Toralf Wittner <[EMAIL PROTECTED]> writes
> [..]
> power x y
> [..]
> | y > 0 = x * power x (y-1)
> | y < 0 = 1 / fromInteger x * power x (y+1)
>
> One recognizes that the function returns either an integer value
> if y > 0 or a float value if y < 0. Therefore I can't write a
> signature like
> pow :: Integer -> Integer -> Integer nor can I do
> pow :: Integer -> Integer -> Double.
>
> [..]
> How then would I write this function in Haskell (concerning types)?
The type Rational fits the case n < 0 too, and it includes Integer.
But if you still need Integer | Double, you can, for example,
introduce a new type of a disjoint union of the above two, and then,
to compute like this:
pow (Intg 2) 2 --> Intg 4
pow (Intg 2) (-2) --> D 0.25
pow (D 2.0) (-2) --> D 0.25
This is achieved by
data PowerDom = Intg Integer | D Double deriving(Eq,Show)
pow :: PowerDom -> Integer -> PowerDom
pow x n = p x n
where
p (Intg m) n = if n > 0 then Intg $ powerInteger m n
else D $ powerDouble (fromInteger m :: Double) n
p(D d) n = D $ powerDouble d n
powerInteger m n = m^n :: Integer
powerDouble :: Double -> Integer -> Double
powerDouble d n = ... usual way for float
- something like this.
-----------------
Serge Mechveliani
[EMAIL PROTECTED]
_______________________________________________
Haskell mailing list
[EMAIL PROTECTED]
http://www.haskell.org/mailman/listinfo/haskell
