Add trim_chars, trim_chars_left, and trim_chars_right

src/gleam/string.gleam

@@ -553,9 +553,35 @@ fn do_trim(string: String) -> String {
   erl_trim(string, Both)
 }
 
+/// Like `trim`, but removes the specified chars on both sides of a `String`
+///
+/// ## Examples
+///
+/// ```gleam
+/// trim_chars_left("..,hats,..", ".,")
+/// // -> "hats"
+/// ```
+pub fn trim_chars(string: String, charset: String) -> String {
+  do_trim_chars(string, charset)
+}
+
+@external(javascript, "../gleam_stdlib.mjs", "trim_chars")
+fn do_trim_chars(string: String, charset: String) -> String {
+  erl_trim_chars(string, Both, erl_to_graphemes(charset))
+}
+
 @external(erlang, "string", "trim")
 fn erl_trim(a: String, b: Direction) -> String
 
+@external(erlang, "string", "trim")
+fn erl_trim_chars(a: String, b: Direction, c: ErlGraphemes) -> String
+
+@external(erlang, "string", "to_graphemes")
+fn erl_to_graphemes(a: String) -> ErlGraphemes
+
+// erlang's string:to_graphemes returns char() | [char()], which cannot be directly represented
+type ErlGraphemes
+
 type Direction {
   Leading
   Trailing
@@ -598,6 +624,40 @@ fn do_trim_right(string: String) -> String {
   erl_trim(string, Trailing)
 }
 
+/// Like `trim_left`, but removes the specified chars on the left of a `String`
+///
+/// ## Examples
+///
+/// ```gleam
+/// trim_chars_left("..,hats,..", ".,")
+/// // -> "hats,.."
+/// ```
+pub fn trim_chars_left(string: String, charset: String) -> String {
+  do_trim_chars_left(string, charset)
+}
+
+@external(javascript, "../gleam_stdlib.mjs", "trim_chars_left")
+fn do_trim_chars_left(string: String, charset: String) -> String {
+  erl_trim_chars(string, Leading, erl_to_graphemes(charset))
+}
+
+/// Like `trim_right`, but removes the specified chars on the right of a `String`
+///
+/// ## Examples
+///
+/// ```gleam
+/// trim_chars_right("..,hats,..", ".,")
+/// // -> "..,hats"
+/// ```
+pub fn trim_chars_right(string: String, charset: String) -> String {
+  do_trim_chars_right(string, charset)
+}
+
+@external(javascript, "../gleam_stdlib.mjs", "trim_chars_right")
+fn do_trim_chars_right(string: String, charset: String) -> String {
+  erl_trim_chars(string, Trailing, erl_to_graphemes(charset))
+}
+
 /// Splits a non-empty `String` into its first element (head) and rest (tail).
 /// This lets you pattern match on `String`s exactly as you would with lists.
 ///

src/gleam_stdlib.mjs

@@ -21,6 +21,9 @@ import Dict from "./dict.mjs";
 
 const Nil = undefined;
 const NOT_FOUND = {};
+// See license note in escape_regexp_chars
+const reRegExpChar = /[\\^$.*+?()[\]{}|]/g;
+const reHasRegExpChar = RegExp(reRegExpChar.source);
 
 export function identity(x) {
   return x;
@@ -259,8 +262,8 @@ const unicode_whitespaces = [
   "\u2029", // Paragraph separator
 ].join("");
 
-const left_trim_regex = new RegExp(`^([${unicode_whitespaces}]*)`, "g");
-const right_trim_regex = new RegExp(`([${unicode_whitespaces}]*)$`, "g");
+const left_trim_regex = new_left_trim_regexp(unicode_whitespaces);
+const right_trim_regex = new_right_trim_regexp(unicode_whitespaces);
 
 export function trim(string) {
   return trim_left(trim_right(string));
@@ -274,6 +277,23 @@ export function trim_right(string) {
   return string.replace(right_trim_regex, "");
 }
 
