Jim Apple wrote:
Does anyone have examples of these? This one scares the foo out of me:
* It's not even safe in general to add a signature giving the same type
that the compiler would infer anyway
Here's an example:
len :: [a] - Int
len xs = let ?accum = 0 in len' xs
len'
Ben Rudiak-Gould wrote:
len :: [a] - Int
len xs = let ?accum = 0 in len' xs
len' :: forall a. (?accum :: Int) = [a] - Int
len' [] = ?accum
len' (x:xs) = let ?accum = ?accum + (1::Int) in len' xs
*Main :t len'
len' :: forall a. (?accum :: Int) = [a] - Int
On 19 January 2005 20:31, Glynn Clements wrote:
Keean Schupke wrote:
Okay, my ignorance of Posix is showing again. Is it currently the
case, then, that every GHC thread will stop running while a disk
read is in progress in any thread? Is this true on all platforms?
It's true on Unix-like
On 19 January 2005 20:33, Glynn Clements wrote:
Simon Marlow wrote:
We do use a thread pool. But you still need as many OS threads as
there are blocked read() calls, unless you have a single thread
doing select() as I described.
How does the select() help? AFAIK, select() on a regular
Why is disk a special case? I have never heard that all processes under
linux
wait for a disk read... The kernel most certainly does not busy wait for
disks
to respond, so the only alternative is that the process that needs to wait
(and only that process) is put to sleep. In which case a second
On 19 January 2005 16:58, Keean Schupke wrote:
Simon Marlow wrote:
This is what GHC does, if I understand you correctly. The thread
running select() does so in its own OS thread, while another OS
thread runs the Haskell code. As long as you use -threaded, that
is. Oh, and before GHC 6.4
Simon Marlow wrote:
We're getting a bit confused here. Keean: the original question was
about whether a disk read will stop all other *Haskell* threads. Not OS
threads. The two are quite different beasts in GHC.
Cheers,
Simon
But if GHC is running with the -threaded flag, then other
On 20 January 2005 09:56, Keean Schupke wrote:
Why is disk a special case? I have never heard that all processes
under linux wait for a disk read...
You were talking about Haskell threads, not processes! These are quite
different things.
The kernel most certainly does not busy wait for
Simon Marlow wrote:
On 20 January 2005 09:56, Keean Schupke wrote:
Why is disk a special case? I have never heard that all processes
under linux wait for a disk read...
You were talking about Haskell threads, not processes! These are quite
different things.
But with -threaded GHC is
On 20 January 2005 10:01, Keean Schupke wrote:
Simon Marlow wrote:
We're getting a bit confused here. Keean: the original question was
about whether a disk read will stop all other *Haskell* threads.
Not OS threads. The two are quite different beasts in GHC.
Cheers,
Simon
Simon Marlow wrote:
Yes, except that you forgot that not all foreign calls can run
concurrently with Haskell code. Only the safe ones can.
Okay, now I understand what is going on. Why is there extra overhead
for a 'safe' call?
Keean.
//
___
On 20/01/2005, at 3:42 AM, Keean Schupke wrote:
Have you read the OOHaskell paper?
http://homepages.cwi.nl/~ralf/OOHaskell/
This shows how to encode many OO idioms in Haskell, without any
extensions
(beyond those that GHC already supports)... Here's some sample code
(from the Shapes.hs
But does it matter... If the select says the read will block you schedule
another haskell thread, if select says the read will not block, you do the
read. I don't see the problem... (Okay, I can see that if select lies,
and the
read takes a long time you might miss the next scheduling timeslot -
Andre Pang wrote:
Just because you can encode the OO idioms in Haskell doesn't mean it's
particularly straightforward to use them. As your example shows,
getting the syntax right for these OOish constructs isn't easy (not to
mention verbose), and even so, the type errors you face when you get
On 20 January 2005 11:30, Keean Schupke wrote:
Simon Marlow wrote:
Yes, except that you forgot that not all foreign calls can run
concurrently with Haskell code. Only the safe ones can.
Okay, now I understand what is going on. Why is there extra overhead
for a 'safe' call?
A safe
On 20/01/2005, at 11:06 PM, Keean Schupke wrote:
I find it no harder than writing with monads for example... certainly
there are some
tricky things going on in both... but that doesn't stop people using
monads for IO,
state etc.
Syntactic sugar over the top for instance and implementation
read. I don't see the problem... (Okay, I can see that if select lies,
and the
read takes a long time you might miss the next scheduling timeslot - but
as far as I am aware select doesn't lie, and read will return immediately
if select says there is data ready)...
select() _does_ lie for
Hello!
I'm trying to compile wxFruit sample program paddleball
(http://zoo.cs.yale.edu/classes/cs490/03-04b/bartholomew.robinson/).
