Hi everyone,
I have written the following program to find "magic numbers" i.e. integers 'n' such
that both (n+1) and (n/2+1) are perfect squares.
-- Program to find magic numbers
Import IO
main :: IO ()
main =
do
print (filter magicP sqs)
sqs :: [Int]
sqs = [x*x | x <- [1,3..mAX]]
magicP :: Int -> Bool
magicP x
| ((x-1) `mod` /= 0 = False
| otherwise = (((x-1) `div` 2) + 1) `elem` sqs)
mAX :: Int
mAX = 20000
-- End of listing
If I try to run the program (compiled using GHC 6), it calculates all members of the
list and then prints the whole list in the end. Since Haskell is 'lazy' I was
expecting behaviour similar to HUGS where it prints the numbers as it finds them. Does
this behaviour have something to do with the monadic IO in Haskell? I am a Haskell
newbie and can't even claim having understood the "gentle introduction" properly.
Now my question is - How do I reproduce such "lazy printing" behaviour in GHC?
Wait... I thought of another one :-), how do I speed up this program?
- AJ
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