Re: [Haskell-cafe] Foreign.Erlang help
First of all, you can write usual TCP server in Haskell and use it from Erlang. It would be handy to use some widely used protocol, like Memcached or Redis. If in some reason you want to use Foreign.Erlang, make sure that you are using the same cookie and the same node name type (short or full) in Erlang node and Haskell application. On 12/24/2012 08:46 PM, Junior White wrote: Hi all, I have a game server programming in erlang, but now i want to write some game logic in haskell, how to write a haskell node for erlang? ps:I have read the introduce of Foreign.Erlang,I use haskell send a message to a erlang echo server, but the server not receive anything. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Best regards, Alexander Alexeev http://eax.me/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to fold on types?
Try folding over data type constructor with $?
вторник, 25 декабря 2012 г. пользователь Magicloud Magiclouds писал:
Forgot to mention, solution without TemplateHaskell.
On Tue, Dec 25, 2012 at 4:59 PM, Magicloud Magiclouds
magicloud.magiclo...@gmail.com javascript:_e({}, 'cvml',
'magicloud.magiclo...@gmail.com'); wrote:
Say I have things like:
data LongDec = LongDef a b c ... x y z
values = [ 'a', 'b', 'c', ... 'x', 'y', 'z' ]
Now I want them to be LongDef 'a' 'b' 'c' ... 'x' 'y' 'z'.
In form, this is something like folding. But since the type changes, so
code like following won't work:
foldl (\def value - def value) LongDef values
Is it possible to do this in some way?
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Re: [Haskell-cafe] How to fold on types?
Thinking from subway (: foldl ($) LongDef values ? вторник, 25 декабря 2012 г. пользователь Тимур Амиров писал: Try folding over data type constructor with $? вторник, 25 декабря 2012 г. пользователь Magicloud Magiclouds писал: Forgot to mention, solution without TemplateHaskell. On Tue, Dec 25, 2012 at 4:59 PM, Magicloud Magiclouds magicloud.magiclo...@gmail.com wrote: Say I have things like: data LongDec = LongDef a b c ... x y z values = [ 'a', 'b', 'c', ... 'x', 'y', 'z' ] Now I want them to be LongDef 'a' 'b' 'c' ... 'x' 'y' 'z'. In form, this is something like folding. But since the type changes, so code like following won't work: foldl (\def value - def value) LongDef values Is it possible to do this in some way? -- 竹密岂妨流水过 山高哪阻野云飞 And for G+, please use magiclouds#gmail.com. -- 竹密岂妨流水过 山高哪阻野云飞 And for G+, please use magiclouds#gmail.com. -- Best Timur DeTeam Amirov Moscow, Russia -- Best Timur DeTeam Amirov Moscow, Russia ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to fold on types?
Magiclouds asked how to build values of data types with many
components from a list of components. For example, suppose we have
data D3 = D3 Int Int Int deriving Show
v3 = [1::Int,2,3]
How can we build the value D3 1 2 3 using the list v3 as the source
for D3's fields? We can't use (foldl ($) D3 values) since the type
changes throughout the iteration: D3 and D3 1 have different type.
The enclosed code shows the solution. It defines the function fcurry
such that
t1 = fcurry D3 v3
-- D3 1 2 3
gives the expected result (D3 1 2 3).
The code is the instance of the general folding over heterogeneous
lists, search for HFoldr in
http://code.haskell.org/HList/Data/HList/HList.hs
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, FlexibleContexts #-}
{-# LANGUAGE TypeFamilies, DataKinds, PolyKinds, ScopedTypeVariables #-}
{-# LANGUAGE UndecidableInstances #-}
-- `Folding' over the data type: creating values of data types
-- with many components from a list of components
-- UndecidableInstances is a bit surprising since everything is decidable,
-- but GHC can't see it.