When I try to compile file paddle.hs (see below where it is availeble) using
the call
call
ghc -fglasgow-exts -farrows -package wx
Andre Pang wrote:
The syntactic sugar is the killer. (Using monads is really no fun if
you don't have do notation, for example. Doable: yes. Pretty:
definitely not!) Even if you use Template Haskell to try to implement
the syntactic sugar, you're very limited by the splice $(...) notation
Keith Wansbrough wrote:
read. I don't see the problem... (Okay, I can see that if select lies,
and the
read takes a long time you might miss the next scheduling timeslot - but
as far as I am aware select doesn't lie, and read will return immediately
if select says there is data ready)...
You hace to add option --make, if you complie haskell program file with
(Bsome files.
(BAnd, you have to change WX.size to Wx.sz .
(BBecause wxHaskell-0.8 changed some functions.
(B
(BOn Thu, 20 Jan 2005 15:50:29 +0100, Dmitri Pissarenko
(B[EMAIL PROTECTED] wrote:
(B I'm trying to compile
Thanks all for the help! Now it works.
--
Dmitri Pissarenko
Software Engineer
http://dapissarenko.com
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David Owen ([EMAIL PROTECTED]) wrote:
Unfortuantely I don't know of anywhere that the exercise answers can be
found, even after some google searching. I would definitely find them
useful though as there are a couple I haven't been able to work out.
Me too. And I hope we're not the only one
Ketil Malde ([EMAIL PROTECTED]) wrote:
Another option is posting the excercise to this list (or perhaps in
comp.lang.functional), along with your current effort at solving it.
I consider it would be useful to have the the whole collection somewhere, maybe
on wiki since Thompson's book (beside
Hello!
I need to write a function in Haskell, which
1) reads a greyscale image (for instance, in JPEG, PNG or the like) and
2) transforms it into a n X m matrix A, where Aij contains an integer value
(in the range 0 to 255). That integer value is zero for a completely black
pixel, 255 for a
I tried writing a little command-line utility to find the relative path of
one thing from another thing (with Unix-like systems in mind). For example,
$ ./pathfromof /etc/init.d/ /etc/X11/XF86Config-4
../X11/XF86Config-4
$ ./pathfromof /tmp/baz/ /tmp/foo/
.
$ ls -l /tmp/baz
lrwxr-xr-x 1 markc
Keean Schupke wrote:
Why is disk a special case?
With slow streams, where there may be an indefinite delay before the
data is available, you can use non-blocking I/O, asynchronous I/O,
select(), poll() etc to determine if the data is available.
If it is, reading the data is essentially just
Keean Schupke wrote:
read. I don't see the problem... (Okay, I can see that if select lies,
and the
read takes a long time you might miss the next scheduling timeslot - but
as far as I am aware select doesn't lie, and read will return immediately
if select says there is data
Hi,
does anybody know, why 'lex' isn't faithful to the Haskell-syntax?
Since it isn't difficult to make it ignore comments, handle qualified names
and recognize octal/hexadecimal literals (the system, be it hugs or ghc, does
it, and I filled in the required code this evening, so for a good
Hi,
I have a simple desire. I have a string that I need to parse as a
date/time string in the local timezone, then convert it to standard
seconds-since-epoch format. This is trivial in C, Perl, Python, etc.
but seems impossible to do reliably in Haskell. I'm hoping someone can
tell me where
Glynn Clements wrote:
Keean Schupke wrote:
Why is disk a special case?
With slow streams, where there may be an indefinite delay before the
data is available, you can use non-blocking I/O, asynchronous I/O,
select(), poll() etc to determine if the data is available.
[...]
With files or block
Satnam Singh wrote:
Ample looks interesting. What license does it use? I had a quick look
over the source and can't find anything. Is there a port to Windows or
does it not do any OS specific UI/graphics?
By default, we're releasing it under GPL. I guess I should place a copy
of the license
Hello,
I just experienced a weird problem while using HUnit. My code (a simple
apache log analyser) used to run in constant space (thanks to the good
suggestions and examples I received from the list :-)), and I wanted to
add some unit tests. To my great surprise, the code started to eat up
lots
On Thursday 20 Jan 2005 7:35 pm, Dmitri Pissarenko wrote:
Hello!
I need to write a function in Haskell, which
1) reads a greyscale image (for instance, in JPEG, PNG or the like) and
2) transforms it into a n X m matrix A, where Aij contains an integer value
(in the range 0 to 255). That
Greg Buchholz [EMAIL PROTECTED] writes:
I need to write a function in Haskell, which
1) reads a greyscale image (for instance, in JPEG, PNG or the like) and
If you can specify any image format you want, and you're not
concerned with efficiency, you can't beat the simplicity of the
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