[Haskell-cafe] translation between two flavors of lexically-scoped type variables
The paper Lexically scoped type variables by Simon Peyton Jones and Mark Shields describes two ways to give type variables lexical scoping. They state that one of the advantages of the GHC-style type-sharing approach over the SML-style type-lambda approach is that the former allows for existential quantification in addition to universal quantification. As an example, they give this code: data Ap = forall a. Ap [a] ([a] - Int) The constructor `Ap` has the type: Ap :: forall a. [a] - ([a] - Int) - Ap And one can write a function: revap :: Ap - Int revap (Ap (xs :: [a]) f) = f ys where ys :: [a] ys = reverse xs with the annotations on `xs` and `ys` being existential instead of universal. But I'm a little confused about *why* type-lambdas don't allow this. Aren't both Haskell and SML translatable into System F, from which type-lambda is directly taken? What does the translation for the above code even look like? Why isn't it possible to write something like: fun 'a revap (Ap (xs : 'a list) f) = f ys where ys :: 'a list ys = reverse xs in SML? -Kangyuan Niu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using syntactic to implement the lambda calculus
Hi Alex! 2012-07-03 20:18, Alex Rozenshteyn skrev: I'm trying to implement the lambda calculus (with CBV evaluation) using the syntactic package, in such a way that a simple extension is also simple to implement. I am stuck on the fact that it seems that the Value type needs to be parametrized over the Expr type and I can't seem to figure out how to do it. The trick is to see that your `Expr` and `Value` can be merged to a single type: data Expr group where Var :: Ident - Expr NONVAL Lam :: Ident - Expr any - Expr VAL App :: Expr any1 - Expr any2 - Expr NONVAL data VAL data NONVAL type Value = Expr VAL eval :: Expr any - Value ... (Here I'm using polymorphic constructors to emulate that `Value` is a sub-type of `Expr`. I could have made a more direct translation with two lambda constructors. Then all constructors would have been monomorphic.) Once this is done, the conversion to Syntactic is easy: data Var :: * - * where Var :: Ident - Var (Full NONVAL) data Lam :: * - * where Lam :: Ident - Lam (any :- Full VAL) data App :: * - * where App :: App (any1 :- any2 :- Full NONVAL) type Expr group = ASTF (Lam :+: Var :+: App) group type Value = ASTF (Lam :+: Var :+: App) VAL eval :: Expr any - Value eval var | Just (Var _) - prj var = error not closed eval e@(lam :$ _) | Just (Lam _) - prj lam = e eval (app :$ e1 :$ e2) | Just App - prj app = case eval e1 of (lam :$ e) | Just (Lam i) - prj lam - subst e (eval e2) i _ - error illegal application subst :: Expr any - Value - Ident - Value subst = undefined Of course, you need to generalize the types of `eval` and `subst` in order to make them extensible. For more details, see this paper: http://www.cse.chalmers.se/~emax/documents/axelsson2012generic.pdf (The paper refers to syntactic-1.0 which hasn't been uploaded yet, so there are some small differences.) / Emil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Is haskell.org down?
Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is haskell.org down?
Not anymore! On 5 July 2012 15:13, C K Kashyap ckkash...@gmail.com wrote: Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com http://IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] existential types and cast
Hi Corentin,
This is how I would model your request (without concrete constructors for
Player and Rule)
I'm sure there are better descriptions also as I'm not an expert.
paolino
{-# LANGUAGE DataKinds, GADTs, KindSignatures #-}
data Player
data Rule
data Data = Player | Rule
data EventKind = Action | Reaction
data Event :: EventKind - * where
NewPlayer :: Player - Event Action
NewRule:: Rule - Event Action
NewHandler :: (Event Action - IO ()) - Event Reaction
handle :: Event Action - Event Reaction - IO ()
handle x (NewHandler f) = f x
reaction :: Event a - [Event Reaction] - IO [Event Reaction]
reaction f@(NewHandler _) es = return $ f:es
reaction p@(NewPlayer _) es = mapM_ (handle p) es return es
reaction r@(NewRule _) es = mapM_ (handle r) es return es
2012/7/4 Corentin Dupont corentin.dup...@gmail.com
Hi,
for example, in my game (Nomic) if a new player arrives, I trigger a
NewPlayer event. All handlers registered for that event should be
triggered, and passed a structure Player containing all the infos of the
incoming player.
If there is a new rule submitted, that the same: the event NewRule is
triggered and the handlers are passed a structure Rule. Thus I want the
handlers registered on NewPlayer to have the type Player - xxx, and on
NewRule to have the type Rule - xxx. I want to be able to associate an
arbitrary data type (here Player and Rule) to an event.
The handlers are inherently of different types, but I want to store them
in a unique list hence the existential...
On Wed, Jul 4, 2012 at 4:33 PM, Paolino paolo.verone...@gmail.com wrote:
Hi Corentin,
If you could explain *why* there should be a type associated to each
event value, it would help, maybe.
If it's a design choice , maybe it's wrong design. One reason to use
dynamic typing would be to plug in new type of events. But if you already
have the events semantics , this is not useful.
If the language of events is complex , possibly recursive, you can use
GADTs to enforce their validity by construction and you don't need to
typefy the event values, but some of their characteristics.
Remember type machinery is good to give correctness at the compilation
time which Typeable defeats moving checks at runtime. So lifting values to
types and eliminating this information with existentials and casting seems
wrong.
paolino
2012/7/4 Corentin Dupont corentin.dup...@gmail.com
Hi Paolino,
the user can add as many handlers he wants for each event.
When a event is triggered along with a data, all handlers associated to
that event should be triggered and passed the data.
The trick is, there is one type of data associated with each event.
That's why I cannot use a Event datatype: how to associate a data type to
each event value? This would be some sort of dependant typing if I'm not
mistaken.
That's why my events exists both on type level and value level:
*data NewPlayer = NewPlayer
*
wich allows me to associate it a typf data with type indexing.*..
*
Regards
Corentin
On Wed, Jul 4, 2012 at 12:58 PM, Paolino paolo.verone...@gmail.comwrote:
Hi
How many handlers for each type of event in the list of handlers ?
If you have only one handler for each type , it should go in the
typeclass, and you don't need typeable.
If you have more than one maybe you can avoid using type indexing at
all, because it doesn't resolve the handler selection issue.
By the way , it's not clear to me why you don't have a simple Event
datatype describing all the possible events in advance.
Regards
paolino
2012/7/3 Corentin Dupont corentin.dup...@gmail.com
Hi all,
I read somewhere (here:
http://stackoverflow.com/questions/2300275/how-to-unpack-a-haskell-existential-type)
that it's bad to try to unbox an existential type using a cast. OK, but
without I really can't figure out how to do what I want:
*data NewPlayer = NewPlayer deriving (Typeable, Eq)
data NewRule = NewRule deriving (Typeable, Eq)
class (Eq e, Typeable e) = Event e where
data EventData e
instance Event NewPlayer where
data EventData NewPlayer = P Int
instance Event NewRule where
data EventData NewRule = R Int
instance Typeable1 EventData where
typeOf1 _ = mkTyConApp (mkTyCon EventData) []
data EventHandler = forall e . (Event e) = EH e (EventData e - IO ())
addEvent :: (Event e) = e - (EventData e - IO ()) - [EventHandler]
- [EventHandler]
addEvent e h ehs = (EH e h):ehs
triggerEvent :: (Event e) = e - (EventData e) - [EventHandler] -
IO ()
triggerEvent e d ehs = do
let r = find (\(EH myEvent _) - cast e == Just myEvent) ehs
case r of
Nothing - return ()
Just (EH _ h) - case cast h of
Just castedH - castedH d
Nothing - return ()*
How to remove the casts from triggerEvent? All that I want is to apply
the handler found on the data passed in parameter.