-- Extensions DataKinds, PolyKinds aren't strictly needed, but
-- they make the code a bit nicer. If we already have them,
-- why suffer avoiding them.
module P where
-- The example from MagicCloud's message
data D3 = D3 Int Int Int deriving Show
v3 = [1::Int,2,3]
type family IsArrow a :: Bool
type instance IsArrow (a-b) = True
type instance IsArrow D3 = False
-- add more instances as needed for other non-arrow types
data Proxy a = Proxy
class FarCurry a r t where
fcurry :: (a-t) - [a] - r
instance ((IsArrow t) ~ f, FarCurry' f a r t) = FarCurry a r t where
fcurry = fcurry' (Proxy::Proxy f)
class FarCurry' f a r t where
fcurry' :: Proxy f - (a-t) - [a] - r
instance r ~ r' = FarCurry' False a r' r where
fcurry' _ cons (x:_) = cons x
instance FarCurry a r t = FarCurry' True a r (a-t) where
fcurry' _ cons (x:t) = fcurry (cons x) t
-- Example
t1 = fcurry D3 v3
-- D3 1 2 3
-- Let's add another data type
data D4 = D4 Int Int Int Int deriving Show
type instance IsArrow D4 = False
t2 = fcurry D4 [1::Int,2,3,4]
-- D4 1 2 3 4
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Re: [Haskell-cafe] multi-thread and lazy evaluation
This seems like a bug in GHC. But it has nothing to do with MVars. I've narrowed this down and filed a bug report here: http://hackage.haskell.org/trac/ghc/ticket/7528 Timothy -- Původní zpráva -- Od: Yuras Shumovich shumovi...@gmail.com Datum: 24. 12. 2012 Předmět: Re: [Haskell-cafe] multi-thread and lazy evaluation On Mon, 2012-12-24 at 16:16 +0100, timothyho...@seznam.cz wrote: The real question is, does this mean that GHC is stopping the world every time it puts an MVar? No, GHC rts only locks the MVar itself. See here: http://hackage.haskell.org/trac/ghc/browser/rts/PrimOps.cmm#L1358 (http://hackage.haskell.org/trac/ghc/browser/rts/PrimOps.cmm#L1358) Yuras___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ghc-heap-view now with recursive pretty-printing
On 21 December 2012 11:16, Joachim Breitner m...@joachim-breitner.de wrote: Prelude :script /home/jojo/.cabal/share/ghc-heap-view-0.4.0.0/ghci Prelude let x = [1..10] Prelude x [1,2,3,4,5,6,7,8,9,10] Prelude :printHeap x _bh [S# 1,S# 2,S# 3,S# 4,S# 5,S# 6,S# 7,S# 8,S# 9,S# 10] Note that the tools shows us that the list is a list of S# constructors, and also that it is still hidden behind a blackhole. After running System.Mem.performGC, this would disappear. Why do you call it a blackhole? I assume you mean a thunk that has been evaluated and updated with its value. The commonly used term for this is indirection. A blackhole is used to detect when a thunk's value depends on itself (e.g., in let x = id x in ... the thunk for x may get turned into a black hole). It's a minor thing, but I think it's a good idea to stick to existing terminology. Otherwise, it looks like a useful tool. Eventually, we probably want an interactive graph where we can click a node to evaluate it (or to show/hide children nodes). -- Push the envelope. Watch it bend. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] multi-thread and lazy evaluation
