Document opaque types

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

1 files changed, 16 insertions, 0 deletions

diff --git a/src/content/chapter5_advanced_features/lesson05_let_assert/code.gleam b/src/content/chapter5_advanced_features/lesson05_let_assert/code.gleam
new file mode 100644
index 0000000..2ba907a
--- /dev/null
+++ b/src/content/chapter5_advanced_features/lesson05_let_assert/code.gleam
@@ -0,0 +1,16 @@
+import gleam/io
+
+pub fn main() {
+  let a = unsafely_get_first_element([123])
+  io.debug(a)
+
+  let b = unsafely_get_first_element([])
+  io.debug(b)
+}
+
+pub fn unsafely_get_first_element(items: List(a)) -> a {
+  // This will panic if the list is empty.
+  // A regular `let` would not permit this partial pattern
+  let assert [first, ..] = items
+  first
+}