I tried to add a function apply in the class, without success:
*apply :: (EventData e -
Re: [Haskell-cafe] existential types and cast
Sorry, drop the data Data line, I was experimenting with a deeper
description.
paolino
2012/7/4 Paolino paolo.verone...@gmail.com
Hi Corentin,
This is how I would model your request (without concrete constructors for
Player and Rule)
I'm sure there are better descriptions also as I'm not an expert.
paolino
{-# LANGUAGE DataKinds, GADTs, KindSignatures #-}
data Player
data Rule
data Data = Player | Rule
data EventKind = Action | Reaction
data Event :: EventKind - * where
NewPlayer :: Player - Event Action
NewRule:: Rule - Event Action
NewHandler :: (Event Action - IO ()) - Event Reaction
handle :: Event Action - Event Reaction - IO ()
handle x (NewHandler f) = f x
reaction :: Event a - [Event Reaction] - IO [Event Reaction]
reaction f@(NewHandler _) es = return $ f:es
reaction p@(NewPlayer _) es = mapM_ (handle p) es return es
reaction r@(NewRule _) es = mapM_ (handle r) es return es
2012/7/4 Corentin Dupont corentin.dup...@gmail.com
Hi,
for example, in my game (Nomic) if a new player arrives, I trigger a
NewPlayer event. All handlers registered for that event should be
triggered, and passed a structure Player containing all the infos of the
incoming player.
If there is a new rule submitted, that the same: the event NewRule is
triggered and the handlers are passed a structure Rule. Thus I want the
handlers registered on NewPlayer to have the type Player - xxx, and on
NewRule to have the type Rule - xxx. I want to be able to associate an
arbitrary data type (here Player and Rule) to an event.
The handlers are inherently of different types, but I want to store them
in a unique list hence the existential...
On Wed, Jul 4, 2012 at 4:33 PM, Paolino paolo.verone...@gmail.comwrote:
Hi Corentin,
If you could explain *why* there should be a type associated to each
event value, it would help, maybe.
If it's a design choice , maybe it's wrong design. One reason to use
dynamic typing would be to plug in new type of events. But if you already
have the events semantics , this is not useful.
If the language of events is complex , possibly recursive, you can use
GADTs to enforce their validity by construction and you don't need to
typefy the event values, but some of their characteristics.
Remember type machinery is good to give correctness at the compilation
time which Typeable defeats moving checks at runtime. So lifting values to
types and eliminating this information with existentials and casting seems
wrong.
paolino
2012/7/4 Corentin Dupont corentin.dup...@gmail.com
Hi Paolino,
the user can add as many handlers he wants for each event.
When a event is triggered along with a data, all handlers associated to
that event should be triggered and passed the data.
The trick is, there is one type of data associated with each event.
That's why I cannot use a Event datatype: how to associate a data type to
each event value? This would be some sort of dependant typing if I'm not
mistaken.
That's why my events exists both on type level and value level:
*data NewPlayer = NewPlayer
*
wich allows me to associate it a typf data with type indexing.*..
*
Regards
Corentin
On Wed, Jul 4, 2012 at 12:58 PM, Paolino paolo.verone...@gmail.comwrote:
Hi
How many handlers for each type of event in the list of handlers ?
If you have only one handler for each type , it should go in the
typeclass, and you don't need typeable.
If you have more than one maybe you can avoid using type indexing at
all, because it doesn't resolve the handler selection issue.
By the way , it's not clear to me why you don't have a simple Event
datatype describing all the possible events in advance.
Regards
paolino
2012/7/3 Corentin Dupont corentin.dup...@gmail.com
Hi all,
I read somewhere (here:
http://stackoverflow.com/questions/2300275/how-to-unpack-a-haskell-existential-type)
that it's bad to try to unbox an existential type using a cast. OK, but
without I really can't figure out how to do what I want:
*data NewPlayer = NewPlayer deriving (Typeable, Eq)
data NewRule = NewRule deriving (Typeable, Eq)
class (Eq e, Typeable e) = Event e where
data EventData e
instance Event NewPlayer where
data EventData NewPlayer = P Int
instance Event NewRule where
data EventData NewRule = R Int
instance Typeable1 EventData where
typeOf1 _ = mkTyConApp (mkTyCon EventData) []
data EventHandler = forall e . (Event e) = EH e (EventData e - IO
())
addEvent :: (Event e) = e - (EventData e - IO ()) -
[EventHandler] - [EventHandler]
addEvent e h ehs = (EH e h):ehs
triggerEvent :: (Event e) = e - (EventData e) - [EventHandler] -
IO ()
triggerEvent e d ehs = do
let r = find (\(EH myEvent _) - cast e == Just myEvent) ehs
case r of
Nothing - return ()
Just (EH _ h) - case cast h of
Just castedH - castedH d
Nothing - return ()*
How to remove the casts from triggerEvent? All that I
Re: [Haskell-cafe] Martin Odersky on What's wrong with Monads
That precedent supports the view that e.g. a command-line flag shouldn't affect behavior without the type reflecting it, e.g. by doing IO, but the de facto use of the unsafe IO trick means not everyone agrees. For those interested, here's [1] a case where treating command line arguments as top level constants went wrong. Look specifically at the section named Crime Doesn't Pay. Best, Facundo [1] http://www.aosabook.org/en/ghc.html Date: Tue, 3 Jul 2012 17:49:48 -0400 From: Alvaro Gutierrez radi...@google.com Subject: Re: [Haskell-cafe] Martin Odersky on What's wrong with Monads To: Dominique Devriese dominique.devri...@cs.kuleuven.be Cc: haskell-cafe@haskell.org Message-ID: cac6k+tpuidrtac_ccfa9ewawdpg1adaht96rgmc_s5wtvjw...@mail.gmail.com Content-Type: text/plain; charset=ISO-8859-1 On Thu, Jun 28, 2012 at 2:53 PM, Dominique Devriese dominique.devri...@cs.kuleuven.be wrote: 2012/6/27 Tillmann Rendel ren...@informatik.uni-marburg.de: How would you implement this requirement in Haskell without changing the line amount (Leaf x) = x? I may be missing the point here, but having worked on large code bases with a wide variety contributors before, I find it very advantageous that programmers are prevented from writing an amount function whose behaviour depends on command line arguments without at least an indication in the type. The fact that the function can not perform stuff like that is precisely the guarantee that the Haskell type gives me... I don't think there's an answer that's uniformly right; it depends on whether you think of the input to the program, e.g. the environment, command-line arguments, etc. as 'constant' and in some sense, pure. The latter are constant in the sense that they never change, but they are not fixed at compile-time. Other languages effectively treat them as pure (by passing them directly to main), whereas Haskell chooses not to, which is probably the reason why getArgs has IO in its type (something that seems unintuitive at first.) That precedent supports the view that e.g. a command-line flag shouldn't affect behavior without the type reflecting it, e.g. by doing IO, but the de facto use of the unsafe IO trick means not everyone agrees. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] existential types and cast
Hi Paolino, the user can add as many handlers he wants for each event. When a event is triggered along with a data, all handlers associated to that event should be triggered and passed the data. The trick is, there is one type of data associated with each event. That's why I cannot use a Event datatype: how to associate a data type to each event value? This would be some sort of dependant typing if I'm not mistaken. That's why my events exists both on type level and value level: *data NewPlayer = NewPlayer *wich allows me to associate it a type of data with type indexing.*.. * Regards Corentin On Wed, Jul 4, 2012 at 12:58 PM, Paolino paolo.verone...@gmail.com wrote: Hi How many handlers for each type of event in the list of handlers ? If you have only one handler for each type , it should go in the typeclass, and you don't need typeable. If you have more than one maybe you can avoid using type indexing at all, because it doesn't resolve the handler selection issue. By the way , it's not clear to me why you don't have a simple Event datatype describing all the possible events in advance. Regards paolino 2012/7/3 Corentin Dupont corentin.dup...@gmail.com Hi all, I read somewhere (here: http://stackoverflow.com/questions/2300275/how-to-unpack-a-haskell-existential-type) that it's bad to try to unbox an existential type using a cast. OK, but without I really can't figure out how to do what I want: *data NewPlayer = NewPlayer deriving (Typeable, Eq) data NewRule = NewRule deriving (Typeable, Eq) class (Eq e, Typeable e) = Event e where data EventData e instance Event NewPlayer where data EventData NewPlayer = P Int instance Event NewRule where data EventData NewRule = R Int instance Typeable1 EventData where typeOf1 _ = mkTyConApp (mkTyCon EventData) [] data EventHandler = forall e . (Event e) = EH e (EventData e - IO ()) addEvent :: (Event e) = e - (EventData e - IO ()) - [EventHandler] - [EventHandler] addEvent e h ehs = (EH e h):ehs triggerEvent :: (Event e) = e - (EventData e) - [EventHandler] - IO () triggerEvent e d ehs = do let r = find (\(EH myEvent _) - cast e == Just myEvent) ehs case r of Nothing - return () Just (EH _ h) - case cast h of Just castedH - castedH d Nothing - return ()* How to remove the casts from triggerEvent? All that I want is to apply the handler found on the data passed in parameter. I tried to add a function apply in the class, without success: *apply :: (EventData e - IO ()) - (EventData e) - IO () apply = ($)* Thanks! Corentin ___ 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] Inferring Safety
