Hi,
I'm trying to do something like the following:
class Foo a where
doit :: (String - IO ()) - a - IO ()
instance Foo Int where
doit f = f . show
instance Foo Char where
doit f = f . (:[])
So now I have a doit function for Ints and Chars, that takes a function
and does the IO
Hello,
I'm learning haskell and I'm having some trouble with type classes. I
understand them conceptually, but when I try to create an instance I run
into problems. As a simple example, I create a class called ToInt:
class ToCh a where
int :: a - Int
Then I create an
At 2001-10-04 08:31, Russo, Tom wrote:
Main int 5
ERROR - Unresolved overloading
*** Type : (Num a, ToInt a) = Int
*** Expression : int 5
Can someone explain what the problem is, and how to interpret the error
message I'm getting?
Oh, 5 isn't necessarily an Int. It's of type Num a = a,
Simon writes:
You correctly say that you want a still more specific type. Without
understanding your application better I am nervous about recommending
this, but you *can* get what you say you want by using a multi-parameter class
class Weird a b c where
...
f2
data Weirder a b = Weirdest a b
class Weird c where
f1 :: c - c
f2 :: Weirder a b - c - Weirder a b
f3 :: Weirder a c - Weirder c a
f4 :: c - c - Bool
instance Weird (d,e) where
f1 (x,y) = (x,y)
f2 w (x,y) = Weirdest x y
f3 (Weirdest x y) = Weirdest y x
: classes and instances
MIME-Version: 1.0
On Mon, 8 Jun 1998, Peter White wrote:
| What I really want is to define a pool of reusable resources. So
| I want a class declaration something like:
|
| class ResourcePool p where
| newp :: p - e - p -- adds new element e to the resource pool p
