening (29th of September) there will be a meeting of people interested in Haskell or functional programming in general in Munich at Cafe Puck: http://www.cafepuck.de/ The meeting will start at 19h30 (german time). Sorry for being late with this announcement. Nevertheless, please feel free to join us. Have a nice day, Heinrich ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: Webwire 0.1.0, netwire 1.2.5
2011/9/16 Ertugrul Soeylemez e...@ertes.de: Hello fellow Haskellers, webwire is an experimental web framework based on the functional reactive programming library netwire. It uses WAI under the hood and right now features only a subset of the very basics of what you need to write web sites Are you going to provide any examples? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Records in Haskell
I added my evaluation of the module-based approach to existing
records, but on second thoughts it's maybe inappropriate, so I'll post
it here. I saw that some people commented on the reddit discussion
that the solution is to put your types in separate modules but it
doesn't seem that anyone has tried to do this on a large scale. I
tried it (and some other record paradigms including Has), but I don't
think it scales. Here's why…
Suppose I have 112 hand-crafted data types in my
project (e.g. see attachment 51369.txt[1]), this creates a lot of
conflicts in field names and constructor names. For example:
{{{
data Comment = Comment {
commentId :: CommentId
, commentContent :: Content
, commentReviewId :: ReviewId
, commentSubmissionId :: SubmissionId
, commentConferenceId :: ConferenceId
, commentDate :: ISODate
, commentReviewerNumber :: Int
} deriving (Show)
}}}
This is a real type in my project. It has fields like “id”, “content”,
“reviewId”, “submissionId”, “date”. There are seven other data types
that have a field name “submissionId”. There are 15 with
“conferenceId”. There are 7 with “content”. And so on. This is just to
demonstrate that field clashes ''do'' occur ''a lot'' in a nontrivial
project.
It also demonstrates that if you propose to put each of these 112 types
into a separate module, you are having a laugh. I tried this around
the 20 type mark and it was, apart from being very slow at compiling,
''very'' tedious to work with. Creating and editing these modules was a
distracting and pointless chore.
It ''also'' demonstrated, to me, that qualified imports are horrible
when used on a large scale. It happened all the time, that'd I'd
import, say, 10 different data types all qualified. Typing map
(Foo.id . BarMu.thisField) and foo Bar.Zot{x=1,y=2} becomes tedious
and distracting, especially having to add every type module when I
want to use a type. And when records use other types in other modules,
you have ''a lot'' of redundancy. With the prefixing paradigm I'd write
fooId and barMuThisField, which is about as tedious but there is at
least less . confusion and no need to make a load of modules and
import lines. Perhaps local modules would solve half of this
problem. Still have to write “Bar.mu bar” rather than “mu bar”, but
it'd be an improvement.
I also have 21 Enum types which often conflict. I end up having to
include the name of the type in the constructor, or rewording it
awkwardly. I guess I should put these all in separate modules and
import qualified,
too. Tedious, though. At least in this case languages like C# and
Java also require that you type EnumName.EnumValue, so c‘est la vie.
