comp.lang.haskell Google Group

Re: 2.0TDI DSG Octavian kulutus

2008-11-18T22:33:52Z

Kun heinäluoma otti 2008 vapun keskusteluaseekseen Suomen NATO-jäsenyyden ja
lupaili, ettei kansamme ole sinne pakko mennä, jossei sitä kaipaa, on
kyseessä tietysti demokratian peruselementti. Vaan miksei Heinäluoma
samantien vaatinut asiasta kansanäänestystä myös?
Olisi jäänyt sitten jatkon Häkämiehen panikoinnit ja vaatimukset koko

Re: help with deriving

2008-11-18T05:58:22Z

Thanks that does help. I have seen this before too, and never knew
exactly what to do.
On the other hand... I removed the library, and edited the file, that
points to the real WordNet, and rebuilt it. Then the library builds
and install fine. Now, I have a new problem: I make a file called
test.hs and all that I do is import the library using

Re: help with deriving

2008-11-18T05:26:31Z

-XDeriveDataTypeable is a flag you can pass when compiling to enable the
extension.
You can also put such flags at the top of a file, with:
{-# OPTIONS_GHC -XDeriveDataTypeable #-}
Along with other options. Or, preferably, when the option is for a language
extension as is the case here, use a LANGUAGE pragma:

help with deriving

2008-11-18T04:23:56Z

Good evening Haskell community!
I am having trouble with something and I am not sure exactly what is
going on. I have a couple of functions defined in a library that are
using Data.Dynamic (Typeable), and I get a compiler flag when I try to
run them. The compiler message says"
0:
Can't make a derived instance of `Typeable POS'

Re: concurrency + state newb question

2008-11-15T23:40:26Z

Just consider that a stateful computation is just a function. So
something of type 'State s a' is, by concept, not a value, but instead a
function of a state value of type 's', which results in a result value
of type 'a' (and an updated state value). In fact, this is really how
State monads work. A quick look at the constructor sheds some light

Re: concurrency + state newb question

2008-11-15T15:20:12Z

Your solution is completely correct. Your handleItCore function does not
yield an I/O action (i.e. something with a type of IO blah) after passing
in the channel argument, but it has the type "StateT ....". The StateT
monad transformer (if it is wrapping the IO monad) is an adapter that
can join I/O actions while also tracking a state. To get an I/O action out

Re: concurrency + state newb question

2008-11-15T02:09:41Z

here is my (hacky?) solution/fix. i'm still very easily confused when
it comes to "calling" upon stateful things; 'handleIt' is my impedance
demismatcher.
import IO
import Control.Monad.State
import Control.Monad.Trans
import Control.Concurrent
data Cmd = Quit | Echo String
handleItCore :: Chan Cmd -> StateT ([String]) IO ()

concurrency + state newb question

2008-11-15T01:30:23Z

how do i fix the "type check fail" line in 'test' fn below to properly
get 'handleIt' going?
import IO
import Control.Monad.State
import Control.Monad.Trans
import Control.Concurrent
data Cmd = Quit | Echo String
handleIt :: Chan Cmd -> StateT ([String]) IO ()
handleIt cmdChan = do
cmd <- liftIO (readChan cmdChan)

vs. erlang, clojure?

2008-11-15T00:43:18Z

hi,
seems like the Control.Concurrent stuff could be used to build either
Actors (a la Erlang, Scala) or Agents (a la Clojure). any thoughts on
how one might do those?
re: Erlang, it seems straight-forward: forkIO off a function that self-
calls and/or uses State monad, and that communicates over some Chan.

Re: monad vs. self-call?

2008-11-12T22:46:57Z

thanks (to you and others) for the help, it really is starting to sink
in to my brain, even if it requires repetition ([link]
65563q) :-}

Re: monad vs. self-call?

2008-11-12T14:04:29Z

I think, this is just your personal view, maybe because you have learned
Haskell another way or with another background than I have. I use
concurrency very heavily, even for very simple things like managing an
object database:
data DBCommand = Add Key Object |
Delete Key |
GetObject k (Maybe v -> IO ())

Re: monad vs. self-call?

2008-11-12T12:30:30Z

Yes. Most programming languages are Turing complete, so all those
languages can emulate each other.
The key word is *natural*. In Erlang, it's natural to have lots of
little processes that represent a very fine grained partitioning of
the whole state. One can imitate that in Haskell, but (at least to me)

Re: Powerset question

2008-11-12T01:08:08Z

Wow, that is interesting - thank you for the pointer. I should get over
being repeatedly intimidated by others' cleverness and make a habit of
catching up with the Monad Readers I've missed as they always seem to
teach me new things.
Mark

Re: Powerset question

2008-11-12T00:53:14Z

That's a really neat approach: I hadn't thought of that. I wonder if I
will find it applies to something else I end up doing someday.
Unfortunately, the sorting approach rather decreases the laziness of the
thing, at least if I try judging by the take n $ map (take n) $ ....
sort of test.
Mark

Re: monad vs. self-call?

2008-11-11T23:09:25Z

Likely I'm misunderstanding you. =) It seems an Erlang process is
something different from a Haskell thread. I don't know Erlang too
well.
On the other hand, many features and concepts that are primitive in
other languages (i.e. language or RTS features) are library
functionalities in Haskell, so in fact you could say about almost