Hi Brandon, indeed in my example if you add: *b - evaluate a* after the definition of a it works. However, in my original program it doesn't work, I suppose because I interpret the user submitted code (here *let (a::String) = a * for the example) via Hint and Hint-server, and the interpretation must be done in another thread... Best, Corentin On Mon, Dec 24, 2012 at 3:46 PM, Brandon Allbery allber...@gmail.comwrote: On Mon, Dec 24, 2012 at 8:45 AM, Corentin Dupont corentin.dup...@gmail.com wrote: *execBlocking :: MVar (Maybe MyData) - IO () execBlocking mv = do let (a::String) = a --If you uncomment the next line, it will work --putStrLn $ show a putMVar mv (Just $ MyData a toto)* It's laziness, yes; you need to do something along the lines of let a = length a `seq` a or possibly Control.Exception.evaluate needs to be involved somewhere. -- brandon s allbery kf8nh sine nomine associates allber...@gmail.com ballb...@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] multi-thread and lazy evaluation
Great, with me compiled with ghc -threaded the bug shows up. However, runnning main in ghci doesn't show the bug (it finishes correctly). I have GHC 7.4.1. Corentin On Tue, Dec 25, 2012 at 3:34 PM, timothyho...@seznam.cz wrote: This seems like a bug in GHC. But it has nothing to do with MVars. I've narrowed this down and filed a bug report here: http://hackage.haskell.org/trac/ghc/ticket/7528 Timothy -- Původní zpráva -- Od: Yuras Shumovich shumovi...@gmail.com Datum: 24. 12. 2012 Předmět: Re: [Haskell-cafe] multi-thread and lazy evaluation On Mon, 2012-12-24 at 16:16 +0100, timothyho...@seznam.cz wrote: The real question is, does this mean that GHC is stopping the world every time it puts an MVar? No, GHC rts only locks the MVar itself. See here: http://hackage.haskell.org/trac/ghc/browser/rts/PrimOps.cmm#L1358 Yuras ___ 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] ghc-heap-view now with recursive pretty-printing
Hi, Am Dienstag, den 25.12.2012, 16:58 +0100 schrieb Thomas Schilling: On 21 December 2012 11:16, Joachim Breitner m...@joachim-breitner.de wrote: Prelude :script /home/jojo/.cabal/share/ghc-heap-view-0.4.0.0/ghci Prelude let x = [1..10] Prelude x [1,2,3,4,5,6,7,8,9,10] Prelude :printHeap x _bh [S# 1,S# 2,S# 3,S# 4,S# 5,S# 6,S# 7,S# 8,S# 9,S# 10] Note that the tools shows us that the list is a list of S# constructors, and also that it is still hidden behind a blackhole. After running System.Mem.performGC, this would disappear. Why do you call it a blackhole? I assume you mean a thunk that has been evaluated and updated with its value. The commonly used term for this is indirection. A blackhole is used to detect when a thunk's value depends on itself (e.g., in let x = id x in ... the thunk for x may get turned into a black hole). I don’t call it a blackhole, GHC does :-). At least it is a closure of type BLACKHOLE http://hackage.haskell.org/trac/ghc/browser/includes/rts/storage/ClosureTypes.h#L61 I assume this is due to lazy blackholing or something, although it still occurs with ghci -fno-eager-blackholing... strange. It's a minor thing, but I think it's a good idea to stick to existing terminology. Otherwise, it looks like a useful tool. Thanks! Eventually, we probably want an interactive graph where we can click a node to evaluate it (or to show/hide children nodes). Looks like I am not as good at advertising my (or my student’s) projects as much as I thought I am: http://felsin9.de/nnis/ghc-vis/ 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] How to fold on types?
{-# LANGUAGE DeriveDataTypeable, ScopedTypeVariables #-}
Hi MagicCloud,
A worse, but perhaps simpler alternative to Oleg's solution uses Data.Dynamic:
import Data.Dynamic
data LongDec a = LongDec a a a a a a a a
deriving (Show, Typeable)
values = abcdefgh
mkLongDec :: forall a. Typeable a = [a] - Maybe (LongDec a)
mkLongDec = (fromDynamic =) .
