From 437d456cd504ca4124ef72ea4fb1576ec29563cd Mon Sep 17 00:00:00 2001
From: Louis Pilfold <louis@lpil.uk>
Date: Sat, 9 Dec 2023 15:21:10 +0000
Subject: More on functions

---
 .../src/lesson019_labelled_arguments/code.gleam    | 16 +++++++++++++++
 lessons/src/lesson019_labelled_arguments/text.html | 23 ++++++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 lessons/src/lesson019_labelled_arguments/code.gleam
 create mode 100644 lessons/src/lesson019_labelled_arguments/text.html

(limited to 'lessons/src/lesson019_labelled_arguments')

diff --git a/lessons/src/lesson019_labelled_arguments/code.gleam b/lessons/src/lesson019_labelled_arguments/code.gleam
new file mode 100644
index 0000000..25bb8c1
--- /dev/null
+++ b/lessons/src/lesson019_labelled_arguments/code.gleam
@@ -0,0 +1,16 @@
+import gleam/io
+
+pub fn main() {
+  // Without using labels
+  io.debug(calculate(1, 2, 3))
+
+  // Using the labels
+  io.debug(calculate(1, add: 2, multiply: 3))
+
+  // Using the labels in a different order
+  io.debug(calculate(1, multiply: 3, add: 2))
+}
+
+fn calculate(value: Int, add addend: Int, multiply multiplier: Int) {
+  value * multiplier + addend
+}
diff --git a/lessons/src/lesson019_labelled_arguments/text.html b/lessons/src/lesson019_labelled_arguments/text.html
new file mode 100644
index 0000000..b1d771c
--- /dev/null
+++ b/lessons/src/lesson019_labelled_arguments/text.html
@@ -0,0 +1,23 @@
+<p>
+  When functions take several arguments it can be difficult to remember what the
+  arguments are, and what order they are expected in.
+</p>
+<p>
+  To help with this Gleam supports labelled arguments, where function arguments
+  are given an external label in addition to their internal name. These labels
+  are written before the argument name in the function definition.
+</p>
+<p>
+  When labelled arguments are used the order of the arguments does not matter,
+  but all unlabelled arguments must come before labelled arguments.
+</p>
+<p>
+  There is no performance cost to using labelled arguments, it does not allocate
+  a dictionary or perform any other runtime work.
+</p>
+<p>
+  Labels are optional when calling a function, it is up to the programmer to
+  decide what is clearest in their code.
+</p>
+
+
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