Re: [Haskell-cafe] serialize an unknown type
Hi,
I designed my event engine like this:
-- | events types
data Player = Arrive | Leave deriving (Typeable, Show, Eq)
data RuleEvent = Proposed | Activated | Rejected | Added | Modified |
Deleted deriving (Typeable, Show, Eq)
data Time deriving Typeable
data InputChoice c deriving Typeable
(...)
-- | events names
data Event a where
Player :: Player - Event Player
RuleEv :: RuleEvent - Event RuleEvent
Time:: UTCTime -Event Time
InputChoice :: (Eq c, Show c) = PlayerNumber - String - [c] - c -
Event (InputChoice c)
(...)
-- | data associated with each events
data EventData a where
PlayerData :: {playerData :: PlayerInfo}- EventData Player
RuleData:: {ruleData :: Rule}- EventData RuleEvent
TimeData:: {timeData :: UTCTime} - EventData Time
InputChoiceData :: (Show c, Read c, Typeable c) = {inputChoiceData ::
c}- EventData (InputChoice c)
(...)
-- associate an event with an handler
data EventHandler where
EH :: (Typeable e, Show e, Eq e) =
{eventNumber :: EventNumber,
event :: Event e,
handler :: (EventNumber, EventData e) - Exp ()} -
EventHandler
--execute all the handlers of the specified event with the given data
triggerEvent :: (Typeable a, Show a, Eq a) = Event a - EventData a -
[EventHandler] - State Game ()
I use a type parameter e on Event and EventData to be sure that the right
data is shuffled to the right event handler.
It worked well until now. But now I'm hitting a wall with the GUI, because
the data sent back for InputChoice can only be a String.
So, I need to call triggerEvent with: Event(InputChoice String) and EventData
(InputChoice String)...
Which doesn't work obviously because the types are not the same than
initially (for example, the event was built with Event(InputChoice Bool)).
Cheers,
C
On Wed, Oct 24, 2012 at 7:25 PM, Stephen Tetley stephen.tet...@gmail.comwrote:
Hi Corentin
It looks like you are writing the event handler on the server side. If
so, the range of events you can handle is fixed to just those you
implement handlers for - having an openly extensible event type is
useless if this is the case.
Ignoring client/server for a moment, a function (State - State) would
be the most extensible API you could allow for clients. You don't
need to worry about an open set of Event types, a client knows the
state exactly and doesn't need extensibility.
Client/Server operation won't allow a state transformer API as Haskell
can't readily serialize functions. But you can implement a command
language enumerating state changing operations. The second Quickcheck
paper gives a very good example of how to implement such a command
language.
Testing Monadic Code with QuickCheck (2002)
Koen Claessen , John Hughes
www.cse.chalmers.se/~rjmh/Papers/QuickCheckST.ps
Or Citeseer if you need a PDF:
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.19.9275
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Re: [Haskell-cafe] serialize an unknown type
I'm trying to get around my problem (still stuck...).
I have really to call a function like this:
triggerEvent :: (Typeable e, Show e, Eq e) = Event e - EventData e -
State Game ()
This function simply execute an event given the corresponding data and
change the state of the game.
Now as explained my web framework won't accept random types (like e) to
be passed around.
So I said to myself OK, so let's store the events in a list and ask the
gui to just give me the number of the event.
So I have an heterogeneous list of events [EventWrap]:
data EventWrap where
EW :: (Typeable e, Show e, Eq e) = {eventNumber :: Int, event :: Event
e} - EventWrap
Do you think this solution can lead me somewhere?? I have actually doubts I
can find back my Event e from the list because of the implicit forall in
the GADT.
Thanks,
Corentin
On Wed, Oct 24, 2012 at 3:37 PM, Chris Smith cdsm...@gmail.com wrote:
Corentin Dupont corentin.dup...@gmail.com wrote:
I could ask my user to make his new type an instance of a class as
suggested by Alberto...
If you are working with unknown types, then your options are: (a)
constrain to some type class, or (b) have your clients pass in functions to
operate on the type alongside the values. Actually the first is just a
special case of the second with syntactic sugar...