Hi, Am Mittwoch, den 04.07.2012, 21:10 +1000 schrieb Ivan Lazar Miljenovic: So what's going on here? you are likely hit by http://hackage.haskell.org/trac/ghc/ticket/5989 Greetings, Joachim -- Joachim nomeata Breitner m...@joachim-breitner.de | nome...@debian.org | GPG: 0x4743206C xmpp: nome...@joachim-breitner.de | http://www.joachim-breitner.de/ signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Martin Odersky on What's wrong with Monads
In practice, the amount of time you have to spend testing each function, to make sure its IO doesn't trip up in some corner case, is usually greater than the amount of time a rewrite-for-IO would take. Tom On Jun 28, 2012 2:54 PM, Dominique Devriese dominique.devri...@cs.kuleuven.be wrote: 2012/6/27 Tillmann Rendel ren...@informatik.uni-marburg.de: MightyByte wrote: Of course every line of your program that uses a Foo will change if you switch to IO Foo instead. But we often have to also change lines that don't use Foo at all. For example, here is the type of binary trees of integers: data Tree = Leaf Integer | Branch (Tree Integer) (Tree Integer) A function to add up all integers in a tree: amount:: Tree - Integer amount (Leaf x) = x amount (Branch t1 t2) = amountt1 + amountt2 All fine so far. Now, consider the following additional requirement: If the command-line flag --multiply is set, the function amount computes the product instead of the sum. In a language with implicit side effects, it is easy to implement this. We just change the third line of the amount function to check whether to call (+) or (*). In particular, we would not touch the other two lines. How would you implement this requirement in Haskell without changing the line amount (Leaf x) = x? I may be missing the point here, but having worked on large code bases with a wide variety contributors before, I find it very advantageous that programmers are prevented from writing an amount function whose behaviour depends on command line arguments without at least an indication in the type. The fact that the function can not perform stuff like that is precisely the guarantee that the Haskell type gives me... Dominique ___ 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] Inferring Safety
On 5 July 2012 01:35, Joachim Breitner m...@joachim-breitner.de wrote: Hi, Am Mittwoch, den 04.07.2012, 21:10 +1000 schrieb Ivan Lazar Miljenovic: So what's going on here? you are likely hit by http://hackage.haskell.org/trac/ghc/ticket/5989 Ahhh, that looks like it; thanks Joachim. Greetings, Joachim -- Joachim nomeata Breitner m...@joachim-breitner.de | nome...@debian.org | GPG: 0x4743206C xmpp: nome...@joachim-breitner.de | http://www.joachim-breitner.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com http://IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal problem re. haskelldb-hdbc-mysql
Hi, the package http://hackage.haskell.org/package/haskelldb-hdbc-mysql/ the use of HDBC 2.3.0 I'm using cabal-install 0.14, and with a fresh install (no packages already installed), cabal-install tries to install HDBC-2.1.1 instead of, say, HDBC-2.2.7.0. The problem is that HDBC-2.1.1 is old (2009) and does not compile. When I download haskelldb-hdbc-mysql manually, change the dependency and then install, it compiles fine. Is the dependency ill-declared, or is that a cabal problem? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] HUnit/cabal integration
I'm working on a little library package (purely for my own consumption) that's built with Cabal, and I have a couple of questions about the pragmatics of using HUnit for it. First, I'd like to be able to run my tests via cabal test from the shell prompt. I've seen http://hackage.haskell.org/trac/hackage/wiki/UpgradingTests and followed that, and it basically works. I'm curious if I'm doing it in the best (or at least most idiomatic) way. I've included my cabal file and test driver below, for specifics. Two questions: First: the web page I cite above describes the interface that the test binary must support to work with cabal, specifically w.r.t. the binary's exit code. Your test suites likely already fit this model. However, if you are using an old version of QuickCheck or HUnit, your executable may not be returning the correct error code. This seems to me to suggest that recent versions of HUnit automatically take care of generating the exit code, but I've found that I have to examine HUnit's results and synthesize the exit code manually, as in the driver program below. (I'm running HUnit 1.2.4.2, but the interface for 1.2.4.3 doesn't appear to differ on this point.) Am I misinterpreting the wiki page, or am I missing something in HUnit's API that generates the exit code automatically? Second: Am I specifying the Build-Depends correctly for the Test-Suite? Specifically: do I need to state a dependency on the library defined in the same package, or does it pick that up automatically? Further, foo-tests doesn't use parsec directly. Is the transitive dependency automatically provided for me, or do I need to list it explicitly as below? Thanks much, Richard My cabal file: Name: foo Version:0.0 Cabal-Version: = 1.2 Author: Richard Cobbe Synopsis: Sample cabal package for HUnit integration Build-Type: Simple Library Exposed-Modules: Foo, Foo.Parser, Foo.Show Build-Depends: base = 4.3.1.0 5, parsec = 3.1.2 Test-Suite foo-tests main-is: foo-tests.hs type: exitcode-stdio-1.0 Build-Depends: base = 4.3.1.0 5, parsec = 3.1.2, HUnit = 1.2.4.2 and foo-tests.hs: module Main where import Test.HUnit import qualified Foo.Parser import System.Exit main :: IO () main = do c - runTestTT (Foo ~: Foo.Parser.tests) if (errors c == 0 failures c == 0) then exitWith ExitSuccess else exitWith (ExitFailure (-1)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] existential types and cast
Hi Corentin, If you could explain *why* there should be a type associated to each event value, it would help, maybe. If it's a design choice , maybe it's wrong design. One reason to use dynamic typing would be to plug in new type of events. But if you already have the events semantics , this is not useful. If the language of events is complex , possibly recursive, you can use GADTs to enforce their validity by construction and you don't need to typefy the event values, but some of their characteristics. Remember type machinery is good to give correctness at the compilation time which Typeable defeats moving checks at runtime. So lifting values to types and eliminating this information with existentials and casting seems wrong. paolino 2012/7/4 Corentin Dupont corentin.dup...@gmail.com Hi Paolino, the user can add as many handlers he wants for each event. When a event is triggered along with a data, all handlers associated to that event should be triggered and passed the data. The trick is, there is one type of data associated with each event. That's why I cannot use a Event datatype: how to associate a data type to each event value? This would be some sort of dependant typing if I'm not mistaken. That's why my events exists both on type level and value level: *data NewPlayer = NewPlayer *wich allows me to associate it a typf data with type indexing.*.. * Regards Corentin On Wed, Jul 4, 2012 at 12:58 PM, Paolino paolo.verone...@gmail.comwrote: Hi How many handlers for each type of event in the list of handlers ? If you have only one handler for each type , it should go in the typeclass, and you don't need typeable. If you have more than one maybe you can avoid using type indexing at all, because it doesn't resolve the handler selection issue. By the way , it's not clear to me why you don't have a simple Event datatype describing all the possible events in advance. Regards paolino 2012/7/3 Corentin Dupont corentin.dup...@gmail.com Hi all, I read somewhere (here: http://stackoverflow.com/questions/2300275/how-to-unpack-a-haskell-existential-type) that it's bad to try to unbox an existential type using a cast. OK, but without I really can't figure out how to do what I want: *data NewPlayer = NewPlayer deriving (Typeable, Eq) data NewRule = NewRule deriving (Typeable, Eq) class (Eq e, Typeable e) = Event e where data EventData e instance Event NewPlayer where data EventData NewPlayer = P Int instance Event NewRule where data EventData NewRule = R Int instance Typeable1 EventData where typeOf1 _ = mkTyConApp (mkTyCon EventData) [] data EventHandler = forall e . (Event e) = EH e (EventData e - IO ()) addEvent :: (Event e) = e - (EventData e - IO ()) - [EventHandler] - [EventHandler] addEvent e h ehs = (EH e h):ehs triggerEvent :: (Event e) = e - (EventData e) - [EventHandler] - IO () triggerEvent e d ehs = do let r = find (\(EH myEvent _) - cast e == Just myEvent) ehs case r of Nothing - return () Just (EH _ h) - case cast h of Just castedH - castedH d Nothing - return ()* How to remove the casts from triggerEvent? All that I want is to apply the handler found on the data passed in parameter. I tried to add a function apply in the class, without success: *apply :: (EventData e - IO ()) - (EventData e) - IO () apply = ($)* Thanks! Corentin ___ 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] existential types and cast
Thanks Paolino, I will try to see how I can use your implementation!
