Move variables / const examples to separate .rs files

deps/examples/destructuring.rs

@@ -0,0 +1,15 @@
+fn main() {
+    // destructuring tuples
+    let (_x, _y, _z) = (1, 2, 3);
+
+    // destructuring structs
+    struct Point {
+        x: i32,
+        y: i32,
+    }
+
+    let p = Point { x: 0, y: 7 };
+    let Point { x: _a, y: _b } = p; // a = 0, b = 7
+    let Point { x, y } = p; // simpler
+    let _ = (x, y);
+}

deps/examples/shadowing.rs

@@ -0,0 +1,9 @@
+fn main() {
+    let x = 5; // x is immutable
+
+    let x = x + 1; // redefines x
+    println!("{x}");
+
+    let x = "example"; // the type can change
+    println!("{x}");
+}

deps/examples/vars_and_consts.rs

@@ -0,0 +1,9 @@
+#![allow(unused)]
+fn main() {
+    // `const` is set to a constant expression; the type must be annotated
+    const THREE_HOURS_IN_SECONDS: u32 = 60 * 60 * 3;
+
+    let apples = 5; // immutable variable
+
+    let mut guess = String::new(); // mutable variable
+}

src/lang/variables_and_constants.md

@@ -1,36 +1,19 @@
 # Variables and Constants
 
 ```rust,editable
-fn main() {
-    const THREE_HOURS_IN_SECONDS: u32 = 60 * 60 * 3;  // set only to a constant expression; type must be annotated
-    let apples = 5;                 // immutable
-    let mut guess = String::new();  // mutable
-}
+{{#include ../../deps/examples/vars_and_consts.rs}}
 ```
 
 ## Shadowing
 
 ```rust,editable
-fn main() {
-    let x = 5;
-    let x = x + 1;  // redefines x; type can change
-}
+{{#include ../../deps/examples/shadowing.rs}}
 ```
 
 ## Destructuring
 
 ```rust,editable
-fn main() {
-    // destructuring tuples
-    let (x, y, z) = (1, 2, 3);
-
-    // destructuring structs
-    struct Point{ x: i32, y: i32, }
-
-    let p = Point { x: 0, y: 7 };
-    let Point { x: a, y: b } = p;   // a = 0, b = 7
-    let Point { x, y } = p;         // simpler
-}
+{{#include ../../deps/examples/destructuring.rs}}
 ```
 
 Starting the name of a variable with an underscore silences unused variable warnings.