I like John's idea with a class Strict, but I think there should also be
a second class Eval for computing whnf's:
class Strict a where
strict :: a -> Bool
class Eval a where
eval :: a -> Bool
Example: for Complex we get:
instance Strict a => Strict (
> Yes, in general it's not possible. That is, I can't write a function
>
> evaluate :: a -> a
>
> which will force its argument to WHNF.
I don't think you mean what you are actually saying, it's perfectly possible
write evaluate :-)
evaluate x = x
This function will evaluate its a
> Hi !
>
> Can anyone tell me whether it's possible to force Haskell to evaluate an
> expression strict ?
Yes, in general it's not possible. That is, I can't write a function
evaluate :: a -> a
which will force its argument to WHNF. I can, as you've noted, write
a function:
e
As others have mentioned, Haskell does not provide a direct means for
strict evaluation. While the class system can be used, the trick of
f x = x | x == x
is not guaranteed to work since == methods defined by the user may not
have the desired strictness property. I could always put
instance E
My apologies for the previous message, which was intended to go to
Cornel Klein only.
-Konstantin
Cornel,
> data Sequ a = Empty
> | Cons (a,Sequ a)
wieso verwendest Du hier nicht einfach [a]?
> If the typevariable "a" would be restricted to range over the typeclass Eq,
> the dirty trick of adding the guard
>
> n==n
>
> to the definition of mergesort could be used
Hi !
Can anyone tell me whether it's possible to force Haskell to evaluate an
expression strict ? Consider the following Haskell program:
---
module Mergesort where
data Sequ a = Empty
| Cons (a,Sequ a)
merge
