Add `capitalize` function to `String`s.

2 files changed, 51 insertions, 0 deletions

diff --git a/src/gleam/string.gleam b/src/gleam/string.gleam
index 3cec7d2..d574242 100644
--- a/src/gleam/string.gleam
+++ b/src/gleam/string.gleam
@@ -785,3 +785,24 @@ pub fn last(s: String) -> Option(String) {
     _ -> Some(slice(s, length(s) - 1, 1))
   }
 }
+
+/// Creates a new `String` with the first grapheme in the input `String`
+/// converted to uppercase and the remaining graphemes to lowercase.
+///
+/// ## Examples
+///
+/// ```gleam
+/// > capitalize("mamouna")
+/// "Mamouna"
+/// ```
+///
+pub fn capitalize(s: String) -> String {
+  let first =
+    slice(s, 0, 1)
+    |> uppercase
+  let rest =
+    slice(s, 1, length(s))
+    |> lowercase
+
+  append(to: first, suffix: rest)
+}
diff --git a/test/gleam/string_test.gleam b/test/gleam/string_test.gleam
index 8ad1080..14b034c 100644
--- a/test/gleam/string_test.gleam
+++ b/test/gleam/string_test.gleam
@@ -388,3 +388,33 @@ pub fn last_test() {
   |> string.last
   |> should.equal(Some(" "))
 }
+
+pub fn capitalize_test() {
+  ""
+  |> string.capitalize
+  |> should.equal("")
+
+  "gleam"
+  |> string.capitalize
+  |> should.equal("Gleam")
+
+  "GLEAM"
+  |> string.capitalize
+  |> should.equal("Gleam")
+
+  "g l e a m"
+  |> string.capitalize
+  |> should.equal("G l e a m")
+
+  "1GLEAM"
+  |> string.capitalize
+  |> should.equal("1gleam")
+
+  "_gLeAm1"
+  |> string.capitalize
+  |> should.equal("_gleam1")
+
+  " gLeAm1"
+  |> string.capitalize
+  |> should.equal(" gleam1")
+}