Corentin
On Wed, Jul 4, 2012 at 9:24 PM, Paolino
paowolo.verone...@gmail.compaolo.verone...@gmail.com
wrote:
Hi Corentin,
This is how I would model your request (without concrete constructors for
Player and Rule)
I'm sure there are better descriptions also as I'm not an expert.
paolino
{-# LANGUAGE DataKinds, GADTs, KindSignatures #-}
data Player
data Rule
data Data = Player | Rule
data EventKind = Action | Reaction
data Event :: EventKind - * where
NewPlayer :: Player - Event Action
NewRule:: Rule - Event Action
NewHandler :: (Event Action - IO ()) - Event Reaction
handle :: Event Action - Event Reaction - IO ()
handle x (NewHandler f) = f x
reaction :: Event a - [Event Reaction] - IO [Event Reaction]
reaction f@(NewHandler _) es = return $ f:es
reaction p@(NewPlayer _) es = mapM_ (handle p) es return es
reaction r@(NewRule _) es = mapM_ (handle r) es return es
2012/7/4 Corentin Dupont corentin.dup...@gmail.com
Hi,
for example, in my game (Nomic) if a new player arrives, I trigger a
NewPlayer event. All handlers registered for that event should be
triggered, and passed a structure Player containing all the infos of the
incoming player.
If there is a new rule submitted, that the same: the event NewRule is
triggered and the handlers are passed a structure Rule. Thus I want the
handlers registered on NewPlayer to have the type Player - xxx, and on
NewRule to have the type Rule - xxx. I want to be able to associate an
arbitrary data type (here Player and Rule) to an event.
The handlers are inherently of different types, but I want to store them
in a unique list hence the existential...
On Wed, Jul 4, 2012 at 4:33 PM, Paolino paolo.verone...@gmail.comwrote:
Hi Corentin,
If you could explain *why* there should be a type associated to each
event value, it would help, maybe.
If it's a design choice , maybe it's wrong design. One reason to use
dynamic typing would be to plug in new type of events. But if you already
have the events semantics , this is not useful.
If the language of events is complex , possibly recursive, you can use
GADTs to enforce their validity by construction and you don't need to
typefy the event values, but some of their characteristics.
Remember type machinery is good to give correctness at the compilation
time which Typeable defeats moving checks at runtime. So lifting values to
types and eliminating this information with existentials and casting seems
wrong.
paolino
2012/7/4 Corentin Dupont corentin.dup...@gmail.com
Hi Paolino,
the user can add as many handlers he wants for each event.
When a event is triggered along with a data, all handlers associated to
that event should be triggered and passed the data.
The trick is, there is one type of data associated with each event.
That's why I cannot use a Event datatype: how to associate a data type to
each event value? This would be some sort of dependant typing if I'm not
mistaken.
That's why my events exists both on type level and value level:
*data NewPlayer = NewPlayer
*
wich allows me to associate it a typf data with type indexing.*..
*
Regards
Corentin
On Wed, Jul 4, 2012 at 12:58 PM, Paolino paolo.verone...@gmail.comwrote:
Hi
How many handlers for each type of event in the list of handlers ?
If you have only one handler for each type , it should go in the
typeclass, and you don't need typeable.
If you have more than one maybe you can avoid using type indexing at
all, because it doesn't resolve the handler selection issue.
By the way , it's not clear to me why you don't have a simple Event
datatype describing all the possible events in advance.
Regards
paolino
2012/7/3 Corentin Dupont corentin.dup...@gmail.com
Hi all,
I read somewhere (here:
http://stackoverflow.com/questions/2300275/how-to-unpack-a-haskell-existential-type)
that it's bad to try to unbox an existential type using a cast. OK, but
without I really can't figure out how to do what I want:
*data NewPlayer = NewPlayer deriving (Typeable, Eq)
data NewRule = NewRule deriving (Typeable, Eq)
class (Eq e, Typeable e) = Event e where
data EventData e
instance Event NewPlayer where
data EventData NewPlayer = P Int
instance Event NewRule where
data EventData NewRule = R Int
instance Typeable1 EventData where
typeOf1 _ = mkTyConApp (mkTyCon EventData) []
data EventHandler = forall e . (Event e) = EH e (EventData e - IO
())
addEvent :: (Event e) = e - (EventData e - IO ()) -
[EventHandler] - [EventHandler]
addEvent e h ehs = (EH e h):ehs
triggerEvent :: (Event e) = e - (EventData e) - [EventHandler] -
IO ()
triggerEvent e d ehs = do
let r = find (\(EH myEvent _) - cast e == Just myEvent) ehs
case r of
Nothing - return ()
Just (EH _ h) - case cast h of
Just castedH - castedH d
Nothing - return ()*
How to
Re: [Haskell-cafe] existential types and cast
Hi, for example, in my game (Nomic) if a new player arrives, I trigger a NewPlayer event. All handlers registered for that event should be triggered, and passed a structure Player containing all the infos of the incoming player. If there is a new rule submitted, that the same: the event NewRule is triggered and the handlers are passed a structure Rule. Thus I want the handlers registered on NewPlayer to have the type Player - xxx, and on NewRule to have the type Rule - xxx. I want to be able to associate an arbitrary data type (here Player and Rule) to an event. The handlers are inherently of different types, but I want to store them in a unique list hence the existential... On Wed, Jul 4, 2012 at 4:33 PM, Paolino paolo.verone...@gmail.com wrote: Hi Corentin, If you could explain *why* there should be a type associated to each event value, it would help, maybe. If it's a design choice , maybe it's wrong design. One reason to use dynamic typing would be to plug in new type of events. But if you already have the events semantics , this is not useful. If the language of events is complex , possibly recursive, you can use GADTs to enforce their validity by construction and you don't need to typefy the event values, but some of their characteristics. Remember type machinery is good to give correctness at the compilation time which Typeable defeats moving checks at runtime. So lifting values to types and eliminating this information with existentials and casting seems wrong. paolino 2012/7/4 Corentin Dupont corentin.dup...@gmail.com Hi Paolino, the user can add as many handlers he wants for each event. When a event is triggered along with a data, all handlers associated to that event should be triggered and passed the data. The trick is, there is one type of data associated with each event. That's why I cannot use a Event datatype: how to associate a data type to each event value? This would be some sort of dependant typing if I'm not mistaken. That's why my events exists both on type level and value level: *data NewPlayer = NewPlayer * wich allows me to associate it a typf data with type indexing.*.. * Regards Corentin On Wed, Jul 4, 2012 at 12:58 PM, Paolino paolo.verone...@gmail.comwrote: Hi How many handlers for each type of event in the list of handlers ? If you have only one handler for each type , it should go in the typeclass, and you don't need typeable. If you have more than one maybe you can avoid using type indexing at all, because it doesn't resolve the handler selection issue. By the way , it's not clear to me why you don't have a simple Event datatype describing all the possible events in advance. Regards paolino 2012/7/3 Corentin Dupont corentin.dup...@gmail.com Hi all, I read somewhere (here: http://stackoverflow.com/questions/2300275/how-to-unpack-a-haskell-existential-type) that it's bad to try to unbox an existential type using a cast. OK, but without I really can't figure out how to do what I want: *data NewPlayer = NewPlayer deriving (Typeable, Eq) data NewRule = NewRule deriving (Typeable, Eq) class (Eq e, Typeable e) = Event e where data EventData e instance Event NewPlayer where data EventData NewPlayer = P Int instance Event NewRule where data EventData NewRule = R Int instance Typeable1 EventData where typeOf1 _ = mkTyConApp (mkTyCon EventData) [] data EventHandler = forall e . (Event e) = EH e (EventData e - IO ()) addEvent :: (Event e) = e - (EventData e - IO ()) - [EventHandler] - [EventHandler] addEvent e h ehs = (EH e h):ehs triggerEvent :: (Event e) = e - (EventData e) - [EventHandler] - IO () triggerEvent e d ehs = do let r = find (\(EH myEvent _) - cast e == Just myEvent) ehs case r of Nothing - return () Just (EH _ h) - case cast h of Just castedH - castedH d Nothing - return ()* How to remove the casts from triggerEvent? All that I want is to apply the handler found on the data passed in parameter. I tried to add a function apply in the class, without success: *apply :: (EventData e - IO ()) - (EventData e) - IO () apply = ($)* Thanks! Corentin ___ 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] haskell.org website ?