[1]: http://hackage.haskell.org/trac/ghc/attachment/wiki/Records/51369.txt
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Re: Records in Haskell
TRex is already mentioned on the wiki as coming at a too high implementation cost. 2011/9/15 J. Garrett Morris jgmor...@cs.pdx.edu: On Thu, Sep 15, 2011 at 6:03 AM, Barney Hilken b.hil...@ntlworld.com wrote: The right way to deal with records is first to agree a mechanism for writing a context which means a is a datatype with a field named n of type b then give the selector n the type a is a datatype with a field named n of type b = n :: a - b There is no reason why this shouldn't be used with the current syntax (although it might clash with more advanced features like first-class labels). Trex is one existing approach in the Haskell design space http://web.cecs.pdx.edu/~mpj/pubs/polyrec.html http://web.cecs.pdx.edu/~mpj/pubs/lightrec.html /g -- I’m surprised you haven’t got a little purple space dog, just to ram home what an intergalactic wag you are. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Records in Haskell
I personally really like the proposal here: http://research.microsoft.com/en-us/um/people/simonpj/Haskell/records.html The wiki doesn't show any opposition to this system. If Haskell had that record system now I would be very happy and would be fine with leaving other record systems as purely research until this whole research area comes to some decisions. I believe the way forward is to implement several of the possible systems, and release them for feedback. To get users to actually try out the libraries, I think we need some concrete syntax for constant records, so I suggest we put in a feature request. It would also be nice if one saintly person could spend the time documenting the available record systems in one document, trying out examples of codebases and collecting surveys on the various systems or something. It's a project in itself. Personally my vote for what it's worth is Worse is Better in this case, and to implement Simon's proposal (not that I think this proposal is Worse, but possibly worse than X-other-really-nice-but-tough-to-decide-on-system). If we still have nothing by this time in six months I'll implement the bloody thing in GHC myself. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Records in Haskell
2011/9/15 Greg Weber g...@gregweber.info: Chris, Thank you for the real word experience report. I had assumed (because everyone else told me) that importing qualified would be much, much better than prefixing. I had thought that in your case since you are big on model separation that you would have liked having a separate file for each model to separate out all your model related code with. As a counter point, in all of my (MVC) web application projects, we do have a separate file for each model, and we like this approach. Each file usually contains a lot of business logic related to the model- the only relatively empty model files are ones that really represent embedded data. When I use MongoDB (which actually supports embedded data instead of forcing you to create a separate table), I will actually place the embedded models in the same file as the model which includes them. Ah, this is because my approach to types is to put them in a ProjectName.Types.X module. I /do/ have separate modules for all my models, e.g. $ ls Confy/Model/*.hs Confy/Model/Actions.hs Confy/Model/Driver.hs Confy/Model/Manuscript.hsConfy/Model/Proceedings.hs Confy/Model/SubmissionAuthor.hs Confy/Model/Token.hs Confy/Model/Activity.hsConfy/Model/Fields.hs Confy/Model/Message.hs Confy/Model/ReviewComment.hs Confy/Model/Submission.hsConfy/Model/Track.hs Confy/Model/Author.hs Confy/Model/FormField.hs Confy/Model/Papertype.hs Confy/Model/ReviewerPreference.hs Confy/Model/Tables.hsConfy/Model/User.hs Confy/Model/Conference.hs Confy/Model/Form.hs Confy/Model/Participant.hs Confy/Model/Review.hs Confy/Model/Template.hs Confy/Model/UserMeta.hs Confy/Model/Deadline.hsConfy/Model/LogEntry.hs Confy/Model/Period.hsConfy/Model/Role.hsConfy/Model/TH.hs Confy/Model/Utils.hs I have my HaskellDB types and then I have my normal Haskell types which contain different fields to the database model. But to put the /type/ in the model file itself causes cyclic import problems when I have to start caring about what imports what and then having modules that just contain types, etc. I find this to be quite laborious, I did it at first but it became a hindrance to development