string.next_grapheme

2 files changed, 22 insertions, 12 deletions

diff --git a/src/gleam/string.gleam b/src/gleam/string.gleam
index 25122b9..cf2a585 100644
--- a/src/gleam/string.gleam
+++ b/src/gleam/string.gleam
@@ -399,6 +399,7 @@ pub fn trim_left(string: String) -> String {
 pub fn trim_right(string: String) -> String {
   erl_trim(string, Trailing)
 }
+
 // TODO
 // /// Convert a string to a list of Graphemes.
 // ///
@@ -407,13 +408,15 @@ pub fn trim_right(string: String) -> String {
 //
 // ///
 // pub fn to_graphemes(string: String) -> List(String) {}
-// TODO
-// Split a non-empty string into its head and tail. This lets you
-// pattern match on strings exactly as you would with lists.
-//
-// ## Examples
-//    > next_grapheme("")
-//    Error(Nil)
-//
-//
-// pub fn next_grapheme(string: String) -> Option(tuple(Grapheme, String)) {}
+/// Split a non-empty string into its head and tail. This lets you
+/// pattern match on strings exactly as you would with lists.
+///
+/// ## Examples
+///    > pop_grapheme("gleam")
+///    Ok(tuple("g", "leam"))
+///
+///    > pop_grapheme("")
+///    Error(Nil)
+///
+pub external fn pop_grapheme(string: String) -> Option(tuple(String, String)) =
+  "gleam_stdlib" "string_pop_grapheme"
diff --git a/src/gleam_stdlib.erl b/src/gleam_stdlib.erl
index 0efedec..fc5499c 100644
--- a/src/gleam_stdlib.erl
+++ b/src/gleam_stdlib.erl
@@ -8,8 +8,8 @@
          decode_int/1, decode_string/1, decode_bool/1, decode_float/1,
          decode_thunk/1, decode_atom/1, decode_list/1, decode_field/2,
          decode_element/2, parse_int/1, parse_float/1, compare_strings/2,
-         string_starts_with/2, string_ends_with/2, string_pad/4,
-         decode_tuple2/1, decode_map/1]).
+         string_pop_grapheme/1, string_starts_with/2, string_ends_with/2,
+         string_pad/4, decode_tuple2/1, decode_map/1]).
 
 should_equal(Actual, Expected) -> ?assertEqual(Expected, Actual).
 should_not_equal(Actual, Expected) -> ?assertNotEqual(Expected, Actual).
@@ -135,3 +135,10 @@ string_ends_with(String, Suffix) ->
 
 string_pad(String, Length, Dir, PadString) ->
     unicode:characters_to_binary(string:pad(String, Length, Dir, PadString)).
+
+string_pop_grapheme(String) ->
+    case string:next_grapheme(String) of
+        [ Next | Rest ] ->
+            {ok, {unicode:characters_to_binary([Next]), unicode:characters_to_binary(Rest)}};
+        _ -> {error, nil}
+    end.