From 267c3b8d2ff3340c022330dfb367128cddb69b51 Mon Sep 17 00:00:00 2001
From: Mathias Jean Johansen <mathias@mjj.io>
Date: Mon, 2 May 2022 18:02:34 +0200
Subject: Refactor `last` to return a `Result`.

---
 src/gleam/string.gleam       | 18 +++++++++---------
 test/gleam/string_test.gleam |  8 ++++----
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/src/gleam/string.gleam b/src/gleam/string.gleam
index 89cdc6c..bc13758 100644
--- a/src/gleam/string.gleam
+++ b/src/gleam/string.gleam
@@ -763,26 +763,26 @@ pub fn first(s: String) -> Result(String, Nil) {
   }
 }
 
-/// Returns the last element in a grapheme and wraps it in an `Option(String)`.
-/// If the `String` is empty, it returns `None`. Otherwise, it returns
-/// `Some(String)`.
+/// Returns the last grapheme cluster in a given `String` and wraps it in a
+/// `Result(String, Nil)`. If the `String` is empty, it returns `Error(Nil)`.
+/// Otherwise, it returns `Ok(String)`.
 ///
 /// ## Examples
 ///
 /// ```gleam
 /// > last("")
-/// None
+/// Error(Nil)
 /// ```
 ///
 /// ```gleam
 /// > last("icecream")
-/// Some("m")
+/// Ok("m")
 /// ```
 ///
-pub fn last(s: String) -> Option(String) {
-  case length(s) {
-    0 -> None
-    _ -> Some(slice(s, -1, 1))
+pub fn last(s: String) -> Result(String, Nil) {
+  case pop_grapheme(s) {
+    Ok(#(_, rest)) -> Ok(slice(rest, -1, 1))
+    Error(e) -> Error(e)
   }
 }
 
diff --git a/test/gleam/string_test.gleam b/test/gleam/string_test.gleam
index 56b50a0..d6e1c23 100644
--- a/test/gleam/string_test.gleam
+++ b/test/gleam/string_test.gleam
@@ -382,19 +382,19 @@ pub fn first_test() {
 pub fn last_test() {
   ""
   |> string.last
-  |> should.equal(None)
+  |> should.be_error
 
   "gleam"
   |> string.last
-  |> should.equal(Some("m"))
+  |> should.equal(Ok("m"))
 
   "gleam "
   |> string.last
-  |> should.equal(Some(" "))
+  |> should.equal(Ok(" "))
 
   "եոգլի"
   |> string.last
-  |> should.equal(Some("ի"))
+  |> should.equal(Ok("ի"))
 }
 
 pub fn capitalize_test() {
-- 
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