Ahh - sorry, too much cut and paste ;-)
data PowerNum = INT Integer | DBL Double deriving (Eq, Show, Read)
pow :: PowerNum -> Integer -> PowerNum
pow x y = z x y where
z (INT x) y = if y > 0 then
INT $ powInteger x y
else if y == 0 then
INT $ 1
else
DBL $ powDouble (fromInteger x) y
z (DBL x) y = DBL $ powDouble x y
powInteger x y
| x == 0 = 0
| y == 0 = 1
| y > 0 = x * powInteger x (y - 1)
powDouble x y
| x == 0 = 0
| y == 0 = 1
| y < 0 = 1 / x * powDouble x (y + 1)
Now it basically works. However wouldn't it have been easier to write
something like this:
module Main where
import System
main = do
[a1, a2] <- getArgs
let x = read a1
let y = read a2 in
if y >= 0 then
putStrLn (show x ++ " ^ " ++ show y ++ " = " ++ show (powPos x
y))
else
putStrLn (show x ++ " ^ " ++ show y ++ " = " ++ show (powNeg x
y))
powPos :: Integer -> Integer -> Integer
powPos x y
| x == 0 = 0
| y == 0 = 1
| y > 0 = x * powPos x (y - 1)
powNeg :: Integer -> Integer -> Double
powNeg x y
| x == 0 = 0
| y == 0 = 1
| y < 0 = 1 / fromInteger x * powNeg x (y + 1)
Initially I wanted something as terse as the Python version, now I either
have to write two functions or I need to define a type. Is there not an
easier way to come as close as possible to the Python version?
Thanks anyway - learnt a lot!
Toralf
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