Re: [Haskell-cafe] Implementing tryReadMVar
On 01.09 18:30, MR K P SCHUPKE wrote: while channel not empty read next event if event high priority process now else queue event in FIFO process first event in FIFO That suffers from the same problem as I described. do e - isEmptyChan ch -- is the channel empty? case e of True - processFifo False- readChan ch = highPriorityOrPush Now there is danger of blocking on the readChan. (consider a case where we create two similar server processes reading the same channel). Now we create a tryReadChan, but we cannot implement it with tryTakeMVar, as that would break dupChan. Rather we need a tryReadMVar or a different channel abstraction. - Einar Karttunen ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Implementing tryReadMVar
On 01.09 13:09, Jan-Willem Maessen - Sun Labs East wrote: I was, however, curious what use you had in mind where writes were racing, but where you nonetheless wanted to perform blind non-blocking reads. Such situations are generally fraught with peril. In this case, the peril is starvation of the debug thread---which you may or may not actually care about. I was trying to implement safe tryReadChan, which seems to be very simple with tryReadMVar, without it it seems to suffer from various concurrency problems. - Einar Karttunen ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] QuickCheck - Extracting data values from tests
Jorge Adriano Aires [EMAIL PROTECTED] writes: Hello all, When using Quickcheck, is there some way to extract generated data values to the IO Monad? I know I can collect and print information about test cases, but that's not enough. Data may be pretty complex, and there may be no parsers for it. If a test suddenly goes wrong, just having it displayed doesn't seem that useful. You may be interested in a QuickCheck hack of mine that saves the offending data value to use immediately in the next test run. You can get the current version with darcs get http://thunderbird.scannedinavian.com/repos/quickcheck; I've only used this for my own code, so I'd be interested in any feedback. In some cases it's a lot easier to generate a value from a seed and size rather than saving the value in some way that you can restore (ie functions). I've been investigating doing test-driven-development with QuickCheck, saving failing test cases is one step towards that goal. If you have more ideas on that topic, I'd like to hear about it. Also, even when I'm implementing a generator, I want to see how it is working. Running a verboseCheck on some dummy property helps, but I may want to analyse the data, or some parts of it better - for instance, for many data structures I have alternative show functions that take parameters as arguments. This isn't clear to me, can you give other examples? -- Shae Matijs Erisson - Programmer - http://www.ScannedInAvian.org/ I will, as we say in rock 'n' roll, run until the wheels come off, because I love what I do. -- David Crosby ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stack overflow in ghci
--- Tomasz Zielonka [EMAIL PROTECTED] wrote: On Thu, Sep 02, 2004 at 08:47:51AM -0700, Ron de Bruijn wrote: I heard of the +RTS option. I used: ghci SomeModule.hs -someoptions +RTS -K150, but this doesn't seem to have any effect. Try +RTS -K150M. -K150 means 150 bytes. Best regards, Tom -- .signature: Too many levels of symbolic links Ok, it works. I thought the K was equivalent to 1000, but the first K doesn't have that meaning. Thanks. __ Do you Yahoo!? Yahoo! Mail is new and improved - Check it out! http://promotions.yahoo.com/new_mail ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Partially-applied type synonyms?
Chung-chieh,
Well, I tried what you suggested, and it seems to work. Unfortunately,
it's not very useful. The point of creating MonadPCont, was, like
MonadCont or MonadState, to automatically provide features to a monad
built from a transformer, without having to redefine them. Since ContT
is the monad transformer, I want any monad created from it to
automatically support the MonadPCont operations. But they can't,
because I can't make ContT an instance of MonadPCont.
I can make FlipContT an instance of MonadPCont, but I can't make
FlipContT a monad transformer. So what you have to do is create your
layered monadwith ContT on top, and then apply the FlipCont constructor
to get a monad with the methods of MonadPCont. Now since FlipContT
isn't a monad transformer, you can't lift things into it. You can lift
them into ContT and then write a wrapper around that.
My point is that, unfortunately, I don't think it's very practical to
create this type class. I think the problem is that, although MonadCont
attempts to describe a monad as having certain operations, MonadPCont
attempts to describe a group of related monads as having certain
operations. They are related by being formed from the same type
constructor.
