More lessons

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diff --git a/lessons/src/lesson023_variable_patterns/code.gleam b/lessons/src/lesson023_variable_patterns/code.gleam
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+import gleam/io
+import gleam/int
+
+pub fn main() {
+  let x = int.random(0, 5)
+  io.debug(x)
+
+  let result = case x {
+    // Match specific values
+    0 -> "Zero"
+    1 -> "One"
+    // Match any other value
+    _ -> "Other"
+  }
+  io.debug(result)
+}
diff --git a/lessons/src/lesson023_variable_patterns/text.html b/lessons/src/lesson023_variable_patterns/text.html
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+<p>
+  The case expression is the most common kind of flow control in Gleam code. It
+  is similar to `switch` in some other languages, but more powerful than most.
+</p> 
+<p>
+  It allows the programmer to say "if the data has this shape then run this
+  code", a process called called <em>pattern matching</em>.
+</p>
+<p>
+  Gleam performs <em>exhaustiveness checking</em> to ensure that the patterns in
+  a case expression cover all possible values. With this you can have confidence
+  that your logic is up-to-date for the design of the data you are working with.
+</p>
+<p>
+  Try commenting out patterns or adding new redundant ones, and see what
+  problems the compiler reports.
+</p>