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Re: [Haskell-cafe] serialize an unknown type
Hi Corentin It looks like you are writing the event handler on the server side. If so, the range of events you can handle is fixed to just those you implement handlers for - having an openly extensible event type is useless if this is the case. Ignoring client/server for a moment, a function (State - State) would be the most extensible API you could allow for clients. You don't need to worry about an open set of Event types, a client knows the state exactly and doesn't need extensibility. Client/Server operation won't allow a state transformer API as Haskell can't readily serialize functions. But you can implement a command language enumerating state changing operations. The second Quickcheck paper gives a very good example of how to implement such a command language. Testing Monadic Code with QuickCheck (2002) Koen Claessen , John Hughes www.cse.chalmers.se/~rjmh/Papers/QuickCheckST.ps Or Citeseer if you need a PDF: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.19.9275 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
On Sun, Oct 21, 2012 at 12:39 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? How were you expecting to serialize/deserialize a function? -- brandon s allbery kf8nh sine nomine associates allber...@gmail.com ballb...@sinenomine.net unix/linux, openafs, kerberos, infrastructure http://sinenomine.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
Seems like nobody really understands what is it that you want to accomplish or what your problem is. Отправлено с iPhone 21.10.2012, в 20:39, Corentin Dupont corentin.dup...@gmail.com написал(а): Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, 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] serialize an unknown type
Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... BR, C On Sun, Oct 21, 2012 at 7:03 PM, MigMit miguelim...@yandex.ru wrote: Seems like nobody really understands what is it that you want to accomplish or what your problem is. Отправлено с iPhone 21.10.2012, в 20:39, Corentin Dupont corentin.dup...@gmail.com написал(а): Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, 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] serialize an unknown type
On Sun, Oct 21, 2012 at 07:20:10PM +0200, Corentin Dupont wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... Can't you simply, when defining the type event, add a deriving (Show, Read)? Then the standard (but slow) read/show serialisation would work for you. If you're asking to de-serialise an unknown type (i.e. you don't know what type it should restore a-priori, but you want to do that based on the contents of the file), things become a little more complex. Unless you can further restrict the type 'a', really complex. Maybe stating your actual problem, rather than the implementation question, would be better? regards, iustin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
Hi Iustin, yes I want to deserialize an unknown type based on the content of the file (in this example). Let's say I can reduce the spectum of types to: Strings, all the types in Enum, Ints. Is it possible? My real problem is that on my web interface I want to use web routes to allow a user to pass an Event back to the engine. The problem is that it seems that web-routes only accepts Strings (or some known types) to be passed on the web route, whereas I need to pass random types. On Sun, Oct 21, 2012 at 8:00 PM, Iustin Pop iu...@k1024.org wrote: On Sun, Oct 21, 2012 at 07:20:10PM +0200, Corentin Dupont wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... Can't you simply, when defining the type event, add a deriving (Show, Read)? Then the standard (but slow) read/show serialisation would work for you. If you're asking to de-serialise an unknown type (i.e. you don't know what type it should restore a-priori, but you want to do that based on the contents of the file), things become a little more complex. Unless you can further restrict the type 'a', really complex. Maybe stating your actual problem, rather than the implementation question, would be better? regards, iustin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
Oh, now I've got it. First of all, functions of type IO () - Event a are impossible (unless you resort to tricks with unsafePerformIO, which is not what you want to deal with right now). You've probably meant something like IO (Event a) (at least, that is the type of function which would read Event a from file or input stream or something else external). Secondly, functions (and values) with parametric types, like IO (Event a) require you to provide the type a in your code. They won't take it from somewhere magically. You can take a look at the read function in Prelude for example. If you really want to store the type information and read it back, you should do it yourself, inventing some representation for your type, writing it to disk, reading back and parsing it. And you can't do that for all types in existence, so you'll need to do that for some specific types (and no, instances of Typeable aren't what you want). And you'll have to deal with type system, which won't allow you to just say hey, let that be whatever type it happens to be, I don't care; you'd have to wrap this into one existentially quantified type (or GADT). Keep in mind that this is not very Haskell-y. First of all, try to analyse, what this a in Event a could be. What are the limits here? And don't say there aren't any, because if you don't know anything about the type, you can't do anything with it. So, maybe you would end up with a finite set of types — this would simplify matters a lot. Or maybe you'd find out that there are inifinitely many types of events — but they can be somehow generated with a finite number of constructors — that would be quite simple as well. So, what is the bigger picture here? On Oct 21, 2012, at 9:20 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... BR, C On Sun, Oct 21, 2012 at 7:03 PM, MigMit miguelim...@yandex.ru wrote: Seems like nobody really understands what is it that you want to accomplish or what your problem is. Отправлено с iPhone 21.10.2012, в 20:39, Corentin Dupont corentin.dup...@gmail.com написал(а): Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, 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] serialize an unknown type
