{"id":2168,"date":"2023-12-13T08:56:10","date_gmt":"2023-12-13T07:56:10","guid":{"rendered":"https:\/\/oopm.org\/?page_id=2168"},"modified":"2024-11-26T14:34:30","modified_gmt":"2024-11-26T13:34:30","slug":"51-1-traffic-light-example51-1","status":"publish","type":"page","link":"https:\/\/oopm.org\/?page_id=2168","title":{"rendered":"15.1 Traffic light example"},"content":{"rendered":"
\"image_pdf\"<\/a>\"image_print\"<\/a><\/div>\n

Below we show an example of a traffic light that alternates between red and green in direction north and south respectively.<\/p>\n\n\n\n

trafficSystem: obj<\/strong>\n   class<\/strong> TrafficLight(direction: ref<\/strong> String):\n      state: ref<\/strong> String\n      cycle\n         state:= \"red\"\n         this(TrafficLight).suspend\n         state:= \"green\"\n         this(TrafficLight).suspend\n   north: obj<\/strong> TrafficLight(\"North:\")\n   south: obj<\/strong> TrafficLight(\"South:\")\n   north.call -- set north to green\n   cycle\n      north.call\n      south.call\n      sleep(1000)<\/code><\/pre>\n\n\n\n
The object trafficSystem<\/code> has a class TrafficLight<\/code>, which represents the concept of a traffic light.<\/p>\n\n\n\n
Two objects\u00a0north<\/code>\u00a0and south of type\u00a0TrafficLight<\/code>\u00a0are declared (and thereby generated). The generation of a\u00a0TrafficLight<\/code>-object implies that the statements in the class are executed. This means execution of\u00a0cycle ...<\/code> This has the effect that the variable\u00a0state<\/code>\u00a0is assigned the string\u00a0\"red\"<\/code>.<\/p>\n\n\n\n
Then the statement this(TrafficLight).suspend <\/code>is executed. This has the effect that execution of the TrafficLight<\/code>-object is temporarily suspended. The effect is that after the declarations of north and south, they both have state = \"red\"<\/code>.<\/p>\n\n\n\n
Immediately after the generation of north<\/code> and south<\/code> the trafficSystem<\/code>executes north.call.<\/code> This has the effect that execution of north<\/code> is resumed, which implies execution of state := \"green\" <\/code>followed by a new suspension of the execution of north<\/code>.<\/p>\n\n\n\n
The situation is then that north.state = \"green\"<\/code> and south.state = \"red\"<\/code>.<\/p>\n\n\n\n
The TrafficSystem<\/code> then executes a cycle<\/code> where north<\/code> and south<\/code> both are resumed implying that their state<\/code> variables swithces from \"green\"<\/code> to \"red\"<\/code>of \"red\"<\/code> to \"green\"<\/code> and so on. The TrafficSystem<\/code> then sleep<\/code>s for some time before another iteration in the cycle.<\/p>\n
\n\t\t<\/a>\n\t\t<\/div>","protected":false},"excerpt":{"rendered":"
Below we show an example of a traffic light that alternates between red and green in direction north and south respectively. The object trafficSystem has a class TrafficLight, which represents the concept of a traffic light. Two objects\u00a0north\u00a0and south of type\u00a0TrafficLight\u00a0are declared (and thereby generated). The generation of a\u00a0TrafficLight-object implies that the statements in the class are executed. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1961,"menu_order":1,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-2168","page","type-page","status-publish","hentry"],"mb":[],"mfb_rest_fields":["title","gutenberg_elementor_mode"],"_links":{"self":[{"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages\/2168","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/oopm.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2168"}],"version-history":[{"count":12,"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages\/2168\/revisions"}],"predecessor-version":[{"id":9873,"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages\/2168\/revisions\/9873"}],"up":[{"embeddable":true,"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages\/1961"}],"wp:attachment":[{"href":"https:\/\/oopm.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2168"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}