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The sieve of eratosthenes

forth

\ Sieve of Eratosthenes in Forth
\ Written by Rob Hoelz
\ To run: Load this file into a Forth interpreter, and call <limit> MAIN

VARIABLE LIMIT

: RANGE RECURSIVE 2DUP =
    IF DROP
    ELSE DUP -ROT 1- RANGE
    THEN ;

: REMOVE RECURSIVE DUP DEPTH 3 - >
    IF DROP
    ELSE DUP 1+ PICK 2 PICK MOD 0=
        IF DUP 1+ ROLL DROP REMOVE
        ELSE 1+ REMOVE
        THEN
    THEN ;

: REMOVE.MULTIPLES 1 REMOVE ;

: GENERATE RECURSIVE DUP . DUP DUP * LIMIT @ >
    IF DROP
    ELSE REMOVE.MULTIPLES DROP GENERATE
    THEN ;

: PRINT.PRIMES RECURSIVE DEPTH 0>
    IF . PRINT.PRIMES
    ELSE CR
    THEN ;

: MAIN
LIMIT !
2 LIMIT @ RANGE GENERATE PRINT.PRIMES ;

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