12 January 2019

Identical to standard Forth except no infinite loop.

65535 constant maxint
: #prime@    2 + cells + ;
: #prime     >r dup r> #prime@ @ ;
: #primes    dup 1 cells + @ ;
: #primes++  #primes 1+ over 1 cells + ! ;
: maxprimes  dup @ ;
: notprime   drop 0 ;
: divides?   mod 0= ;
: initialize dup >r here dup r> 2 + cells allot rot swap ! 0 over 1 cells + ! ;
: isprime!   dup . cr over #primes #prime@ ! #primes++ ;

: isprime?
  over #primes 0 do
    i #prime 2 pick swap divides?
      if notprime leave then
  loop ;

: primes
  decimal initialize cr 2 isprime! maxint 3 do
    i isprime? if isprime! else drop then
    maxprimes >r #primes r> = if leave then
  loop ;

There's a bug that causes the value of here to be left on the stack when the program exits. Some word isn't behaving exactly the same as in standard Forth, but since it doesn't affect the benchmark results, I haven't tried to track it down yet.