(*
   FILE: sieve.kln
   AUTHOR: Eugene Wallingford
   DATE  : 2007/09/25
   TASK  : computes and prints a Sieve of Eratosthenes
*)

function main( n : integer ) : boolean
   sieveAt(2, n)

function sieveAt(current : integer, max : integer) : boolean
   if max < current then
      true
   else
      doSieveAt(current, max)

(*
   doSieveAt exists only because calls to print are allowed
   only as the first expression in the body of function.
*)

function doSieveAt(current : integer, max : integer) : boolean
   print( if isPrime(current) then current else 0 )
   sieveAt(current+1, max)

function isPrime( n : integer ) : boolean
   not hasDivisorFrom(2, n)

function hasDivisorFrom( i : integer, n : integer) : boolean
   if i < n then
      divides(i, n) or hasDivisorFrom(i+1, n)
   else
      false

function divides( a : integer, b : integer) : boolean
   rem(b, a) = 0

function rem( num : integer, den : integer) : integer
   if num < den then
      num
   else
      rem( num-den, den)