implemeting local variables (ch22)

samples/ch22_local_vars1.lox

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+{
+    var a = "first";
+    var a = "second";
+}

samples/ch22_local_vars2.lox

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+// This is showing:
+//
+// global
+// outer
+// inner
+// outer
+// global
+
+var a = "global";
+{
+    print "in outer block: " + a;
+    var a = "outer";
+    {
+        print "in inner block: " + a;
+        var a = "inner";
+        print "in inner block: " + a;
+    }
+    print "in outer block: " + a;
+}
+print "global: " + a;

samples/ch22_local_vars3.lox

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+{
+    var a = "outer";
+    {
+        // this is reporting "Error at 'a': Can't read local variable in its own initializer."
+        var a = a;
+        print a;
+    }
+}