> Please, get rid off the primes example, as it is horrible inefficient (in the sense of, "Ok, let's find the first n primes by a simple well-known algorithm, like the Sieve of Eratosthenes") and a simple (non-pure) array-based approach will kick its ass.

The primes example may be a bit awkward for people with no background in math but it's also an excellent example to demonstrate lazy evaluation in Haskell.

The interesting bit is that primes is an infinite list, containing all prime numbers. Don't try to print the whole list or count the sum unless you have a computer with infinite memory :)