practice for me. Have you not found that you have this problem if you put types in the same modules as code in a large project? Examples welcome, too. After my blog post complaining about records, I had a few people telling me that I can just use existing polymorphism to avoid the name-spacing issue. I collected the approaches here: http://www.yesodweb.com/wiki/record-hacks I didn't think any of those telling me what i should do had actually tried to do this themselves, particularly at any kind of larger scale. I am interested to see if anyone has experience trying this approach, or if you have considered it. I considered that approach but never tried it, one would probably enlist the help of TemplateHaskell to do that approach properly. Maybe it's not so bad? I suppose I could try making a few branches in my project and try out this approach. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Records in Haskell
2011/9/15 Greg Weber g...@gregweber.info: I should be clear that in my counter point I am using Ruby, not Haskell on those projects. In Ruby one can use a string for the name of a class (which will be evaluated later) and other general dynamic typing tricks to avoid cyclical dependencies. Ah, okay. Sure, late binding (that's what it's called) makes it convenient. I have worked on one large Yesod project. I felt they were creating artificially shortened field names in some cases (that I found difficult to understand/remember) to try and ease the pain of large prefixed record selectors. I can understand that. Accessors like reviewAssignSubmissionId for a ReviewAssign record are pretty tedious but at least I don't have trouble remembering them. However, Yesod does create all the records with prefixes in one module/file- so all the types are in there. They create a new model file for each model (conceptually, but not for a model representing simple embedded data). The model file can import all the record types. Right, that's what I do. Types in one big types file, and then the functions for the model in Project.Model.X which imports the types file. This is an internal project, but it will be released as open source in a few months so showing you the haddock output isn't a big deal: http://chrisdone.com/confy-doc/ My militantness regarding adding haddock docs is scant due to deadline pressures as you'd expect, but it's not so bad. E.g. checkout http://chrisdone.com/confy-doc/Confy-Model-Conference.html and it's blatant I'm using a lot of other types. All entities or entity-like things are in: http://chrisdone.com/confy-doc/Confy-Types-Entities.html and enums in http://chrisdone.com/confy-doc/Confy-Types-Enums.html And do not look at http://chrisdone.com/confy-doc/Confy-Model-Tables.html because it is frightening and will make you go bald. If you're already bald, feel free! HaskellDB and its HList-like record system. Personally I would prefer to define my type in the model file so I can quickly see my type with the related code if it were possible, but it seems that it isn't. I guess it can be possible with a lot of discipline and patience. Maybe others have done this in large projects and found it not so bad? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
[Haskell-cafe] Next European Hackathon
‘Ello! Any plans for the next European hackathon location that will presumably be in 6~ months? I need time to reap potential participants. Wonder if we could arrange an Italian hackathon? Verohac? Hm. :-) Maybe Utrecht? Hac6? Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHCI Feature Request: Last Successful Compilation State Saved
On 30 August 2011 06:46, Albert Y. C. Lai tre...@vex.net wrote: In #haskell, we came up with the idea of running two instances of ghci. Try loading in one instance first; if good, commit to the other instance too; if bad, you still have the other instance in a functional state. Presumably, this should be automated by some middleware. See my post from two days ago. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHCI Feature Request: Last Successful Compilation State Saved
