fmod SIEVE is
    protecting MACHINE-INT .
    sort IntList .
    subsort MachineInt < IntList .
    op nil : -> IntList .
    op _._ : IntList IntList -> IntList 
        [assoc id: nil strat (0)] .
    op force : IntList IntList -> IntList [strat (1 2 0)] .
    op show_upto_ : IntList MachineInt -> IntList .
    op filter_with_ : IntList MachineInt -> IntList .
    op ints-from_ : MachineInt -> IntList .
    op sieve_ : IntList -> IntList .
    op primes : -> IntList .

    var P I E : MachineInt .
    var S L : IntList .

    eq force(L, S) = L . S .
    eq show nil upto I = nil .
    eq show E . S upto I 
      = if I == 0 then nil
        else force(E, show S upto (I - 1)) 
        fi . 
    eq filter nil with P = nil .
    eq filter I . S with P 
      = if (I % P) == 0 then filter S with P
        else I . filter S with P 
        fi .
    eq ints-from I = I . ints-from (I + 1) .
    eq sieve nil = nil .
    eq sieve (I . S) = I . sieve (filter S with I) .
    eq primes = sieve ints-from 2 .
  endfm

  reduce show primes upto 10 .
  *** result IntList: 2 . 3 . 5 . 7 . 11 . 13 . 17 . 19 . 23 . 29