List functions

2 files changed, 35 insertions, 0 deletions

diff --git a/lessons/src/lesson020_lists/code.gleam b/lessons/src/lesson020_lists/code.gleam
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+++ b/lessons/src/lesson020_lists/code.gleam
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+import gleam/io
+
+pub fn main() {
+  let ints = [1, 2, 3]
+
+  io.debug(ints)
+
+  // Immutably prepend
+  io.debug([-1, 0, ..ints])
+
+  // Uncomment this to see the error
+  // io.debug(["zero", ..ints])
+
+  // The original lists are unchanged
+  io.debug(ints)
+}
diff --git a/lessons/src/lesson020_lists/text.html b/lessons/src/lesson020_lists/text.html
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+++ b/lessons/src/lesson020_lists/text.html
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+<p>
+  Lists are ordered collections of values.
+</p>
+<p>
+  <code>List</code> is a generic type, having a type parameter
+  for the type of values it contains. A list of ints has the type
+  <code>List(Int)</code>, and a list of strings has the type
+  <code>List(String)</code>.
+</p>
+<p>
+  Lists are immutable single-linked lists, meaning they are very efficient to
+  add and remove elements from the front of the list.
+</p>
+<p>
+  Counting the length of a list or getting elements from other positions in the
+  list is expensive and rarely done. It is rare to write algorithms that index
+  into sequences in Gleam, but but when they are written a list is not the right
+  choice of data structure.
+</p>