Oh, I didn't reply all. Whoops. On 28 August 2011 13:40, Christopher Done chrisd...@googlemail.com wrote: On 27 August 2011 22:59, aditya siram aditya.si...@gmail.com wrote: I would like for the GHCI interpreter to save its environment before reloading a file and allowed the user to revert back to that state if the compilation was unsuccessful. Many times I've changed files, loaded them, hit a compilation error and needed, for example, the inferred type signature of some function. Even though that function hasn't been changed I have to either fix my code, undo a bunch of changes or comment out the last change I made and reload in order to do a :type on the function. This really breaks the flow of development. This has been bugging me for a long time and it's been on my TODO list for haskell-emacs: https://github.com/chrisdone/haskell-emacs I just implemented it. http://i.imgur.com/A71T5.png I just run two ghci processes, one for compiling, one for merely loading the code in when the former succeeds. It's not a very pleasant hack but in conjunction with :set -fobject-code it is fast and does not consume that much more memory. Considering tibbe's report is 4 years old, I think this solution is better than nothing. Set hs-config-preliminary-load-file to t in hs-config.el and it will do a preliminary load in a separate GHCi process. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHCI Feature Request: Last Successful Compilation State Saved
On 30 August 2011 17:48, Daniel Patterson lists.hask...@dbp.mm.st wrote: Chris, this is amazing! One question - do you have support for tramping in and running ghci remotely (or would that be easy to add)? I primarily develop inside virtual-machines, so while the source code lives where emacs lives, all the libraries are installed inside the virtual-machine (and the source also lives there, of course). So either 1) You put all your source files on the server, too and then run the GHCi process under tramp and access the files via tramp. 2) Sounds like you'd prefer to keep your files local, which, I suppose means you want to send code to the server when you trigger a compile? Could be done, could be done. I'll ponder it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Off-topic: Mathematics
Possibly: http://math.stackexchange.com/ On 29 August 2011 10:34, Andrew Coppin andrewcop...@btinternet.com wrote: This is fairly wildly off-topic but... does anybody know of a good forum where I can ask questions about mathematics and get authoritative answers? (Apart from go visit the nearest university, that is.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Off-topic: Mathematics
There's also #math on freenode, but it's a scary wilderness. On 29 August 2011 13:34, Benedict Eastaugh ionf...@gmail.com wrote: On 29 August 2011 09:34, Andrew Coppin andrewcop...@btinternet.com wrote: This is fairly wildly off-topic but... does anybody know of a good forum where I can ask questions about mathematics and get authoritative answers? Apart from math.stackexchange.com and mathoverflow.net, which people have already mentioned, people often discuss mathematics on #haskell-blah on Freenode. Benedict ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Truly Really Off-topic: (Was: Mathematics)
Wherever its origin, it is featured in SICP which was out in 1984: http://www.youtube.com/watch?v=zQLUPjefuWA It's a sound analogy. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ambiguous module name `System.Directory'
On 26 August 2011 18:00, informationen informatio...@gmx.de wrote: Hi, i am using ghc version 7.0.3 and a pretty recent version of the haskell-platform. Whenever i use the System.Directory module, i run into this conflict: Ambiguous module name `System.Directory': it was found in multiple packages: system-fileio-0.2.1 directory-1.1.0.0 How can i resolve this conflict permamently (i know about :set -hide-package ... )? And shouldn't there be a rule in the haskell platform which forbids modules of the same name? 1) Use PackageImports: http://www.haskell.org/ghc/docs/7.0.3/html/users_guide/syntax-extns.html#package-imports import network Network.Socket 2) Use cabal-dev ghci which will only have packages available that you specify in your .cabal file. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] why the name lambda calculus?
IIRC Church found it easy to write on paper. On 21 August 2011 21:11, Jack Henahan jhena...@uvm.edu wrote: The short answer is because Church said so. But yes, it is basically because λ is the abstraction operator in the calculus. Why not alpha or beta calculus? What would we call alpha and beta conversion, then? :D On Aug 21, 2011, at 12:37 PM, C K Kashyap wrote: Hi, Can someone please tell me what is the root of the name lambda calculus? Is it just because of the symbol lambda that is used? Why not alpha or beta calculus? Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Jack Henahan jhena...@uvm.edu == Computer science is no more about computers than astronomy is about telescopes. -- Edsger Dijkstra == ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Diffs for hackage
