Question

I started learning haskell yesterday and I got stuck on a problem. After a bit of trying different things I thought I’d finally come here and ask how to fix this. Also, feel free to criticize the way I have done things so far so I can know what direction to go. Thanks.

module Main where
main = putStrLn lastPrime
    where
        lastPrime :: String
        lastPrime = show(last(take 10001 primes))
        primes :: [Int]
        primes = [x| x <- [1..],length [a| a <- [1..lessen(x)], mod x a /= 0] == x - 2]
        lessen :: Int -> Int
        lessen a = ceiling(sqrt(a))

Answer 1

To fix your type error, you want this:

    lessen :: Int -> Int
    lessen a = ceiling (sqrt (fromIntegral a))

a has type Int, but sqrt is expecting a floating point type, and the easiest way to convert an integral type to another numeric type is fromIntegral.