foldl
(\f x - do
f' - f
dynApply f' (toDyn x))
(Just (toDyn (\x - LongDec (x :: a
main = do
print (mkLongDec values)
print (mkLongDec [1 .. 8 :: Integer])
*Main main
Just (LongDec 'a' 'b' 'c' 'd' 'e' 'f' 'g' 'h')
Just (LongDec 1 2 3 4 5 6 7 8)
There is no check that all arguments of LongDec are the same
type (in this case a specific instance of Typeable): you'd only
be able to get Nothing out of mkLongDec was defined as:
data LongDec a = LongDec a Int a a a Char
Regards,
Adam Vogt
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Re: [Haskell-cafe] multi-thread and lazy evaluation
I'm not sure that there is anything great about this bug. It seems to me to be a rather severe demonstration of a somewhat already known design flaw in the runtime :( Could you please comment on the actual bug rather than replying here so that the devs see that this behaviour has been confirmed? Tim -- Původní zpráva -- Od: Corentin Dupont corentin.dup...@gmail.com Datum: 25. 12. 2012 Předmět: Re: [Haskell-cafe] multi-thread and lazy evaluation Great, with me compiled with ghc -threaded the bug shows up. However, runnning main in ghci doesn't show the bug (it finishes correctly). I have GHC 7.4.1. Corentin On Tue, Dec 25, 2012 at 3:34 PM, timothyho...@seznam.cz (mailto:timothyho...@seznam.cz) wrote: This seems like a bug in GHC. But it has nothing to do with MVars. I've narrowed this down and filed a bug report here: http://hackage.haskell.org/trac/ghc/ticket/7528 (http://hackage.haskell.org/trac/ghc/ticket/7528) Timothy -- Původní zpráva -- Od: Yuras Shumovich shumovi...@gmail.com(mailto:shumovi...@gmail.com) Datum: 24. 12. 2012 Předmět: Re: [Haskell-cafe] multi-thread and lazy evaluation On Mon, 2012-12-24 at 16:16 +0100, timothyho...@seznam.cz (mailto:timothyho...@seznam.cz) wrote: The real question is, does this mean that GHC is stopping the world every time it puts an MVar? No, GHC rts only locks the MVar itself. See here: http://hackage.haskell.org/trac/ghc/browser/rts/PrimOps.cmm#L1358 (http://hackage.haskell.org/trac/ghc/browser/rts/PrimOps.cmm#L1358) Yuras ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org(mailto:Haskell-Cafe@haskell.org) http://www.haskell.org/mailman/listinfo/haskell-cafe (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] Substituting values
Hey Petr,
On Sat, Dec 22, 2012 at 9:52 AM, Petr P petr@gmail.com wrote:
I think you need something wha Scala has - the ability to create a partial
function from a case expression. In Scala you could write
def update[A](f: PartialFunction[A,A])(v: A): A =
f.orElse({ case x = x } : PartialFunction[A,A]).apply(v);
and then use it like
update[Int]({ case Foo = Bar })
Thanks for the pointer. One distinction I remember from dabbling in Scala
some years ago is that Scala seems to formalize partiality whereas, if I'm
not mistaken, Haskell doesn't (though perhaps there are libraries that let
you do that). That is, to me a partial function in Haskell is almost
uniformly an error, whereas in Scala it's a somewhat common pattern.
But AFAIK there is nothing like this in Haskell. Maybe separating 'of'
from 'case' would be the way to extend Haskell with such a feature
http://www.haskell.org/pipermail/haskell-cafe/2012-November/104884.html
Does Haskell have a way to query at runtime whether a function is partial?
(Not in the full sense, since it would be necessary to prove totality, but
in the sense that a case expression is not exhaustive.) Otherwise, I'm not
sure how you could use a partial lambda without reaching `undefined`. (I
guess you could catch the exception.)
