Q'Nial

# Generating primes in the old fashioned way


# Test if a number is a prime by examining the residue of division
# by all numbers less than or equal to the square root of the number.
# If no residue is 0 the number is a prime. 

isp is operation X { 
    (X > 1) and (and (0 < (X eachright mod (2 drop tell (1 + floor sqrt X))))) }


# Find all primes up to the supplied number by testing each to see if it
# is a prime and then selecting the sublist of numbers that are primes.

isp_list is op N {
  r := each isp (count N);
  r sublist (count N)
}

# Find the primes up to 1000. If you want to run this interactively
# then remove the 'bye' line and use
#
#     Nial -i
#     loaddefs "primes

write ('Primes to 1000' (isp_list 1000));

# That's all folks

bye;