examples/ex-49.rkt
#lang racket
(require (planet wcy/mpost-wrapper))
(provide main)
(define (arc O A B rou)
  (let ((alpha (op-angle (op- A O)))
        (beta  (op-angle (op- B O))))
    (path (op+ O (polar rou alpha)) (dir-spec (dir (op+ alpha 90))) ".."
          (op+ O (polar rou beta )) (dir-spec (dir (op+ beta  90))))))
(define (main)
  (let* ((O (point 0 0))
         (alpha 30)
         (A (polar '2cm 0))
         (B (polar '2cm alpha)))
    (draw (path O ".." A))
    (draw (path O ".." B))
    (draw (arc O A B '1cm))
    (draw (arc O A B '1.1cm))))