From 5e91a50eb28a292eb56b8d5e5a268c115ffdc86d Mon Sep 17 00:00:00 2001
From: Louis Pilfold <louis@lpil.uk>
Date: Wed, 20 Dec 2023 15:20:27 +0000
Subject: List lessons

---
 lessons/src/lesson027_multiple_subjects/code.gleam    | 17 +++++++++++++++++
 lessons/src/lesson027_multiple_subjects/text.html     | 13 +++++++++++++
 lessons/src/lesson028_alternative_patterns/code.gleam | 14 ++++++++++++++
 lessons/src/lesson028_alternative_patterns/text.html  | 17 +++++++++++++++++
 lessons/src/lesson029_pattern_aliases/code.gleam      | 15 +++++++++++++++
 lessons/src/lesson029_pattern_aliases/text.html       |  7 +++++++
 6 files changed, 83 insertions(+)
 create mode 100644 lessons/src/lesson027_multiple_subjects/code.gleam
 create mode 100644 lessons/src/lesson027_multiple_subjects/text.html
 create mode 100644 lessons/src/lesson028_alternative_patterns/code.gleam
 create mode 100644 lessons/src/lesson028_alternative_patterns/text.html
 create mode 100644 lessons/src/lesson029_pattern_aliases/code.gleam
 create mode 100644 lessons/src/lesson029_pattern_aliases/text.html

(limited to 'lessons/src')

diff --git a/lessons/src/lesson027_multiple_subjects/code.gleam b/lessons/src/lesson027_multiple_subjects/code.gleam
new file mode 100644
index 0000000..d7aa34a
--- /dev/null
+++ b/lessons/src/lesson027_multiple_subjects/code.gleam
@@ -0,0 +1,17 @@
+import gleam/io
+import gleam/int
+
+pub fn main() {
+  let x = int.random(2)
+  let y = int.random(2)
+  io.debug(x)
+  io.debug(y)
+
+  let result = case x, y {
+    0, 0 -> "Both are zero"
+    0, _ -> "First is zero"
+    _, 0 -> "Second is zero"
+    _, _ -> "Neither are zero"
+  }
+  io.debug(result)
+}
diff --git a/lessons/src/lesson027_multiple_subjects/text.html b/lessons/src/lesson027_multiple_subjects/text.html
new file mode 100644
index 0000000..26a7ea3
--- /dev/null
+++ b/lessons/src/lesson027_multiple_subjects/text.html
@@ -0,0 +1,13 @@
+<p>
+  Sometimes it is useful to pattern match on multiple values at the same time in
+  one case experession.
+</p>
+<p>
+  To do this you can give multiple subjects and multiple patterns, separated
+  commas.
+</p>
+<p>
+  When matching on multiple subjects there must be the same number of patterns
+  as there are subjects. Try removing one of the <code>_,</code> sub-patterns to
+  see the compile time error that is returned.
+</p>
diff --git a/lessons/src/lesson028_alternative_patterns/code.gleam b/lessons/src/lesson028_alternative_patterns/code.gleam
new file mode 100644
index 0000000..06a6562
--- /dev/null
+++ b/lessons/src/lesson028_alternative_patterns/code.gleam
@@ -0,0 +1,14 @@
+import gleam/io
+import gleam/int
+
+pub fn main() {
+  let number = int.random(10)
+  io.debug(number)
+
+  let result = case number {
+    2 | 4 | 6 | 8 -> "This is an even number"
+    1 | 3 | 5 | 7 -> "This is an odd number"
+    _ -> "I'm not sure"
+  }
+  io.debug(result)
+}
diff --git a/lessons/src/lesson028_alternative_patterns/text.html b/lessons/src/lesson028_alternative_patterns/text.html
new file mode 100644
index 0000000..10ad731
--- /dev/null
+++ b/lessons/src/lesson028_alternative_patterns/text.html
@@ -0,0 +1,17 @@
+<p>
+  Alternative patterns can be given for a case clause using the
+  <code>|</code> operator. If any of the patterns match then the clause matches.
+</p>
+<p>
+  When matching on multiple subjects there must be the same number of patterns
+  as there are subjects. Try removing one of the <code>_,</code> sub-patterns to
+  see the compile time error that is returned.
+</p>
+<p>
+  If a pattern defines a variable then all of the alternative patterns for that
+  clause must also define a variable with the same name and same type.
+</p>
+<p>
+  Currently it is not possible to have nested alternative patterns, so the
+  pattern <code>[1 | 2 | 3]</code> is not valid.
+</p>
diff --git a/lessons/src/lesson029_pattern_aliases/code.gleam b/lessons/src/lesson029_pattern_aliases/code.gleam
new file mode 100644
index 0000000..ee40a26
--- /dev/null
+++ b/lessons/src/lesson029_pattern_aliases/code.gleam
@@ -0,0 +1,15 @@
+import gleam/io
+
+pub fn main() {
+  io.debug(get_first_non_empty([[], [1, 2, 3], [4, 5]]))
+  io.debug(get_first_non_empty([[1, 2], [3, 4, 5], []]))
+  io.debug(get_first_non_empty([[], [], []]))
+}
+
+fn get_first_non_empty(lists: List(List(t))) -> List(t) {
+  case lists {
+    [[_, ..] as first, ..] -> first
+    [_, ..rest] -> get_first_non_empty(rest)
+    [] -> []
+  }
+}
diff --git a/lessons/src/lesson029_pattern_aliases/text.html b/lessons/src/lesson029_pattern_aliases/text.html
new file mode 100644
index 0000000..5aa8a81
--- /dev/null
+++ b/lessons/src/lesson029_pattern_aliases/text.html
@@ -0,0 +1,7 @@
+<p>
+  The <code>as</code> operator can be used to assign sub patterns to variables.
+</p>
+<p>
+  For example, the pattern <code>[_, ..] as it</code> will match any non-empty
+  list and assign that list to the variable <code>it</code>.
+</p>
-- 
cgit v1.2.3