(define *pi* 3.14159265358979323846)

(define (->radians gps)
    (list (* (/ *pi* 180) (car gps))
          (* (/ *pi* 180) (cadr gps))))

(define (gdist l1 l2)
    (let* ((min1 (->radians l1))
           (min2 (->radians l2))
           (dlat (- (car min1) (car min2)))
           (dlon (- (cadr min1) (cadr min2)))
           (haver (+ (sq (sin (/ dlat 2))) (* (cos (car min1)) 
                (cos (car min2)) (sq (sin (/ dlon 2)))))))
           (* 6371 2 (asin (sqrt haver)))))