Hi, Haskell.org website seems dropping offline at this moment. Anyone know what's happening to it? Thanks, Qi ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Is there a GHC flag that will allow mutable top level state while you are debugging and then ...
you can turn the flag off when you are ready to do the computational heavy lifting so that you don't have to modify your code base? That is, GHC can then apply its algebraic transformation optimizations to the code algebra of the pure functions. -- -- Regards, KC ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HUnit/cabal integration
First: the web page I cite above describes the interface that the test binary must support to work with cabal, specifically w.r.t. the binary's exit code. Your test suites likely already fit this model. However, if you are using an old version of QuickCheck or HUnit, your executable may not be returning the correct error code. This seems to me to suggest that recent versions of HUnit automatically take care of generating the exit code, but I've found that I have to examine HUnit's results and synthesize the exit code manually, as in the driver program below. (I'm running HUnit 1.2.4.2, but the interface for 1.2.4.3 doesn't appear to differ on this point.) Am I misinterpreting the wiki page, or am I missing something in HUnit's API that generates the exit code automatically? AFAIK, you have to do it explicitly. But you can shorten it to something like this: when (errors c /= 0 || failures c /= 0) exitFailure Personally I'd use some test framework that is build on top of HUnit and QuickCheck. My weapon of choice is Hspec [1], but there are other options. Second: Am I specifying the Build-Depends correctly for the Test-Suite? Specifically: do I need to state a dependency on the library defined in the same package, or does it pick that up automatically? Further, foo-tests doesn't use parsec directly. Is the transitive dependency automatically provided for me, or do I need to list it explicitly as below? You only have to add dependencies on what you actually use, so if you depend on your library and only use stuff from your library, you do not need to depend on parsec. On a broader scope, you have two options, either (a) Depend on your library in your Cabal test section. or (b) Include the source files of your library in your Cabal test section. Whether you want (a) or (b) depends on the circumstances. Here is a (possibly not complete) list of differences: - (a) Is suitable when you only want to test the public interface of your library, but it does not allow you to test stuff that is not exposed. In contrast, (b) allows you to test stuff that is not exposed. - (a) usually gives you a short test section in your Cabal file (and is more DRY). (b) requires you to repeat all dependencies, options, etc. of your library section in your test section. - Compilation is slower with (b), because the source files of your library are compiled twice. - (b) even works in the rare case, when your test framework depends on your library (e.g. if you use HUnit to test a dependency of HUnit). I'm assuming here, that your library sources and test sources live in different directory hierarchies, and I'm not sure what the exact behavior is, if they don't! Let's look at an example. If your library sources are in '.' and your test sources are in 'test' option (a) looks like so: test-suite foo-tests type: exitcode-stdio-1.0 main-is: foo-tests.hs hs-source-dirs: test build-depends: base = 4.3.1.0 5 , foo-- depend on your library , HUnit = 1.2.4.2 And option (b) looks like so: test-suite foo-tests type: exitcode-stdio-1.0 main-is: foo-tests.hs hs-source-dirs: . -- include the sources of your library , test build-depends: base = 4.3.1.0 5 , parsec = 3.1.2-- inculde the depencencies of your library , HUnit = 1.2.4.2 Hope that helps. Feel free to ask, if anything is unclear. Cheers, Simon [1] http://hspec.github.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Call to arms: lambda-case is stuck and needs your help
Hi. After 21 months of occasional arguing the lambda-case proposal(s) is in danger of being buried under its own trac ticket comments. We need fresh blood to finally reach an agreement on the syntax. Read the wiki page[1], take a look at the ticket[2], vote and comment on the proposals! P.S. I'm CC-ing Cafe to attract more people, but please keep the discussion to the GHC Users list. [1] http://hackage.haskell.org/trac/ghc/wiki/LambdasVsPatternMatching [2] http://hackage.haskell.org/trac/ghc/ticket/4359 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a GHC flag that will allow mutable top level state while you are debugging and then ...
At Wed, 4 Jul 2012 09:06:32 -0700, KC wrote: you can turn the flag off when you are ready to do the computational heavy lifting so that you don't have to modify your code base? That is, GHC can then apply its algebraic transformation optimizations to the code algebra of the pure functions. What do you mean allow mutable top level state? As in import Foreign.Ptr import Foreign.StablePtr import Foreign.Storable import System.IO.Unsafe destructiveUpdate :: Storable a = a - a - () destructiveUpdate x y = unsafePerformIO $ do ptr - newStablePtr x poke (castPtr (castStablePtrToPtr ptr)) y freeStablePtr ptr ? The only problem that the above function does not work - you can't poke or peek off StablePtrs. If that's what you mean, no. And I doubt it'll ever exist, since it breaks the most important invariant in Haskell - that is, that values don't change. An Haskell compiler will rely on this assumption quite heavily, so changes to that are likely to disrupt things seriously. Also, I don't see how destructive updates help debugging. -- Francesco * Often in error, never in doubt ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News: Issue 234
Welcome to issue 234 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of June 24 to 30, 2012. Quotes of the Week * monochrom: shae ericsson is shae erisson's evil twin who prefers erlang to haskell :) * shapr: If I were to do this in Python, it would be done by now. and it would be full of bugs. Top Reddit Stories * Performance: yes, it’s worth looking at the small stuff Domain: serpentine.com, Score: 61, Comments: 11 On Reddit: [1] http://goo.gl/x2pGf Original: [2] http://goo.gl/SHBNB * Awesome Haskell plugins for Vim! Domain: self.haskell, Score: 61, Comments: 32 On Reddit: [3] http://goo.gl/Bm6wI Original: [4] http://goo.gl/Bm6wI * Galois is Hiring! Domain: haskell.org, Score: 56, Comments: 7 On Reddit: [5] http://goo.gl/c7zj8 Original: [6] http://goo.gl/y7nBd * Haskell Symposium 2012 list of accepted papers Domain: haskell.org, Score: 43, Comments: 12 On Reddit: [7] http://goo.gl/Fq0rD Original: [8] http://goo.gl/CGZV3 * Live coding the game of Sokoban with GUI. Please give me your input for future sessions. Domain: youtu.be, Score: 42, Comments: 38 On Reddit: [9] http://goo.gl/HslD9 Original: [10] http://goo.gl/0ZeMA * Mirrored Lenses Domain: comonad.com, Score: 36, Comments: 30 On Reddit: [11] http://goo.gl/UyGco Original: [12] http://goo.gl/9ltWW * The Game of Distributed Systems Programming. Which Level Are You? Incubaid Research Domain: blog.incubaid.com, Score: 30, Comments: 7 On Reddit: [13] http://goo.gl/EYWj7 Original: [14] http://goo.gl/P0vhZ * SugarHaskell: language extensions in sugar modules[pdf] Domain: informatik.uni-marburg.de, Score: 27, Comments: 7 On Reddit: [15] http://goo.gl/Z4fL5 Original: [16] http://goo.gl/I78Md * parallel cabal-install patches Domain: haskell.org, Score: 26, Comments: 4 On Reddit: [17] http://goo.gl/Yr1JR Original: [18] http://goo.gl/P9WPK * Is anybody using Sublime Text for their Haskell editing? Domain: self.haskell, Score: 19, Comments: 16 On Reddit: [19] http://goo.gl/pmor9 Original: [20] http://goo.gl/pmor9 * Runge–Kutta in Haskell (RK4) Domain: stochastix.wordpress.com, Score: 19, Comments: 7 On Reddit: [21] http://goo.gl/9Bd2b Original: [22] http://goo.gl/H27Fv * How to build an example proxy server using conduit 0.5 Domain: yesodweb.com, Score: 19, Comments: 14 On Reddit: [23] http://goo.gl/BHLRd Original: [24] http://goo.gl/PtOxh * Found myself wanting lambda-case again Domain: self.haskell, Score: 16, Comments: 13 On Reddit: [25] http://goo.gl/LIOKa Original: [26] http://goo.gl/LIOKa * What is the advantage of monad transformers over monad coproducts? Domain: self.haskell, Score: 16, Comments: 28 On Reddit: [27] http://goo.gl/lxX2D Original: [28] http://goo.gl/lxX2D * Elm 0.3.5: JavaScript Integration, Signal Filters, space savings, ... Domain: testblogpleaseignore.com, Score: 15, Comments: 2 On Reddit: [29] http://goo.gl/jTwAz Original: [30] http://goo.gl/UzoZL * Scribd's AI Challenge Now Supports Haskell Domain: groups.google.com, Score: 14, Comments: 6 On Reddit: [31] http://goo.gl/xmuwG Original: [32] http://goo.gl/oQsTG * EclipseFP: integrating stylish-haskell Domain: jpmoresmau.blogspot.fr, Score: 11, Comments: On Reddit: [33] http://goo.gl/reK9T Original: [34] http://goo.gl/2416v Top StackOverflow Questions * Bug in Data.Map implementation? votes: 15, answers: 1 Read on SO: [35] http://goo.gl/xcgC1 * Monads with Join() instead of Bind() votes: 15, answers: 6 Read on SO: [36] http://goo.gl/phgVU * Haskell numbers and type system? votes: 11, answers: 2 Read on SO: [37] http://goo.gl/nv7Be * How to put constraints on the associated data? votes: 10, answers: 2 Read on SO: [38] http://goo.gl/6zOr9 * How to run Snap haskell webapp in production? votes: 9, answers: 3 Read on SO: [39] http://goo.gl/kx2DR * How can I search a hackage package for a function? votes: 8, answers: 2 Read on SO: [40] http://goo.gl/9fm4O * In Haskell, + is a function, (+ 2) is a function, (+ 2 3) is 5. What exactly is going on there? votes: 8, answers: 4 Read on SO: [41] http://goo.gl/PP2X2 * How can I emulate pointers in Haskell? votes: 8, answers: 1 Read on SO: [42] http://goo.gl/Yq01G * Haskell Precedence: Lambda and operator votes: 8, answers: 2 Read on SO: [43] http://goo.gl/X8yvV * Binding name in type signature using DataKind votes: 8, answers: 2 Read on SO: [44] http://goo.gl/rYcS8 * Missing something with Reader monad - passing the damn thing around everywhere votes: 7,
[Haskell-cafe] OpenShift a free PaaS from RedHat
Hi Folks, I just found out about OpenShift - its a free PaaS from RedHat. It has some interesting offerings. It does not support Haskell out of the box as of now. Please do check it out and if you like it - vote for Haskell support on it here - https://openshift.redhat.com/community/content/support-for-haskell Meanwhile, I am trying to get complied Haskell executable to run on that platform. Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is haskell.org down?
Thanks! Regards, Kashyap On Thu, Jul 5, 2012 at 4:20 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Not anymore! On 5 July 2012 15:13, C K Kashyap ckkash...@gmail.com wrote: Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com http://IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Parallel Haskell Digest 11
Parallel Haskell Digest 11 == HTML version: http://www.well-typed.com/blog/67 Hello Haskellers! It's time for another Parallel Haskell Digest! Unfortunately, this may just be our last one, at least within the context of the Parallel GHC project. That said, we may as a community be at the very beginnings of Haskell as *the* language of choice for your parallel and concurrent needs. Maybe we need to keep something like the Digest going to help our little FP monster through its infancy? Any volunteers in the community? If you're interested in picking up the torch, please give us a shout! Otherwise, if you can't take on a (perhaps rotating) digest commitment, but still want to help, would you be kind enough to fill out a small [survey](http://goo.gl/bP2fn) on the digest? There are just five questions on it, plus a feedback form. Anything you can say will help those of us in the Secret Haskell Propaganda Commitee to fine tune our efforts: http://goo.gl/bP2fn It's been a fantastic year for me, working on the Parallel GHC project, learning about all sorts of neat ideas and technologies (as a basic parallel-naive Haskeller), and trying to reflect them back in a way that hopefully helps the broader community. Thanks to all of you in the parallel Haskell world first for cranking out all this great stuff for us to use, and second for your patience and support. Thanks especially to my follow Well-Typed-ers for all the fun chats, the feedback on drafts, and help getting up to speed. One last thing before signing off as your Parallel Haskell Digester. While the digest may be coming to an end, there will at least be one encore! It turns out we had so much to say in our last word of the month, that we'll have to put in in a follow-up posting. In the meantime, we'll just leave you with a little teaser… News -- *[Announce: Haskell Platform 2012.2.0.0][n1] (3 Jun) The new Haskell Platform is out! If you've been waiting for Haskell Platform before moving on GHC 7.4, now's a great time to upgrade. Of particular interest to parallel Haskellers, this latest GHC offers better profiling flags, multicore profiling, vastly improved DPH, event logging [allows ThreadScope spark profiling], and more convenient RTS flags. *[Introducing FP Complete][n2] (6 Jun) You might have Bartosz Milewski around. If not, have a look at the [Downfall of Imperative Programming][downfall]. Bartosz posted a quick message introducing himself to the community along with the new company FP Complete, which aims to commercialise Haskell. Bartosz believes that “now is the right time for Haskell to become a strong software industry player, especially that functional programming is being widely recognized as the answer to the recent multicore and GPU explosion.” We'll hopefully find out more about FP Complete have in mind as their plans stabilise a bit. *[3 year Bioinformatics RD position in Granada, Spain][n3] Love Functional Programming and concurrency? If you are a CS/Math/IT graduate without a PhD, and have had no more than 4 years of research experience, and have not lived in Spain for more than 12 months (within the last 3 years), Era7 has a position for you! You'll be hacking Scala and using AWS for everything. So if Akka is the sort of thing you're into, this could be the job for you. Word of the month (teaser!) -- The word of the month series has given us a chance to survey the arsenal of Haskell parallelism and concurrency constructs: *some low level foundations (sparks and threads), *three ways to do parallelism (parallel arrays, strategies, dataflow), *and some concurrency abstractions (locks, transactions, channels) The Haskell approach has been to explicitly recognise the vastness of the parallelism/concurrency space, in other words, to provide a multitude of right tools for a multitude of right jobs. Better still, the tools we have are largely interoperable, should we find ourselves with jobs that don't neatly fit into a single category. The Haskell of 2012 may be in a great place for parallelism and concurrency, but don't think this is the end of the story! What we've seen so far is only a snapshot of the technology as it hurtles through the twenty-tens (How quaint are we, Future Haskeller?). While we can't say what exactly the future will bring, we can look at one of the directions that Haskell might branch into in the coming decade. The series so far has focused on things you might do with a single computer, using parallelism to speed up your software, or using concurrency abstractions to preserve your sanity in the face of non-determinism. But now what if you have more than one computer? Our final word of the month is *actor*. Actors
[Haskell-cafe] arbitrary rank polymorphism and ghc language pragmas
Hi All: I've been working through some details in these papers [1], [2] and noticed a language pragma configuration that I hope you can confirm. When using explicit foralls in a data constructor, it appears that GHC 7.4.2 requires Rank2Types in the Language pragma for what the papers consider rank 1 types. Here's an example: data T = TC (forall a b. a - b - a) Am I correct, or is there another extension? The ExplicitForAll does not appear to support rank 1 types in data constructors. 1. Practical Type Inference for Arbitrary-Rank Types. 2. A Direct Algorithm for Type Inference in the Rank 2 Fragment of the Second-Order Lambda Calculus. -- Rick ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
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
Re: [Haskell-cafe] arbitrary rank polymorphism and ghc language pragmas
At Thu, 05 Jul 2012 11:18:00 -0400, rickmurphy wrote: data T = TC (forall a b. a - b - a) The type of `TC' will be `(forall a b. a - b - a) - T', a Rank-2 type. -- Francesco * Often in error, never in doubt ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] arbitrary rank polymorphism and ghc language pragmas