Wow, really nice stuff. Great work! I'll find this very useful. On 13 August 2011 08:11, Luite Stegeman stege...@gmail.com wrote: hi all, often when a new version of a package is available on hackage, I want to see what has changed since the previous release. Unfortunately many packages don't have a changelog or a public source code repository. That's why I have made a simple website with git repositories that contain all versions of all hackage packages: http://hdiff.luite.com/ The home page contains a bookmarklet that takes you directly from the index page of a package version (for example http://hackage.haskell.org/package/parsec-3.1.0 ) to the commit diff, showing the difference with the previous version ( http://hdiff.luite.com/cgit/parsec/commit?id=3.1.0 ) I hope some people will find this useful, luite ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] xmonad on xkcd
Y'all missing out: http://www.reddit.com/r/haskell/comments/j9nef/that_seems_like_a_challenge_whatever_happened_to/ On 7 August 2011 20:31, Brandon Allbery allber...@gmail.com wrote: On Sun, Aug 7, 2011 at 08:07, Jon Fairbairn jon.fairba...@cl.cam.ac.uk wrote: http://xkcd.com/934/ I am suddenly imagining an unexpected increase in development activity on YHC and the YHC Core to JavaScript translator -- brandon s allbery allber...@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Contract opportunity with Biosimilarity LLC
On 29 July 2011 01:18, Greg Meredith lgreg.mered...@biosimilarity.com wrote: Biosimilarity LLC is looking for a the next Merlin! We need an artiste with a certain taste and technical instinct that have attracted them to next generation functional programming languages and other high magic. We need a technologist who can make the demons and dragons of web front ends do their bidding while making sound architectural and platform choices. Naturally, comfort with the Open Source ecosystem from git and GitHub to mvn and/or sbt to Jenkins is a given. For such a candidate we don't have to talk about familiarity with Scala or Haskell or ML or JavaScript or Clojure because they eat languages for breakfast and graphics libraries for lunch. Ahh, so this is what people mean when they talk about rock star job ads. ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fwd: C9 video in the Monadic Design Patterns for the Web series
On 27 July 2011 10:31, Greg Meredith lgreg.mered...@biosimilarity.com wrote: Dear Haskellians, A new C9 video in the series! So, you folks already know most of this... except for maybe the generalization of the Conway construction! Best wishes, --greg Thanks for the heads up! I love these videos. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ur tutorial, and a challenge
On 19 July 2011 17:22, Adam Chlipala ad...@impredicative.com wrote: http://www.impredicative.com/ur/demo/crud1.html The example involves a library component encapsulating functionality like that of Ruby on Rails's scaffolding: automatic generation of a standard web-based admin interface to an SQL database table. The Ur/Web version uses static typing to guarantee that any applications generated by this component are free of injection attacks and other generic problems. The guarantees apply both to app communication with server-side pieces (e.g., static type-checking of SQL) and client-side pieces (e.g., static type-checking of HTML). This is not done by type-checking individual invocations of the admin-interface component. Rather, the component is checked at a static type which guarantees correct operation for _any_specialization_parameters_. So, the challenge is, can this functionality be implemented in Haskell (GHC extensions fair game, any web framework allowed)? Is TemplateHaskell fair game? Because if so these problems are not hard. Yesod employs static typing for templates. HaskellDB achieves injectionless static type checking even without TemplateHaskell, and templatepg has type safe SQL queries based on parsing the SQL itself and inspecting the types involved by asking the PostgreSQL server directly at compile time. This doesn't protect you from runtime changes to the DB schema of course. I think there's a lot of interesting work to be done based on inspecting the data base schema by querying the database server and analyzing queries at compile time. Ferry, anyone? Statically avoiding SQL and HTML injection/type problems are trivial problems that have been solved since forever ago, I don't think those are Ur's best secret weapon (dependent types goes without saying). Of Ur I particularly like that you can write Ur that will be compiled to JS. That is something that is hard to do in Haskell right now (ghcjs is a great base, but it's alpha). I don't anyone will spend time to answer the crud challenge. If so, how pretty is it? :) Anything's gonna be prettier than what you've presented there. ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ur tutorial, and a challenge
