Paste: nsieve with stack

: init-sieve ( n -- xs )
    [ 1 ] B{ } replicate-as
    0 over set-first
    0 over set-second ; inline

: set-all ( elt indices seq -- )
    swap [ swap set-nth ] with with each ; inline

: multiples ( i n -- range )
    over [ 2 * ] [ 1 - ] [ ] tri* <range> ; inline

: sieve-step ( i n xs -- )
    [ [ 0 ] 2dip multiples ] dip set-all ; inline

: sieve-loop ( n xs -- )
    tuck '[ swap 1 = [ _ _ sieve-step ] [ drop ] if ] each-index ;

: nsieve ( n -- pi(n) )
    dup init-sieve [ sieve-loop ] [ sum ] bi ;