Here's the modified code:
module MonadPCont where
import Control.Monad
import Control.Monad.Cont
import Control.Monad.Trans
import Control.Monad.Reader
import Control.Monad.Writer
import Control.Monad.State
import Control.Monad.RWS
class (Monad (mc a), Monad (mc r)) = MonadPCont mc a r where
shift :: ((forall b. Monad (mc b) = a - mc b r) - mc r r) - mc r a
reset :: mc a a - mc r a
instance MonadPCont Cont a r where
shift f = Cont (\c - runCont (f (\x - Cont (\c' - c' (c x id)
reset m = Cont (\c - c (runCont m id))
data FlipContT m r a = FlipContT { unFlipContT :: (ContT r m a)}
instance Monad m = Monad (FlipContT m r) where
return x = FlipContT $ return x
(FlipContT m') = f = FlipContT $ m' = (unFlipContT . f)
runFlipContT :: FlipContT m r a - (a - m r) - m r
runFlipContT (FlipContT m) = runContT m
instance Monad m = MonadPCont (FlipContT m) a r where
shift f = FlipContT $ ContT $ \c -
runFlipContT (f (\x - FlipContT $ ContT $ \c' - c x
= c'))
return
reset m = FlipContT $ ContT $ \c - runFlipContT m return = c
- Lyle
Chung-chieh Shan wrote:
On 2004-08-31T09:55:10-0700, Lyle Kopnicky wrote:
Sorry, I don't think I made myself clear. I'm not defining PI, it's the
standard type binding operator, like lambda is the variable binding
operator. Maybe I could write it as 'II' so it looks more like a
capital pi. It's not a feature of Haskell, but part of type theory
(dependent types). I was mixing and matching and making it look like
Haskell. So instead of 'PI r - ContT r m', I could write 'flip ContT',
except that 'flip' needs to work on a type level instead of a value
level. Or I could write '(`ContT` m)', or 'ContT _ m', where the '_' is
a hole. Does this make sense now?
Yes, it makes sense now. You need to define
newtype FlipContT m r a = FlipContT (ContT r m a)
or more generally,
newtype Flip c (m :: * - *) r a = Flip (c r m a)
The rationale for disallowing matching partially-applied type synonyms
is that higher-order unification is undecidable.
See also:
Neubauer, Matthias, and Peter Thiemann. 2002. Type classes with
more higher-order polymorphism. In ICFP '02: Proceedings of the ACM
international conference on functional programming. New York: ACM Press.
http://www.informatik.uni-freiburg.de/~neubauer/papers/icfp02.pdf
http://www.informatik.uni-freiburg.de/~neubauer/papers/icfp02.ps.gz
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Re: [Haskell-cafe] QuickCheck - Extracting data values from tests
Hello all, When using Quickcheck, is there some way to extract generated data values to the IO Monad? I know I can collect and print information about test cases, but that's not enough. Data may be pretty complex, and there may be no parsers for it. If a test suddenly goes wrong, just having it displayed doesn't seem that useful. You may be interested in a QuickCheck hack of mine that saves the offending data value to use immediately in the next test run. Nice! It's different from what I was looking for but also quite usefull. You can get the current version with darcs get http://thunderbird.scannedinavian.com/repos/quickcheck; I've only used this for my own code, so I'd be interested in any feedback. Ok. In some cases it's a lot easier to generate a value from a seed and size rather than saving the value in some way that you can restore (ie functions). I've been investigating doing test-driven-development with QuickCheck, saving failing test cases is one step towards that goal. If you have more ideas on that topic, I'd like to hear about it. Well, returning (part of) the generated data is one of them :) Also, even when I'm implementing a generator, I want to see how it is working. Running a verboseCheck on some dummy property helps, but I may want to analyse the data, or some parts of it better - for instance, for many data structures I have alternative show functions that take parameters as arguments. This isn't clear to me, can you give other examples? Not sure which part is not clear... I'll just try to explain each of them. Lets say I'm implementing a generators for Graphs. Also, even when I'm implementing a generator, I want to see how it is working. I want to check if the generated Graphs are like I intended them to be. Running a verboseCheck on some dummy property helps, but I may verboseCheck by default prints all the data. I can run it on a dummy function that always returns True to see what kind of data I'm getting. want to analyse the data, or some parts of it better May want to print the 'actual graphs' on the screen (ASCII art, or maybe using some function that calls Gnuplot). Then I may want to check in more detail the info in contained in some of the nodes. Then I may decide to run some functions on it. many data structures I have alternative show functions that take parameters as arguments. Like I just said, I may want to show the graph in many ways. But there are more possibilities. Why limitate the usefulness of QuickCheck? Suppose I just implemented generators for a few kinds of terms and formulas to test some properties. Now I want to benchmark a couple of different unification functions... I'd expect to be able to use my generator for that. Unless I'm missing something, I cannot. Am I right? J.A. ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
