feat(parsely): Add stringUntil() parser

The counterpart of stringOf(), it reads characters until it matches its
parameter.

packages/phoenix/packages/parsely/exports.js

@@ -1,6 +1,6 @@
 import { adapt_parser, VALUE } from './parser.js';
 import { Discard, FirstMatch, Optional, Repeat, Sequence } from './parsers/combinators.js';
-import { Fail, Literal, None, StringOf, Symbol } from './parsers/terminals.js';
+import { Fail, Literal, None, StringOf, StringUntil, Symbol } from './parsers/terminals.js';
 
 class ParserWithAction {
     #parser;
@@ -89,6 +89,7 @@ export const standard_parsers = () => {
         repeat: Repeat,
         sequence: Sequence,
         stringOf: StringOf,
+        stringUntil: StringUntil,
         symbol: Symbol,
     }
 }

packages/phoenix/packages/parsely/parsers/terminals.js

@@ -53,6 +53,53 @@ export class StringOf extends Parser {
     }
 }
 
+/**
+ * Parses characters into a string, until it encounters the given character, unescaped.
+ * @param testOrCharacter End of the string. Either a character, or a function that takes a character,
+ *                        and returns whether it ends the string.
+ * @param escapeCharacter Character to use as the escape character. By default, is '\'.
+ */
+export class StringUntil extends Parser {
+    _create(testOrCharacter, { escapeCharacter = '\\' } = {}) {
+        if (typeof testOrCharacter === 'string') {
+            this.test = (c => c === testOrCharacter);
+        } else {
+            this.test = testOrCharacter;
+        }
+        this.escapeCharacter = escapeCharacter;
+    }
+
+    _parse(stream) {
+        const subStream = stream.fork();
+        let text = '';
+        let lastWasEscape = false;
+
+        while (true) {
+            let { done, value } = subStream.look();
+            if ( done ) break;
+            if ( !lastWasEscape && this.test(value) )
+                break;
+
+            subStream.next();
+            if (value === this.escapeCharacter) {
+                lastWasEscape = true;
+                continue;
+            }
+            lastWasEscape = false;
+            text += value;
+        }
+
+        if (lastWasEscape)
+            return INVALID;
+
+        if (text.length === 0)
+            return UNRECOGNIZED;
+
+        stream.join(subStream);
+        return { status: VALUE, $: 'stringUntil', value: text };
+    }
+}
+
 /**
  * Parses an object defined by the symbol registry.
  * @param symbolName The name of the symbol to parse.