Nil and bit arrays

2 files changed, 26 insertions, 0 deletions

diff --git a/lessons/src/lesson035_nil/code.gleam b/lessons/src/lesson035_nil/code.gleam
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--- /dev/null
+++ b/lessons/src/lesson035_nil/code.gleam
@@ -0,0 +1,11 @@
+import gleam/io
+
+pub fn main() {
+  let x = Nil
+  io.debug(x)
+
+  // let y: List(String) = Nil
+
+  let result = io.println("Hello!")
+  io.debug(result == Nil)
+}
diff --git a/lessons/src/lesson035_nil/text.html b/lessons/src/lesson035_nil/text.html
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+++ b/lessons/src/lesson035_nil/text.html
@@ -0,0 +1,15 @@
+<p>
+  <code>Nil</code> is Gleam's unit type. It is a value that is returned by
+  functions that have nothing else to return, as all functions much return
+  something.
+</p>
+<p>
+  <code>Nil</code> is not a valid value of any other types, that is values in
+  Gleam are not nullable. If the type of a value is <code>Nil</code> then it is
+  the value <code>nil</code>. If it is some other type then the value is not
+  <code>Nil</code>.
+</p>
+<p>
+  Uncomment the line that assigns <code>Nil</code> to a variable with an
+  incompatible type annotation to see the comile time error it produces.
+</p>