[Haskell-cafe] Prime numbers

[Daniel Carrera]

John Peterson wrote:
> Add a type signature:
> 
> prime :: Integer -> Bool
> 
> It's defaulting to Int and you're getting overflows

Thanks. Hmm... it's still not working.

Btw, I mis-reported the problem. The offending number is 38466629, which 
is /not/ prime but the sample program reports as prime.

38466629 = 31 * 1240859

The offending program is:
--//--
prime :: Integer -> Bool
prime n = not (factors 2 n)

factors :: Integer -> Integer -> Bool
factors m n | m == n = False
             | m < n  = divides m n || factors (m+1) n

divides :: Integer -> Integer -> Bool
divides a b = (mod a b == 0)
--//--

The math behind the program seems correct... :(

Cheers,
Daniel.



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