Thanks,
Alvaro
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Re: [Haskell-cafe] multi-thread and lazy evaluation
Hi, AFAIK it is (partially?) fixed in HEAD, see http://hackage.haskell.org/trac/ghc/ticket/367 It works for me with -fno-omit-yields Thanks, Yuras On Tue, 2012-12-25 at 19:35 +0100, timothyho...@seznam.cz wrote: I'm not sure that there is anything great about this bug. It seems to me to be a rather severe demonstration of a somewhat already known design flaw in the runtime :( Could you please comment on the actual bug rather than replying here so that the devs see that this behaviour has been confirmed? Tim -- Původní zpráva -- Od: Corentin Dupont corentin.dup...@gmail.com Datum: 25. 12. 2012 Předmět: Re: [Haskell-cafe] multi-thread and lazy evaluation Great, with me compiled with ghc -threaded the bug shows up. However, runnning main in ghci doesn't show the bug (it finishes correctly). I have GHC 7.4.1. Corentin On Tue, Dec 25, 2012 at 3:34 PM, timothyho...@seznam.cz (mailto:timothyho...@seznam.cz) wrote: This seems like a bug in GHC. But it has nothing to do with MVars. I've narrowed this down and filed a bug report here: http://hackage.haskell.org/trac/ghc/ticket/7528 (http://hackage.haskell.org/trac/ghc/ticket/7528) Timothy -- Původní zpráva -- Od: Yuras Shumovich shumovi...@gmail.com(mailto:shumovi...@gmail.com) Datum: 24. 12. 2012 Předmět: Re: [Haskell-cafe] multi-thread and lazy evaluation On Mon, 2012-12-24 at 16:16 +0100, timothyho...@seznam.cz (mailto:timothyho...@seznam.cz) wrote: The real question is, does this mean that GHC is stopping the world every time it puts an MVar? No, GHC rts only locks the MVar itself. See here: http://hackage.haskell.org/trac/ghc/browser/rts/PrimOps.cmm#L1358 (http://hackage.haskell.org/trac/ghc/browser/rts/PrimOps.cmm#L1358) Yuras ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org(mailto:Haskell-Cafe@haskell.org) http://www.haskell.org/mailman/listinfo/haskell-cafe (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] How to fold on types?
On 12/25/2012 09:59 AM, Magicloud Magiclouds wrote:
Say I have things like:
data LongDec = LongDef a b c ... x y z
values = [ 'a', 'b', 'c', ... 'x', 'y', 'z' ]
Now I want them to be LongDef 'a' 'b' 'c' ... 'x' 'y' 'z'.
In form, this is something like folding. But since the type changes, so
code like following won't work:
foldl (\def value - def value) LongDef values
Is it possible to do this in some way?
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And for G+, please use magiclouds#gmail.com http://gmail.com/.
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This hack works, in case that helps:
{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses #-}
data LongDec = LongDef Char Char Char Char Char Char
deriving Show
values = [ 'a', 'b', 'c', 'x', 'y', 'z' ]
class Apply a b c where
apply :: b - [a] - c
instance Apply a b b where
apply = const
instance (Apply a b c) = Apply a (a - b) c where
apply f (x:xs) = apply (f x) xs
main = print (apply LongDef values :: LongDec)
It requires an explicit type annotation to fix type parameter 'c'. It
cannot be a function type. (I am not sure why though.)
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Re: [Haskell-cafe] How to fold on types?
You guys are great! Thanks.
On Wed, Dec 26, 2012 at 9:04 AM, Timon Gehr timon.g...@gmx.ch wrote:
On 12/25/2012 09:59 AM, Magicloud Magiclouds wrote:
Say I have things like:
data LongDec = LongDef a b c ... x y z
values = [ 'a', 'b', 'c', ... 'x', 'y', 'z' ]
Now I want them to be LongDef 'a' 'b' 'c' ... 'x' 'y' 'z'.
In form, this is something like folding. But since the type changes, so
code like following won't work:
foldl (\def value - def value) LongDef values
Is it possible to do this in some way?
--
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山高哪阻野云飞
And for G+, please use magiclouds#gmail.com http://gmail.com/.
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This hack works, in case that helps:
{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses #-}
data LongDec = LongDef Char Char Char Char Char Char
deriving Show
values = [ 'a', 'b', 'c', 'x', 'y', 'z' ]
class Apply a b c where
apply :: b - [a] - c
instance Apply a b b where
apply = const
instance (Apply a b c) = Apply a (a - b) c where
apply f (x:xs) = apply (f x) xs
main = print (apply LongDef values :: LongDec)
It requires an explicit type annotation to fix type parameter 'c'. It
cannot be a function type. (I am not sure why though.)
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