haskell - primes

Primes.hs

{- LANGUAGE ForeignFunctionInterface #-}                      
module Prime where                                            
                                                              
import Foreign.C.Types                                        

-- | Take a boolean and convert it to an integer
bool_to_int :: Bool -> Int                                    
bool_to_int False = 0                                         
bool_to_int True = 1                                          

-- | Brute force division style prime number testing
is_prime :: Int -> Int                                        
is_prime x = bool_to_int ptest                                
   where divisible = [n | n <- [3,5..(x-1)], x `mod` n == 0]  
         ptest     = length (divisible) == 0                  

-- | Interface exposed into C land
is_prime_hs :: CInt -> CInt                                   
is_prime_hs = fromIntegral . is_prime . fromIntegral          
                                                              
-- | Export symbols into C land                                                                                                                            
foreign export ccall is_prime_hs :: CInt -> CInt