September 2017 Update

Task/Abstract-type/Zkl/abstract-type-1.zkl

@@ -0,0 +1,21 @@
+class Stream{	// Mostly virtural base class
+   var [proxy protected]
+      isBroken = fcn { _broken.isSet() },
+      isClosed = fcn { return(_closed.isSet() or _broken.isSet()); };
+   fcn init{
+      var [protected]
+         _closed	= Atomic.Bool(True),
+	 _broken	= Atomic.Bool(False),
+	 whyBroken	= Void;
+   }
+   fcn clear	  { _closed.clear(); _broken.clear(); return(self.topdog); }
+   fcn open       { return(topdog.init(vm.pasteArgs())); }
+   fcn toStream   { return(self); }
+   fcn close      { _closed.set(); return(self.topdog); }
+   fcn flush      { return(self.topdog); }
+   fcn read       { throw(Exception.TheEnd); }	// destructive or advance
+   fcn readln     { throw(Exception.TheEnd); }
+   fcn write(x)	  { return(self.topdog); }
+   fcn writeln(x) { return(self.topdog); }
+   fcn walker	  { return((0).walker(*,wap((self.topdog.read.fpM(""))))); }
+}

Task/Abstract-type/Zkl/abstract-type-2.zkl

@@ -0,0 +1,5 @@
+class DevNull(Stream){
+   var [const] fileName = "DevNull";	// compatibility with File
+   fcn init     { Stream.init() }
+   fcn write(x) { return(0); }
+}