You can include the type in the serialized string. When recovering you can read the type and use to look for the appropriate deserializer in a lookup table where you have registered the deserializer. I use this trick in the IDynamic package,. that serializes-deserializes dynamic types: http://hackage.haskell.org/package/IDynamic-0.1 2012/10/20 Corentin Dupont corentin.dup...@gmail.com Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Alberto. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
On Sun, Oct 21, 2012 at 08:11:50PM +0200, Corentin Dupont wrote: Hi Iustin, yes I want to deserialize an unknown type based on the content of the file (in this example). Let's say I can reduce the spectum of types to: Strings, all the types in Enum, Ints. Is it possible? Maybe :) I don't know how to do all the types in enum. For Strings, Ints and Float, you could have something like: serialise a pair instead of just the type, and decode: data Event = EventString String | EventInt Int | EventFloat Float … (kind, val) - read in_data return $ case kind of string - EventString val int - EventInt (read val) float - EventFloat (read val) But this is only for a very few specific types. My real problem is that on my web interface I want to use web routes to allow a user to pass an Event back to the engine. The problem is that it seems that web-routes only accepts Strings (or some known types) to be passed on the web route, whereas I need to pass random types. Are you sure you need to pass random types? Can't you define a (large) set of known types, for example? regards, iustin On Sun, Oct 21, 2012 at 8:00 PM, Iustin Pop iu...@k1024.org wrote: On Sun, Oct 21, 2012 at 07:20:10PM +0200, Corentin Dupont wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... Can't you simply, when defining the type event, add a deriving (Show, Read)? Then the standard (but slow) read/show serialisation would work for you. If you're asking to de-serialise an unknown type (i.e. you don't know what type it should restore a-priori, but you want to do that based on the contents of the file), things become a little more complex. Unless you can further restrict the type 'a', really complex. Maybe stating your actual problem, rather than the implementation question, would be better? regards, iustin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
On Sun, Oct 21, 2012 at 8:42 PM, MigMit miguelim...@yandex.ru wrote: Oh, now I've got it. First of all, functions of type IO () - Event a are impossible (unless you resort to tricks with unsafePerformIO, which is not what you want to deal with right now). You've probably meant something like IO (Event a) (at least, that is the type of function which would read Event a from file or input stream or something else external). Yes, sorry, that's what I meant. Secondly, functions (and values) with parametric types, like IO (Event a) require you to provide the type a in your code. They won't take it from somewhere magically. You can take a look at the read function in Prelude for example. If you really want to store the type information and read it back, you should do it yourself, inventing some representation for your type, writing it to disk, reading back and parsing it. And you can't do that for all types in existence, so you'll need to do that for some specific types (and no, instances of Typeable aren't what you want). And you'll have to deal with type system, which won't allow you to just say hey, let that be whatever type it happens to be, I don't care; you'd have to wrap this into one existentially quantified type (or GADT). Keep in mind that this is not very Haskell-y. First of all, try to analyse, what this a in Event a could be. What are the limits here? And don't say there aren't any, because if you don't know anything about the type, you can't do anything with it. So, maybe you would end up with a finite set of types -- this would simplify matters a lot. Or maybe you'd find out that there are inifinitely many types of events -- but they can be somehow generated with a finite number of constructors -- that would be quite simple as well. So, what is the bigger picture here? In my application, the user can define the a. That's what makes it difficult. For example, the user can define a new enumerate and submit it to the program (it will be interpreted by hint): data Choice = You | Me | Them | Everybody deriving (Enum, Typeable, Show, Eq, Bounded) So, the list of types is not known in advance. I could ask my user to make his new type an instance of a class as suggested by Alberto... On Oct 21, 2012, at 9:20 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... BR, C On Sun, Oct 21, 2012 at 7:03 PM, MigMit miguelim...@yandex.ru wrote: Seems like nobody really understands what is it that you want to accomplish or what your problem is. Отправлено с iPhone 21.10.2012, в 20:39, Corentin Dupont corentin.dup...@gmail.com написал(а): Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, 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] serialize an unknown type
Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