+export function trim_chars(string, charset) {
+    const trimmed_right = trim_chars_right(string, charset);
+    return trim_chars_left(trimmed_right, charset);
+}
+
+export function trim_chars_left(string, charset) {
+  const trim_regexp = new_left_trim_regexp(charset);
+
+  return string.replace(trim_regexp, "")
+}
+
+export function trim_chars_right(string, charset) {
+  const trim_regexp = new_right_trim_regexp(charset);
+
+  return string.replace(trim_regexp, "")
+}
+
 export function bit_array_from_string(string) {
   return toBitArray([stringBits(string)]);
 }
@@ -296,7 +316,7 @@ export function crash(message) {
 
 export function bit_array_to_string(bit_array) {
   try {
-    const decoder = new TextDecoder("utf-8", { fatal: true });
+    const decoder = new TextDecoder("utf-8", { fatarl: true });
     return new Ok(decoder.decode(bit_array.buffer));
   } catch {
     return new Error(Nil);
@@ -953,3 +973,69 @@ export function bit_array_compare(first, second) {
   }
   return new Lt();  // second has more items
 }
+
+function new_left_trim_regexp(charset) {
+  return new RegExp(`^([${charset}]*)`, "g");
+}
+
+function new_right_trim_regexp(charset) {
+  const escaped_charset = escape_regexp_chars(charset);
+  return new RegExp(`([${escaped_charset}]*)$`, "g");
+}
+
+function escape_regexp_chars(string) {
+  /*
+   * The MIT License
+
+   * Copyright JS Foundation and other contributors <https://js.foundation/>
+   *
+   * Based on Underscore.js, copyright Jeremy Ashkenas,
+   * DocumentCloud and Investigative Reporters & Editors <http://underscorejs.org/>
+   *
+   * This software consists of voluntary contributions made by many
+   * individuals. For exact contribution history, see the revision history
+   * available at https://github.com/lodash/lodash
+   *
+   * The following license applies to all parts of this software except as
+   * documented below:
+   *
+   * ====
+   *
+   * Permission is hereby granted, free of charge, to any person obtaining
+   * a copy of this software and associated documentation files (the
+   * "Software"), to deal in the Software without restriction, including
+   * without limitation the rights to use, copy, modify, merge, publish,
+   * distribute, sublicense, and/or sell copies of the Software, and to
+   * permit persons to whom the Software is furnished to do so, subject to
+   * the following conditions:
+   *
+   * The above copyright notice and this permission notice shall be
+   * included in all copies or substantial portions of the Software.
+   *
+   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+   * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+   * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+   * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+   * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+   * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+   *
+   * ====
+   *
+   * Copyright and related rights for sample code are waived via CC0. Sample
+   * code is defined as all source code displayed within the prose of the
+   * documentation.
+   *
+   * CC0: http://creativecommons.org/publicdomain/zero/1.0/
+   *
+   * ====
+   *
+   * Files located in the node_modules and vendor directories are externally
+   * maintained libraries used by this software which have their own
+   * licenses; we recommend you read them, as their terms may differ from the
+   * terms above.
+   */
+   return string && reHasRegExpChar.test(string)
+        ? string.replace(reRegExpChar, '\\$&')
+        : string || '';
+}

test/gleam/string_test.gleam

@@ -176,6 +176,18 @@ pub fn trim_right_test() {
   |> should.equal("  hats")
 }
 
+pub fn trim_chars_left_test() {
+  ",..hats..,"
+  |> string.trim_chars_left(",.")
+  |> should.equal("hats..,")
+}
+
+pub fn trim_chars_right_test() {
+  ",..hats..,"
+  |> string.trim_chars_right(",.")
+  |> should.equal(",..hats")
+}
+
 // unicode whitespaces
 pub fn trim_horizontal_tab_test() {
   "hats\u{0009}"
@@ -364,6 +376,36 @@ pub fn trim_comma_test() {
   |> should.equal("hats,")
 }
 
+pub fn trim_chars_test() {
+  ",,hats,"
+  |> string.trim_chars(",")
+  |> should.equal("hats")
+}
+
+pub fn trim_chars_commas_and_periods_test() {
+  ",,hats,..."
+  |> string.trim_chars(",.")
+  |> should.equal("hats")
+}
+
+pub fn trim_chars_keeps_whitespace_not_in_charset_test() {
+  ",,hats ,..."
+  |> string.trim_chars(",.")
+  |> should.equal("hats ")
+}
+
+pub fn trim_chars_does_not_trim_from_middle_of_string_test() {
+  ",,hats,hats,hats,..."
+  |> string.trim_chars(",.")
+  |> should.equal("hats,hats,hats")
+}
+
+pub fn trim_chars_trims_complex_graphemes_test() {
+  "hats👍👍👍👍"
+  |> string.trim_chars("👍")
+  |> should.equal("hats")
+}
+
 pub fn starts_with_test() {
   "theory"
   |> string.starts_with("")