On 05/07/12 17:18, rickmurphy wrote: Hi All: I've been working through some details in these papers [1], [2] and noticed a language pragma configuration that I hope you can confirm. When using explicit foralls in a data constructor, it appears that GHC 7.4.2 requires Rank2Types in the Language pragma for what the papers consider rank 1 types. Here's an example: data T = TC (forall a b. a - b - a) Am I correct, or is there another extension? The ExplicitForAll does not appear to support rank 1 types in data constructors. There is the PolymorphicComponents extension precisely for this use case. Twan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] OpenShift a free PaaS from RedHat
Hi, --- On Thu, Jul 5, 2012 at 8:41 PM, C K Kashyap ckkash...@gmail.com wrote: | I just found out about OpenShift - its a free PaaS from RedHat. It has some | interesting offerings. It does not support Haskell out of the box as of now. | Please do check it out and if you like it - vote for Haskell support on it | here - https://openshift.redhat.com/community/content/support-for-haskell | | Meanwhile, I am trying to get complied Haskell executable to run on that | platform. \-- We already have a Fedora Haskell SIG [1] where we are working on shipping Haskell packages in Fedora. Recently, support for EL-6 was added, and one can get Haskell packages through the EPEL [2] repository. Please feel free to ping us on #fedora-haskell on irc.freenode.net. SK [1] Fedora Haskell SIG. http://fedoraproject.org/wiki/Haskell_SIG [2] Extra Packages for Enterprise Linux (EPEL). http://fedoraproject.org/wiki/EPEL -- Shakthi Kannan http://www.shakthimaan.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal problem re. haskelldb-hdbc-mysql
On Wed, Jul 4, 2012 at 3:58 PM, Yves Parès yves.pa...@gmail.com wrote: Hi, the package http://hackage.haskell.org/package/haskelldb-hdbc-mysql/ the use of HDBC 2.3.0 I'm using cabal-install 0.14, and with a fresh install (no packages already installed), cabal-install tries to install HDBC-2.1.1 instead of, say, HDBC-2.2.7.0. The problem is that HDBC-2.1.1 is old (2009) and does not compile. When I download haskelldb-hdbc-mysql manually, change the dependency and then install, it compiles fine. Is the dependency ill-declared, or is that a cabal problem? Apart from the change of license, there were no serious changes to the HDBC interface between the 2.2.* and 2.3.* series: as far as I know, it should be fine to change the dependency. That said, I've not worked with haskelldb-hdbc-mysql, so I can't say for sure. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] arbitrary rank polymorphism and ghc language pragmas
Thanks Francesco. And I did verify that ExplicitForAll does in fact allow Rank 1 Types in functions like the following ... f :: (forall a. a - a) -- Rick On Thu, 2012-07-05 at 16:28 +0100, Francesco Mazzoli wrote: At Thu, 05 Jul 2012 11:18:00 -0400, rickmurphy wrote: data T = TC (forall a b. a - b - a) The type of `TC' will be `(forall a b. a - b - a) - T', a Rank-2 type. -- Francesco * Often in error, never in doubt ___ 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] Bad interface problem.
On 12-07-03 04:19 AM, Magicloud Magiclouds wrote: $ cabal --upgrade-dependencies --enable-documentation --force-reinstalls --solver=topdown QuickCheck-2.5 Test/QuickCheck/All.hs:15:1: Bad interface file: /home/magicloud/.cabal/lib/template-haskell-2.6.0.0/ghc-7.4.2/Language/Haskell/TH.hi Something is amiss; requested module template-haskell-2.6.0.0:Language.Haskell.TH differs from name found in the interface file template-haskell:Language.Haskell.TH I think things are so messed up that it is time to clean out everything. See my http://www.vex.net/~trebla/haskell/sicp.xhtml#remove In fact, time to read the whole article and avoid unsafe re-installs and upgrades. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Posting jobs on Haskellers.com
There are no job postings on Haskellers.com and I'm wondering whether it's because you have to wait for the verified status before you can post (and that's after you have successfully verified your email). Posting the job on the CUFP site, on the other hand, was painless: http://cufp.org/jobs/haskell-systems-administrator .___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Plain lambda inside banana brackets in the arrow notation
Hello, In a program, I have an arrow MyArr and a combinator called repeat of the following type: repeat :: Int - (Int - MyArr e a) - MyArr e a My problem is that the code becomes messy when I use this combinator inside the arrow notation, and I am looking for a way to write the code in a more readable way. To explain the problem, first consider the following combinator repeat', which is less general than repeat: repeat' :: Int - MyArr (e, Int) a - MyArr e a repeat' n f = repeat n g where g i = arr (\e - (e, i)) f Combinator repeat' is nice to use in the arrow notation, thanks to banana brackets and the interpretation of lambda: test1 :: MyArr [Double] String test1 = proc xs - do let y = func1 xs z - job1 - xs (|(repeat' 100) (\i - job2 - xs !! i + y + z)|) -- func1 :: [Double] - Double -- job1 :: MyArr [Double] Double -- job2 :: MyArr Double String However, in my program, I often have to use repeat instead of repeat' like: test2 :: MyArr [Double] String test2 = proc xs - do let y = func1 xs z - job1 - xs repeat 100 (\i - proc (xs, y, z) - job3 (i * 2) - xs !! i + y + z) - (xs, y, z) -- job3 :: Int - MyArr Double String Note that variable i is used as an argument to function job3 outside MyArr, and this cannot be done with repeat'. The code for test2 looks messy to me because I have to write “(xs, y, z)”, that is, the list of variables used inside the subcomputation explicitly (and twice). It does not seem possible to use banana brackets here because the type of the subcomputation does not meet the requirements stated in http://www.haskell.org/ghc/docs/7.4.2/html/users_guide/arrow-notation.html#id686230. How can I use combinators like repeat, which takes a plain function as an argument, in the arrow notation in a more readable way? Or am I trying to do an impossible thing? Best regards, Tsuyoshi ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal problem re. haskelldb-hdbc-mysql
On 12-07-04 10:58 AM, Yves Parès wrote: the package http://hackage.haskell.org/package/haskelldb-hdbc-mysql/ the use of HDBC 2.3.0 I'm using cabal-install 0.14, and with a fresh install (no packages already installed), cabal-install tries to install HDBC-2.1.1 instead of, say, HDBC-2.2.7.0. HDBC 2.2.* all want time=1.1.2.4 =1.2.0.3, GHC 7.4.1 comes with time-1.4, therefore HDBC 2.2.* are all rejected. 2.1.1 is the topmost one without the upper bound. This analysis is made possible by cabal install --dry-run -v3 haskelldb-hdbc-mysql of cabal-install 0.14. Now with actually relevant output! (As part of the new modular solver, I guess.) P.S. haskelldb-hdbc wants mtl-2.0.*, but you already have mtl-2.1 because you have cabal-install 0.14. mtl-2.0.1.0 in turn wants transformers-0.2.*, but you already have transformers-0.3.0.0 again because you have cabal-install 0.14. Expect mysterious problems in the future. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HUnit/cabal integration
On Thu, Jul 05, 2012 at 04:17:33PM +0200, Simon Hengel wrote: First: the web page I cite above describes the interface that the test binary must support to work with cabal, specifically w.r.t. the binary's exit code. Your test suites likely already fit this model. However, if you are using an old version of QuickCheck or HUnit, your executable may not be returning the correct error code. This seems to me to suggest that recent versions of HUnit automatically take care of generating the exit code, but I've found that I have to examine HUnit's results and synthesize the exit code manually, as in the driver program below. (I'm running HUnit 1.2.4.2, but the interface for 1.2.4.3 doesn't appear to differ on this point.) Am I misinterpreting the wiki page, or am I missing something in HUnit's API that generates the exit code automatically? AFAIK, you have to do it explicitly. But you can shorten it to something like this: when (errors c /= 0 || failures c /= 0) exitFailure Ah, good suggestion. Thanks! Second: Am I specifying the Build-Depends correctly for the Test-Suite? Specifically: do I need to state a dependency on the library defined in the same package, or does it pick that up automatically? Further, foo-tests doesn't use parsec directly. Is the transitive dependency automatically provided for me, or do I need to list it explicitly as below? snip Let's look at an example. Many thanks for your advice -- and I particularly appreciate the examples! I haven't had a chance to try them out yet, but I hope to be able to soon. Thanks a bunch for your help, Richard ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: Sifflet visual programming language, release 2.0.0.0
