;; $Id: grav-force-example.scm,v 1.2 2006/01/05 22:24:09 leavens Exp $
;;; AUTHOR: Gary T. Leavens
(module grav-force-example (lib "typedscm.ss" "typedscm")
(provide G grav-force grav-force-c mass-of-earth
         radius-of-earth earths-force force-at-surface)
(define G
  ;; UNITS: N * m^2 / kg^2
  6.670e-11)

(define square
  ;; UNITS: (-> (m) m^2)
  (lambda (r) (* r r)))

(define grav-force
  ;; UNITS: (-> (kg m kg) N)
  (lambda (m1 r m2)     
    (if (zero? r) 
        0.0
        (/ (* G (* m1 m2))
           (square r)))))

(define grav-force-c 
  ;; UNITS: (-> (kg) (-> (m) (-> (kg) N)))
  (lambda (m1)                  ; kg 
    (lambda (r)                 ; m
      (lambda (m2)              ; kg 
          (if (zero? r) 
              0.0
              (/ (* G (* m1 m2))
                 (square r)))))))

;;              USING IT
(define mass-of-earth
  ;; UNITS: kg
  5.96e24)

(define radius-of-earth
  ;; UNITS: m
    6.37e6)

(define earths-force
  ;; UNITS: (-> (m) (-> (kg) N))
  (lambda (r)
    ((grav-force-c mass-of-earth) r)))

(define force-at-surface
  ;; UNITS: (-> (kg) N)
  (lambda (m2)
    ((earths-force radius-of-earth) m2)))
) ;; end module