support unicode escape codes

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+- Added support for `\x`, `\u` and `\U` escape codes
+
 ## v2.1.0 - 2026-04-30
 
 - Added parsing of TOML documents to `Dynamic`.

README.md

@@ -34,11 +34,3 @@ pub fn main() {
 ```
 
 Further documentation can be found at <https://hexdocs.pm/tom>.
-
-## Status
-
-The following string escape sequences are not supported yet:
-
-- `\xHH`
-- `\uHHHH`
-- `\UHHHHHHHH`

src/tom.gleam

@@ -631,7 +631,10 @@ fn merge(
   }
 }
 
-fn expect_end_of_line(input: Tokens, next: fn(Tokens) -> Parsed(a)) -> Parsed(a) {
+fn expect_end_of_line(
+  input: Tokens,
+  next: fn(Tokens) -> Parsed(a),
+) -> Parsed(a) {
   case input {
     ["\n", ..input] -> next(input)
     ["\r\n", ..input] -> next(input)
@@ -1113,6 +1116,21 @@ fn parse_string(input: Tokens, string: String) -> Parsed(Toml) {
     ["\\", "f", ..input] -> parse_string(input, string <> "\f")
     ["\\", "\"", ..input] -> parse_string(input, string <> "\"")
     ["\\", "\\", ..input] -> parse_string(input, string <> "\\")
+    ["\\", "x", ..input] -> {
+      let #(hex_codepoints, input) = list.split(input, 2)
+      use str <- result.try(hex_codepoint_to_string(hex_codepoints))
+      parse_string(input, string <> str)
+    }
+    ["\\", "u", ..input] -> {
+      let #(hex_codepoints, input) = list.split(input, 4)
+      use str <- result.try(hex_codepoint_to_string(hex_codepoints))
+      parse_string(input, string <> str)
+    }
+    ["\\", "U", ..input] -> {
+      let #(hex_codepoints, input) = list.split(input, 8)
+      use str <- result.try(hex_codepoint_to_string(hex_codepoints))
+      parse_string(input, string <> str)
+    }
     [] -> Error(Unexpected("EOF", "\""))
     ["\n", ..] -> Error(Unexpected("\n", "\""))
     ["\r\n", ..] -> Error(Unexpected("\r\n", "\""))
@@ -1135,6 +1153,21 @@ fn parse_multi_line_string(input: Tokens, string: String) -> Parsed(Toml) {
     ["\\", "r", ..input] -> parse_multi_line_string(input, string <> "\r")
     ["\\", "\"", ..input] -> parse_multi_line_string(input, string <> "\"")
     ["\\", "\\", ..input] -> parse_multi_line_string(input, string <> "\\")
+    ["\\", "x", ..input] -> {
+      let #(hex_codepoints, input) = input |> skip_whitespace |> list.split(2)
+      use str <- result.try(hex_codepoint_to_string(hex_codepoints))
+      parse_multi_line_string(input, string <> str)
+    }
+    ["\\", "u", ..input] -> {
+      let #(hex_codepoints, input) = input |> skip_whitespace |> list.split(4)
+      use str <- result.try(hex_codepoint_to_string(hex_codepoints))
+      parse_multi_line_string(input, string <> str)
+    }
+    ["\\", "U", ..input] -> {
+      let #(hex_codepoints, input) = input |> skip_whitespace |> list.split(8)
+      use str <- result.try(hex_codepoint_to_string(hex_codepoints))
+      parse_multi_line_string(input, string <> str)
+    }
     [] -> Error(Unexpected("EOF", "\""))
     [g, ..input] -> parse_multi_line_string(input, string <> g)
   }
@@ -1166,6 +1199,18 @@ fn parse_literal_string(input: Tokens, string: String) -> Parsed(Toml) {
   }
 }
 
+fn hex_codepoint_to_string(input: Tokens) -> Result(String, ParseError) {
+  let hex_codepoints = string.concat(input)
+
+  use codepoint <- result.map(
+    int.base_parse(hex_codepoints, 16)
+    |> result.try(string.utf_codepoint)
+    |> result.replace_error(Unexpected(hex_codepoints, "0 to F")),
+  )
+
+  string.from_utf_codepoints([codepoint])
+}
+
 fn reverse_arrays_of_tables(toml: Toml) -> Toml {
   case toml {
     ArrayOfTables(tables) ->

test/tom_test.gleam

@@ -97,6 +97,21 @@ pub fn parse_string_linefeed_test() {
   assert tom.parse("hello = \"\\r\"\n") == Ok(expected)
 }
 
+pub fn parse_string_unicode_x_escape_test() {
+  let expected = dict.from_list([#("hello", tom.String("\u{00E9}"))])
+  assert tom.parse("hello = \"\\xE9\"\n") == Ok(expected)
+}
+
+pub fn parse_string_unicode_escape_test() {
+  let expected = dict.from_list([#("hello", tom.String("\u{1111}"))])
+  assert tom.parse("hello = \"\\u1111\"\n") == Ok(expected)
+}
+
+pub fn parse_string_unicode_wide_escape_test() {
+  let expected = dict.from_list([#("hello", tom.String("🌟"))])
+  assert tom.parse("hello = \"\\U0001F31F\"\n") == Ok(expected)
+}
+
 pub fn parse_escaped_slash_test() {
   let expected = dict.from_list([#("hello", tom.String("\\"))])
   assert tom.parse("hello = \"\\\\\"\n") == Ok(expected)