fact :: Integer -> Integer
fact n = if n == 0 then 1 else n * fact (n - 1)

-- try
-- take 5 (myfrom 1)

myfrom :: Integer -> [Integer]
myfrom n = n : myfrom (n+1)

-- try
-- fact 100

sieve :: [Integer] -> [Integer]
sieve (p:xs) = filter (\ x -> x `mod` p /= 0) xs
sieve []     = []

primes :: [Integer]
primes = map head (iterate sieve [2 ..])

-- try
-- take 100 primes

check (i,j) (m,n) = j == n || (i + j == m + n) || (i - j == m - n)
safe p n  = all not [ check (i, j) (1 + length p, n) | (i, j) <- zip [1..] p ]

queens 0  = [[]]
queens m  = [ p ++ [n] | p <- queens (m - 1), n <- [1..8], safe p n ]

-- try
-- queens 7
-- head (queens 8)