examples/ex-23.rkt
#lang racket
(require (planet wcy/mpost-wrapper))
(provide main)
(define (A-B-C)
  (values (point 0 0)
          (point '1cm 0)
          (point 0 '1cm)))
(define (main)
  (call-with-values A-B-C
    (lambda (A B C)
      (draw (op-- A B C 'cycle) #:withpen (scale '2bp 'pencircle))
      (fill (op-- A B C 'cycle) #:withcolor (op* 0.8 'white)))))