Document opaque types

Closes https://github.com/gleam-lang/language-tour/issues/63

1 files changed, 30 insertions, 0 deletions

diff --git a/src/content/chapter5_advanced_features/lesson02_use_sugar/code.gleam b/src/content/chapter5_advanced_features/lesson02_use_sugar/code.gleam
new file mode 100644
index 0000000..6c5ccaa
--- /dev/null
+++ b/src/content/chapter5_advanced_features/lesson02_use_sugar/code.gleam
@@ -0,0 +1,30 @@
+import gleam/io
+import gleam/result
+
+pub fn main() {
+  let x = {
+    use username <- result.try(get_username())
+    use password <- result.try(get_password())
+    use greeting <- result.map(log_in(username, password))
+    greeting <> ", " <> username
+  }
+
+  case x {
+    Ok(greeting) -> io.println(greeting)
+    Error(error) -> io.println("ERROR:" <> error)
+  }
+}
+
+// Here are some pretend functions for this example:
+
+fn get_username() {
+  Ok("alice")
+}
+
+fn get_password() {
+  Ok("hunter2")
+}
+
+fn log_in(_username: String, _password: String) {
+  Ok("Welcome")
+}