Duncan
Oleg's recent message to Haskell-Café tackles your real problem, but I thought I'd
just say what is going on with your apparent bug below. Here's a much simpler example:
class Foo a b where
to :: a - b
fro :: b - a
-- foo :: forall b1 b a. (Foo a
Hello,
I've put my Haskell bindings to SDL,SDL_Image, and SDL_TTF
here..
http://homepages.nildram.co.uk/~ahey/HLibs/Multimedia.SDL.Core/
http://homepages.nildram.co.uk/~ahey/HLibs/Multimedia.SDL.Image/
http://homepages.nildram.co.uk/~ahey/HLibs/Multimedia.SDL.TTF/
It's not really as polished as
On Wed, Jul 07, 2004 at 01:18:54PM +0100, Graham Klyne wrote:
There's a pattern of higher-order function usage I find myself repeatedly
wanting to use, exemplified by the following:
[[
-- combineTest :: (Bool-Bool-Bool) - (a-Bool) - (a-Bool) - (a-Bool)
combineTest :: (b-c-d) - (a-b) -
Hi folks
Iavor S. Diatchki wrote:
hi,
you can use the reader (environment monad) for this.
lately i have been using 2 combinators to do things like that (thanks to
Thomas Hallgren for showing me this):
-- a nicer name for fmap (or liftM if one prefers)
(#) :: Functor f = (a - b) - f a - f b
--
Hi all,
I am pretty new to haskell, but while exploring the haskell module
system, I came along some questions. As far as I found out, haskell
supports separated namespaces, i.e. every module has its own symbol
space. Thus, when defining a class in one module like
module A(Foo(f)) where
class
Stephan Herhut [EMAIL PROTECTED] writes:
module B(bar) where
instance Foo Integer where
module C(tango)
instance Foo Integer where
import B(bar)
import C(tango)
But now, ghc complains about two instances of Foo Integer, although
there should be none in the namespace main.
I suspect
On Thu, Jul 08, 2004 at 03:47:08PM +1000, Bernard James POPE wrote:
I use almost exactly the same thing in my code. And I nearly came
up with the same names as you! (I have .. and .||.)
I find them very useful in guards:
foo x y
| (this .. that) x = ...
I don't believe this
We apologize if you receive multiple copies of this mail.
Sincerely,
Clemens Grelck and Frank Huch
IFL'04
Announcement, Call for Papers and Call for Participation
for the
Conor T McBride writes:
As some of you know, I like them a lot too. In fact, if you have a
return-like thing and an ap-like thing, you can make fmap as well.
(Note that the return for the environment monad is none other than
S's best friend K.)
So I got hacking, a little while ago...
I start some ip networks related work in haskell and wrote two basic
classes Location and Packet. Before writing IpLocation and IpPacket
instances i have written simple TestLocation and TestPacket instances
just to compile this and check for errors in class definitions. But
looks like i
Ivan,
It's the type of source and destination that is playing you parts. Let's
write them explicitly quantified,
source :: forall a b . (Packet a, Location b) = a - b
destination :: forall a b . (Packet a, Location b) = a - b
and reflect on this for a while. This basicly says that
Ivan,
I don't yet know how to explain this formally, but I know how to fix
your problem..
You need to add a parameter to the Packet class so the compiler knows
what type to use for the Location.
.. The following code works for me.. You'll need to use a
compiler/interpreter which supports
Ivan,
Oops ...
SH and write the following function, knowing that
SH TestPacket is an instance of Packet,
SH
SH getFoo:: Packet - Foo
SH getFoo packet = source packet .
Clearly, I meant to write
getFoo :: TestPacket - Foo
here.
Regards,
Stefan
Stefan Holdermans wrote:
Huh. I'm really get stuck. Can someone write me working implementation
of my crap?
___
Haskell-Cafe mailing list
[EMAIL PROTECTED]
http://www.haskell.org/mailman/listinfo/haskell-cafe
Ivan..
Uh.. by 'works' I meant 'compiles' :)
Here is a fixed version..
As I understand it, the 2 parameter class (Location loc = Packet p loc)
means
loc is a Location, and types p and loc are related by class Packet
with just that information, if you try (as you did) something like
$ source
Ivan,
IT Stefan Holdermans wrote:
IT
IT Huh. I'm really get stuck. Can someone write me working
IT implementation of my crap?
Huh? Did *I* wrote that ... ? ;)
\begin{code}
{-# -OPTIONS -fglasgow-exts #-}
class Location a where
point :: a - String
class (Location b) = Packet a b
Ivan Tihonov wrote:
I start some ip networks related work in haskell and wrote two basic
classes Location and Packet. Before writing IpLocation and IpPacket
instances i have written simple TestLocation and TestPacket instances
just to compile this and check for errors in class
thanks a lot, functional dependencies is my choice.
___
Haskell-Cafe mailing list
[EMAIL PROTECTED]
http://www.haskell.org/mailman/listinfo/haskell-cafe
It sounds a little as though you want a family of n-ary union type
constructor. A crude first attempt would be:
data Either2 t1 t2 = In1 t1 | In2 t2
data Either3 t1 t2 t3 = In1 t1 | In2 t2 | In3 t3
...
but this would be a bit tedious to use because the names are a bit meaningless
-
Once again, I find myself making code that I think may exist somewhere in
the libraries:
[[
-- list find and remove
extract0 :: (a-Bool) - [a] - Maybe (a,[a])
extract0 p as = ex [] as
where
ex seen (a:more)
| p a = Just (a,revcat seen more)
| otherwise =
Crypt Master,
CM Thanks for your help so far, but I am still not
CM getting this IO stuff. After reading your
CM previous help and reading several articles on
CM it I still cant phathom how you convert the IO
CM Int into an Int.
Welcome to pure functional programming! :)
Well, since
The root problem is that random number generation is inherently
stateful, and so the familiar imperative idioms don't translate
directly into a pure functional language. In a C-like language, each
invocation of rand() mutates a secret piece of state lurking
off-stage; pure functional code doesn't
Most of my imperative pieces of software find their answers by touching
around in some space
of solutions and my favourite approximation algorithms use random
distributions.
Is it haskell the wrong languages for those, as I'm obliged to code them
inside Monads
loosing the benefits of lazyness?
My original question was related to use of existing facilities. I find it
somewhat surprising how rich and complex a language Haskell turns out to
be. I'm wary of yet more features.
That said, you seem to be suggesting a kind of anonymous union type (to
complement the proposed anonymous
At 21:40 08/07/04 +0200, paolo veronelli wrote:
Most of my imperative pieces of software find their answers by touching
around in some space
of solutions and my favourite approximation algorithms use random
distributions.
Is it haskell the wrong languages for those, as I'm obliged to code them
[...]
So I am still in IO Int land despite having used the = in the do syntax.
[...]
The idea of the IO type is that it marks code that can behave differently each
time it is called. For this reason, the IO monad 'infects' everything above
it in the call chain and, for this reason, the
On Thursday 08 July 2004 20:40, paolo veronelli wrote:
Most of my imperative pieces of software find their answers by
touching around in some space of solutions and my favourite
approximation algorithms use random distributions.
Is it haskell the wrong languages for those, as I'm obliged to
On 09/07/2004, at 4:50 AM, Crypt Master wrote:
One person mentioned how random just returns an interative program
which when eveluated returns the Int. Also from the school of
expression book he says The right way to think of (=) above is
simply this: It Executes e1 ... in relation to do
28 matches
Mail list logo