On 27 July 2011 13:58, Adam Chlipala ad...@impredicative.com wrote: Maybe, but I don't think you've outlined any solutions that meet my criteria. The key property is what I've highlighted in my self-quote above: the challenge is to type-check _the_code_generator_, not just the individual programs it generates. I want a static theorem that every program coming out of the code generator will play by the rules. No, I didn't outline any solutions for that criteria. I'm not competent to answer that. Yesod employs static typing for templates. Does this static type system support metaprogramming strong enough to implement my challenge problem with the level of static guarantee for all specialization parameters that I ask for? Again I don't really know what you're talking about so I'll drop it. Agda is still on my list of things to learn. As is Ur. But that order seems appropriate. Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] partial inheritance
On 17 July 2011 11:36, Patrick Browne patrick.bro...@dit.ie wrote: Hi, Is it possible to model partial inheritance using Haskell type classes? For example, if the class Bird has a flying method can we represent Penguins as a sub-class of Bird without a flying method? Possibly with duck typing[1], but that's not vanilla Haskell type classes. FWIW I think you'd have to have: class (Flying a,Wings a,Feathers a,Beak a) = Bird a class (Wings a,Feathers a,Beak a) = Penguin a But I think that's nice anyway. Your functions, IMHO, should ask for only the properties of the object it needs, so: nomOnCorn :: Beak a = a - Corn - a nomOnCorn = ... Rather than nomOnCorn :: Bird a = a - Corn - a nomOnCorn = ... As there's no need to restrict yourself by having a Bird class, IMHO. I don't think the subclassing/hierarchy concept scales as well as a graph. [1]: http://chrisdone.com/posts/2010-11-22-duck-typing-in-haskell.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Paid work available in functional web programming
On 13 July 2011 15:28, Adam Chlipala ad...@impredicative.com wrote: I write to mention briefly that I'm looking for people interested in writing Ur/Web programs for pay. Ur/Web is a DSL for building modern web applications, and I believe it is truly a secret weapon for that domain, and one that should appeal to many Haskell fans. I have one customer now for whom I'm leading a project to develop a particular web application, and I'd like to have more. The current project would benefit from more programming help, and I would also like to develop a network of people interested in future projects. More information on Ur/Web can be found here: http://www.impredicative.com/ur/ I would like to see a real application in Ur/Web. There are many simple examples. I don't and wouldn't want to develop like that, writing raw HTML and SQL seems going backwards despite the incredible advances in consistency and correctness that Ur/Web offers. I also find it hard to understand the type system in a non-superficial level because the related paper was very hard to grok. I tried to get it running a while ago and could not get it to compile. I would also like to see how it handles non-web stuff as inevitably IME web applications involve more than merely reading and writing to a database. I like the idea, please keep us posted about it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Inconsistent trailing comma in export list and record syntax
On 11 July 2011 10:49, L Corbijn aspergesoe...@gmail.com wrote: You could of course say that I'm using a bad style, but it remains that it seems to be inconsistent to allow a trailing comma in one place and not in the other. So is there an reason for this? I've also noticed that I can write data X = X deriving Show But not import Prelude hiding print But we can write x :: Foo x = … x :: (Foo x) = … Can write class X But not module X I wouldn't expect that there are particular argued reasons for these inconsistencies. It's difficult to balance a consistent syntax in a language while trying to be convenient. I don't think it matters too much. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] video for linux two (v4l2) bindings
