#lang racket
(require math)
(define earth-radius 6371)

(define (distance lat1 long1 lat2 long2)
  (define (h a b) (sqr (sin (/ (- b a) 2))))
  (* 2 earth-radius
     (asin (sqrt (+ (h lat1 lat2)
                    (* (cos lat1) (cos lat2) (h long1 long2)))))))

(define (deg-to-rad d m s)
  (* (/ pi 180) (+ d (/ m 60) (/ s 3600))))

(distance (deg-to-rad 36  7.2 0) (deg-to-rad  86 40.2 0)
          (deg-to-rad 33 56.4 0) (deg-to-rad 118 24.0 0))