examples/ex-78.rkt
#lang racket
(require (planet wcy/mpost-wrapper))
(provide main)
(define (main)
  (let ((p (path (op--
                  (point 0 0)
                  (point '1cm 0)))))
    (drawarrow p #:withpen (scale '2bp 'pencircle))
    (drawarrow (zscale (point 1 2) p))))