On 3 July 2011 21:46, Daniel Fischer daniel.is.fisc...@googlemail.com wrote: On Sunday 03 July 2011, 21:34:17, Christopher Done wrote: I just had a quick try with cabal-install and got the below. I'm not sure where linux/posix_types is supposed to come from. Is this error obvious to you? glibc-devel or the equivalent package for your distro, I think. It turned out that I needed the linux development files from linux-libc-dev. FWIW to anyone, I'm on Ubuntu. The packages I installed were: sudo apt-get install linux-libc-dev sudo apt-get install libv4l-dev Then I got this problem: /home/chris/Programs/bin/ghc --make -o dist/build/v4l2-capture/v4l2-capture -hide-all-packages -fbuilding-cabal-package -package-conf dist/package.conf.inplace -i -idist/build/v4l2-capture/v4l2-capture-tmp -i. -idist/build/autogen -Idist/build/autogen -Idist/build/v4l2-capture/v4l2-capture-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build/v4l2-capture/v4l2-capture-tmp -hidir dist/build/v4l2-capture/v4l2-capture-tmp -stubdir dist/build/v4l2-capture/v4l2-capture-tmp -package-id base-4.2.0.2-5fc3ebcb886ceae9a06b0bab7e8d4680 -package-id bindings-libv4l2-0.1-8dde216a9ec82cb90bbe93e20783ff8c -package-id bindings-linux-videodev2-0.1-7a032e0014085bf53e381d004d794b50 -package-id bindings-mmap-0.1-3144f93204d922458a3be21650b85f1f -package-id bindings-posix-1.2.2-00b879b119996c2d3acc7989dde2ba63 -package-id c-io-0.1.0-dcc629f98d0e4b2e0d55acbaaa6262b6 -package-id ioctl-0.0.1-60f1d8091a07bb23f1736fec7d2b4dd8 -O -Wall ./src/v4l2-capture.hs [1 of 1] Compiling Main ( src/v4l2-capture.hs, dist/build/v4l2-capture/v4l2-capture-tmp/Main.o ) Linking dist/build/v4l2-capture/v4l2-capture ... /usr/bin/ld: /home/chris/.cabal/lib/bindings-posix-1.2.2/ghc-6.12.3/libHSbindings-posix-1.2.2.a(Signal.o):(.text+0x5dfb): error: undefined reference to 'pthread_kill' /usr/bin/ld: /home/chris/.cabal/lib/bindings-posix-1.2.2/ghc-6.12.3/libHSbindings-posix-1.2.2.a(Signal.o):(.text+0x5ee2): error: undefined reference to 'pthread_kill' /usr/bin/ld: /home/chris/.cabal/lib/bindings-posix-1.2.2/ghc-6.12.3/libHSbindings-posix-1.2.2.a(Signal.o):(.text+0x5f87): error: undefined reference to 'pthread_sigmask' /usr/bin/ld: /home/chris/.cabal/lib/bindings-posix-1.2.2/ghc-6.12.3/libHSbindings-posix-1.2.2.a(Signal.o):(.text+0x6092): error: undefined reference to 'pthread_sigmask' collect2: ld returned 1 exit status cabal: Error: some packages failed to install: v4l2-examples-0.1 failed during the building phase. The exception was: ExitFailure 1 chris@cn-done:~/v4l2-examples-0.1$ But I solved it by adding -lpthread: chris@cn-done:~/v4l2-examples-0.1$ /home/chris/Programs/bin/ghc --make -o dist/build/v4l2-capture/v4l2-capture -hide-all-packages -fbuilding-cabal-package -package-conf dist/package.conf.inplace -i -idist/build/v4l2-capture/v4l2-capture-tmp -i. -idist/build/autogen -Idist/build/autogen -Idist/build/v4l2-capture/v4l2-capture-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build/v4l2-capture/v4l2-capture-tmp -hidir dist/build/v4l2-capture/v4l2-capture-tmp -stubdir dist/build/v4l2-capture/v4l2-capture-tmp -package-id base-4.2.0.2-5fc3ebcb886ceae9a06b0bab7e8d4680 -package-id bindings-libv4l2-0.1-8dde216a9ec82cb90bbe93e20783ff8c -package-id bindings-linux-videodev2-0.1-7a032e0014085bf53e381d004d794b50 -package-id bindings-mmap-0.1-3144f93204d922458a3be21650b85f1f -package-id bindings-posix-1.2.2-00b879b119996c2d3acc7989dde2ba63 -package-id c-io-0.1.0-dcc629f98d0e4b2e0d55acbaaa6262b6 -package-id ioctl-0.0.1-60f1d8091a07bb23f1736fec7d2b4dd8 -O -Wall ./src/v4l2-capture.hs -lpthread Linking dist/build/v4l2-capture/v4l2-capture ... chris@cn-done:~/v4l2-examples-0.1$ I guess on Claude's system it's linked to by default. So for guys trying the examples with that error I'd recommend the following commandline: cabal install v4l2-examples --ghc-option=-lpthread Can't really play about with the webcam right now but I'd had a small but cool project I've had in mind for a while that v4l is perfectly suited for, so I'll get back to you with my experiences. Thanks for releasing it, Claude. :-) Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
