added events example.

Former-commit-id: 3665c36d27

src/test/events/README.md

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+**events example in oberon**
+
+Just a simple example which helps to explain how events are implemented, what is callback procedure, and how easy it is.
+
+Some languages simplify programmer's work, hide details, so that it's not obvious to him what's going on when he defines it's own OnSomething function.
+
+Callbacks are common when dealing with gui events like OnClick but they can be used with any events. I guess code is simple enough, it doesn't need explanation.

src/test/events/clb.Mod

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+MODULE clb;
+
+IMPORT Console;
+
+TYPE OnSomething = PROCEDURE (x, y : INTEGER);
+
+PROCEDURE ProcessEvents(x, y : INTEGER; onsomething : OnSomething);
+
+BEGIN
+
+IF onsomething # NIL THEN onsomething(x, y)
+ELSE
+   Console.String("didn't happen"); Console.Ln
+END;
+
+END ProcessEvents;
+
+
+PROCEDURE OnEvent(x, y : INTEGER);
+
+BEGIN
+
+Console.String("event happened"); Console.Ln
+
+END OnEvent;
+
+PROCEDURE OnEvent2(x, y : INTEGER);
+
+BEGIN
+
+Console.String("happened"); Console.Ln
+
+END OnEvent2;
+
+PROCEDURE Something;
+VAR onsmth : OnSomething;
+
+BEGIN
+
+   onsmth := NIL;
+   ProcessEvents(0, 0, onsmth);
+
+   onsmth := OnEvent;
+   ProcessEvents(0, 0, onsmth);
+
+END Something;
+
+BEGIN
+   Something;
+(*
+ProcessEvents(0, 0, NIL);
+ProcessEvents(0, 0, OnEvent);
+ProcessEvents(0, 0, OnEvent2);
+*)
+END clb.

src/test/events/makefile

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+
+
+all:
+	/opt/voc/bin/voc -M clb.Mod