Project Euler

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# [[Problem 10]]

```scheme

#!r6rs

#!chezscheme

(import (chezscheme))

(define (sum-prime prime?-table)

  (let* ([len (vector-length prime?-table)]

         [index-list (iota len)]

         [prime?-list (vector->list prime?-table)])

    (fold-left

      (lambda (sum index prime?)

        (if prime?

          (+ sum index)

          sum))

      0

      index-list

      prime?-list)))

(define (eratosthenes-sub! table erase-num)

  (assert (vector-ref table erase-num))

  (let loop ([current (* erase-num 2)])

    (cond

      [(<= (vector-length table) current) table]

      [else

        (vector-set! table current #f)

        (loop (+ current erase-num))])))

(define (eratosthenes num)

  (let ([table (make-vector num #t)]

        [count (isqrt (sub1 num))])

    (vector-set! table 0 #f)

    (vector-set! table 1 #f)

    (let loop ([index 2] [table table])

      (cond

        [(< count index) table]

        [(vector-ref table index)

         (loop (add1 index) (eratosthenes-sub! table index))]

        [else (loop (add1 index) table)]))))

(define answer-10

  (sum-prime (eratosthenes 2000001)))

(printf "10: ~D~%" answer-10)

```