(define (scalar op array number) (map (lambda (x) (op x number) ) array))
(define (sum array) (apply + array))
(define (mean x) (/ (sum x) (length x)))
;(define (sqrt x) (expt x 0.5))

(define (pearson x y) (
  (lambda (x y)
    (
      if (not (= (length x) (length y)))
      (error "x and y have incompatible dimensions")
      (
        let* (
          (n (length x))
          (mx (mean x))
          (my (mean y))
          (xm (scalar - x mx))
          (ym (scalar - y my))
          (sx (sqrt (/ (sum (map * xm xm)) (- n 1))))
          (sy (sqrt (/ (sum (map * ym ym)) (- n 1))))
          (sxy (/ (sum (map * xm ym)) (- n 1)))
        )
        (/ sxy (* sx sy))
      )
    )
  ) x y
))