I don't usually get this excited about a release, but after nearly a year of not being able to do any work on Sifflet, I am now *Extremely Happy* to announce -- Sifflet and sifflet-lib 2.0.0.0, now available on Hackage! This version introduces a type checker and partial support for higher order functions in Sifflet, the visual, functional programming language and support system for students learning about recursion. Sifflet programmers define functions by drawing diagrams, and the Sifflet interpreter uses the diagrams to show how function calls are evaluated. Sifflet-lib is the library containing many modules of the Sifflet application. What's New -- July 5, 2012, Version 2.0.0.0: * Partial support for higher order functions, like map and filter. See Lesson 10 in the Sifflet Tutorial. * Sifflet now provides type checking and type inference. This should make it possible to provide exporters to languages, like Java, that require type declarations. (Unfortunately, the error messages for incorrectly typed functions are not yet friendly for novice programmers.) * Added a menu command (File / Save image ...) to save vector graphic images of functions in the Sifflet Workspace or Edit function windows. Images can be saved in SVG, Postscript, and PDF formats. * Reorganized hierarchical modules in the library to conform to the recommended practice. See the RELEASE-NOTES for details. * Several bugs are fixed, including one which crashed Sifflet when applying a function definition with an incomplete `if` tree. See ISSUES for details. * There is a new file format for saving function definitions to support higher-order function types. The new format, siffml 2.0, has a RELAX NG schema; siffml 1.0 files can still be opened in Sifflet 2.0. About Sifflet - Sifflet is a visual, functional programming language intended as an aid for learning about recursion. * A picture explains Sifflet better than words: please see the screenshot showing how to evaluate 3!: http://mypage.iu.edu/~gdweber/software/sifflet/home.html * Features: - Visual editor. - Visual tracer/debugger which shows how recursive and other function calls are evaluated. To support active learning and avoid screen clutter, Sifflet displays only as much of the computation as the user requests. - Carefully crafted tutorial with 44 pictures, about 26 pages if printed. - Number, string, and list data types. - Small collection of primitive functions. - Runnable examples of compound functions. - Sifflet functions can be exported to Scheme, Python 3, and Haskell. References -- * Download: http://hackage.haskell.org/package/sifflet-lib http://hackage.haskell.org/package/sifflet * Home page: http://mypage.iu.edu/~gdweber/software/sifflet/home.html * Sifflet Tutorial: http://mypage.iu.edu/~gdweber/software/sifflet/doc/tutorial.html * RELEASE-NOTES: http://mypage.iu.edu/~gdweber/software/sifflet/RELEASE-NOTES * ISSUES: http://mypage.iu.edu/~gdweber/software/sifflet/ISSUES -- Gregory D. Weber, Ph. D.: Associate Professor of Informatics / \ Indiana University East 0 : Tel. (765) 973-8420; FAX (765) 973-8550 / \ http://mypage.iu.edu/~gdweber/ 1 [] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] OpenShift a free PaaS from RedHat
Hey Shakti, OpenShift gives access to Linux virtual machines on the cloud. However, we do not have root access so we cannot install any new package. I was trying to get my haskell code compiled into native on my local linux box and taking it to those machines. That does not seem to work because of two things - 1. GLIBC version mismatch 2. libgmp missing on the openshift box Regards, Kashyap On Thu, Jul 5, 2012 at 9:19 PM, Shakthi Kannan shakthim...@gmail.comwrote: Hi, --- On Thu, Jul 5, 2012 at 8:41 PM, C K Kashyap ckkash...@gmail.com wrote: | I just found out about OpenShift - its a free PaaS from RedHat. It has some | interesting offerings. It does not support Haskell out of the box as of now. | Please do check it out and if you like it - vote for Haskell support on it | here - https://openshift.redhat.com/community/content/support-for-haskell | | Meanwhile, I am trying to get complied Haskell executable to run on that | platform. \-- We already have a Fedora Haskell SIG [1] where we are working on shipping Haskell packages in Fedora. Recently, support for EL-6 was added, and one can get Haskell packages through the EPEL [2] repository. Please feel free to ping us on #fedora-haskell on irc.freenode.net. SK [1] Fedora Haskell SIG. http://fedoraproject.org/wiki/Haskell_SIG [2] Extra Packages for Enterprise Linux (EPEL). http://fedoraproject.org/wiki/EPEL -- Shakthi Kannan http://www.shakthimaan.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] OpenShift a free PaaS from RedHat
Hi Kashyap, I'm not sure if it will solve the problem, but I ran across a tool[1] the other day that bundles up applications with all of the libraries and other resources they need. I wouldn't be surprised if, with this, you can get your code to run on OpenShift. Michael [1] http://www.pgbovine.net/cde.html On Fri, Jul 6, 2012 at 7:51 AM, C K Kashyap ckkash...@gmail.com wrote: Hey Shakti, OpenShift gives access to Linux virtual machines on the cloud. However, we do not have root access so we cannot install any new package. I was trying to get my haskell code compiled into native on my local linux box and taking it to those machines. That does not seem to work because of two things - 1. GLIBC version mismatch 2. libgmp missing on the openshift box Regards, Kashyap On Thu, Jul 5, 2012 at 9:19 PM, Shakthi Kannan shakthim...@gmail.com wrote: Hi, --- On Thu, Jul 5, 2012 at 8:41 PM, C K Kashyap ckkash...@gmail.com wrote: | I just found out about OpenShift - its a free PaaS from RedHat. It has some | interesting offerings. It does not support Haskell out of the box as of now. | Please do check it out and if you like it - vote for Haskell support on it | here - https://openshift.redhat.com/community/content/support-for-haskell | | Meanwhile, I am trying to get complied Haskell executable to run on that | platform. \-- We already have a Fedora Haskell SIG [1] where we are working on shipping Haskell packages in Fedora. Recently, support for EL-6 was added, and one can get Haskell packages through the EPEL [2] repository. Please feel free to ping us on #fedora-haskell on irc.freenode.net. SK [1] Fedora Haskell SIG. http://fedoraproject.org/wiki/Haskell_SIG [2] Extra Packages for Enterprise Linux (EPEL). http://fedoraproject.org/wiki/EPEL -- Shakthi Kannan http://www.shakthimaan.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
Re: [Haskell-cafe] OpenShift a free PaaS from RedHat
OpenShift gives access to Linux virtual machines on the cloud. However, we do not have root access so we cannot install any new package. I was trying to get my haskell code compiled into native on my local linux box and taking it to those machines. That does not seem to work because of two things - 1. GLIBC version mismatch 2. libgmp missing on the openshift box Regards, Kashyap I think you might want to check out CDE. http://www.pgbovine.net/cde.html This will take care of the version mismatch of the libraries. - Satvik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] OpenShift a free PaaS from RedHat
Thank you Micheal and Satvik. I think cde should solve the problem - I'll confirm later - for some reason, I do not have SSH connectivity from my office. What'll be best though is - yesod on OpenShift :) Regards, Kashyap On Fri, Jul 6, 2012 at 10:51 AM, satvik chauhan mystic.sat...@gmail.comwrote: OpenShift gives access to Linux virtual machines on the cloud. However, we do not have root access so we cannot install any new package. I was trying to get my haskell code compiled into native on my local linux box and taking it to those machines. That does not seem to work because of two things - 1. GLIBC version mismatch 2. libgmp missing on the openshift box Regards, Kashyap I think you might want to check out CDE. http://www.pgbovine.net/cde.html This will take care of the version mismatch of the libraries. - Satvik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] OpenShift a free PaaS from RedHat
Hi, --- On Fri, Jul 6, 2012 at 11:16 AM, C K Kashyap ckkash...@gmail.com wrote: | What'll be best though is - yesod on OpenShift :) \-- The review is pending due to dependencies that need to be reviewed first. https://bugzilla.redhat.com/show_bug.cgi?id=630303 SK -- Shakthi Kannan http://www.shakthimaan.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
