string.starts_with & string.ends_with

1 files changed, 13 insertions, 1 deletions

diff --git a/src/gleam_stdlib.erl b/src/gleam_stdlib.erl
index 49a7e2a..fbd84da 100644
--- a/src/gleam_stdlib.erl
+++ b/src/gleam_stdlib.erl
@@ -7,7 +7,7 @@
          iodata_append/2, iodata_prepend/2, identity/1, 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_contains/2]).
+         string_contains/2, string_starts_with/2, string_ends_with/2]).
 
 should_equal(Actual, Expected) -> ?assertEqual(Expected, Actual).
 should_not_equal(Actual, Expected) -> ?assertNotEqual(Expected, Actual).
@@ -127,3 +127,15 @@ string_contains(Haystack, Needle) ->
     _ ->
       true
   end.
+
+string_starts_with(_, <<>>) -> true;
+string_starts_with(String, Prefix) when byte_size(Prefix) > byte_size(String) -> false;
+string_starts_with(String, Prefix) ->
+    PrefixSize = byte_size(Prefix),
+    Prefix == binary_part(String, 0, PrefixSize).
+
+string_ends_with(_, <<>>) -> true;
+string_ends_with(String, Suffix) when byte_size(Suffix) > byte_size(String) -> false;
+string_ends_with(String, Suffix) ->
+    SuffixSize = byte_size(Suffix),
+    Suffix == binary_part(String, byte_size(String) - SuffixSize, SuffixSize).