Split out variable shadowing example

Author: xiaochuanyu

src/variable_bindings/scope.md

@@ -1,9 +1,7 @@
 # Scope and Shadowing
 
 Variable bindings have a scope, and are constrained to live in a *block*. A
-block is a collection of statements enclosed by braces `{}`. Also, [variable
-shadowing][variable-shadow] is allowed.
-
+block is a collection of statements enclosed by braces `{}`. 
 ```rust,editable,ignore,mdbook-runnable
 fn main() {
     // This binding lives in the main function
@@ -15,11 +13,6 @@ fn main() {
         let short_lived_binding = 2;
 
         println!("inner short: {}", short_lived_binding);
-
-        // This binding *shadows* the outer one
-        let long_lived_binding = 5_f32;
-
-        println!("inner long: {}", long_lived_binding);
     }
     // End of the block
 
@@ -28,12 +21,23 @@ fn main() {
     // FIXME ^ Comment out this line
 
     println!("outer long: {}", long_lived_binding);
-    
-    // This binding also *shadows* the previous binding
-    let long_lived_binding = 'a';
-    
-    println!("outer long: {}", long_lived_binding);
 }
 ```
+Also, a binding may have the same name as a binding from an outer block. This is
+known as [variable shadowing][variable-shadow].
+```rust,editable,ignore,mdbook-runnable
+fn main() {
+    let shadowed_binding = 1;
 
+    {
+        println!("before being shadowed: {}", shadowed_binding);
+
+        // This binding *shadows* the outer one
+        let shadowed_binding = "a";
+
+        println!("after being shadowed: {}", shadowed_binding);
+    }
+
+}
+```
 [variable-shadow]: https://en.wikipedia.org/wiki/Variable_shadowing