;;;; A diamond, with a type crossing it.
;;;;
;;;; The tree is pkg-diamond -> {area, draw} -> shape, which is the case that
;;;; only works if a package may import a package and if the shared bottom is
;;;; loaded once. The proof is not that it compiles but that a shape/Box built
;;;; inside area/ is accepted by a function declared inside draw/: two copies
;;;; of one struct would be two types, and passing one to the other would fail
;;;; to unify with a message naming shape/Box twice and explaining nothing.
;;;;
;;;; shape is never imported here directly. It arrives only through the two
;;;; middles, so its names are in scope because a package's import qualified
;;;; them, not because this file did — which is the inner-alias rule, visible.

(import area "pkgs/area")
(import draw "pkgs/draw")

(defn main [] i32
  (let [b (area/unit)]
    ;; Built in area/, measured in draw/ — one type or no program.
    (print (draw/describe b)) (println "")
    (print (area/of b)) (println "")
    ;; And the bottom package's own constructor, reached through the chain.
    (print (area/of (shape/box 4 5))) (println ""))
  0)